Which pole is moved to low frequency in Miller compensation?

[tandr]

It is said that in Miller compensation , the input node 's pole is moved to low
frequency , and the output node's pole to highfrequency in many materials ,
but my opinion is reversal . Is there some one can expain ?

 

[engrvip]

IT is the pole at the o/p of first stage that movs to lower req. because due to forward path the capacitance at that node increases due to miller effec and hence brings that pole to lower freq.

 

[tandr]

Re: Which pole is moved to low frequency in Miller compensat

But for Miller equevalent , it is the input node that is added by a
capicitance equal to Cm * A . So the input node 's cap is increased , and so is
the pole of input node

 

[vinodjn]

Re: Which pole is moved to low frequency in Miller compensat

but pole frequency is 1/RC, so increasing C causes pole moves toward lower frequency.

 

[tandr]

Re: Which pole is moved to low frequency in Miller compensat

So it is the input node's pole is put to low frequency ?

 

[ipsc]

Re: Which pole is moved to low frequency in Miller compensat

So it is the input node's pole is put to low frequency ?

YES.

 

[zyyang]

Re: Which pole is moved to low frequency in Miller compensat

hi the input node is the output of the first stage ,and the output node is the output of the second stage,using feedback to thinking ,youwill know inside.

 

[Mike-Chen]

Re: Which pole is moved to low frequency in Miller compensat

input capacitor Cin=(1+A)CF , output node capacitor
Cout=(1+1/A)CF , CF is Miller capacitor

 

[venkateshr]

Re: Which pole is moved to low frequency in Miller compensat

HI ,
Input cap. is moved closer to origin thereby reducing our 3-db BW(BW compensation0 and the op pole is (pole due to load cap & others) is moved away from the origin .Thus it is called as Miller compensation or Pole splitting.

The reason for the movement of second pole is the decrease in the op resistance of
the second stage to a possible 1/gm. hence out next pole is approx. -Gm/(Cc+CL)
instead of -1/Ro*CL which is more.

p.s: due to more cap. the Gate & Drain is more like shorted so the op res. reduces and the gain is close to unity.

Hope you got that.