The schematic of a potentiometric mixer is shown in Figure 1.
Transistors M1-M4 operate in triode region, and act as resistors.
and form a virtual short through capacitor CV for high frequency signals.
The RF signals and control the drain resistance of respective transistor.
Drain to source voltage across each transistor is determined by and .
Drain currents in the MOS transistor are given by,
The differential output current is given by .
After rearranging above equation and substituting Eq-(1), it can simplified to
The differential output voltage is given by
In the absence of mismatch between different paths, the output contains only the sum and different frequency components. is filtered out, whereas the opamp should have the bandwidth to handle .