OPA4171-Q1: propagation delay time

Hi Ethan, 

Chuqiang Wen said:

I would like to know the amplifier itself delay time, not include external RC components. 

There is no delay or insignificant delay between input and output if it is operating within a flat region of AC response BW. 

OPA171 Squarewave 05072025.TSC

OPA171 has UGBW of 3MHz, and its AC response behavior looks like the following, where there should not be delay in the flat region of the Bode plot (based on GBWP linear approx.). If an input signal is approx. 1 decade before the cutoff frequency or pole of the op amp response curve, there is no time delay or phase delay. 

Within one decade and one decade after of the cutoff frequency, there is a slightly delay, where the phase delay, theta (θ) is approx. -arctan(f/fp), depending on the operating frequency. And the time delay = θ/(360*f) is the conversion between angle and frequency. 

For certain low slew rate op amp, you may see slew portion of the square wave in a large signal, but this is not specified as time delay.  

If you have other questions, please let me know. 

Best,

Raymond