Analysis and Reduction of Cross-Modulation Distortion in CDMA Receivers

The jammer cross modulation (XM) transferred from a transmitter (TX) CDMA leakage by a receiver circuit is analyzed using the Volterra series and statistical theory. The measured "double-hump" XM spectrum is explained based on the CDMA signal statistics derived using the proposed system model of a reverse-link CDMA signal. The analysis shows that the XM distortion is affected by the circuit behavior not only at the jammer and the TX leakage frequencies, but also in the CDMA signal baseband and at the sum and difference of the excitation frequencies. This theory was verified on a 2-GHz Si bipolar junction transistor low-noise amplifier whose out-of-band terminations were optimally tuned to significantly reduce its XM distortion.