Amplifying a DC Micro Voltage signal using Proteus [OP AMP]

Thread Starter


Joined Apr 20, 2022
I am trying to amplify the signal (7.5uV) using OP AMP in proteus , but I am getting un expected results (the gain of the op amp is 1+R1/R2 = 11) So it's expected to get output voltage equal to (7.5*11)uV which is not the case here.
Any help?

Audioguru again

Joined Oct 21, 2019
The very old MC3403 is still available. Its input bias current is 0.5uA maximum and its input offset voltage is 10mV maximum. Its inputs are PNP transistors so they work with the input voltages as low as the negative supply voltage which is 0V in your circuit.
I do not know if Proteus knows that it can work without a negative supply voltage.

Even if you cancel the input bias currents and offset voltages, your signal level is far below the opamp's fairly high noise level.


Joined Jul 29, 2018
Another issue is that rail-to-rail output amplifiers have a very hard time actually reaching either supply rail. Close maybe, but not exact. Your example would be looking to see less than 100uV from the negative rail, I doubt any amplifier would work down that close. And a bipolar amplifier like the MC3403 would be hard pressed to hit 1V, which is why it is often used with a negative supply voltage.

Audioguru again

Joined Oct 21, 2019
The antique MC3403 is not rail-to-rail but its inputs can go all the way down to its negative supply that can be 0V and its output goes down to "essentially 0V". Texas Instruments have a new version that is rail-to-rail.

These opamps cannot amplify the tiny DC input voltage without huge errors.
EDIT: Unless the SIM program assumes that the opamp is "perfect".