ON THE RELATIONSHIP BETWEEN SCHOTTKY-BARRIER CAPACITANCE AND MIXER PERFORMANCE AT CRYOGENIC TEMPERATURES

The flat-hand voltage is the Schottky junction voltage required to shr ink the depletion width to zero, At cryogenic temperatures, mixer diod es are generally biased and/or pumped beyond the Rat-hand condition to minimize conversion loss and noise figure, This occurs despite the pr esumed sharp increase in junction capacitance near flat-band, which sh ould instead limit mixer performance. Past moderate forward bias, the diode C-V relationship is difficult to measure, A simple analytic expr ession for C(V) is usually used to model and predict mixer performance , This letter provides experimental data on C(V) at 77 K based on a mi crowave measurement and modeling technique, Data is also provided on t he conversion loss of a singly balanced mixer optimized for 77 K opera tion, The connection between junction capacitance, flat-hand potential , and conversion loss is examined. It is shown that the analytic expre ssion greatly overestimates the junction capacitance that occurs as fl at-band is approached.