A single ended switching mixer is shown in Figure 1.
The Linear -block convert the RF signal from voltage to current domain.
The switch(S) is turned ON and OFF by the LO signal. LO signal is a square wave with 50% duty-cycle.
By Fourier series,
When the switch is driven by LO, the RF signal gets multiplied by square wave … changes sign.
Therefore output voltage () is given by,
Eq.(3) points out that, the output of a single ended mixer contain DC, RF feed-through, LO feed-through and mixed components.
RF feedthough to the output is due to DC component in LO signal.
LO feedthrough is due to DC component in the RF signal.
Figure 2. illustrates the output voltage spectrum of a single ended switching mixer. The LO feedthrough problem of single ended mixer can be mitigated through single balanced switching mixer using differential LO signals.