This op amp does not have gain?

In summary, the conversation discusses the use of an op amp in both DC and AC circuits. The coupling cap is used to block DC and does not contribute to gain, while a cap in the feedback loop is needed for gain in the AC circuit. The circuit shown may not work under ideal conditions and can be unstable under real conditions. A cap in the feedback path will decrease the overall AC gain. It is recommended to study feedback and frequency dependent behavior of components for a better understanding of amplifier performance.
  • #1
EENSEEY
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1
TL;DR Summary
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.

1628515130391.png
 
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  • #2
Welcome to PF. :smile:

It looks fine to me...

1628516050512.png

https://www.electronics-tutorials.ws/opamp/opamp_7.html
 
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Likes EENSEEY
  • #3
Thanks!
 
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  • #4
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?
 
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  • #5
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.
 

What does it mean when an op amp does not have gain?

When an op amp does not have gain, it means that the output voltage is equal to the input voltage. In other words, the op amp is not amplifying the signal and is functioning as a unity gain buffer.

Why would an op amp not have gain?

There are several reasons why an op amp may not have gain. It could be due to incorrect circuit connections, damaged components, or incorrect values for the feedback resistors. It is important to troubleshoot and identify the root cause in order to restore the gain of the op amp.

Can an op amp be used without gain?

Yes, an op amp can be used without gain. In some circuits, a unity gain buffer may be necessary to prevent loading effects or to isolate different parts of the circuit. In these cases, the op amp is used for its high input impedance and low output impedance rather than for its amplification capabilities.

How can I increase the gain of an op amp?

To increase the gain of an op amp, you can adjust the feedback resistors in the circuit. The gain of an inverting op amp is equal to the ratio of the feedback resistor to the input resistor. For a non-inverting op amp, the gain is equal to 1 + (Rf/Rin). Increasing the values of these resistors will result in a higher gain.

What are some common causes of op amp gain loss?

Some common causes of op amp gain loss include damaged components, incorrect circuit connections, incorrect values for the feedback resistors, and power supply issues. It is important to carefully check the circuit and troubleshoot to identify and resolve the issue causing the gain loss.

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