Investigating effects of quadrature imperfection of vector multiplier in implementing RF/Digital predistortion

RF linear vector multiplier is a key component in hybrid RF/Digital predistortion systems. It adjusts, through I and Q baseband control signals, the input signal´s magnitude and phase according to the gain and phase required by the predistortion synthesis. In practical situations, due to hardware impairments, the I and Q correction signals combine in some non quadrature phase relation to give error in terms of implemented gain and phase of the predistortion functions. This quadrature imperfection can lead to poor correction in terms of predistortion and hence reduces the linearization capability of the predistortion system. This paper analyzes the effects of such quadrature imperfection in RF/Digital predistortion schemes. Experimental validation is carried out on a power amplifier biased in class B mode and driven by 3G WCDMA signal.