Third order intermodulation cencellation for RF transconductors

摘要

A mixer in an RF demodulator includes a transconductance amplifier (12) that converts an RF input voltage (Vin), applied to the base of a first bipolar transistor (Q1), to a first output current (I) containing third order intermodulation (IM3) products, an IM3 canceller (14) being connected in parallel with the transconductance amplifier. The base of a second bipolar transistor (Q2) in the IM3 canceller is coupled to the DC component of Vin, and the AC component of Vin is coupled to the emitter of the second bipolar transistor, such that the currents though the first bipolar transistor and the currents through the second bipolar transistor change oppositely. The collectors of the transistors are coupled together. The values of components in the IM3 canceller are set during simulation and calibration so that the current generated by the IM3 canceller substantially cancels out IM3 distortion in the first current or other current generated in a demodulator of Vin.