 ### Network # Op amp max frequency based upon slew rate and gain

#### cps13

Feb 25, 2013
54
Hi,

I have the following question in my HND...

Estimate the maximum frequency of a sinusoidal input signal of 10 mV peak, for distortion-free output, when applied to an op-amp circuit of closed-loop gain of 100.

I have searched all through my course material, online for ages and have only found one thing which relates the gain of an op-amp to the maximum frequency which is here...

5.4: Slew Rate and Power Bandwidth - Engineering LibreTexts

Specifically section 5.4.2 which states:

"...Note that slew rate calculations are not dependent on either the circuit gain or small-signal bandwidth..."

Can somebody please confirm this is correct?

I know sometimes exams will throw in curve balls, but my experience with op-amps is so much learning material works on "ideal" scenarios and just have this feeling that many of the texts are just ignoring gain for simplification.

Thanks

#### crutschow

May 7, 2021
787
.Note that slew rate calculations are not dependent on either the circuit gain or small-signal bandwidth..."

Can somebody please confirm this is correct?
Yes, slew-rate is an intrinsic op-amp characteristic that is unaffected by frequency or gain.

Do you know how to calculate the slew-rate for a sinusoidal signal, given its frequency and amplitude?

#### cps13

Feb 25, 2013
54
Yes, slew-rate is an intrinsic op-amp characteristic that is unaffected by frequency or gain.

Do you know how to calculate the slew-rate for a sinusoidal signal, given its frequency and amplitude?

Thanks for the reply - I think I may have worded my question poorly.

I have a given slew rate for my op-amp, I need to calculate the maximum frequency (power bandwidth) of the amp. The equation I want to use is:

Fmax (Hz) = SR / (2 . Pi . V)​

This is where I'm struggling to find out the impact of the circuit gain on the calculation. As the equation above ignores gain.

I know that Vout = Acl . Vin

Which is closed loop gain . Vin

But I'm not sure if this even relates to my power bandwidth calculation.

Thanks

#### crutschow

May 7, 2021
787
This is where I'm struggling to find out the impact of the circuit gain on the calculation. As the equation above ignores gain.
It ignores gain because the voltage in the slew-rate equation is the output voltage, not the input voltage.

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