CA2199708C - Efficient linear power amplification - Google Patents
Efficient linear power amplification Download PDFInfo
- Publication number
- CA2199708C CA2199708C CA002199708A CA2199708A CA2199708C CA 2199708 C CA2199708 C CA 2199708C CA 002199708 A CA002199708 A CA 002199708A CA 2199708 A CA2199708 A CA 2199708A CA 2199708 C CA2199708 C CA 2199708C
- Authority
- CA
- Canada
- Prior art keywords
- signal
- signals
- adjacent channel
- channel energy
- constant
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
- 230000003321 amplification Effects 0.000 title description 6
- 238000003199 nucleic acid amplification method Methods 0.000 title description 6
- 238000000034 method Methods 0.000 claims abstract description 34
- 238000004891 communication Methods 0.000 claims abstract description 9
- 238000001914 filtration Methods 0.000 claims description 18
- 230000001747 exhibiting effect Effects 0.000 claims description 6
- 230000008878 coupling Effects 0.000 claims description 4
- 238000010168 coupling process Methods 0.000 claims description 4
- 238000005859 coupling reaction Methods 0.000 claims description 4
- 238000004519 manufacturing process Methods 0.000 claims 1
- 230000003595 spectral effect Effects 0.000 description 10
- 230000004044 response Effects 0.000 description 7
- 238000001228 spectrum Methods 0.000 description 7
- 238000012360 testing method Methods 0.000 description 4
- 230000008901 benefit Effects 0.000 description 3
- 241001494479 Pecora Species 0.000 description 2
- 230000001413 cellular effect Effects 0.000 description 2
- 238000012546 transfer Methods 0.000 description 2
- 244000198134 Agave sisalana Species 0.000 description 1
- 241000195940 Bryophyta Species 0.000 description 1
- JGFZNNIVVJXRND-UHFFFAOYSA-N N,N-Diisopropylethylamine (DIPEA) Chemical compound CCN(C(C)C)C(C)C JGFZNNIVVJXRND-UHFFFAOYSA-N 0.000 description 1
- 101150051715 Phax gene Proteins 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000006870 function Effects 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/32—Modifications of amplifiers to reduce non-linear distortion
- H03F1/3223—Modifications of amplifiers to reduce non-linear distortion using feed-forward
Abstract
A method and apparatus for producing amplified signals for communications having reduced adjacent channel energy involving generating a first signal having an undesired amount of adjacent channel energy, generating a second signal corresponding to the undesired amount of adjacent channel energy, and subtracting the second signal from the first signal to remove the undesired amount of adjacent channel energy. Several embodiments are disclosed.
Description
w0 96!08866 PCTlITS95/11754 EFFICIEV1'T LINEAR POWER AMPLIFICATION
BACKGROUND OF THE INVENTION
1. ~ Field of the Invention The present invention relates to a linear power amplifier and a method of linear amplification suitable for use in a transmitter, such as a Class-C CPFSK
transmitter.
BACKGROUND OF THE INVENTION
1. ~ Field of the Invention The present invention relates to a linear power amplifier and a method of linear amplification suitable for use in a transmitter, such as a Class-C CPFSK
transmitter.
2. Discussion of Related Art Signals used for radio communications fall into one of the following three categories: (i) Pure amplitude modulation (AIVI); ('ti) Pure angle modulation or IO constant envelope signals such as frequency modulation (FM) or phase modulation (PM); or ('iir~ complex modulation which has both AM and FM components, such as single sideband (SSB).
The abbreviations AM, FM and SSB refer historically to modulation of radio waves with analog speech waveforms. More recently; modulation with digital data signals has assumed greater importance. Digitally modulated signals occupy a wide bandwidth unless means are employed to contain the transmitted spectrum. On one hand, there are limits to how well the spectrum can be contained using constant envelope modulation for data signals. On the other hand, the use of non-constant envelope modulation requires a linear transmitter power amplifier which preserves both the amplitude and phase of the signals it amplifies and these devices are less efficient than constant envelope power amplifiers.
Prior art recognizes a number of classes of power amplifier depending on the type of signal that is w be amplified.
Class-A amplifiers conduct signal current throughout the cycle of the signal waveform and are the most linear amplifiers. Class-A amplifiers are suitable for signals that can vary in amplitude, and their power consumption from the supply (e.g., battery) is a constant irrespective of the signal Level, at least so long as the signal level does not exceed the maximum power capability or satzuation point. Class-A
amplifier's wo ~»
are wasteful of power during moments when a varying amplitude signal is below the sanuated power output level. This aspect is improved upon in Class-B
amplifiers.
Class-B atapIifiers conduct signal current exactly for one-half of the cycle of the input signal waveform. In a push-pull Class-B amplifier one device conducts for one half-cycle, and the other device conducts for the remaining half-cycle. Class-B
amplifiers consume a varying amount of current from the supply Proportional to the square root of the mome~ry output power level. Although Class-B amplifiers consume no current when not delivering output power and their efficiency at ' intermediate power levels between zero and saturation is better than Class-A
amplifiers, IO Class-B amplifier's efficiency is nevertheless lower at lower output powers than at saturation, so that the mean efficiency with varying amplitude signals is less than the maximum efficiency at saturated output power.
Class-C amplifiers conduct for less than one half of a complete signal cycle and are used primarily as radio-frequency amplifiers with the load tuned to the signal IS frequency. Class-C amplifiers are suitable only for constant envelope signals, and operate at full saturation e~ciency the whole time. If it is attempted to amplify non-constant envelope signals with a Class-C power amplifier, the signal emreiope fluctuations will not be faithfully reproduced, but will be clipped off or distorted.
Prior art also encompasses various circuit configurations used to improve the 20 linearity of Class-B and Class-C amplifiers, and these can be broadly categorized as feedback, feedforward, or envelope re-modulation.
As an example of feedback techniques, amplifiers have been built in which an amplitude detector senses the output amplitude and compares it with the desired amplitude of the input signal. The error is used to generate a feedback signal that 25 increases or decreases the power amplifier gain, or alters the bias or some other ' parameter in a direction which will correct the amplitude.
Feedback techniques have also been descn'bed in the prior art in which both amplitude and phase feedback are employed, the latter also eliminating a source of non-Rarity known as AM to PM conversion.
w0 96/08866 PC'TlUS95111754 Feedback techniques are known in which neither the amplitude and phase angle but rather compiea vector components are sensed, compared to what they should be, and two taor signals generated and fed back to adjust the each component to the desired value. This is known as Cartesian loop feedback whereas the amplitude and phase feedback technique is known as a polar loop.
Feedforward techniques known to the art include subuacting a proportion of the power amplifier output signal from a proportion of the input signal to obtain an error signal, amplifying the error signal, and then subuacting the error signal from the power amplifier output signal. This is normally only technically advantageous when the error signal is already small at the power amplifier output, i.e., when the amplifier is already substantially linear.
Non-linearity is often measured by a so-called two-tone test, where two signals close together in frequency fl and f1 are added to.produce a non-constant envelope test signal. No~Iinearity shows up in the appearance of other frequencies in the power amplifier output particularly at 2f1-#2 and 2fl-fl, Imown as third order intetmodulation products. Typically a good linear power amplifier will achieve intermodulation levels 30 to 35 dB below the test tone levels without the above-mentioned circuit configurations, while feedforward can a this performance to 60 dB below the test tone levels.
Also belonging to the class of feedforward techniques is a technique known as predistortion, in which the power amplifier is driven with a modified input signal precalculated to produce the desired output signal, using lmowiedge of the non linear input-output transfer function.
Envelope re modulation can be used with a Class-C power amplifier to restore the amplitude variations that the Class-C power amplifier does not normally reproduce.
The most efficient form of envelope remodulation is to vary the power supply voltage to the power amplifier. This is known as high level amplitude modulation (AM), and is most efficiently accomplished by means of pulse width modulation. However, all forms of high level AM require-the use of bulky components. _ .
The abbreviations AM, FM and SSB refer historically to modulation of radio waves with analog speech waveforms. More recently; modulation with digital data signals has assumed greater importance. Digitally modulated signals occupy a wide bandwidth unless means are employed to contain the transmitted spectrum. On one hand, there are limits to how well the spectrum can be contained using constant envelope modulation for data signals. On the other hand, the use of non-constant envelope modulation requires a linear transmitter power amplifier which preserves both the amplitude and phase of the signals it amplifies and these devices are less efficient than constant envelope power amplifiers.
Prior art recognizes a number of classes of power amplifier depending on the type of signal that is w be amplified.
Class-A amplifiers conduct signal current throughout the cycle of the signal waveform and are the most linear amplifiers. Class-A amplifiers are suitable for signals that can vary in amplitude, and their power consumption from the supply (e.g., battery) is a constant irrespective of the signal Level, at least so long as the signal level does not exceed the maximum power capability or satzuation point. Class-A
amplifier's wo ~»
are wasteful of power during moments when a varying amplitude signal is below the sanuated power output level. This aspect is improved upon in Class-B
amplifiers.
Class-B atapIifiers conduct signal current exactly for one-half of the cycle of the input signal waveform. In a push-pull Class-B amplifier one device conducts for one half-cycle, and the other device conducts for the remaining half-cycle. Class-B
amplifiers consume a varying amount of current from the supply Proportional to the square root of the mome~ry output power level. Although Class-B amplifiers consume no current when not delivering output power and their efficiency at ' intermediate power levels between zero and saturation is better than Class-A
amplifiers, IO Class-B amplifier's efficiency is nevertheless lower at lower output powers than at saturation, so that the mean efficiency with varying amplitude signals is less than the maximum efficiency at saturated output power.
Class-C amplifiers conduct for less than one half of a complete signal cycle and are used primarily as radio-frequency amplifiers with the load tuned to the signal IS frequency. Class-C amplifiers are suitable only for constant envelope signals, and operate at full saturation e~ciency the whole time. If it is attempted to amplify non-constant envelope signals with a Class-C power amplifier, the signal emreiope fluctuations will not be faithfully reproduced, but will be clipped off or distorted.
Prior art also encompasses various circuit configurations used to improve the 20 linearity of Class-B and Class-C amplifiers, and these can be broadly categorized as feedback, feedforward, or envelope re-modulation.
As an example of feedback techniques, amplifiers have been built in which an amplitude detector senses the output amplitude and compares it with the desired amplitude of the input signal. The error is used to generate a feedback signal that 25 increases or decreases the power amplifier gain, or alters the bias or some other ' parameter in a direction which will correct the amplitude.
Feedback techniques have also been descn'bed in the prior art in which both amplitude and phase feedback are employed, the latter also eliminating a source of non-Rarity known as AM to PM conversion.
w0 96/08866 PC'TlUS95111754 Feedback techniques are known in which neither the amplitude and phase angle but rather compiea vector components are sensed, compared to what they should be, and two taor signals generated and fed back to adjust the each component to the desired value. This is known as Cartesian loop feedback whereas the amplitude and phase feedback technique is known as a polar loop.
Feedforward techniques known to the art include subuacting a proportion of the power amplifier output signal from a proportion of the input signal to obtain an error signal, amplifying the error signal, and then subuacting the error signal from the power amplifier output signal. This is normally only technically advantageous when the error signal is already small at the power amplifier output, i.e., when the amplifier is already substantially linear.
Non-linearity is often measured by a so-called two-tone test, where two signals close together in frequency fl and f1 are added to.produce a non-constant envelope test signal. No~Iinearity shows up in the appearance of other frequencies in the power amplifier output particularly at 2f1-#2 and 2fl-fl, Imown as third order intetmodulation products. Typically a good linear power amplifier will achieve intermodulation levels 30 to 35 dB below the test tone levels without the above-mentioned circuit configurations, while feedforward can a this performance to 60 dB below the test tone levels.
Also belonging to the class of feedforward techniques is a technique known as predistortion, in which the power amplifier is driven with a modified input signal precalculated to produce the desired output signal, using lmowiedge of the non linear input-output transfer function.
Envelope re modulation can be used with a Class-C power amplifier to restore the amplitude variations that the Class-C power amplifier does not normally reproduce.
The most efficient form of envelope remodulation is to vary the power supply voltage to the power amplifier. This is known as high level amplitude modulation (AM), and is most efficiently accomplished by means of pulse width modulation. However, all forms of high level AM require-the use of bulky components. _ .
CPFSK (Continuous-Phase, Frequency-Shift Keying) is a constant envelope modulation, i.e., a pure phase modulation which the phax trajectories are heavily smoothed to control adjacent chapel energy. The advantage of CPFSK is that it can be amplified using a Class-C transmit power amplifier.
Unfortunately, a constant envelope signal does not achieve a sufficient compromise between adjacent channel and communication efficiency for digital land mobile radio (DLMR) such as used in cellular telephone systems.
Adjacent channel energy can be reduced by filtering the CPFSK signal in the ' I, Q domain, which is equivalent to RF band pass filtering. However, this introduces amplitude modulation and a Class-C power amplifier can no longer be used.
In U.S. Patent 5,574,967 naming as inventors Dent and Lampe and filed January 11, 1994, it is disclosed that two Class-C power amplifiers can be driven with different CPFSK signals and combined in such a way that the desired amplitude variations can be cre~aied. The present invention comprises power amplifiers of unequal power that may be combined to substantially reduce adjacent channel energy produced by the larger amplifier operating with constant envelope modulation.
The present invention avoids a disadvantage of the prior Dent-Lampe invention which generates two signals of increased adjacent channel energy, which when combined should give reduced adjacent channel energy. Instead, the present invention generates one signal of normal adjacent channel energy and a compensation signal of lower power having only the same power-to-adjacent channel energy. The present invention is based on combining a Class-C power amplifier signal with a very much lower linear power amplifier signal.
The invention descn'bed herein is a method of obtaining spectral containment benefits of non-constant envelope modulation, while achieving substantially the tzansmiacr power amplifier efficiency of constant envelope modulation.
The present invention belo~s to the class of feedforward techniques, but is not limited to the case where the power amplifier is already substantially linear.
It is not 2 ~ 9 ~ ~ o s PypS95/11754 w0 96!08866 conceived for making an already linear power amplifier even better, but rather as a means of using a high-e~ciency Class-C power amplifier to produce bandwidth contained signals.
Specifically, the present invention involves a method and apparatus for producing amplified signals for communications having reduced adjacent channel energy involving generating a first signal having an undesired amount of adjacent channel energy, generating a second signal corresponding to the undesired amount of adjacent channel energy, and subtracting the sxond signal from the first sisal to remove the undesired amount of adjacent channel energy.
In an alternative embodiment, the present invention imroives a method and apparatus for amplifying communications signals exhibiting reduced adjacent channel energy including generating I, Q modulation signals wherein a sum of the squares of instantaneous I and Q signals is a constant, applying the I, Q signals to a quadrature modulator operating on sine and cosine carrier fiequency signals to obtain a constant IS envelope signal, amplifying the constant envelope signal using a power amplifier designed to yield high efficiency with constant-envelope signals, high-pass filtering the I and Q signals and applying the high-pass filtered signals to a second quadrature modulator to obtain an ermr signal, amplifying the error signal using a linear amplifier adapted to effectively amplify varying amplitude signals, and adding- an output of the power amplifier to an output of the linear amplifier in order to obtain a signal having reduced adjacent channel energy.
In yet another embodiment, the present invention involves a method and apparatus for producing digital data signals exhibiting reduced adjacent channel energy including generating I, Q modulated signals representing digital data, the signals having greater than desired adjacent channel energy, applying the I, Q signals to a quadrature modulator operating on sine and cosine carrier frequency signals to obtain a first signal, high pass filtering the I, Q modulation signals to obtain high pass filtered I, Q
signals, applying the high-pass filtered I, Q signals to a second quadrature modulator to obtain a second signal, and amplifying and adding the first and second signals to obtain a signal having reduced adjacent channel energy.
2199708 ~C~l~~ 95 /1I 754 IPEA/U~ 19 NOU 1996 In a further alternative embodiment, the present invention involves a method and apparatus for amplifying digital data signals exhibiting reduced adjacent channel energy including feeding digital data signals through a shift register of N
stages, coupling N signals from the shifr register corresponding to the Iast N data bits of the digital data signals to address input lines of a read only memory, connecting address lines of the read only memory to the digit lines of a counter, incrementing the counter to obtain sequentially a number of sets of four output values from the read only memory, digital-to-analog converting the four output values to obtain a first I, Q signal and a second I, Q signal, applying the first I, Q signal to a first quadrature modulator to obtain a first signal of higher than desired adjacent channel energy, applying the second I, Q signal to a second quadrature modulator to obtain a second signal, and amplifying and adding the first signal to the second signal in an optimum ratio to obtain a signal of reduced adjacent channel energy.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be descn'bed with reference to the accompanying drawings in which:
Figure 1 is a graph of a typical spectrum of a radio signal with digital data in a constant envelope;
Figure 2 is a schematic of an adjacent channel energy canceling Circuit;
Figure 3 is a schematic of a power amplification circuit for amplification of non~onstant envelope modulated signals, in accordance with the present invention;
Figure 4 is a schematic of a power amplification circuit including direct generation of the difference signal by high pass filtering, in accordance with the present invention; and Figure 5 is a schematic of an embodiment using a ROM modulator, in acrardance with the present invention.
AMENDED SHEEP
2199708 P~TIUS 95 /11754 -7_ DETAILED DESCRIPTION OF THE
PREFERRED EMBODTMENTS
Figure 1 shows the typical spectrum of a radio signal modulated with digital data in a constant envelope fashion, such as can be handled by an efficient Class-C
power amplifies. The spectrum consists of a main lobe containing the wanted signal energy, but has attendant "tails" or "skirts" of energy reaching into neighboring channels. 'These cause the undesired phenomenon of adjacent channel interference.
It is unnecessary to transmit the energy in the spectral tails, as they lie outside the pass bandwidth of the intended receiver. Therefore, if they could be omitted, the intended receiver would not know the difference. Unintentional receivers tuned to the adjacent radio channels would however benefit from the removal of this source of interference, which is a main objective of the present invention.
The interference energy in the tails represents only a small fraction of the total energy and could in principle be removed using a bandpass filter after the power amplifier. Unfortunately, bandpass filters of narrow bandwidth at a RF output frequency are generally impracticable. On the other hand, a bandpass filter equivalent can be formed at low power levels by generating the desired signal using a so-ca3Ied quadrature modulator. This quadrature modulator which can be constructed according to U.S. Patent Application No. 071967,027, naming the present inventor and B.
Ekelund, filed October 27, 1992, and its CIP application, U.S. Patent No. 5,530,722, entitled ° Quadrature Modulator with Integrated Distributed RC Filters"
(Attorney Dockei No. 027540-28?), decomposes the desired signal into a sine and cosine waves of varying amplitudes, indicated by the waveforms I(t) and Q(t).
It is well-known that Iow pass filtering the I and Q signals is equivalent to bandpass filtering the RF output signal, producing a contained spectrum with Iow tail energy. However, a signal so-generated is not guaranteed to be a ccastant envelope signal, which requires that I squared plus Q squared be a constant (IZ + QZ =
C). A
signal not conforming to this would not be faithfully reproduc~i by a Class-C
amplifier.
r..~s. <
w0 96!08866 PCT/US95I11754 -$-Generally, I, Q waveforms are created for digital transmitters whether of a CPFSK type (e.g., GSM type) or otherwise (e.g., U.S. IS-54 digital cellular type) by means of a so-called ROM modulator. The ROM modulator relies on being able to truncate the impulse response of the premodulation filter to a reasonable number of bit _periods, N, where 2H gives a ROM of a reasonable size. Using the truncated impulse response, the filter can produce, over each bit interval, one of a finite number, 2N, of possible waveforms. By storing each I, Q waveform at an adequate number of samples per bit in a ROM, the modulation and filtering is achieved simply by feeding the data stream through an N-bit shift register which addresses the ROM to output waveforms for that bit interval.
The present invention is based in part on the following premise: a second I, Q
waveform can be generated by a second ROM modulator of the same impulse response length N as the first modulator, but. which has the spectrum only of the adjacent channel energy which is to be eliminated. The present invention is based on the proposition that a very low power, linear pow er amplifier can be used to amplify the second signal, which would then be added to the original constant envelope signal produced by an efficient Class-C power amplifier. Since the adjacent power channel energy of the original waveform is perhaps already 40 dB down, the linear power amplifier would be 20 dB below the main power amplifier and added via a -20 dB
coupler. For a 3 watt main power amplifier, the linear power amplifier would be only milliwatrs average power.
With reference to Figure 2, a digital data stream is input to an N-bit shift register 21 the contents of which are input in parallel to a CPFSK ROM
modulator 22 and an adjacent channel canceier ROM modulator 23. The bits in the digital data 25 stream act as addresses in the ROM modulators 22 and 23, the output of which are I
and Q signals which correspond to the input data including skirts and the skirts per se.
The I and Q outputs of the CPFSK RObi modulator 22 and the adjacent channel cxnceler ROM modulator 23 are input to quad=anire modulators 24 and 25, each having respective sine and cosine miters 24a, 24b, ZSa, 25b the outputs of which are inputs 30 to respective summation devices 24c and 25c. The output of the first summation 2199708 ~~~~U~ 95 /II75~.
device 24c associated with the CPFSK ROM modulator ZZ is input to a Class-C
power amplifier 26, while the output of the summation device ZSc associated with the adjacent channel cancrier ROM modulator 23 is input to a linear power amplifier 27.
The Class-C power amplifier Z6 has a restive power of Pi equal to approacimately 3 watts, for e.~cample. The relative power output of the linear power amplifier 27 is Pl - A/2 dBw, for e.~cample, 30 miIliwatts, wherein A is the number of dB the adjacent channel ene ay is below Pl.
The output of the linear power amplifier 27 is then coupled to the output of the Class-C power amplifier 26 by a coupler 28, having a relative transfer power ratio I0 A/Z dB, for example, -20 dB.
An alternative embodiment is depicted in Fi~L~re 3, wherein a constant amplitude signal is initially generated from an input did tal data stream or modulating waveform using, e.g., an I, Q modulator 30, and amplines the constsnt amplitude signal with a Class-C power amplifier 3I. The I, Q modulator may be configured as disclosed in U.S. Patent application No. 07/967,027, naming the present inventor and B. Ekelund, filed October 27, 1992, and its CIP application, U.S. Patent No. 5,530,722, entitled °Quadrature Modulator with Integrated Distributed RC Filters"
(Attorney Docket No. 027540-28 i~. Then, on a parallel line, a corresponding non-constant amplitude signal is produced from the input data stream in a second I, Q
modulator 32 having the low energy spectral tails. The non-constant envelope modulator separates out the spectral tails from the rest of the input signal by means of the ROM modulator 23 (Fig. 2) or by means of a low pass filter. The constant envelope modulator 30 and the non-constant envelope modulator 32 are each supplied a carrier frequency from a common source (not shown). The difference between the spectrally contained signal from the I, Q modulator 32 and the constant eaveiope signal from the power amplifier 31 is then formed in a signal subtractor 33.
The difference signal from the subtractor 33 is a non-constant amplitude signal which is amplified using a linear power amplifier 34. The amplified diffemnce signal AI~~tDED SHEEP
wo mosses rcrms~msa from the linear amplifier 34 is added to the Class-C power amplifier 31 output using a directional coupler 35 to cancel the undesired spectral tails.
In this technique the error signal consists only of low energy spectral tads and thus requires only a very low power linear power amplifier to scale them to the output signal level.
It is well (mown that no adding device such as such as the directional coupler 35 can add signals of the same frequency without some Ions. However, the loss can be minimized by choosing the coupling ratio to be of the order of the square root of the ratio of the power levels of the main Class-C power amplifier 31 and the error amplifier 34 peak power level. For example, if the Class-C power amplifier 31 is of 1 kilowatt, and the error amplifier 34 needs only to be of i watt by virtue of the spectral tail energy being more than 30 dB down, then a directional coupler 35 preferably has a loss of 0.3 dB to the main 1 Ia'lowatt power amplifier, a -15 dB
coupling ratio to the crror amplifier 34, and accordingly the error amplifier 34 is increased in power level by 15 dB from 1 watt to 30 watts to compensate.
In this way, the lower power amplifier 34 is given the highest loss path and the higher power amplifier 3 i is given the lowest loss path, minimizing the impact on overall efficiency of loss in the addiag network 35.
A more refined version of the present invention wdI now be descn'bed with reference to Figure 4.
The non-constant envelope signal may be produced by low pass filtering the constant envelop I, Q signals and applying them to a second I, Q modulator.
Since the difference of the output signal from this modulator and the first, constant amplitude modulator is required, this difference can be calculated at the I, Q signal points.
Moreover, the difference between a signal and a low-pass filtered version of it is merely a high pass filtered version.
Therefore, a preferred implementation shown in Figure 4 forms the difference signal directly by high pass filtering the I, Q signals using a pair of high pass filters 40 (one for each signal) and applying than to a second quadrature modulator 42. The difference signal is amplified as before in a linear error amplifier 44 and then added 219 9 7 0 8 P~/pS95/11754 wo x~ossss in a directional coupler 45 to the output of a constant envelope amplifier 43 which receives a constant envelope signal from a first quadrature modulator 41.
Optional low pass filters 46 may be included; both the upper filters 46 and lower filters 40 might, however, comprise digital to-analog convertors if the I, Q
signals originate in digital form.
In practice, the generation of constant envelope modulated data signals and/or linearly filtered data signals may be accomplished with the aid of a so-called ROM
modulator. The ROM (Read Only Memory) modulator assumes that the filter used to shape the I, Q or phase angle transitions has a finite impulse response of a few data symbols (e.g., bits) duration. That means that each segment of I or Q waveform over a symbol period depends only on that finite number of bits. For example, if the filter impulse is five bit periods long, there are only 32 (2s) possibilities for the output waveform. Plus/minus and time reversal symmetries permit a compression of these waveform types so that all may be stored in a small ROM. Modulation and filtering are then combined in the operation of simply retrieving a waveform from a memory location given by the last five data bits.
An implementation of the present invention can be constructed where both the constant envelope modulation and the high-pass filtered version of it can be represented by finite impulse response filter funarons. The finite number of I and Q
waveforms which can arise are then stored in a ROM for both versions.
Referring to Figure 5, every bit period a new bit is shifted into an N bit shift register 50, and the last N bits, where N corresponds to the impulse response length of the filter, are presented to a ROM 51. Two I and two. Q waveforms (corresponding respectively to the constant envelope waveform and the high-pass filtered waveform) are selected from the ROM and converted from digital to analog form in four digital-to-analog converters 52 - 55.
In response to a clock input, a counter 61 then steps M times during each bit period of the input digital data stream to produce a sequence of M points representing in discrete steps in the waveform aver the bit period. The D-to-A converted - waveforms are filtered in anti-aliasing low-pass filters 62 to remove the step granularity 219 9 7 p g pCT~S~11754 wo ~ossss ~d ~~ panted respectively to a constant envelope modulator 56 and an error signal modulator 57, respectively. The constant envelope modulator output may be amplified by a Class-C power amplifier 58 while the error signal is amplified by a linear power amplifier 59. The outputs of the two power amplifiers are then added in a directional . coupler 60.
It is pointed out that, to obtain best cancellation of the unwanted spectral components, it may be necessary to build in a relative delay of the constant envelope siD°nal relative to the error signal to compensate for the inherent delay in the high-pass filtering operation. This can be accomplished in the implementation of Figure 4 bY.
10. digitally retiming the data stream by means of high-pass filters 40 used to produce the constant envelope I, Q signals using a suitable clock. If the high pass filters 40 exhibit a delay, the filters 46 can delay the constant envelope signals to align them in time for coaect cancel>ation of spectzal energy tails- In the case of, the ROM
modulator, the relative delay can be befit into the ROM contents.
Other embodiments of the present invention w01 be apparent to a person stalled in the art which differ in detail, but embodying the present invention's general principle .y of generating an amplified error signal corresponding to the unwanted spectral energy tads of a constant envelope signal, adding this signal to the constant envelope signal so as to cancel those unwanted spectral componeats, leaving a signal with greatly 20 reduced adjacent channel energy.
While only particular embodiments of the present invention have been shown and descn'bed herein, it will be obvious that further modifications may be made without departing from the invention in its broader aspects. For example, various other implementations could be devised ut~Iizing other hardware devices, digital signal 25 processors, or memory configurations- Accordingly, the claims are intended to cover all such changes and alternative constructions that fall within the scope and spirit of the invention.
Unfortunately, a constant envelope signal does not achieve a sufficient compromise between adjacent channel and communication efficiency for digital land mobile radio (DLMR) such as used in cellular telephone systems.
Adjacent channel energy can be reduced by filtering the CPFSK signal in the ' I, Q domain, which is equivalent to RF band pass filtering. However, this introduces amplitude modulation and a Class-C power amplifier can no longer be used.
In U.S. Patent 5,574,967 naming as inventors Dent and Lampe and filed January 11, 1994, it is disclosed that two Class-C power amplifiers can be driven with different CPFSK signals and combined in such a way that the desired amplitude variations can be cre~aied. The present invention comprises power amplifiers of unequal power that may be combined to substantially reduce adjacent channel energy produced by the larger amplifier operating with constant envelope modulation.
The present invention avoids a disadvantage of the prior Dent-Lampe invention which generates two signals of increased adjacent channel energy, which when combined should give reduced adjacent channel energy. Instead, the present invention generates one signal of normal adjacent channel energy and a compensation signal of lower power having only the same power-to-adjacent channel energy. The present invention is based on combining a Class-C power amplifier signal with a very much lower linear power amplifier signal.
The invention descn'bed herein is a method of obtaining spectral containment benefits of non-constant envelope modulation, while achieving substantially the tzansmiacr power amplifier efficiency of constant envelope modulation.
The present invention belo~s to the class of feedforward techniques, but is not limited to the case where the power amplifier is already substantially linear.
It is not 2 ~ 9 ~ ~ o s PypS95/11754 w0 96!08866 conceived for making an already linear power amplifier even better, but rather as a means of using a high-e~ciency Class-C power amplifier to produce bandwidth contained signals.
Specifically, the present invention involves a method and apparatus for producing amplified signals for communications having reduced adjacent channel energy involving generating a first signal having an undesired amount of adjacent channel energy, generating a second signal corresponding to the undesired amount of adjacent channel energy, and subtracting the sxond signal from the first sisal to remove the undesired amount of adjacent channel energy.
In an alternative embodiment, the present invention imroives a method and apparatus for amplifying communications signals exhibiting reduced adjacent channel energy including generating I, Q modulation signals wherein a sum of the squares of instantaneous I and Q signals is a constant, applying the I, Q signals to a quadrature modulator operating on sine and cosine carrier fiequency signals to obtain a constant IS envelope signal, amplifying the constant envelope signal using a power amplifier designed to yield high efficiency with constant-envelope signals, high-pass filtering the I and Q signals and applying the high-pass filtered signals to a second quadrature modulator to obtain an ermr signal, amplifying the error signal using a linear amplifier adapted to effectively amplify varying amplitude signals, and adding- an output of the power amplifier to an output of the linear amplifier in order to obtain a signal having reduced adjacent channel energy.
In yet another embodiment, the present invention involves a method and apparatus for producing digital data signals exhibiting reduced adjacent channel energy including generating I, Q modulated signals representing digital data, the signals having greater than desired adjacent channel energy, applying the I, Q signals to a quadrature modulator operating on sine and cosine carrier frequency signals to obtain a first signal, high pass filtering the I, Q modulation signals to obtain high pass filtered I, Q
signals, applying the high-pass filtered I, Q signals to a second quadrature modulator to obtain a second signal, and amplifying and adding the first and second signals to obtain a signal having reduced adjacent channel energy.
2199708 ~C~l~~ 95 /1I 754 IPEA/U~ 19 NOU 1996 In a further alternative embodiment, the present invention involves a method and apparatus for amplifying digital data signals exhibiting reduced adjacent channel energy including feeding digital data signals through a shift register of N
stages, coupling N signals from the shifr register corresponding to the Iast N data bits of the digital data signals to address input lines of a read only memory, connecting address lines of the read only memory to the digit lines of a counter, incrementing the counter to obtain sequentially a number of sets of four output values from the read only memory, digital-to-analog converting the four output values to obtain a first I, Q signal and a second I, Q signal, applying the first I, Q signal to a first quadrature modulator to obtain a first signal of higher than desired adjacent channel energy, applying the second I, Q signal to a second quadrature modulator to obtain a second signal, and amplifying and adding the first signal to the second signal in an optimum ratio to obtain a signal of reduced adjacent channel energy.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be descn'bed with reference to the accompanying drawings in which:
Figure 1 is a graph of a typical spectrum of a radio signal with digital data in a constant envelope;
Figure 2 is a schematic of an adjacent channel energy canceling Circuit;
Figure 3 is a schematic of a power amplification circuit for amplification of non~onstant envelope modulated signals, in accordance with the present invention;
Figure 4 is a schematic of a power amplification circuit including direct generation of the difference signal by high pass filtering, in accordance with the present invention; and Figure 5 is a schematic of an embodiment using a ROM modulator, in acrardance with the present invention.
AMENDED SHEEP
2199708 P~TIUS 95 /11754 -7_ DETAILED DESCRIPTION OF THE
PREFERRED EMBODTMENTS
Figure 1 shows the typical spectrum of a radio signal modulated with digital data in a constant envelope fashion, such as can be handled by an efficient Class-C
power amplifies. The spectrum consists of a main lobe containing the wanted signal energy, but has attendant "tails" or "skirts" of energy reaching into neighboring channels. 'These cause the undesired phenomenon of adjacent channel interference.
It is unnecessary to transmit the energy in the spectral tails, as they lie outside the pass bandwidth of the intended receiver. Therefore, if they could be omitted, the intended receiver would not know the difference. Unintentional receivers tuned to the adjacent radio channels would however benefit from the removal of this source of interference, which is a main objective of the present invention.
The interference energy in the tails represents only a small fraction of the total energy and could in principle be removed using a bandpass filter after the power amplifier. Unfortunately, bandpass filters of narrow bandwidth at a RF output frequency are generally impracticable. On the other hand, a bandpass filter equivalent can be formed at low power levels by generating the desired signal using a so-ca3Ied quadrature modulator. This quadrature modulator which can be constructed according to U.S. Patent Application No. 071967,027, naming the present inventor and B.
Ekelund, filed October 27, 1992, and its CIP application, U.S. Patent No. 5,530,722, entitled ° Quadrature Modulator with Integrated Distributed RC Filters"
(Attorney Dockei No. 027540-28?), decomposes the desired signal into a sine and cosine waves of varying amplitudes, indicated by the waveforms I(t) and Q(t).
It is well-known that Iow pass filtering the I and Q signals is equivalent to bandpass filtering the RF output signal, producing a contained spectrum with Iow tail energy. However, a signal so-generated is not guaranteed to be a ccastant envelope signal, which requires that I squared plus Q squared be a constant (IZ + QZ =
C). A
signal not conforming to this would not be faithfully reproduc~i by a Class-C
amplifier.
r..~s. <
w0 96!08866 PCT/US95I11754 -$-Generally, I, Q waveforms are created for digital transmitters whether of a CPFSK type (e.g., GSM type) or otherwise (e.g., U.S. IS-54 digital cellular type) by means of a so-called ROM modulator. The ROM modulator relies on being able to truncate the impulse response of the premodulation filter to a reasonable number of bit _periods, N, where 2H gives a ROM of a reasonable size. Using the truncated impulse response, the filter can produce, over each bit interval, one of a finite number, 2N, of possible waveforms. By storing each I, Q waveform at an adequate number of samples per bit in a ROM, the modulation and filtering is achieved simply by feeding the data stream through an N-bit shift register which addresses the ROM to output waveforms for that bit interval.
The present invention is based in part on the following premise: a second I, Q
waveform can be generated by a second ROM modulator of the same impulse response length N as the first modulator, but. which has the spectrum only of the adjacent channel energy which is to be eliminated. The present invention is based on the proposition that a very low power, linear pow er amplifier can be used to amplify the second signal, which would then be added to the original constant envelope signal produced by an efficient Class-C power amplifier. Since the adjacent power channel energy of the original waveform is perhaps already 40 dB down, the linear power amplifier would be 20 dB below the main power amplifier and added via a -20 dB
coupler. For a 3 watt main power amplifier, the linear power amplifier would be only milliwatrs average power.
With reference to Figure 2, a digital data stream is input to an N-bit shift register 21 the contents of which are input in parallel to a CPFSK ROM
modulator 22 and an adjacent channel canceier ROM modulator 23. The bits in the digital data 25 stream act as addresses in the ROM modulators 22 and 23, the output of which are I
and Q signals which correspond to the input data including skirts and the skirts per se.
The I and Q outputs of the CPFSK RObi modulator 22 and the adjacent channel cxnceler ROM modulator 23 are input to quad=anire modulators 24 and 25, each having respective sine and cosine miters 24a, 24b, ZSa, 25b the outputs of which are inputs 30 to respective summation devices 24c and 25c. The output of the first summation 2199708 ~~~~U~ 95 /II75~.
device 24c associated with the CPFSK ROM modulator ZZ is input to a Class-C
power amplifier 26, while the output of the summation device ZSc associated with the adjacent channel cancrier ROM modulator 23 is input to a linear power amplifier 27.
The Class-C power amplifier Z6 has a restive power of Pi equal to approacimately 3 watts, for e.~cample. The relative power output of the linear power amplifier 27 is Pl - A/2 dBw, for e.~cample, 30 miIliwatts, wherein A is the number of dB the adjacent channel ene ay is below Pl.
The output of the linear power amplifier 27 is then coupled to the output of the Class-C power amplifier 26 by a coupler 28, having a relative transfer power ratio I0 A/Z dB, for example, -20 dB.
An alternative embodiment is depicted in Fi~L~re 3, wherein a constant amplitude signal is initially generated from an input did tal data stream or modulating waveform using, e.g., an I, Q modulator 30, and amplines the constsnt amplitude signal with a Class-C power amplifier 3I. The I, Q modulator may be configured as disclosed in U.S. Patent application No. 07/967,027, naming the present inventor and B. Ekelund, filed October 27, 1992, and its CIP application, U.S. Patent No. 5,530,722, entitled °Quadrature Modulator with Integrated Distributed RC Filters"
(Attorney Docket No. 027540-28 i~. Then, on a parallel line, a corresponding non-constant amplitude signal is produced from the input data stream in a second I, Q
modulator 32 having the low energy spectral tails. The non-constant envelope modulator separates out the spectral tails from the rest of the input signal by means of the ROM modulator 23 (Fig. 2) or by means of a low pass filter. The constant envelope modulator 30 and the non-constant envelope modulator 32 are each supplied a carrier frequency from a common source (not shown). The difference between the spectrally contained signal from the I, Q modulator 32 and the constant eaveiope signal from the power amplifier 31 is then formed in a signal subtractor 33.
The difference signal from the subtractor 33 is a non-constant amplitude signal which is amplified using a linear power amplifier 34. The amplified diffemnce signal AI~~tDED SHEEP
wo mosses rcrms~msa from the linear amplifier 34 is added to the Class-C power amplifier 31 output using a directional coupler 35 to cancel the undesired spectral tails.
In this technique the error signal consists only of low energy spectral tads and thus requires only a very low power linear power amplifier to scale them to the output signal level.
It is well (mown that no adding device such as such as the directional coupler 35 can add signals of the same frequency without some Ions. However, the loss can be minimized by choosing the coupling ratio to be of the order of the square root of the ratio of the power levels of the main Class-C power amplifier 31 and the error amplifier 34 peak power level. For example, if the Class-C power amplifier 31 is of 1 kilowatt, and the error amplifier 34 needs only to be of i watt by virtue of the spectral tail energy being more than 30 dB down, then a directional coupler 35 preferably has a loss of 0.3 dB to the main 1 Ia'lowatt power amplifier, a -15 dB
coupling ratio to the crror amplifier 34, and accordingly the error amplifier 34 is increased in power level by 15 dB from 1 watt to 30 watts to compensate.
In this way, the lower power amplifier 34 is given the highest loss path and the higher power amplifier 3 i is given the lowest loss path, minimizing the impact on overall efficiency of loss in the addiag network 35.
A more refined version of the present invention wdI now be descn'bed with reference to Figure 4.
The non-constant envelope signal may be produced by low pass filtering the constant envelop I, Q signals and applying them to a second I, Q modulator.
Since the difference of the output signal from this modulator and the first, constant amplitude modulator is required, this difference can be calculated at the I, Q signal points.
Moreover, the difference between a signal and a low-pass filtered version of it is merely a high pass filtered version.
Therefore, a preferred implementation shown in Figure 4 forms the difference signal directly by high pass filtering the I, Q signals using a pair of high pass filters 40 (one for each signal) and applying than to a second quadrature modulator 42. The difference signal is amplified as before in a linear error amplifier 44 and then added 219 9 7 0 8 P~/pS95/11754 wo x~ossss in a directional coupler 45 to the output of a constant envelope amplifier 43 which receives a constant envelope signal from a first quadrature modulator 41.
Optional low pass filters 46 may be included; both the upper filters 46 and lower filters 40 might, however, comprise digital to-analog convertors if the I, Q
signals originate in digital form.
In practice, the generation of constant envelope modulated data signals and/or linearly filtered data signals may be accomplished with the aid of a so-called ROM
modulator. The ROM (Read Only Memory) modulator assumes that the filter used to shape the I, Q or phase angle transitions has a finite impulse response of a few data symbols (e.g., bits) duration. That means that each segment of I or Q waveform over a symbol period depends only on that finite number of bits. For example, if the filter impulse is five bit periods long, there are only 32 (2s) possibilities for the output waveform. Plus/minus and time reversal symmetries permit a compression of these waveform types so that all may be stored in a small ROM. Modulation and filtering are then combined in the operation of simply retrieving a waveform from a memory location given by the last five data bits.
An implementation of the present invention can be constructed where both the constant envelope modulation and the high-pass filtered version of it can be represented by finite impulse response filter funarons. The finite number of I and Q
waveforms which can arise are then stored in a ROM for both versions.
Referring to Figure 5, every bit period a new bit is shifted into an N bit shift register 50, and the last N bits, where N corresponds to the impulse response length of the filter, are presented to a ROM 51. Two I and two. Q waveforms (corresponding respectively to the constant envelope waveform and the high-pass filtered waveform) are selected from the ROM and converted from digital to analog form in four digital-to-analog converters 52 - 55.
In response to a clock input, a counter 61 then steps M times during each bit period of the input digital data stream to produce a sequence of M points representing in discrete steps in the waveform aver the bit period. The D-to-A converted - waveforms are filtered in anti-aliasing low-pass filters 62 to remove the step granularity 219 9 7 p g pCT~S~11754 wo ~ossss ~d ~~ panted respectively to a constant envelope modulator 56 and an error signal modulator 57, respectively. The constant envelope modulator output may be amplified by a Class-C power amplifier 58 while the error signal is amplified by a linear power amplifier 59. The outputs of the two power amplifiers are then added in a directional . coupler 60.
It is pointed out that, to obtain best cancellation of the unwanted spectral components, it may be necessary to build in a relative delay of the constant envelope siD°nal relative to the error signal to compensate for the inherent delay in the high-pass filtering operation. This can be accomplished in the implementation of Figure 4 bY.
10. digitally retiming the data stream by means of high-pass filters 40 used to produce the constant envelope I, Q signals using a suitable clock. If the high pass filters 40 exhibit a delay, the filters 46 can delay the constant envelope signals to align them in time for coaect cancel>ation of spectzal energy tails- In the case of, the ROM
modulator, the relative delay can be befit into the ROM contents.
Other embodiments of the present invention w01 be apparent to a person stalled in the art which differ in detail, but embodying the present invention's general principle .y of generating an amplified error signal corresponding to the unwanted spectral energy tads of a constant envelope signal, adding this signal to the constant envelope signal so as to cancel those unwanted spectral componeats, leaving a signal with greatly 20 reduced adjacent channel energy.
While only particular embodiments of the present invention have been shown and descn'bed herein, it will be obvious that further modifications may be made without departing from the invention in its broader aspects. For example, various other implementations could be devised ut~Iizing other hardware devices, digital signal 25 processors, or memory configurations- Accordingly, the claims are intended to cover all such changes and alternative constructions that fall within the scope and spirit of the invention.
Claims (29)
1. A method for producing amplified signals for communications having reduced adjacent channel energy, the method comprising the steps of:
generating a first signal through modulating and amplifying, the first signal having an undesired amount of adjacent channel energy;
generating through modulating and amplifying independent of the first signal, a second signal corresponding to the undesired amount of adjacent channel energy; and combining said second signal and said first signal to reduce said undesired amount of adjacent channel energy.
generating a first signal through modulating and amplifying, the first signal having an undesired amount of adjacent channel energy;
generating through modulating and amplifying independent of the first signal, a second signal corresponding to the undesired amount of adjacent channel energy; and combining said second signal and said first signal to reduce said undesired amount of adjacent channel energy.
2. A method according to claim 1, wherein said first signal is a constant-envelope signal.
3. A method according to claim 1 or 2, wherein said step of generating said first signal includes phase modulating a carrier frequency signal.
4. A method according to claim 3, wherein said phase modulating step includes quadrature modulation using sine and cosine carrier frequency signals.
5. A method according to claim 1 or 2, wherein said step of generating said first signal includes modulating a signal with digital data.
6. A method according to any one of claims 1 to 5, further comprising the step of amplifying said first signal by a Class-C power amplifier.
7. A method according to any one of claims 1 to 6, further comprising the step of amplifying said second signal by a linear amplifier.
8. A method according to any one of claims 1 to 7, wherein said subtraction step includes combining in a directional coupler said first and second signals in a predetermined ratio.
9. A method for amplifying communications signals exhibiting reduced adjacent channel energy, the method comprising the steps of:
generating I, Q modulation signals wherein a sum of the squares of instantaneous I, Q
signals is a constant;
applying said I, Q signals to a quadrature modulator operating on sine and cosine carrier frequency signals to obtain a constant-envelope signal;
amplifying said constant envelope signal using a power amplifier designed to yield high efficiency with constant-envelope signals;
high-pass filtering said I, Q signals and applying said high-pass filtered signals to a second quadrature modulator to obtain an error signal;
amplifying said error signal using a linear amplifier adapted to effectively amplify varying amplitude signals; and adding an output of said power amplifier to an output of said linear amplifier in order to obtain a signal having reduced adjacent channel energy.
generating I, Q modulation signals wherein a sum of the squares of instantaneous I, Q
signals is a constant;
applying said I, Q signals to a quadrature modulator operating on sine and cosine carrier frequency signals to obtain a constant-envelope signal;
amplifying said constant envelope signal using a power amplifier designed to yield high efficiency with constant-envelope signals;
high-pass filtering said I, Q signals and applying said high-pass filtered signals to a second quadrature modulator to obtain an error signal;
amplifying said error signal using a linear amplifier adapted to effectively amplify varying amplitude signals; and adding an output of said power amplifier to an output of said linear amplifier in order to obtain a signal having reduced adjacent channel energy.
10. A method according to claim 9, wherein said I, Q signals represent digital data modulation signals.
11. A method of generating amplified, digital data-modulated signals exhibiting reduced adjacent channel energy, the method comprising the steps of:
generating I, Q modulated signals representing digital data, the signals having greater than desired adjacent channel energy;
applying said I, Q signals to a quadrature modulator operating on sine and cosine carrier frequency signals to obtain a first signal;
high-pass filtering said I, Q modulation signals to obtain high-pass filtered I, Q signals;
applying said high-pass filtered I, Q signals to a second quadrature modulator to obtain a second signal; and amplifying and adding said first and second signals to obtain a signal having reduced adjacent channel energy.
generating I, Q modulated signals representing digital data, the signals having greater than desired adjacent channel energy;
applying said I, Q signals to a quadrature modulator operating on sine and cosine carrier frequency signals to obtain a first signal;
high-pass filtering said I, Q modulation signals to obtain high-pass filtered I, Q signals;
applying said high-pass filtered I, Q signals to a second quadrature modulator to obtain a second signal; and amplifying and adding said first and second signals to obtain a signal having reduced adjacent channel energy.
12. A method for generating amplified, digital data modulated to obtain signals reduced adjacent channel energy, the method comprising the steps of:
generating I, Q signals corresponding to a constant-envelope digital data modulation;
applying said I, Q signals to a quadrature modulator operating on sine and cosine carrier frequency signals to obtain a constant-envelope signal;
amplifying said constant-envelope signal using a power amplifier designed to yield high efficiency with constant-envelope signals;
high-pass filtering said I, Q signals and applying the resulting high-pass filtered signals to a second quadrature modulator to obtain an error signal;
amplifying said error signal using a linear amplifier adapted to varying amplitude signals; and adding output of said power amplifier to output of said linear amplifier to obtain a signal having reduced adjacent channel energy.
generating I, Q signals corresponding to a constant-envelope digital data modulation;
applying said I, Q signals to a quadrature modulator operating on sine and cosine carrier frequency signals to obtain a constant-envelope signal;
amplifying said constant-envelope signal using a power amplifier designed to yield high efficiency with constant-envelope signals;
high-pass filtering said I, Q signals and applying the resulting high-pass filtered signals to a second quadrature modulator to obtain an error signal;
amplifying said error signal using a linear amplifier adapted to varying amplitude signals; and adding output of said power amplifier to output of said linear amplifier to obtain a signal having reduced adjacent channel energy.
13. A method according to claim 12, further comprising the step of retrievably storing precalculated I, Q signals as values numerically stored in and retrieved from a Read Only Memory.
14. A method of generating amplified, digital data modulated signals to provide reduced adjacent channel energy, the method comprising the steps of feeding digital data signals through a shift register of N stages;
coupling N signals from said shift register corresponding to the last N data bits of said digital data signals to address input lines of a read only memory;
connecting address lines of said read only memory to the digit lines of a counter;
incrementing said counter to obtain sequentially a number of sets of four output values from said read only memory;
digital-to-analog converting said four output values to obtain a first I, Q
signal and a second I, Q signal;
applying said first I, Q signal to a first quadrature modulator to obtain a first signal of higher than desired adjacent channel energy;
applying said second I, Q signal to a second quadrature modulator to obtain a second signal; and adding said first signal to said second signal in an optimum ratio to obtain a signal of reduced adjacent channel energy.
coupling N signals from said shift register corresponding to the last N data bits of said digital data signals to address input lines of a read only memory;
connecting address lines of said read only memory to the digit lines of a counter;
incrementing said counter to obtain sequentially a number of sets of four output values from said read only memory;
digital-to-analog converting said four output values to obtain a first I, Q
signal and a second I, Q signal;
applying said first I, Q signal to a first quadrature modulator to obtain a first signal of higher than desired adjacent channel energy;
applying said second I, Q signal to a second quadrature modulator to obtain a second signal; and adding said first signal to said second signal in an optimum ratio to obtain a signal of reduced adjacent channel energy.
15. An apparatus for producing amplified signals for communications having reduced adjacent channel energy, the apparatus comprising:
first modulating and amplifying means for generating a first signal having an undesired amount of adjacent channel energy;
second modulating and amplifying means for generating, independent of the first signal, a second signal corresponding to the undesired amount of adjacent channel energy; and means for combining said second signal and said first signal to reduce said undesired amount of adjacent channel energy.
first modulating and amplifying means for generating a first signal having an undesired amount of adjacent channel energy;
second modulating and amplifying means for generating, independent of the first signal, a second signal corresponding to the undesired amount of adjacent channel energy; and means for combining said second signal and said first signal to reduce said undesired amount of adjacent channel energy.
16. An apparatus according to claim 15, wherein said first signal is a constant-envelope signal.
17. An apparatus according to claim 15 or 16, wherein said means for generating said first signal includes a phase modulator for phase modulating a carrier frequency signal.
18. An apparatus according to claim 17, wherein said phase modulator includes a quadrature modulator for quadrature modulation using sine and cosine carrier frequency signals.
19. An apparatus according to claim 15 or 16, wherein said means for generating said first signal includes a modulator for modulating a signal with digital data.
20. An apparatus according to any one of claims 15 to 19, further comprising a Class-C power amplifier for amplifying said first signal.
21. An apparatus according to any one of claims 15 to 20, further comprising a linear amplifier for amplifying said second signal.
22. An apparatus according to any one of claims 15 to 21, wherein said means for subtraction includes a directional coupler for combining said first and second signals in a predetermined ratio.
23. An apparatus for producing amplified communications signals with reduced adjacent channel energy, the apparatus comprising:
means for generating I, Q modulation signals wherein a sum of the squares of instantaneous I, Q signals is a constant;
a first quadrature modulator for applying sine and cosine carrier frequency signals to said I, Q signals to obtain a constant-envelope signal;
a power amplifier designed to yield high efficiency with constant-envelope signals for amplifying said constant-envelope signal;
a high-pass filter for high-pass filtering said I, Q signals;
a second quadrature modulator for applying sine and cosine carrier frequency signals to said high-pass filtered signals to obtain an error signal;
a linear amplifier adapted to effectively amplify varying amplitude signals for amplifying said error signal; and an adder for adding an output of said power amplifier to an output of said linear amplifier in order to obtain a signal having reduced adjacent channel energy.
means for generating I, Q modulation signals wherein a sum of the squares of instantaneous I, Q signals is a constant;
a first quadrature modulator for applying sine and cosine carrier frequency signals to said I, Q signals to obtain a constant-envelope signal;
a power amplifier designed to yield high efficiency with constant-envelope signals for amplifying said constant-envelope signal;
a high-pass filter for high-pass filtering said I, Q signals;
a second quadrature modulator for applying sine and cosine carrier frequency signals to said high-pass filtered signals to obtain an error signal;
a linear amplifier adapted to effectively amplify varying amplitude signals for amplifying said error signal; and an adder for adding an output of said power amplifier to an output of said linear amplifier in order to obtain a signal having reduced adjacent channel energy.
24. An apparatus according to claim 23, wherein said power amplifier is a Class-C
power amplifier.
power amplifier.
25. A device according to claim 23 or 24, wherein said I, Q signals represent digital data modulation signals.
26. An apparatus for generating amplified, digital data modulated signals exhibiting with adjacent channel energy, the apparatus comprising:
means for generating I, Q signals representing digital data modulation, said signals having greater than desired adjacent channel energy;
a first quadrature modulator to which said I, Q signals are applied and operating on sine and cosine carrier frequency signals to obtain a first signal;
means for high-pass filtering said I, Q modulation signals to obtain high-pass filtered I, Q signals;
a second quadrature modulator to which said high-pass filtered I, Q signals are applied to obtain a second signal; and an adder for adding said first and second signals to obtain a signal having reduced adjacent channel energy.
means for generating I, Q signals representing digital data modulation, said signals having greater than desired adjacent channel energy;
a first quadrature modulator to which said I, Q signals are applied and operating on sine and cosine carrier frequency signals to obtain a first signal;
means for high-pass filtering said I, Q modulation signals to obtain high-pass filtered I, Q signals;
a second quadrature modulator to which said high-pass filtered I, Q signals are applied to obtain a second signal; and an adder for adding said first and second signals to obtain a signal having reduced adjacent channel energy.
27. An apparatus for generating amplified, digital data modulated signals with reduced adjacent channel energy, the apparatus comprising:
means for generating I, Q signals corresponding to a constant-envelope digital data modulation;
a first quadrature modulator to which said I, Q signals are applied and operating on sine and cosine carrier frequency signals to obtain a constant-envelope signal;
a power amplifier designed to yield high efficiency with constant-envelope signals for amplifying said constant-envelope signal;
means for high-pass filtering said I, Q signals;
a second quadrature modulator to which said high-pass filtered signals to obtain an error signal;
a linear amplifier adapted to varying amplitude signals for amplifying said error signal;
and an adder for adding output of said power amplifier to output of said linear amplifier to obtain a signal having reduced adjacent channel energy.
means for generating I, Q signals corresponding to a constant-envelope digital data modulation;
a first quadrature modulator to which said I, Q signals are applied and operating on sine and cosine carrier frequency signals to obtain a constant-envelope signal;
a power amplifier designed to yield high efficiency with constant-envelope signals for amplifying said constant-envelope signal;
means for high-pass filtering said I, Q signals;
a second quadrature modulator to which said high-pass filtered signals to obtain an error signal;
a linear amplifier adapted to varying amplitude signals for amplifying said error signal;
and an adder for adding output of said power amplifier to output of said linear amplifier to obtain a signal having reduced adjacent channel energy.
28. An apparatus according to claim 27, further comprising a memory for retrievably storing precalculated I, Q signals as values numerically stored therein.
29. An apparatus for generating amplified, digital data modulated signals with reduced adjacent channel energy, the apparatus comprising:
a shift register of N stages to which digital data input signals are input;
a read only memory having address input lines to which are coupled to N
signals from said shift register corresponding to the last N data bits of said digital data signals;
a counter having digit lines to which are connected to address lines of said read only memory;
means for incrementing said counter to obtain sequentially a number of sets of four output values from said read only memory;
digital-to-analog convertor for converting said four output values to obtain a first I, Q
signal and a second I, Q signal;
a first quadrature modulator to which said first I, Q signal is applied to obtain a first signal of higher than desired adjacent channel energy;
a second quadrature modulator to which said second I, Q signal is applied to obtain a second signal; and an adder for adding said first signal to said second signal in an optimum ratio to obtain a signal of reduced adjacent channel energy.
a shift register of N stages to which digital data input signals are input;
a read only memory having address input lines to which are coupled to N
signals from said shift register corresponding to the last N data bits of said digital data signals;
a counter having digit lines to which are connected to address lines of said read only memory;
means for incrementing said counter to obtain sequentially a number of sets of four output values from said read only memory;
digital-to-analog convertor for converting said four output values to obtain a first I, Q
signal and a second I, Q signal;
a first quadrature modulator to which said first I, Q signal is applied to obtain a first signal of higher than desired adjacent channel energy;
a second quadrature modulator to which said second I, Q signal is applied to obtain a second signal; and an adder for adding said first signal to said second signal in an optimum ratio to obtain a signal of reduced adjacent channel energy.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/305,729 | 1994-09-14 | ||
| US08/305,729 US5694433A (en) | 1994-09-14 | 1994-09-14 | Efficient linear power amplification |
| PCT/US1995/011754 WO1996008866A1 (en) | 1994-09-14 | 1995-09-14 | Efficient linear power amplification |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2199708A1 CA2199708A1 (en) | 1996-03-21 |
| CA2199708C true CA2199708C (en) | 2005-07-12 |
Family
ID=23182083
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002199708A Expired - Fee Related CA2199708C (en) | 1994-09-14 | 1995-09-14 | Efficient linear power amplification |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US5694433A (en) |
| EP (1) | EP0782789B1 (en) |
| JP (1) | JP3644965B2 (en) |
| KR (1) | KR100398302B1 (en) |
| CN (1) | CN1076903C (en) |
| AU (1) | AU691346B2 (en) |
| CA (1) | CA2199708C (en) |
| DE (1) | DE69530778T2 (en) |
| FI (1) | FI114667B (en) |
| WO (1) | WO1996008866A1 (en) |
Families Citing this family (37)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5920596A (en) * | 1995-01-31 | 1999-07-06 | Motorola, Inc. | Apparatus for amplifying a signal using a digital processor |
| US5815531A (en) * | 1996-06-12 | 1998-09-29 | Ericsson Inc. | Transmitter for encoded data bits |
| US6185259B1 (en) | 1996-06-12 | 2001-02-06 | Ericsson Inc. | Transmitter/receiver for GMSK and offset-QAM |
| US6298221B1 (en) * | 1998-04-01 | 2001-10-02 | Denso Corporation | Adaptive receiver linearity techniques for a radio transceiver |
| US6600792B2 (en) | 1998-06-26 | 2003-07-29 | Qualcomm Incorporated | Predistortion technique for high power amplifiers |
| US6404823B1 (en) * | 1998-07-01 | 2002-06-11 | Conexant Systems, Inc. | Envelope feedforward technique with power control for efficient linear RF power amplification |
| US6349216B1 (en) * | 1999-07-22 | 2002-02-19 | Motorola, Inc. | Load envelope following amplifier system |
| JP2001203540A (en) | 2000-01-19 | 2001-07-27 | Hitachi Ltd | High frequency power amplifier |
| US7003025B2 (en) * | 2000-08-31 | 2006-02-21 | Nokia Mobile Phones Ltd. | Envelope stabilization method and apparatus |
| US6545541B2 (en) | 2001-05-29 | 2003-04-08 | Ericsson Inc. | Power amplifier embedded cell bias detection, methods of detecting bias in power amplifiers and systems utilizing embedded cell bias detection |
| US6665525B2 (en) | 2001-05-29 | 2003-12-16 | Ericsson Inc. | High-level modulation method and apparatus |
| US7088958B2 (en) * | 2001-06-19 | 2006-08-08 | Intersil Americas Inc. | Remote power amplifier linearization |
| WO2003021826A1 (en) * | 2001-09-05 | 2003-03-13 | Envara Ltd. | Method for measuring and compensating gain and phase imbalances in quadrature modulators |
| US20030179830A1 (en) * | 2002-03-25 | 2003-09-25 | Eidson Donald B. | Efficient, high fidelity transmission of modulation schemes through power-constrained remote relay stations by local transmit predistortion and local receiver feedback |
| US7882346B2 (en) * | 2002-10-15 | 2011-02-01 | Qualcomm Incorporated | Method and apparatus for providing authentication, authorization and accounting to roaming nodes |
| US7869803B2 (en) | 2002-10-15 | 2011-01-11 | Qualcomm Incorporated | Profile modification for roaming in a communications environment |
| US7349679B1 (en) | 2004-06-30 | 2008-03-25 | Qualcomm Inc. | Integrated power amplifier |
| US7355470B2 (en) | 2006-04-24 | 2008-04-08 | Parkervision, Inc. | Systems and methods of RF power transmission, modulation, and amplification, including embodiments for amplifier class transitioning |
| US7327803B2 (en) | 2004-10-22 | 2008-02-05 | Parkervision, Inc. | Systems and methods for vector power amplification |
| KR100756041B1 (en) * | 2005-06-27 | 2007-09-07 | 삼성전자주식회사 | Doherty Amplifier and Transmitter Using Mixer |
| US9066344B2 (en) | 2005-09-19 | 2015-06-23 | Qualcomm Incorporated | State synchronization of access routers |
| US7911272B2 (en) | 2007-06-19 | 2011-03-22 | Parkervision, Inc. | Systems and methods of RF power transmission, modulation, and amplification, including blended control embodiments |
| US8334722B2 (en) | 2007-06-28 | 2012-12-18 | Parkervision, Inc. | Systems and methods of RF power transmission, modulation and amplification |
| WO2007094241A1 (en) * | 2006-02-15 | 2007-08-23 | Matsushita Electric Industrial Co., Ltd. | Transmission circuit |
| JP4646845B2 (en) * | 2006-03-30 | 2011-03-09 | 富士通株式会社 | Transmitter |
| US8031804B2 (en) | 2006-04-24 | 2011-10-04 | Parkervision, Inc. | Systems and methods of RF tower transmission, modulation, and amplification, including embodiments for compensating for waveform distortion |
| US7937106B2 (en) | 2006-04-24 | 2011-05-03 | ParkerVision, Inc, | Systems and methods of RF power transmission, modulation, and amplification, including architectural embodiments of same |
| US8315336B2 (en) | 2007-05-18 | 2012-11-20 | Parkervision, Inc. | Systems and methods of RF power transmission, modulation, and amplification, including a switching stage embodiment |
| US7719355B2 (en) * | 2007-05-31 | 2010-05-18 | Motorola, Inc. | Method and apparatus for providing a Cartesian training waveform |
| WO2008156800A1 (en) | 2007-06-19 | 2008-12-24 | Parkervision, Inc. | Combiner-less multiple input single output (miso) amplification with blended control |
| WO2009145887A1 (en) | 2008-05-27 | 2009-12-03 | Parkervision, Inc. | Systems and methods of rf power transmission, modulation, and amplification |
| WO2012139126A1 (en) | 2011-04-08 | 2012-10-11 | Parkervision, Inc. | Systems and methods of rf power transmission, modulation, and amplification |
| WO2012167111A2 (en) | 2011-06-02 | 2012-12-06 | Parkervision, Inc. | Antenna control |
| KR20160058855A (en) | 2013-09-17 | 2016-05-25 | 파커비전, 인크. | Method, apparatus and system for rendering an information bearing function of time |
| EP3057279A1 (en) * | 2015-02-16 | 2016-08-17 | Universität der Bundeswehr München | Device and method for transmitting data |
| CN105490650A (en) * | 2015-12-31 | 2016-04-13 | 智坤（江苏）半导体有限公司 | Power amplifier and application thereof |
| US10128875B1 (en) * | 2018-03-30 | 2018-11-13 | Mitsubishi Electric Research Laboratories, Inc. | Methods and system of a digital transmitter with reduced quantization noise |
Family Cites Families (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2520957A1 (en) * | 1982-01-29 | 1983-08-05 | Thomson Csf | DEVICE FOR CORRECTING INTERMODULATION PRODUCED BY A HIGH-FREQUENCY CONTROLLED SIGNAL AMPLIFIER |
| US4490684A (en) * | 1983-01-03 | 1984-12-25 | Motorola, Inc. | Adaptive quadrature combining apparatus |
| US5187721A (en) * | 1987-03-04 | 1993-02-16 | National Semiconductor Corporation | Frequency shift keying modulator |
| US4843615A (en) * | 1987-05-08 | 1989-06-27 | Harris Corp. | CPFSK communication system employing nyquist-filtered modulator/demodulator |
| US5121412A (en) * | 1989-01-03 | 1992-06-09 | Motorola, Inc. | All-digital quadrature modulator |
| US5132639A (en) * | 1989-09-07 | 1992-07-21 | Ortel Corporation | Predistorter for linearization of electronic and optical signals |
| SE465494B (en) * | 1990-01-22 | 1991-09-16 | Ericsson Telefon Ab L M | PROCEDURE TO COMPENSATE FOR OILARITIES IN A FINAL AMPLIFIER |
| JP3044057B2 (en) * | 1990-03-27 | 2000-05-22 | 日本電信電話株式会社 | Variable output transmitter |
| US5307022A (en) * | 1991-04-15 | 1994-04-26 | Motorola, Inc. | High dynamic range modulation independent feed forward amplifier network |
| JPH05129845A (en) * | 1991-11-01 | 1993-05-25 | Oki Electric Ind Co Ltd | Linear power amplifier |
| US5436749A (en) * | 1991-12-09 | 1995-07-25 | Scientific-Atlanta, Inc. | Method and apparatus for predistortion |
| JPH0637551A (en) * | 1992-07-17 | 1994-02-10 | Fujitsu Ltd | Distortion compensation circuit |
| US5481389A (en) * | 1992-10-09 | 1996-01-02 | Scientific-Atlanta, Inc. | Postdistortion circuit for reducing distortion in an optical communications system |
| JPH0795664B2 (en) * | 1992-11-27 | 1995-10-11 | 日本電気株式会社 | High frequency high power amplifier |
| JPH06244647A (en) * | 1993-02-19 | 1994-09-02 | Kokusai Electric Co Ltd | Non-linear distortion compensation control circuit for amplifier |
-
1994
- 1994-09-14 US US08/305,729 patent/US5694433A/en not_active Expired - Lifetime
-
1995
- 1995-09-14 EP EP95934430A patent/EP0782789B1/en not_active Expired - Lifetime
- 1995-09-14 WO PCT/US1995/011754 patent/WO1996008866A1/en active IP Right Grant
- 1995-09-14 CA CA002199708A patent/CA2199708C/en not_active Expired - Fee Related
- 1995-09-14 JP JP51037796A patent/JP3644965B2/en not_active Expired - Fee Related
- 1995-09-14 AU AU36768/95A patent/AU691346B2/en not_active Ceased
- 1995-09-14 CN CN95195058A patent/CN1076903C/en not_active Expired - Fee Related
- 1995-09-14 DE DE69530778T patent/DE69530778T2/en not_active Expired - Lifetime
- 1995-09-14 KR KR1019970701658A patent/KR100398302B1/en not_active IP Right Cessation
-
1997
- 1997-03-13 FI FI971051A patent/FI114667B/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| AU691346B2 (en) | 1998-05-14 |
| JP3644965B2 (en) | 2005-05-11 |
| CN1157676A (en) | 1997-08-20 |
| CN1076903C (en) | 2001-12-26 |
| CA2199708A1 (en) | 1996-03-21 |
| FI971051A0 (en) | 1997-03-13 |
| DE69530778D1 (en) | 2003-06-18 |
| FI114667B (en) | 2004-11-30 |
| EP0782789A1 (en) | 1997-07-09 |
| EP0782789B1 (en) | 2003-05-14 |
| WO1996008866A1 (en) | 1996-03-21 |
| JPH10511235A (en) | 1998-10-27 |
| US5694433A (en) | 1997-12-02 |
| DE69530778T2 (en) | 2004-02-26 |
| FI971051A (en) | 1997-05-14 |
| KR100398302B1 (en) | 2003-12-31 |
| AU3676895A (en) | 1996-03-29 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA2199708C (en) | Efficient linear power amplification | |
| US6181199B1 (en) | Power IQ modulation systems and methods | |
| US6928122B2 (en) | Amplifier predistortion system and method | |
| US5021753A (en) | Splatter controlled amplifier | |
| US6647073B2 (en) | Linearisation and modulation device | |
| CN100364239C (en) | Transmitting circuit device and wireless communications device | |
| US6993091B2 (en) | Correction of DC-offset of I/Q modulator | |
| US7932790B2 (en) | Switched modulation of a radio-frequency amplifier | |
| WO2007113726A1 (en) | Multi-mode radio transmitters and a method of their operation | |
| CA2164465A1 (en) | Converter for converting a modulating signal with variable envelope to two modulating signals without variable envelope, transmitter using the converter and method for transmitting a modulated wave with variable envelope | |
| WO2000038388A1 (en) | Qam modulator for radio communications | |
| JP2000004267A (en) | Non-linear constant envelope modulator and transmission architecture | |
| JP2009524329A (en) | Cartesian modulation system with multi-level pulse width modulation. | |
| US20040132470A1 (en) | Amplitude- and frequency- or phase-modulated radio frequency signal generator and the transmitter incorporating same | |
| US7310382B2 (en) | Linearized switch-based power amplifier | |
| US9602325B2 (en) | Transmitter and method of transmitting | |
| JP2006528457A (en) | Amplifier circuit including envelope modulation limit cycle modulator circuit | |
| KR100751999B1 (en) | Method and apparatus for generating an rf signal | |
| KR100251385B1 (en) | Apparatus and method for linearizing power amp with adaptive predistortion and modem error compensation | |
| Matsuura et al. | A high efficiency transmitter with a delta-sigma modulator and a noise cancellation circuit | |
| JPH11196140A (en) | Power amplifier | |
| CN217904431U (en) | Analog predistortion circuit for digital modulation signal | |
| JP2561506B2 (en) | SSB transmitter | |
| FI108377B (en) | Linearisation of a transmitter's power amplifier | |
| WO2005064877A1 (en) | Digital rf modulator comprising a phase or frequency return path |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |
Effective date: 20150914 |