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(12) United States Patent
Xuan et al.
(io) Patent No.: (45) Date of Patent:
US 7,383,025 B2 Jun. 3, 2008
H04B 7/00 (2006.01)
H04B 1/00 (2006.01)
H03C 3/00 (2006.01)
H03K 7/06 (2006.01)
H04L 27/12 (2006.01)
(52) U.S. CI 455/86; 455/108; 455/208;
455/255; 375/132; 375/307
(58) Field of Classification Search 455/42,
455/61, 76, 86, 108, 208, 230, 255, 293; 375/132, 307, 303, 133, 134, 135, 136, 137 See application file for complete search history.
(56) References Cited
U.S. PATENT DOCUMENTS
3,641,434 A * 2/1972 Yates et al 455/76
4,520,474 A * 5/1985 Vilmur 370/278
4,777,449 A * 10/1988 O'Connor 329/323
5,390,346 A * 2/1995 Marz 455/260
5,483,679 A * 1/1996 Sasaki 455/86
5,603,097 A * 2/1997 Kanou 455/76
5,689,819 A * 11/1997 Nishimura et al 455/86
5,781,538 A * 7/1998 Ganesan et al 370/310
5,937,335 A * 8/1999 Park et al 455/86
Primary Examiner—Nay Maung
Assistant Examiner—Andrew Wendell
(74) Attorney, Agent, or Firm—Thorpe North & Western
U.S. PATENT DOCUMENTS
6,028,885 A * 2/2000 Minarik et al 375/135
6,246,713 Bl * 6/2001 Mattisson 375/132
6,334,051 Bl * 12/2001 Tsurami et al 455/324
6,343,209 Bl * 1/2002 Maeda et al 455/160.1
6,438,358 Bl * 8/2002
6,724,804 Bl* 4/2004
6,738,602 Bl* 5/2004
* cited by examiner
Kegasa et al 375/130
Heinen et al 455/76
METHOD FOR PROCESSING RF SIGNALS
FOR RECEIVING AND TRANSMISSION
CROSS-REFERENCE TO RELATED
This utility patent application claims benefit of and priority to International Application, PCT/CN01/01625, filed on Dec. 14, 2001 and published as WO 02/56483 Al on Jul. 18, 2002, which in turn claims priority to China patent 10 application No. CN 01102802.5 filed on Jan. 12, 2001.
FIELD OF THE INVENTION
The present invention relates to a methodology for the 15 processing of radio frequency (RF) signals during receiving and transmission, and particularly to such a method for suppressing interference signals in (a) image and other interference signals in receiving and (b) interference to the channel and the receiving sides of the circuit when trans- 20 mitring, without using high quality filtering components at RF frequencies which are difficult to integrate into integrated circuits (ICs).
BACKGROUND OF THE INVENTION 25
In communication fields, RF frequencies are often used as carriers for signal receiving and transmission. Using current techniques in the receiver, modulated RF frequency signals are received and filtered to attenuate interference, especially 30 image signals, before being down converted to intermediate frequency (IF) frequencies. In the transmitter, filtering is also needed before the signals are transmitted, in order to reduce their interferences to communication channels and the receiving side of the circuits. In either of the receiving 35 and transmitting processes, due to the strict signal filtering requirements, filtering components, such as filters and duplexers, usually cannot be made using normal inductors and capacitors, especially those which can be integrated into semiconductor ICs. Instead, components using, for example, 40 dielectric resonators, surface acoustic wave elements and the like are needed. While these components works well, they are bulky in size, expensive, sensitive to manufacturing and assembly tolerances and are difficult to integrate into ICs. This is one of the major obstacles to integrate a circuit 45 system into a single chip. Zero IF techniques used in receivers solved effectively the image interference problem. However, its application has been limited to certain types of systems, due to issues such as DC offset, sensitivities, and the like, which lower the performance of the receivers and 50 require demanding compensation and processes.
It is an object of this invention to provide a methodology for RF frequency signal processing for receiving and transmission that solve the above problems associated with the current techniques. 55
BRIEF SUMMARY OF THE INVENTION
According to an embodiment of the invention, in the receiver, a received signal is mixed in mixer 4 with a local 60 oscillator (LO) signal generated by local oscillator source 5 with varied frequencies. The resultant desired signal from mixer 4 is selected by IF filter 6 with correspondingly varied center frequencies. It can then be mixed again in mixer 7 with a second LO signal generated by local oscillator source 65 8 with correspondingly varied center frequencies and then be selected by filter 9. In the transmitter, a signal to be
transmitted is mixed in mixer 11 with a LO signal generated by local oscillator source 12 with varied frequencies. The resultant IF signal is selected by filter 13 with correspondingly varied center frequencies. It is then further mixed in mixer 14 with a LO signal generated by local oscillator source 15 with correspondingly varied frequencies and then filtered by Filter 16.
There are a number of benefits using the process of the invention. Benefits associated with embodiments of the receiver include:
(1) The receiving of the desired signal is effective because it is spread, filter selected, de-spread and filter selected, while image and other interference signals are effectively attenuated, since the other interference signals are spread, filter-rejected, spread and filter-rejected.
(2) Due to the variation of the frequencies of local oscillator source 5 and local oscillator source 8, the image interference is not overlapping with the desired received signal at the 1 st and 2nd IF. So filtering of the image can be implemented at the IF stages, which can be done with good performance and lower cost, compared with doing it at front end RF frequencies. The filters at IF frequencies are also easier to be integrated into ICs.
(3) Due to (1) and (2) above, the receiver in this invention has relaxed requirements on the performance of the RF filtering components. This leads to (A) it is easier to implement them using inductors and capacitors, rather than bulkier and more expensive components, such as ceramic or SAW components and (B) the receiver can operate at wider bands.
(4) Due to (B) in (3) above, it is easier to use software to set or change the operating frequency bands by controlling the frequencies of the LOs.
(5) Due to (A) in (3) above, it is easier to integrate the whole receiver, including the front end filtering components, into semiconductor ICs.
(6) Referring to (3) above, since the requirements for the RF filtering is relaxed, its insertion loss can be lowered at the front end, which increases the sensitivity of the receiver.
Benefits associated with embodiments of the transmitter include:
(1) The spurious mixing products of mixer 11 are spread and can then be effectively rejected, due to the frequency variation of the LO source 11.
(2) Due to the frequency variation of the LO source 15, the leakage of the LO signal through mixer 14 is spread and has less interference to the channel and the receiving side.
(3) Modulated signals can be produced with carriers with fixed or hopping frequencies by selecting the ways of the frequency variation of the LO source 15.
(4) Due to the spreading of various spurious signals, the filtering requirement for filter component 16 is lowered. So it is easier to implement it using inductors and capacitors, making it easier to integrate the whole transmitter into ICs.
(5) Due to the spreading of various spurious signals, which leads to relaxed filtering requirements for the filtering component 16, the component 16 can be of wider bandwidth. Thus by choosing parameters of the varied frequencies of the LOs 12 and 15, which can be programmed, the transmitter can operate in different frequency bands.
(6) Due to the spreading of various spurious signals, which leads to relaxed filtering requirements for the filtering component 16, the insertion loss of 16 can be reduced, which effectively increases the gain and the power consumption efficiency of the transmitter.