This op amp does not have gain?

4 replies · 2K views · last reply
EENSEEY
Messages
2
Reaction score
1
TL;DR
this op amp doe snot have again in AC or DC
Had this as a question from a class mate. This op amp should not have any gain in the DC or AC circuit. The coupling cap blocks DC and has no reference to get gain, while the AC needs a cap in the feedback loop to get gain. Is that correct? Oh, this is supposed to be in the inverting configuration.

Hand-drawn op amp circuit schematic: input Vi through a series capacitor to the non-inverting (+) input, a resistor feedback from output to the same input, the other input grounded, and output Vo.
 
Welcome to PF. :smile:

It looks fine to me...

Schematic of a differentiator op-amp circuit: Vin feeds a capacitor C in series, the input node X connects to the inverting input, and resistor Rf feeds back from the output Vout; the title reads The Differentiator Amplifier.

https://www.electronics-tutorials.ws/opamp/opamp_7.html
 
EENSEEY, you should realize that the shown circuit (differentiator) will work under ideal conditions only (ideal opamp with a gain that is not frequency-dependent).
Under real conditions the circuit will be unstable.
Question: Why do you think that a cap is required in the feedback path to get gain?
 
Yes, what @LvW said. This is actually a very difficult circuit to make work without oscillation. You'll learn more about that later when you've studied more about feedback stability, bode plots, and and the bandwidth limitations of real world amplifiers.

A cap in the feedback path will reduce the overall AC gain, not increase it. More feedback makes less forward gain.

Your next step should be to study about feedback in simple amplifiers, and the frequency dependent behavior of the basic components: inductors, capacitors and resistors.