Signal Distortion Due To Spectral Re-Growth Of Adjacent Channel Interferers in WCDMA Receivers

In WCDMA receivers, WCDMA modulated adjacent channel interferers (ACI) can distort the useful signal due to non linearity of the front end RF components. Non linearity of the RF front end transfers the modulation of the transmitter (TX) leakage onto the ACI, resulting in cross-modulation distortion. In addition to this, if the ACI signal is strong, it would undergo spectral re-growth and some fraction of its power will leak into the adjacent desired channel. The adjacent channel selectivity (ACS) scenarios in the 3GPP RX specification outline the performance requirement for the receiver in the presence of a strong as well as a weak ACI signal. For the ACS high power scenario (in which the ACI signal is strong), the distortion due to ACI leakage is much more significant compared to the cross-modulation distortion. Therefore, understanding the ACI leakage distortion becomes important, in order to ensure reliable receiver performance. In this paper, we analyze and report observations of the ACI leakage phenomenon on a WCDMA receiver chip. Measurement results have also been reported for the 3GPP ACS high power scenario. The chip measurements are supported with time-domain simulation results