Asymmetric DC Offsets and IIP2 in the Presence of LO Leakage in a Wireless Receiver

We present mathematical analysis to prove that LO leakage at the input of RF circuits in the presence of finite IIP3 results in asymmetry in DC offsets and IIP2 between in-phase and quadrature channels in a wireless receiver. The asymmetry in IIP2 causes effective IIP2 of the receiver to be at best only 3 dB higher than the smaller of two IIP2 values. Measurement data from a quad-band GSM/GPRS receiver implemented in 90-nm digital CMOS process is also presented to support mathematical analysis.