High Efficiency Feedforward Linearizers

Abstract

The effective feedforward linearization of a power amplifier can be achieved using an auxiliary amplifier of lower power rating than the main amplifier. The developed technique overcomes the inherent inefficiency of the classic feedforward configuration which requires two amplifiers of the same power rating, without compromising the performance. Analysis bf the lineaizer's sensitivity to loop imbalance demonstrates that the circuit is more sensitive to amplitude or phase imbalance in the first loop than in the second. First loop imbalance increases the error signal applied to the auxiliary amplifier, leading to degradation of the linearizer performance due to its nonlinearity. Consequently, lowering the auxiliary amplifier power rating increases the sensitivity of the circuit to first loop imbalance. Preliminary experimental results presented in this paper indicate better than 17 dB cancellation of the intermodulation products in an X band linearizer with a 500 MHz bandwidth, verifying the predicted results.