I'm designing an oscillator with a quartz (Pierce model). The circuit is basically an amplifier and the quartz. I would like to measure the open loop gain and phase however I'm not sure about the method.
First method I tried is the following :
I disconnected the loop at the gate of the MOS amplifier inverter. Put a vac source and set the AC amplitude to 1V.I copied the schematic of the amplifier and pasted it at the output of the crystal, this way the crystal will see the same load as if it was in closed-loop. Then I measure the gain at the output of the crystal using a HB analysis.
Second method is :
I used the middlebrook analysis, which is stb in cadence. However I'm skeptical about this method as stb is to check the stability of the system. And, as I'm using an oscillator, I'm not supposed to be stable. However I'm still measuring an open loop gain and phase with stb analysis.
My question is which method is correct? I really have no idea on how to answer that question, so I'm here.
Thank you very much for your help.
I'm trying the negative resistance right now.
However one of my colleague asked me if I could tell him why the first method doesn't work, and I must admit that I really don't know. It looks good on paper.
So if it's not too much (as it's not really related to my topic), why is the first method not good for measuring open loop gain?
Thank you again.