Development of a "Distortion Feedback" C-band Amplifier

The Next -generation LEO System Research Center of TAO has developed a C -band solid-state amplifier (SSPA) using a principle called “distortion feedback.” In distortion feedback, input and output signals of the amplifier are compared, amplifier distortion is extracted, and the distortion is feed back with the inverted phase of the input signals. The amplifier compensating for distortion uses less power than a feed-forward amplifier because of its low output power loss and lack of sub-amplifiers having high power consumption. Difficulties in oscillation were avoided in a circuit configuration in which the distortion feedback point is located before the point where the input signal is taken out in order to compare it with the output signal and determine distortion. To determine voltages of phase shifters and attenuators, a simpl ex method was used without phase measurement tools. As a result, compensation of third-order distortion of over 20 dB at an output back off of 5 dB was accomplished. This circuit type is suitable for use in compact-sized high-linearity amplifiers for digital signals.