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I think that the capacitor size indeed affect the response time. In fact it affects the loop gain and phase (therefore reponse time).
So I think the cap shouldn't be too big.
Furthermore, they shouldn't be too small, otherwise the switch parasitics cannot be neglected. Especially the charge injection that would make the output voltage differ from the target value.
As for the ratio, it is said in the book by Johns and Martin that a 1:4 to 1:10 is a good value. I remember once using a 1:5.
while choosing the value of the capacitor for the sc cmgb ckt you need to take follosing care.
1) Capacitor is size is big enough so that the droop in output common mode is withing range.
2) Capacitor size should be below the value where it start loading the circuit and reduce the gain (sc resistance)
This is with assumption that your update frequency is constant (if not then you can also play around with it.)
Capacitance can't be set so large, it will affect the work speed, this maybe the reason why the system work normally after several clock cycles.
Advise to set the ratio to 1:1 or 2:1, just try it!
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analoger said:
When I choose the ratio of Ccm/Cs=10:1 ,then I have to wait multiple clock cycles for the circuit to start funtioning correctly.
So if the OTA is used in the ADC,the system have to work normally after several clock cycles. Is it right?
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