I want to know what is the ideal circuit to measure open-loop frequency response and why?I have seen the typical open-loop frequency response curve for an op-amp a lot of times. But when I try to plot it for my circuit simulation even though it resembles the shape, it varies a lot with the input signal. I am simply sending a small AC signal with no feedback and plotting output. What will be the ideal input AC signal to plot it assuming I want to use this later for Differentiator design assuming I want to use an inverting op-amp for it.
Drive with 1 micro volt (swinging +- 0.5 micro volt above and below ground), and ground either vin-, or vin+ pin.
Try an AC simulation, from 1 Hz to 100 MHz. Log, 10 steps/dcades.
Examine the dc conditions, observing the Vout is very near 0 volts.
If not, then add a dc feedback , to ensure the opamp is biased as an amplifier:
apply the +-0.5uV only to the Vin+, other pin of source to ground.
connect Vin- to ground, thru a 1ohm resistor
attach th efeedback, by using 100,000 ohm resistor from Vout to Vin-
Now examine what you have on the nodes.
The 2nd circuit has large closed loop gain, yet the opamp only provides high gain at very low frequencies.
Try with 100 Hz in, 1uv, symmetric around ground.
And try with 100,000 Hz in, 1uv, symmetric around ground.