Two-Stage Op Amp Ideal Vref Help

*** Vdd = 1.2

Dear Tianix,

Tianix said:

However I would like to know if the values for the  test bench that I made is right 

Please excuse my lack of understanding, but I am not sure what your question is. Are you looking for someone to verify your simulation result?

The only comment I might add after reviewing your schematic and test bench is that I am not sure why you set the magnitude of your AC source to 1.2.

I would think you might want to use a value of acm = 1.0. With a value  of acm of 1, the output voltage will represent voltage gain since the input source has a magnitude of 1. In your case, I think you need to divide the output voltage by 1.20 to determine the voltage gain. I noticed in your expressions, you did not divide Vout by the magnitudeof your input AC source of 1.2.

Shawn

Dear Shawn,
Im very sorry for the confusion, but yes im looking for someone to verify my simulation result
As per advice, I changed the value of acm to 1V
And these pictures below are my latest simulation and results





I also changed the Vref from 1.2 to 800mv
I would like to know your opinion
Thank you for taking your time to review the matter

Dear Tanix,

Tianix said:

but yes im looking for someone to verify my simulation result

This requires that someone recreate your schematic by hand, have access to the models you are using (which you did not state) and have access to the Cadence simulator you are using (i.e., version and tool). Not only is that is a lot of work, but you did not provide enough information to allow someone to do that.

As a minimum, it might be possible and easier for someone who might be interested in re-simulating your circuit who happens to have access to the Cadence tools you are using if you provided:

a.  Your input.scs file

b. Your run file (file runSimulation file from your netlist directory)

c. Your output log (spectre.out file from your psf directory)

d. Any models that are not available from the Cadence libraries.

Tianix said:

I also changed the Vref from 1.2 to 800mv
I would like to know your opinion

When you changed the AC magnitude to 1 and the value of Vref from 1.20 V to 800 mV, it appears your gain has changed from 67.93 dB at 2 Hz to 61.24 dB at 2 Hz. This corresponds to change in voltage gain from 2492 to 1153. This is a very large change and much greater than the factor of 1.20 I would have expected. Are you sure the lower value of vref is not reducing the voltage of net n3 to such a level than M4 is no longer in its saturated mode? If you just change your AC magnitude from 1.20 VAC to 1 VAC and dod not change the value of Vref from its former value of 1.20 V, how much does your gain at 2 Hz change?

Shawn