Explain to me the working of op-amp in this low pass filter

[zarric]

about filter design

For the below low pass filter:


OP is basic two stage
two points i wanted to know:
1. C1 connected Vout and negative input , how to know it's stability and how to compensate.
2. the OP has two pole about 100khz, but when i put a ac source at vin , the gain and phase at Vout shows that only a input pole about 5hz, then no any pole or zero unit 10Mhz. why for this.

thanks

 

[naalald]

Re: about filter design

Hi,
See the topic:

Firstly, you should insure the stability of the opamp. If the opamp has two poles at 100kHz it might be unstable. You should compensate it. The miller compensation or cascode compensation could be used (for more information on how to apply the methods, you can see the Gray book or Razavi book).

 

[zarric]

Re: about filter design

thanks.

the feedback ratio may larger than 1 , so whether this loop is always stability , and how to simulater and know that is stability.