High Frequency Differential Passive FET Direct Conversion Mixer/Modulator

A passive FET differential mixer/modulator for direct conversion and low IF applications is described. Operation of the example circuits are in the HF spectrum using discrete components, but the design is scalable to microwave and millimeter waves using common IC processes. LO drive level is from -10 to +10 dBm, measured conversion loss is 7 dB, input 3rd order intercept is +17 dBm, and estimated noise figure is within 2 dB of conversion loss. The mixer ports are 50 ohm differential, and there is no internal or external ground connection. Elimination of ground isolates the signal path from ground noise, and eases scaling to microwaves and mm waves where ground via inductance is significant. The internal bias circuit has large value decoupling resistors and draws 190 microamps from a 3 to 15 volt dc supply