Frequency compensation for two poles

[zahrein]

Frequency Compensation

Guyz,

I have tried to simulate using one pole which is just putting one capacitor.
For the two pole, i have simulate it and the result is tremendously different. When i read the book, a lot of calculations and theory about the two pole.

I still cant understand how it works for the two pole. Can anyone help me.


Here i attach the first pole and the two pole simulation results. Hope u all can help me. Thank you.

 

[flatulent]

Re: Frequency Compensation

The wild swings in phase in the second plot shows that there are several extra poles and zeros compared to the first plot. The added capaciitor you put in the circuit is in the wrong place. Can you post the circuit schematic for us to look at?

 

[nEuron]

Frequency Compensation

I dun understand why a resistor of 33KOhm is connected at the middle of two capacitors. I think that's the reason why there are so many poles and zeros being created.

 

[zahrein]

Frequency Compensation

r u saying that i should eliminate the resistor. By doing so, i believe it will make the phase margin decreases.

 

[flatulent]

Re: Frequency Compensation

You are not doing this the standard way that most circuits work best at. You need to find which stage has the lowest pole frequency and add to the miller capacitance by putting the capacitor from base to collector on that stage. This will lower the dominant pole. I would guess that this is the second gain stage where you have the capacitor from base to somewhat ground via the high value resistor.