A Mixer With Third-Order Nonlinearity Cancellation Technique for CDMA Applications

A feedforward technique to improve the third-order nonlinearity of mixers in a direct conversion transceiver is presented. The third-order intermodulation (IM3) generated by the main transconductance (G
_m
) stage of mixer with inductively degenerated emitter is cancelled by that generated by the sub-G
_m
stage with degeneration resistor. The circuit allows the mixer to be optimized independently, and has minimal impact on noise figure (NF), gain, area, and current consumption. The proposed technique reduced IM3 by approximately 16 dB with a current increase of approximately 7%. The mixer achieved an input-referred third-order intercept point of 5 dBm, a gain of 37 dB, and an NF of 9.8 dB drawing 7.9 mA from a 2.85-V supply. The transceiver including the calibration circuitry was implemented in a SiGe bipolar transistor with f
_T
= 35GHz for U.S. cellular code division multiple access application