WO2003026236A2 - Adaptive equalizer which is independent of the amplitude of the transmited signal - Google Patents
Adaptive equalizer which is independent of the amplitude of the transmited signal Download PDFInfo
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- WO2003026236A2 WO2003026236A2 PCT/CA2002/001419 CA0201419W WO03026236A2 WO 2003026236 A2 WO2003026236 A2 WO 2003026236A2 CA 0201419 W CA0201419 W CA 0201419W WO 03026236 A2 WO03026236 A2 WO 03026236A2
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03878—Line equalisers; line build-out devices
- H04L25/03885—Line equalisers; line build-out devices adaptive
Definitions
- This invention relates generally to the field of equalizers. More particularly, the invention provides a transmit amplitude independent adaptive equalizer that is capable of compensating for transmission losses in an input signal when the transmit signal amplitude is unknown.
- the invention is particularly well suited for use in digital communication components, such as receivers, equalizers, high-speed backplanes, Printed Circuit Board Trace equalizers, automatic gain control devices, and other types of digital communication components.
- Fig. 1 is a block diagram showing an equalizer 12 implemented in a typical digital communications system 10 in which an input signal 14 is transmitted through a transmission medium 16.
- Typical transmission media 16 used for transmission of digital signals over relatively short distances include, for example, printed circuit board (PCB) traces and coaxial cables. These, and other known transmission media, typically cause significant frequency dependant losses in digital signals being transmitted over the media and consequently distort the digital data, often resulting in pulse spreading and interference between neighboring pulses (known as intersymbol interference).
- intersymbol interference pulse spreading and interference between neighboring pulses
- the input signal 14 is further corrupted during transmission by noise 18 induced by the transmission medium 16.
- the equalizer 12 regenerates the transmitted signal 20 by providing gain to compensate for the frequency dependant losses caused by the transmission medium 16 (up to some maximum length) while preferably minimizing the effect of noise 18. This function is typically achieved by applying a transfer function to the received signal 20 that approximates the inverse of the transmission losses.
- Fig. 2 is a graph 30 showing the loss (in dB) incurred in the transmission medium 16, plotted as a function of both the length (/) of the medium 16 and the frequency (/) of the
- the loss over a transmission medium (such as a coaxial cable or PCB trace) may be approximated in the frequency domain by the following equation:
- Length 1 '(shorter) and Length 2 (longer) As the length (/) of the transmission
- an equalizer 12 should have a frequency characteristic that is the inverse of the loss function of the transmission medium.
- the inverse loss function may be approximated as follows:
- K is a control variable that is proportional to the length (/) of the transmission medium.
- Fig. 3 is a graph 40 showing the inverse loss function G(f) , plotted in dB on the same
- Fig. 4 is a block diagram of an equalizer core 50 that implements the inverse loss function G(f) .
- the equalizer core 50 includes a transfer function block 52 (H(/)), a multiplier
- This circuit 50 applies variable gain to an input signal 57 by applying the transfer function H(f) in order to generate a resultant signal and then by multiplying the
- the gain control signal 58 (K) preferably controls the amount of gain applied by the transfer function H(f) by multiplying the output of the transfer function block 52 by a factor typically varying
- Fig. 5 is a block diagram of an alternative equalizer core 60 that implements a bandwidth- limited inverse loss function.
- a low-pass filter 62 is added to the equalizer core 50 shown in Fig. 4 to reduce noise encountered in the transmission medium 16.
- This alternative implementation 60 reduces the amplification of high frequency noise, and thus increases the signal-to-noise ratio (SNR) of the equalized output signal 64.
- SNR signal-to-noise ratio
- a graphical representation 70 of the bandwidth-limited inverse loss function 72, plotted on the same axes as the loss function L(f) is shown in Fig. 6.
- Fig. 7 is a block diagram showing a multiple-stage equalizer core 80 having three equalizer stages 82, 84 and 86, each of which implements the inverse loss function G(f) .
- each equalizer stage 82, 84 and 86 includes a gain control signal (Kl, K2 or K3) that is used to control the gain implemented by the transfer function H(f) in proportion to the length of the transmission
- each stage 82, 84 and 86 in the multiple-stage equalizer core 80 is configured to equalize signals transmitted over transmission media up to a percentage of the total maximum transmission medium length. For instance, if the multiple-stage equalizer core 80 is capable of equalizing losses incurred in a printed circuit board ("PCB") trace of up to 30 inches, then each core stage 82, 84, and 86 will typically be configured to equalize losses in PCB traces of up to 10 inches. The stages 82, 84 and 86 are then cascaded such that they operate sequentially to equalize PCB traces of up to 30 inches.
- PCB printed circuit board
- Fig. 8 is a graph 90 showing how the gain control signals Kl, K2 and K3 in the multiple- stage equalizer core 80 are varied according to the length of the transmission medium.
- the value K shown along the x-axis in Fig. 8, represents the percentage of the transfer function H(f) that
- Fig. 8 shows that the gain control signals Kl, K2 and K3 cause gain to be supplied sequentially by the equalizer stages 82, 84 and 86.
- each equalizer stage 82, 84 and 86 is capable of providing the necessary gain to equalize 10 inches of a PCB trace
- the gain control signal Kl would typically control the gain necessary for PCB traces from 0 to 10 inches
- the combined gain control signals Kl (at unity) and K2 would typically control the gain necessary for PCB traces from 10 to 20 inches
- the combined gain control signals Kl (at unity), K2 (at unity) and K3 would typically provide the gain for PCB traces from 20 to 30 inches.
- Kl would be at its maximum value (unity)
- K2 would be at the value necessary to cause the second equalizer stage 84 to equalize a 5 inch transmission medium
- K3 would be zero.
- Fig. 9 is a block diagram showing an exemplary equalizer system 100 such as described in the referenced '515 Application.
- This equalizer system 100 includes an equalizer core 102, a sheer 104, an automatic gain control circuit (AGC) 106, a transmitter 108, and a transmission medium 110.
- the equalizer core 102 may be either a single-stage core as shown in Figs. 4 or 5 or a multiple-stage core as shown in Fig. 7, and operates, as described above, to compensate for the losses incurred in the transmission medium 110.
- the output 112 of the equalizer core 102 is coupled to the sheer 104, which converts the output signal 112 from the core 102 to a digital output signal 114 having a known swing (A) that .approximates the swing (B) of the data sent from the transmitter 108. Since the swing (B) of the transmitted data is known and reproduced as the swing (A) of the digital output signal 114 from the slicer 104, the difference in energy between the equalizer core output signal 112 and the digital output signal 114 approximates the energy lost in the transmission medium 110, which is proportional to its length.
- the AGC 106 compares the energy of the equalizer core output signal 112 with the energy of the digital output signal 114 from the slicer 104 to generate the gain control signal K.
- the AGC 106 includes a core-side band-pass filter 116, a core-side envelope detector 118, a slicer-side band-pass filter 120, a slicer-side envelope detector 122, an adder 124, and a sequencer 126. Operationally, the AGC 106 filters the core and digital outputs 112 and 114 to mid-band frequencies using the band-pass filters 116 and 120. The advantage of filtering the core and digital outputs 112 and 114 to their mid-band frequencies is explained in detail in the '515 Application. Following this filtering function, the AGC 106 then detects the signal energy of the two band-limited signals with the envelope detectors 118 and 122.
- the adder 124 determines the difference between the two signal energies with the adder 124, which provides the gain control signal K. If the equalizer core 102 is single-stage, then the gain control signal K is typically coupled directly to the core 102 to control the variable gain as described above. If, however, the equalizer core 102 is of the multiple-stage type, then the sequencer 126 is used to convert the gain control signal K from the adder 124 into a plurality of multiple-stage gain control signals Ki, such as Kl, K2 and K3 described above with reference to Figs. 7 and 8.
- the gain control signal(s) K (or Ki) enable the equalizer core 102 to equalize the core output signal 112 by forcing it to the same energy level as the digital output signal 114 from the slicer 104-
- the signal swing (B) at the transmitter 108 must be known a priori and accurately replicated by the slicer 104 if the equalizer system 100 shown in Fig. 9 is to achieve optimal performance. Any significant difference between the signal swing (B) at the transmitter 108 and the signal swing (A) of the digital output signal 114 will directly result in a gain (equalization) error.
- a transmit amplitude independent adaptive equalizer comprises an equalizer core, a controllable-swing slicer and an amplitude control loop.
- the equalizer core is coupled to an input signal from a transmission medium, and generates a core output signal by applying a frequency dependant gain to the input signal to compensate for losses incurred in the transmission medium.
- the controllable-swing slicer is coupled to the core output signal and a swing control input, and converts the core output signal into a digital output signal having a variable swing that is controlled by the swing control input.
- the amplitude control loop is coupled to the core output signal and the digital output signal, and generates the swing control input by comparing the core output signal with the digital output signal.
- a second embodiment of the equalizer comprises an equalizer core, a fixed-swing slicer, and a control loop.
- the equalizer core is coupled to an input signal from a transmission medium and a gain control input, and generates a core output signal by applying a frequency dependant gain to the input signal.
- the frequency dependant gain is controlled by the gain control input and compensates for losses incurred in the transmission medium.
- the fixed-swing slicer is coupled to the core output signal and converts the core output signal to a digital output signal having a fixed digital output swing.
- the control loop is coupled to the core output signal and the digital output signal and normalizes the core and digital output signals with respect to their low- frequency energy levels, compares the normalized core output signal with the normalized digital output signal to approximate a normalized energy level difference, and generates the gain control input.
- a third embodiment of the equalizer comprises a variable gain amplifier, a variable gain amplifier control loop, and an equalizer core.
- the variable gain amplifier is coupled to an input signal from a transmission medium and a variable gain control signal, and applies a variable gain to the input signal to generate an equalizer core input signal having a pre-determined signal swing.
- the variable gain amplifier control loop is coupled to the input signal and the equalizer core input signal, and compares the input signal with the equalizer core input signal in order to generate the variable gain control signal.
- the equalizer core is coupled to the equalizer core input signal, and applies a frequency dependant gain to the amplifier output in order to compensate for attenuation of the input signal caused by losses incurred in the transmission medium.
- a fourth embodiment of the equalizer cornprises a variable gain amplifier, an equalizer core, a fixed-swing slicer and a variable gain amplifier control loop.
- the variable gain amplifier is coupled to an input signal from a transmission medium and is also coupled to a variable gain control signal.
- the variable gain amplifier applies a variable gain to the input signal in order to generate an equalizer core input signal having a pre-determined signal swing.
- the equalizer core is coupled to the equalizer core input signal, and applies a frequency dependant gain to the amplifier output in order to compensate for attenuation of the input signal that is caused by losses incurred in the transmission medium and generates a core output signal.
- the fixed-swing slicer is coupled to the core output signal, and converts the core output signal into a digital output signal having the pre-determined signal swing.
- the variable gain amplifier control loop is coupled to the core output signal and the digital output signal, and compares the core output signal with the digital output signal in order to generate the variable gain control signal.
- Fig. 1 is a block diagram showing the use of an equalizer in a typical serial digital data communication system in which an input signal is transmitted through a transmission medium;
- Fig. 2 is a graph showing the loss (in dB) incurred in the transmission medium, plotted as a function of both the length (/) of the medium and the frequency (/) of the signal;
- Fig. 3 is a graph showing the inverse loss function G(f) plotted on the same axes as the
- Fig. 4 is a block diagram of an equalizer core that implements the inverse loss function G(f);
- Fig. 5 is a block diagram of an alternative equalizer core that implements a bandwidth-limited inverse loss function
- Fig. 6 is a graphical representation of the bandwidth-limited inverse loss function, plotted on the same axes as the loss function L(f) ;
- Fig. 7 is a block diagram showing a known multiple-stage equalizer core in which each stage implements the inverse loss function G(f) ;
- Fig. 8 is a graph showing how the gain control signals in the multiple-stage equalizer core are adjusted according to the length of the transmission medium
- Fig. 9 is a block diagram showing an exemplary equalizer system such as described in the referenced '515 Application;
- Fig. 10 is a block diagram of an exemplary transmit amplitude independent adaptive equalizer having a controllable-swing slicer according to one embodiment of the claimed invention
- Fig. 11 is a block diagram of an exemplary transmit amplitude independent adaptive equalizer having a fixed-swing slicer according to another embodiment of the claimed invention.
- Fig. 12 is a block diagram of a transmit amplitude leveling circuit for an equalizer
- Fig. 13 is a block diagram illustrating an exemplary implementation of the received data swing detection circuit and the core input swing detection circuit shown in Fig. 12;
- Fig. 14 is a block diagram of an exemplary transmit amplitude independent adaptive equalizer utilizing a variable gain amplifier.
- Fig. 10 is a block diagram of an exemplary transmit amplitude independent adaptive equalizer 200 having a controllable-swing slicer 204.
- the equalizer 200 includes an equalizer core 202, a controllable-swing slicer 204, a gain control loop (G-Loop) 206, and an amplitude control loop (A-Loop) 208.
- the G-Loop 206 includes two high band-pass filters 220 and 222, two envelope detectors 224 and 226, an adder 228, and a sequencer 230.
- the amplitude control loop (A-Loop) 208 includes two low band-pass filters 240 and 242, two envelope detectors 244 and 246, and an adder 248.
- the amplitude independent adaptive equalizer 200 tracks the amplitude at which its input signal 210 was transmitted by varying the swing of its digital output signal 214 to approximate the swing of the transmitted data. Because the loss incurred in a transmission medium is frequency dependant, the low frequency portion of the equalizer's input signal 210 shows substantially less attenuation than the higher frequency portions. The equalizer 200 thus detects the amplitude of its input signal 210 at a low frequency, and uses this low-frequency amplitude to approximate the swing of the transmitted data.
- the equalizer core 202 receives the input signal 210 from a transmission medium and generates a core output signal 212.
- the input signal 210 is preferably a digital signal that has been attenuated during transmission over a transmission medium.
- the equalizer core 202 compensates for attenuation and distortion in the input signal 210 by applying an inverse loss function G(f) as described above with reference to Figs. 2-8.
- the equalizer core 202 also
- controllable-swing slicer 204 which converts the core output signal 212 into a digital output signal 214 having a swing that is controlled by the amplitude control loop (A-Loop) 208.
- the A-Loop 208 isolates the low frequency portions of the core output signal 212 and the digital output signal 214, and compares the signal energies, of the two low band-limited signals to set the controllable-swing slicer 204 to approximate the swing of the equalizer input 210 prior to transmission.
- the high frequency portions of the core output signal 212 and the digital output signal 214 are isolated by the gain control loop (G-Loop) 206, which compares the signal energies of the high band-limited signals to generate the gain control signal (Ki) 226.
- G-Loop gain control loop
- the low band-limited signals are centered towards the low end of the transmit spectrum at which the transmission losses are minimal, and the high band-limited signals are centered towards the higher end of the transmit spectrum at which the transmission losses are more significant.
- the low and high band-limited signals may be centered at alternative points within the transmit spectrum as long as the A-Loop 208 isolates a lower spectral range than the G-Loop 206.
- the low frequency portions of the core output signal 212 and the digital output signal 214 are isolated by the low band-pass filters 240 and 242.
- the low band- limited signals are each coupled to one of the envelope detectors 244 and 246, which detect the signal energies.
- the envelope detectors 244 and 246 may preferably be comprised of rectifiers, but could alternatively be any device or combination of devices capable of generating an output signal proportional to the signal energy of its input. The difference between the energy-level outputs from the envelope detectors 244 and 246 is then determined by the adder 248.
- the energy difference is calculated by coupling the energy-level output from one envelope detector 244 as a positive input to the adder 248, and the energy-level output from the other envelope detector 246 as a negative input to the adder 248.
- the adder 248 generates a swing control signal 249 that is proportional to the energy difference between the low band-limited signals.
- the swing control signal 249 is coupled to the controllable-swing slicer 204 to control the energy level of the digital output signal 214.
- the A-Loop swing control signal 250 forces the swing of the digital output 214 to match the swing of the low band-limited core output. Because the low band-limited core output is typically not significantly attenuated by the transmission medium, the swing of the digital output 214 is thus made to approximate the swing of the equalizer input 210 prior to transmission.
- the higher frequency portions of the core output signal 212 and the digital output signal 214 are isolated by the high band-pass filters 220 and 222.
- the bandwidths of the high band-pass filters 220 and 222 are preferably set to isolate the' frequency band in which the equalizer input signal 210 is most significantly effected by transmission losses.
- the difference between the energy-level outputs of the envelope detectors 224 and 226 is preferably determined by coupling one energy-level output as a negative input to the adder 228 and coupling the other energy-level output as a positive input to the adder 228.
- the adder 21 then generates a single-stage gain control signal (K) 232 that is proportional to the energy difference between the band-limited core and digital output signals. Because this energy difference approximates the energy lost during transmission over the transmission medium, the single-stage gain control signal (K) 232 settles to a value proportional to the transmission loss which is a function of the length of the transmission medium.
- the single-stage gain control signal (K) 232 is coupled to the sequencer 230, which generates the gain control signal Ki 234 that is fed back to control the gain of the equalizer core 202 as described above with reference to Figs. 7 and 8.
- the equalizer core 202 is a single-stage equalizer core as described above with reference to Fig. 4 or Fig. 5, then the single-stage gain control signal (K) 232 may be directly fed back to the equalizer core 202. It should be understood that many types of controllers could be used to implement the A- Loop 208 and the G-Loop 206 shown in Fig. 10.
- the A-Loop 208 and the G-Loop 206 may be implemented as either a proportional type controller (P-Type), an integral type controller (I-Type) or a combination Pl-type controller.
- P-Type proportional type controller
- I-Type integral type controller
- Pl-type controller a combination Pl-type controller
- an integrator Kj/s
- the A-Loop 208 and the G- Loop 206 are preferably implemented as different controller types such that one control loop 206 or 208 has a dominant time constant/pole.
- the G-Loop 206 may preferably be implemented as a slower I-type loop, while the A-Loop 208 is implemented as a faster P-Type loop.
- Fig. 11 is a block diagram of an exemplary transmit amplitude independent adaptive equalizer 300 having a fixed-swing slicer 304.
- the amplitude independent adaptive equalizer 300 includes an equalizer core 302, a slicer 304, and a control loop 305.
- the control loop includes a core-side low band-pass filter 306, a core-side high bandpass filter 308, a slicer-side low band-pass filter 310, a slicer-side high band-pass filter 312, four envelope detectors 314, 316, 318 and 320, a core-side multiplier 340, a slicer-side multiplier 342, an adder 322, and a sequencer 324.
- the equalizer 300 utilizes a fixed-swing slicer 304, which is independent from the amplitude of the equalizer's input signal 332.
- the equalizer 300 calculates the necessary gain by first normalizing the energy level at the outputs of the equalizer core 302 and the fixed-swing slicer 304 with respect to their low-frequency amplitudes, and then comparing the normalized signals.
- the equalizer core 302 receives an input signal 332 from a transmission medium and a gain control signal (Ki) 303 from the control loop 305.
- the equalizer core 302 applies a frequency dependant gain to the equalizer input signal 332 as a function of the gain control signal (Ki), and generates a core output signal 326.
- the core output signal 326 is then coupled to the fixed-swing slicer 304, which converts the core output signal 326 into a digital output signal 328 having a fixed swing.
- the swing (A) of the digital output signal is fixed at a nominal value at which data is most often transmitted to the equalizer 300. Because the equalizer 300 is independent of the amplitude of the input signal 332, however, the swing (A) of the digital slicer output 328 may not approximate the swing of the equalizer input signal 332 prior to transmission.
- the control loop 305 sets the gain control signal (Ki) by normalizing the energy level of the core and digital output signals 328 and 326 with respect to their respective low-frequency amplitudes before comparing the signals to determine the necessary gain to be implemented by the core 302.
- the control loop 305 may be implemented, for example, as either a proportional type controller (P-Type), an integral type controller (I- Type) or a combination Pl-type controller.
- the low frequency portions of the core output signal 326 and the digital output signal 328 are isolated by the core-side low band-pass filter 306 and the slicer- side low band-pass filter 310, respectively.
- the center frequency of the low band-pass filters 306 and 310 is preferably chosen to match the frequency band at which the equalizer input signal 332 exhibits minimal attenuation.
- the higher frequency portions of the core output signal 326 and the digital output signal 328 are isolated by the core-side high band-pass filter 308 and the slicer-side high band-pass filter 312, respectively.
- the bandwidths of the high band-pass filters 308 and 312 are preferably chosen to isolate the frequency band at which the equalizer input signal 332 is attenuated and distorted by the transmission medium.
- the energy level of the output of each band-pass filter 306, 308, 310 and 312 is then determined by one of the envelope detectors 314, 316, 320 and 318, each of which generates an energy-level signal (a, x, b, and y) proportional to the energy of its input.
- This relationship between the energy-level signals (x and y) loses its significance, however, when the swing (A) generated by the slicer 304 is not substantially equal to the swing of the data prior to transmission.
- the energy-level signal (y) of the high frequency portion of the digital output signal 328 is weighted with the energy-level signal (a) of the low frequency portion of the core output signal 326.
- the energy-level signal (x) of the high frequency portion of the core output signal 326 is weighted with the energy-level signal (b) of the low frequency portion of the digital output signal 328.
- the core-side multiplier 340 multiplies the signals a and y to generate the output a*y
- the slicer-side multiplier 342 multiplies the signals b and x to generate the output b*x.
- This multiplication function is equivalent to normalizing the energy levels of the core and slicer outputs 326 and 328 with respect to their amplitudes (x/a is the normalized core signal and y/b is the normalized slicer signal).
- the energy-level difference between the weighted signals (a*y and b*x) is measured by the adder 322. If the equalizer core 302 is multiple-stage, then the single-stage gain control signal (K) 330 is coupled to the sequencer 324, which generates the gain control signal (Ki) 303 that is fed back to the equalizer core 302 as described above. Alternatively, if the equalizer core 302 is single-stage, then the single-stage gain control signal is preferably fed back directly to the equalizer core 302.
- the values of K 330 and Ki 303 are made proportional to the transmission losses even though the amplitude of the equalizer input signal 332 is an unknown.
- the gain control signal (Ki) 303 (or K 330) forces the normalized energy level of the core output (x/a) to approximate the normalized energy level of the slicer output (y/b), and the input signal 332 is correctly equalized.
- Fig. 12 is a block diagram of a transmit amplitude leveling circuit 400 for an equalizer.
- This circuit 400 includes a variable gain amplifier 402, an adder 404, a received data swing detection circuit 406, and a core input swing detection circuit 408.
- the variable gain amplifier 402 receives an input signal 410 from a transmission medium with an unknown transmit amplitude (B), and generates an equalizer core input signal 412 that settles to a fixed amplitude (A).
- the variable gain amplifier 402 also receives a variable gain control signal 414 that sets the gain of the amplifier 402 to either amplify or attenuate the input signal 410 to the fixed swing (A) expected by the equalizer core.
- the variable gain control signal 414 is preferably generated by the adder 404, which compares the transmit swing (B) of the input signal 410 from the transmission medium with the swing (A) of the equalizer core input signal 412.
- the transmit swing (B) of the input signal 410 is calculated with the received data swing detect circuit 406, which generates an energy-level output that is preferably coupled as a negative input to the adder 404.
- the swing (A) of the equalizer core input signal 412 is calculated with the core input swing detect circuit 408, which generates an energy-level output that is preferably coupled as a positive input to the adder 404.
- P-Type proportional type controller
- I-Type integral type controller
- Pl-type controller a combination Pl-type controller.
- the transmit amplitude leveling circuit 400 may be implemented, for example, in the equalizer system 100 described above with reference to Fig. 9 by coupling the output of the variable gain amplifier 412 as the input to the equalizer core 102.
- the variable gain control signal 414 would preferably adjust the gain of the variable gain amplifier 402 to 0.666 in order to reduce the signal swing of the received data signal. If, however, the data is transmitted at 800mV as expected in the equalizer core, then the gain of the variable gain control signal 414 would preferably be set to unity (1) by the variable gain control signal 414, and thus the amplifier 402 would be operating as a buffer.
- Fig. 13 is a block diagram illustrating an exemplary implementation of the received data swing detection circuit 406 and the core input-swing detection circuit 408 shown in Fig. 12.
- the exemplary received data swing detection circuit 406 includes a low band-pass filter 502 and an envelope detector 504.
- the low band-pass filter 502 preferably filters the input signal 410 from the transmission medium to a frequency range centered towards the low end of the transmit spectrum at which the transmission losses are minimal. In this manner, the output from the low band-pass filter 502 approximates the transmit swing (B) of the input signal 410.
- the output from the low band-pass filter 502 is then coupled to the envelope detector 504, which detects the energy level of the signal and generates the output of the received data swing detection circuit.
- the exemplary core input swing detection circuit 408 includes a fixed-swing slicer 506, a low band-pass filter 508, and an envelope detector 510.
- the fixed-swing slicer 506 is coupled to the equalizer core input signal 412, which is converted by the slicer 506 into a digital output signal having the swing (A) expected in the equalizer core.
- This digital signal is then filtered by the low band-pass filter 508, which preferably has a bandwidth substantially the same as that of the low band-pass filter 502 in the received data swing detection circuit 406.
- the filtered output from the low band-pass filter 508 is coupled to the envelope detector 510, which detects the energy level of the signal and generates the output of the swing detection circuit 408.
- the output from the core input swing detection circuit 408 is preferably coupled as the positive input to the adder 404, and the output from the received data swing detection circuit 406 is preferably coupled as the negative input to the adder 404.
- the variable control signal 414 generated by the adder 404 is thus proportional to the difference between the transmit swing (B) of the input signal 410 and the swing (A) expected in the equalizer core.
- Fig. 14 is a block diagram of an exemplary transmit amplitude independent adaptive equalizer 600 utilizing a variable gain amplifier 402.
- the equalizer 600 includes a variable gain amplifier 402, an equalizer core 202, a fixed-swing slicer 602, a gain control loop 206, and a variable gain amplifier control loop (VG-Loop) 604.
- the VG-Loop 604 includes two low bandpass filters 606 and 608, two envelope detectors 610 and 612, and an adder 614.
- the variable gain amplifier 402 preferably receives an input signal 410 that has been attenuated from its transmit swing B) as a result of losses incurred in a transmission medium.
- the variable gain amplifier 402 also receives a variable gain control signal 616 from the VG- Loop 604 that controls the amount of gain applied by the amplifier 402 in order to generate an equalizer core input 412 that settles to a fixed swing (A).
- the equalizer core 202 operates as described above to compensate for transmission losses incurred in the transmission medium, and generates a core output signal 618.
- the core output signal is then coupled to the fixed-swing slicer 602, which converts the core output signal 618 into a digital output signal 620 having a fixed swing (A).
- the gain control loop 206 operates as described above with reference to Fig.
- the VG-Loop 604 preferably isolates the low frequency portions of the core output signal 618 and the digital output signal 620, and compares the signal energies of the two low band-limited singles to generate the variable gain control signal 616.
- the low band-limited signals are centered towards the low end of the transmit spectrum at which the losses from the transmission medium are minimal.
- the low band-limited signals may be centered at alternative points within the transmit spectrum as long as the VG-Loop 604 isolates a lower spectral range than the gain control loop 206.
- the low frequency portions of the core output signal 618 and the digital output signal 620 are isolated by the low band-pass filters 606 and 608.
- the low band-limited signals are each coupled to one of the envelope detectors 610 and 612, which generate energy-level outputs that are proportional to the signal energies.
- the energy-level output from one envelop detector 612 is preferably coupled as a positive input to the adder 614, and the energy-level output from the other envelop detector 610 is preferably coupled as a negative input to the adder 614.
- the adder 614 generates the variable gain control signal 616, which is proportional to the difference between the energy levels of the low band-limited signals.
- variable gain control signal 616 forces the output of the variable gain amplifier to settle at a swing level (A) substantially equal to the fixed swing (A) of the slicer.
- controllers many types of controllers could be used to implement the VG-Loop 604 and the gain control loop 206 shown in Fig. 14.
- the VG-Loop 604 or the gain control loop 206 may be implemented as a proportional type controller (P-Type), an integral type controller (I-Type) or a combination proportional-integral type controller (Pi-Type).
- the VG-Loop 604 and the gain control loop 206 are preferably implemented as different controller types in order to maintain stability in the system.
Abstract
Description
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Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2003529719A JP2005503093A (en) | 2001-09-19 | 2002-09-17 | Transmission amplitude independent adaptive control equalizer |
EP02762178A EP1486043A2 (en) | 2001-09-19 | 2002-09-17 | Adaptive equalizer which is independent of the amplitude of the transmitted signal |
CA002460988A CA2460988A1 (en) | 2001-09-19 | 2002-09-17 | Adaptive equalizer which is independent of the amplitude of the transmited signal |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/957,064 US6956914B2 (en) | 2001-09-19 | 2001-09-19 | Transmit amplitude independent adaptive equalizer |
US09/957,064 | 2001-09-19 |
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WO2003026236A2 true WO2003026236A2 (en) | 2003-03-27 |
WO2003026236A3 WO2003026236A3 (en) | 2003-09-18 |
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PCT/CA2002/001419 WO2003026236A2 (en) | 2001-09-19 | 2002-09-17 | Adaptive equalizer which is independent of the amplitude of the transmited signal |
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US (4) | US6956914B2 (en) |
EP (1) | EP1486043A2 (en) |
JP (1) | JP2005503093A (en) |
CA (1) | CA2460988A1 (en) |
TW (1) | TW569525B (en) |
WO (1) | WO2003026236A2 (en) |
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2005
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Also Published As
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CA2460988A1 (en) | 2003-03-27 |
US7415064B2 (en) | 2008-08-19 |
US7180941B2 (en) | 2007-02-20 |
US20050254567A1 (en) | 2005-11-17 |
US20050254566A1 (en) | 2005-11-17 |
TW569525B (en) | 2004-01-01 |
US20050254565A1 (en) | 2005-11-17 |
US7317757B2 (en) | 2008-01-08 |
JP2005503093A (en) | 2005-01-27 |
US6956914B2 (en) | 2005-10-18 |
EP1486043A2 (en) | 2004-12-15 |
US20030053534A1 (en) | 2003-03-20 |
WO2003026236A3 (en) | 2003-09-18 |
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