Sensitivity analysis with Eldo

Hello,

I am trying to write the sensitivity analysis code in eldo for a flf filter topology. I've tried the following set of statements:

.ac dec 100 1 10g
.plot V(vop,von)
.extract (V(vop,von),2.97meg)
.sensac V(vop,von) freq=2.97meg

However, I don't seem to get any result.
Could you please help me how to write the sensitivity analysis code, but for the corner frequency of my filter. I've tried

.extract (V(vop,von),-3dB)

but this gives a syntax error.

Thank you!!!

Well, I've (finally) figured this out, so should anyone be interested, I'll just list the code as follows. Then I have another question.

.ac dec 100 1m 10
.extract ac label=vmax max(vdb(vop,von))
.extract ac label=frecv xdown(vdb(vop,von),extract(vmax)-3)
.sensac v(vop,von) freq=extract(frecv)

Now, I run the sensac simulation, but I don't get any result. I use ideal OpAMP in my circuit, that is a voltage controlled voltage source with a gain of 10000. If however a replace the ideal OpAMP with a real one, the only sensitivity value I get is in respect to the Miller capacitance within the amplifier.

Then, the question is, what exactly am I supposed to do/simulate in order to get some sensitivity values. The reason I need these values is for topology choice when implementing a filter.

Thanks!