Hi!

I am trying to design an LC oscillator (cross coupled NMOS) to oscillate at 2GHz. I have tried some of the commonly used topologies like NMOS(D=S, Bulk=gnd) or PMOS(B=D=S) and PMOS(D=S,B=Vdd).

The problem is when I sweep the varactor control codes(at the DC point of output) for frequency steps/behviour, the resulting frequency does not remain constant for some steps (or code values) rather it jumps back and forth in magnitudes of 2-4MHZ. I am confused as to why this is happening.

It would be great if some could propose a solution to this issue  :-/

Thanks for the reply, will look in to it.