The design of the IMD signal extraction circuit in the high power amplifier

In this paper, a novel control circuit applicable to the intermodulation signal extraction circuit in a high power amplifier (HPA) is proposed. The circuit is composed of a linear and a nonlinear path so that the nonlinear characteristics of the path containing nonlinear elements can be efficiently compensated through an amplitude and phase offset detection circuit which is made of power dividers and detectors. Over the 10 dB power range, the circuit not only operates stably but also eliminates the main carrier signals more than 40 dB. Theoretically, the main carrier cancellation level of 40 dB occurs about the amplitude error 0.12 dB and the phase error 0.02°. It is also verified experimentally that the control circuit can precisely compensate for the variation of nonlinear characteristics in high power amplifiers, caused by the variations of input power.