Stability Analysis of Multiple Opamp circuits using LTSPICE

Thread Starter

hoyyoth

Joined Mar 21, 2020
224
Dear Team,

I need to find the phase margin of the below circuit. It contains 3 opamps.I found a method in ADI website (https://www.analog.com/en/education/education-library/videos/5579254320001.html)

They are breaking the loop and applying the stimulus. In my circuit, 3 loops are there do I need to break each loop and apply stimulus individually
and test the circuit.
My LTspice file is attached here.In this one component is from TI (LMC662A/NS).

My schematic given below for your reference
1635328167255.png

Regards
HARI
 

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ericgibbs

Joined Jan 29, 2010
16,830
Hi HARI,
Do you have the model or .net file for the LMC662A, that you could post.?
E

Update:
What is the purpose of this circuit.?:)
 
Last edited:

Thread Starter

hoyyoth

Joined Mar 21, 2020
224
Hi Eric,

Thank you very much.
May I know will we get phase margin from .AC analysis.

This circuit is used to measure voltage from a source which has an O/P impedance in the range of Tera ohms.
The output voltage is 36V to 38V that is why I bootstrapped the rails

Regards
HARI
 

Thread Starter

hoyyoth

Joined Mar 21, 2020
224
Hi Eric,

Supply voltage is -10V only .I forgot to update the net name.
May I know how to find phase margin.

Regards
HARI
 
Last edited:

ericgibbs

Joined Jan 29, 2010
16,830
Hi HARI,
I know the data sheet states 1Tohm, but the LTS model shows 100k, so be aware if you add any circuit on a LTS sim to the OPA input, it may give misleading plots.??

What will be the input source and signal levels.?

Where did you get the model.?
E
 

Thread Starter

hoyyoth

Joined Mar 21, 2020
224
Dear Team,

I need to measure voltage from a high impedance node. Its impedance is 10G ohm and the expected voltage is 36V.

The circuit which I am using is given below. This circuit is working fine at room temperature.
I am using LMC662A as a bootstrapped buffer. This opamp has an input impedance of 1T ohm.

The requirement is it should work from -40Deg to 150Deg. I am not able to see any opamp with this Spec.

Can anyone suggest some other method to measure the same at high temperature.
1640342308611.png
Regards
HARI
 

Thread Starter

hoyyoth

Joined Mar 21, 2020
224
Hi Eric,

This circuit is a part of our ASIC evaluation board.ASIC performance needs to be tested from -40Deg to 150Deg.

Regards
Hari
 
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