Pulse or digital communications – Receivers – Automatic gain control
Reexamination Certificate
2000-12-18
2004-01-27
Tran, Khai (Department: 2631)
Pulse or digital communications
Receivers
Automatic gain control
C455S138000
Reexamination Certificate
active
06683926
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to electronic circuits having in-phase and quadrature channels, and more particularly, to a gain controller for such circuits.
BACKGROUND OF THE INVENTION
Receiver circuits and transmitter circuits (collectively “radio circuits”) of the direct conversion type are often used for radio frequency (RF) filtering in communication devices such as mobile phones, television receivers or the like.
Such a radio circuit uses signal pairs having an in-phase signal (I) and a quadrature signal (Q). Both signals I and Q have a substantially equal carrier frequency. The Q signal is 90° phase shifted to the I signal. In other words, both signals are in quadrature to each other.
The radio circuit has a first channel for the I signal and second channel for Q signal. Each channel independently forwards and processes its signal, for example by digital-to-analog converting and low-pass filtering. Other signal processing is also possible, for example, analog-to-digital converting. Exact processing of the I and Q signals requires, among other things, that both signals have the same amplitude.
However, differences in the gains (amplitude transfer function) of the channels commonly occur as a result of changes in temperature, frequency, manufacturing variations of the electrical components and other parameters. Small gain differences, (“mismatch”) can result in distortions that lead to unwanted discrete tones in further circuitry coupled to the radio circuit. Useful references can be found in U.S. Pat. Nos. 5,604,929; 5,249,203; 5,230,099; 5,179,730; 5,095,536; 5;095;533, all to Looper; as well as in U.S. Pat. No. 4,926,443 to Reich; U.S. Pat. No. 4,633,315 to Kasperkovitz; U.S. Pat. No. 5,930,286 to Walley; and U.S. Pat. No. 4,799,212 to Mehrgardt.
The present invention seeks to provide an improved gain controller which mitigates or avoids disadvantages and limitations of the prior art.
REFERENCES:
patent: 4633315 (1986-12-01), Kasperkovitz
patent: 4799212 (1989-01-01), Mehrgardt
patent: 4926443 (1990-05-01), Reich
patent: 5095533 (1992-03-01), Loper et al.
patent: 5095536 (1992-03-01), Loper
patent: 5179730 (1993-01-01), Loper
patent: 5230099 (1993-07-01), Loper
patent: 5249203 (1993-09-01), Loper
patent: 5604929 (1997-02-01), Loper et al.
patent: 5659582 (1997-08-01), Kojima et al.
patent: 5930286 (1999-07-01), Walley
“Interpolation and Decimation of Digital Signals—A Tutorial Review” by Crochiere, R. E. and Rabiner, L. R., Proceedings of the IEEE, vol. 69, No. 3, Mar. 1981.
“Multirate Digital Signal Processing” excerpt of “Digital Signal Processing”, Third Edition, Prentice Hall, Upper Saddle River, 1996 by Proakis, J. G.and Manolakis, D. G., ISBN: 0-13-373762-4, sections 10.1 to 10.6 of chapter 10.
“Compensation of frequency dependent quadrature imbalance in a zero-if downconverter” by J. Michels and S. Jasper, excerpt of Motorola Technical Developments, vol. 38, Jun. 1999, pp. 183-186.
Koifman Vladimir
Paz Ronen
Zarubinsky Michael
Motorola Inc.
Tran Khai
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