A single balanced switching mixer is shown in Figure 1.
MOS transistors and switch the current from the -block between the + and – output terminals. The differential LO signals that drive the switches are shown in the Figure 1.
By Fourier series,
From Eq.(3), we can notice RF feedthrough suppression by differential LO signaling. Figure 2 illustrates the output voltage spectrum of a single balanced switching mixer.
Apart from sum and difference components due to mixing action, LO feedthrough still exists which is due to DC component in RF signal. This can be eliminated through differential RF signal in double balanced switching mixer.