Compensation capacitor in amplifier

Wesley Huang

Hi Team,

When I read the TI's datasheet of amplifier, it is always suggested that a compensation capacitor should be added in the feedback loop as shown below. But I don't know why and select what value.

1. Could you please share the application note or document to me about:

Why the compensation capacitor should be add in the amplifier circuit?
How to select the value of compensation capacitor under different situation?
How to test the circuit to verify if I select the right compensation capacitor?

Best Regards

Zhihong Huang

over 5 years ago

0 Michael Steffes over 5 years ago

Guru 48395 points

That is really not very good advice.

Running non-inverting the feedback cap has the effect of shaping the noise gain (and gain in this case) from whatever the DC value is down to 1 at higher frequencies.

Combined with that heavy load cap, it is actually just asking for phase margin problems.

A pretty thorough discussion of phase margin testing and how to get into (and out) of problems appears here -

https://www.planetanalog.com/stability-issues-for-high-speed-amplifiers-introductory-background-and-improved-analysis-insight-5/

Part 6 then goes through VFA issues specifically

And then this one tries to clear up gain bandwidth product confusion, which is certainly justified given all the bad data out there,

https://www.planetanalog.com/why-is-amplifier-gbp-so-confusing-insight-12/

0 Former Member over 5 years ago

Hello Zhihong,

You do not always want to have a feedback capacitor. These are only to be used sometimes, depending on the application and the desired circuit function. To answer your questions.

1. Compensation capacitors can be added for filtering effects. The compensation capacitor may be used to reduce bandwidth, for example in a case where that signal frequency is not needed and the designer wishes to reduce noise. As Michael has pointed out, some feedback capacitors can contribute to stability problems. To learn more about this, please see this presentation.

2. The value of the feedback capacitor will be chosen to create the desired frequency response. It will depend on the circuit designer's intended effect.

3. You can test the circuit using our free simulation software, TINA-TI.

Regards,

Daniel

0 kai klaas69 over 5 years ago

Guru 140200 points

Hi Zhihong,

I would recommend to watch these TI's stability training videos:

https://training.ti.com/node/1138805

Kai

0 Wesley Huang over 5 years ago in reply to Former Member

Expert 1030 points

Hi Daniel,

Thanks for your reply. It helps me a lot.

Best Regards

Zhihong Huang

0 Wesley Huang over 5 years ago in reply to kai klaas69

Expert 1030 points

Hi Kai,

Thanks for your reply. It helps me a lot.

Best Regards

Zhihong Huang

0 Wesley Huang over 5 years ago in reply to Michael Steffes

Expert 1030 points

Hi Michael,

Thanks for your reply. It helps me a lot.

Best Regards

Zhihong Huang

Amplifiers

Amplifiers forum

Compensation capacitor in amplifier

https://training.ti.com/node/1138805