Measuring S-Parameters of a Differential Mixer

by Kenneth S. Kundert.

Consider a fully differential mixer with an input at 2.4 GHz, an output of 400 MHz, and an LO of 2 GHz. Assume that the mixer is constructed by simply combining two single ended mixers, each with port impedances of 50 Ω in parallel. In this way the differential impedance seen at each port of the combined circuit is 100 Ω, and the common-mode impedance is 25 Ω. Consider the S-parameters of this mixer. Since the mixer is fully differential, the mixer has two balanced inputs and outputs. However, knowing the traditional 4-port S-param- eters for the mixer, as measured by the testbench shown in Figure 1, are not very helpful [via]

http://www.designers-guide.org/Analysis/diff-...