saturaion

For a Gilbert mixer, should the switching quad operates in saturation or triode region to maxmize the gain ?

Since the switching quad just acts as a current switch, I thought it can operate in triode region. But simulation result shows that this will significantly decrease the gain. I don't know why.

Can somebody explain this to me?

Thanks a lot.

-The gain of the mixer is proportional to gm
-Higher overdrive voltage means higher gain.
-Increasing current also increases the gain.
-Decreasing the source degeneration resistor will increase the gain but decreases linearity.

The gain will be higher for larger LO (saturation) because output voltage will become insensitive to the LO amplitude. However, when the LO becomes too large, this leads to spikes in the signals, reducing switching speed and increase LO feedthrough.
The result of the spikes can also cause transistors to leave the saturation region.