Patent ID: 7856221

Claim:
A mixer circuit for receiving a local oscillator signal and providing mixer outputs having reduced second order intermodulation comprising: four bipolar mixer transistors, all of the same conductivity type, each having an emitter, a base and a collector, the emitters and collectors being coupled to mixer inputs and mixer outputs, respectively, thereby forming a doubly balanced mixer; a local oscillator amplifier having an input coupled to receive the local oscillator signal and to provide a local oscillator amplifier differential output; one of the local oscillator outputs being coupled to the bases of two of the four bipolar mixer transistors and the other of the local oscillator outputs being coupled to the bases of the other two of the four bipolar mixer transistors, the bases of the four bipolar mixer transistors also being resistively coupled to a common mode voltage, the resistance of each resistive coupling being less than the total base input impedances of the bipolar mixer transistors coupled thereto to reduce the effect of beta mismatches in the bipolar transistors, the local oscillator amplifier having a local oscillator output impedance that is less than the combined resistance of the resistive coupling.