NON-Inverting OPAMP (Pole zero)

non inverting op amp explained

How are the poles’s and zeros calculated for a non-inverting opamp?

I thought the way I was doing it below was correct but I checked my results and they are wrong.

non inverting op amp

did you take into account the internal poles of the opamp being used....

op amp pole zero

saro_k_82 said:

The zero is at R2C3

Click to expand...

So for figure #1.) the equation above for the zero is correct?

For the values in the above schematic #1.) I get a zero at 159.155 kHz.
When I plug those values in at this site it gives a zero at 79.5775 kHz.

Site link


Results



There is also a similar discrepancy when plugging in the values for my second figure. According to the site above.

When I try known correct values for an inverting OP the site gives identical results.

non-inverting op amp

Because you have calculated for a non-inverting amp., but have shown a inverting amp here. Check for inverting config in that site. It should match

non inverting compensation

saro_k_82 said:

Because you have calculated for a non-inverting amp., but have shown a inverting amp here.

Click to expand...

All the schematics I’m showing are of NON-Inverting op amps. The input is on the “+” terminal of the opamp. Where are you seeing an inverting opamp?

The 1.24V is a reference voltage .The positive terminal of the AMP is connected to resistive divider for sensing. I am trying to compensate a regulator. The EA output is connected to a P-Channel mosfet through a 10 ohm resistor. The output capacitor is a 1uf ceramic I’m trying to place a zero at the best location to get maximum BW. My simulations agree with the calculated values from the site I show above for a “Non –inverting” op amp.

I am able to obtain a 160 kHz BW and 48 deg PM using the compensation network in figure 1. I think I can improve that by using the compensation network in figure 2. Ideally I would like 260 kHz BW. But obviously I am calculating the poles and zeros wrong. I know where I want them but ...

op pole zero

OK., There was enough clues for me to identify that as inverting.,
1. Pole at origin., zero at (R1+R2)*C3.
2. Pole at origin and R2CT (where CT is the series equivalent of C1 and C2 (i.eC1||C2).
Two zeros and difficult to factorize !!

pole zero op amp

Thanks saro_k_82

saro_k_82 said:

1. Pole at origin., zero at (R1+R2)*C3.

Click to expand...

That works,solves one mystery.

I may have to stick with the simpler compensation network.

* For anyone interested the site I posted above has several tools. It's worth browsing.

Here is a link to the online tools,the site has.