APPARATUS AND METHOD FOR REDUCING DISTORTION IN AMPLIFICATION

摘要

Broadband amplifiers which are intended to be linear suffer from distortion and although many techniques have been devised to overcome this problem significant improvements are required especially at frequencies above 100 MHz. An error signal is formed from the output of an amplifier by comparison in a subtractor with its input and the error signal is combined in a coupler with the amplifier output to reduce distortion. The present invention provides automatic amplitude and phase control of the signals forming the error signal by two groups of adjustment means, one group in a multi-channel input path and one group in the error signal path. These groups receive control signals from respective feedback networks which each process two of three input signals from: couplers before the subtractor, a coupler which passes the error signal and a coupler situated after the coupler which combines the amplifier output signal and the error signal. Preferably the two input signals used by a feedback network are used to form in-phase and quadrature signals using a 90 DEG phase shifter and two mixers. These signals are each amplified and integrated to provide the control signals. The input signals from the feedback networks may be reduced in frequency and applied to a DSP which then provides the control signals.