No it's not first order. First order means phase margin of 90 degree. There's considerable phase lag from additional poles, it causes gain peaking and the increased -3dB frequency in closed loop.Open loop frequency response showing first order performance
Don't want to decide about right or wrong, but there are at least other commonly used definitions. According to Analog Devices and TI application notes and datasheets, GBW is the product of (non-inverting) gain and small signal bandwidth. It's usually measured at higher gains (e.g. 10 or 100). Particularly for decompensated OPs, the GBW is considerably different from the open loop unity gain frequency, but smaller differences occur as soon as the phase margin is different from 90 degree.GBW has nothing to do with the -3dB point. It simply identifies the frequency point where, if the opamp where open loop, the gain drops to 1.
Don't want to decide about right or wrong, but there are at least other commonly used definitions. According to Analog Devices and TI application notes and datasheets, GBW is the product of (non-inverting) gain and small signal bandwidth. It's usually measured at higher gains (e.g. 10 or 100). Particularly for decompensated OPs, the GBW is considerably different from the open loop unity gain frequency, but smaller differences occur as soon as the phase margin is different from 90 degree.
I assume you are simulating your loop gain with already compensated amplifier and if it is compensated well, meaning the non-dominant pole is about 3x farther in frequency than the UGBW, then closing the loop should have a -3dB frequency pretty close to the GBW.
However, from your original plot of the loop gain I see that right about 0dB crossing there seems to be some slight flattening of the magnitude response and at the same time the phase drops. This suggest for RHP zero. If your amplifier is Miller compensated, did you take care for mitigating the effects of the RHP zero that usually appears in that kind of compensation? Also, it will be better if you simulated your loop gain to higher frequency, this way you can see what happens after it crosses 0dB and where the non-dominant poles are.
OK, I see. If you do Ahuja compensation, you don't need the resistor in series with the Miller capacitor, that's true. However, Ahuja compensation needs careful design. It can lead to complex conjugate poles in your loop gain if not designed correctly. I think you have a bit of this showing in your plots - the slight bump in the Bode plot near crossover frequency. And it, of course will roll-off your phase faster. Did you check the stability of the internal feedback loop of the Ahuja compensation?
There is an internal loop when using the Ahuja compensation, which needs to be stable. You probably forgot but we have already discussed this point before.
https://www.edaboard.com/showthread...ded-OPAMP-with-nulling-resistor-or-transistor
Do you use min L for M10? Also, in that older post I pointed to a reference where there are other ways to compensate for the Ahuja loop.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?