HdrChopper wrote on Jul 7th, 2009, 2:32pm:Hi subgold,
Actually I was not suggesting the input cap was a switched cap. I was only suggesting a switch in series with it and the input of the opamp. that would provide sampling on your input cap and still perform a HPF action. Since there would be no reset during ck2 on such cap then it would not act as a resistor in average (in which case then you would get a LPF).
I agree that not switching the input cap performs HPF action, but without a sampled input (as opposed to what I was suggesting). Therefore you have a continuous-time output and I do not see why the opamp needs special settling requirements during ck2 (reset phase).
Regards
Tosei
Hi Tosei,
that's exactly my question.
do you mean for the shown schematic (no sampling on the input cap), it is not necessary to settle in ck2? other replies of this topic suggested it should, which is also what i thought at first. because although the information is only sampled in the end of ck1, the capacitor should also get the correct charge in ck2, in order to further process the information in ck1.