An optimum bias point study of low local oscillator power operation for 60GHz drain mixer

The optimum bias point for a drain mixer operating on low local oscillator (LO) power was investigated. The bias voltage dependence of the required LO power and the conversion gain in the drain mixer was clarified by a simpli fied nonlinear model which the drain current characteristics around knee vo ltage is approximated by two straight line segments. It was found that an o ptimum gate bias voltage V-gs exists for a given applied LO power, and the optimum gate bias voltage moves toward the pinch-off voltage as the injecti on LO power level decreases. In order to verify the variation of the optimu m gate bias voltage, a 60 GHz MMIC drain mixer adopting the optimum gate bi as voltage for low LO power level was fabricated. The fabricated drain mixe r exhibited a conversion gain of 0 dB with the injection LO power level of 0 dBm. This value of 0 dBm is the best performance get obtained for a 60 GH z MMIC drain mixer. The measured optimum gate bias voltage was near the pin ch-off voltage. This result was in good agreement with the theoretical anal ysis. The LO power level of a drain mixer has been improved so that it is o n a par with that of a gate mixer.