about calculation of GBW- what is the meaning of CL?

[lhlbluesky]

gbw calculate

for an open-loop and a closed-loop opamp, their GBW is the same. is that right?

for calculation of GBW, we can use the formula:

GBW=gm,in/2pi*CL

i want to ask,what is the mean of CL?for a pipelined adc, there are many stages, if

i want to get the GBW of first stage's opamp, then how to calculate CL,

CL=(Cs+Cf) of next(second) stage + gate capacitance of comparators of current(first)stage + parasitic capapcitance + equivalent capacitance of current(first) stage(Cs and Cf in series)

is the above formula right?

someone says, the last term equivalent capacitance of current(first) stage(Cs and

Cf in series) should not be included, then which is right?


pls give me a clear explanation, thanks everyone for your reply.

 

[Usman Hai]

closed loop gbw

How can openloop GBW and closedloop GBW be the same? They are different by the factor β, which is the feedback factor. β=Cf/(Cs+Cf+Cin)

Your equation to find Cl is right. We have to include all the capacitors loading the opamp which also includes CMFB capacitors as well. Also read the latest paper on pipelined ADC https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=4787552&isnumber=4787550

They have claculated the CL so you will be sure of what you are doing.

 

[LvW]

Re: about calculation of GBW

How can openloop GBW and closedloop GBW be the same? They are different by the factor β, which is the feedback factor. β=Cf/(Cs+Cf+Cin)
.

If an opamp has a 20dB/dec roll-off the GBW is a fixed value (identical to the transit frequency).
That means - the product of gain and corresponding BW is a constant - and thus INDEPENDENT if there is feedback or not.
In summary: GBW is identical for open and closed loop.

 

[lhlbluesky]

about calculation of GBW

any more advice,pls? thanks all.

 

[Usman Hai]

Re: about calculation of GBW

Sorry LvW, I mistaken GBW for unit-gain frequency. I was reviewing a paper few days back and they used GBW for unit gain so that was in my mind...gain-bandwidth product must always be constant

 

[LvW]

Re: about calculation of GBW

Sorry LvW, I mistaken GBW for unit-gain frequency. I was reviewing a paper few days back and they used GBW for unit gain so that was in my mind...gain-bandwidth product must always be constant

.. and we are all only human beings....

 

[lhlbluesky]

about calculation of GBW

more ideas?

 

[Usman Hai]

Re: about calculation of GBW

ideas about what?

 

[lhlbluesky]

about calculation of GBW

about the estimate of CL in sc circuit.?