Amplifiers – Signal feedback – Variable impedance in feedback path varied by separate...
Patent
1984-10-01
1986-05-27
Mullins, James B.
Amplifiers
Signal feedback
Variable impedance in feedback path varied by separate...
330293, 330149, H03F 132, H03F 126
Patent
active
045918007
ABSTRACT:
An improvement to a linear power amplifying system is disclosed which maintains the DC balance of the envelope feedback loop under adverse conditions, thereby improving the accuracy of the system. The improvement is realized through the addition of two differential amplifier stages to the feedback loop. A first differential amplifier 103 is added to the balanced outputs of the synchronous envelope detector 102, which is comprised of an active balanced modulator/demodulator device, to correct for the common-mode DC drift of the detector. An auxiliary feedback loop, comprised of a second differential amplifier 104 and a low-pass filter, compares the average DC value of the envelope error signal to a system reference voltage V.sub.R, and produces a loop gain error signal which corrects for variations in envelope feedback loop gain. The improvement provides envelope modulation transmitters with a substantial reduction in adjacent-channel interference and lower on-channel distortion.
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Arthanayake, T. and Wood, H. B., "Linear Amplification Using Envelope Feedback," Electronic Letters, vol. 7, No. 7, Apr. 8, 1971, pp. 145-146.
Petrovic, V. and Gosling, W., "A Radically New Approach to SSB Transmitter Design," University of Bath, England, Colloquium and Exhibition, Sep. 18, 1980.
Motorola Inc.
Mullins James B.
Roney Edward M.
Southard Donald B.
Wan G.
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