A Quadrature Demodulator for WCDMA Receiver Using Common-Base Input Stage with Robustness to Transmitter Leakage

A quadrature demodulator (QDEMOD) for WCDMA direct-conversion receiver using common-base input stage is reported. A common-base input stage is robust to parasitic elements and is suitable for on-chip matching circuits to realize small and low-cost RF front-end modules. However, a common-mode blocker signal, such as the transmitter (TX) leakage signal, degrades the noise performance due to intermodulation distortion of the TX leakage signal and noise. We propose a QDEMOD with a common-base input stage that is capable of suppressing the TX leakage signal using symmetrical inductors. The QDEMOD was fabricated using Si-Ge BiCMOS process with f_T of 75 GHz. The measured results show that the NF degradation does not occur until the TX leakage signal input is larger than -13 dBm