>> This sort of OK, except the capacitor connects across the (+) terminals of the two input opamps, and does not connect to ground:
>> Also, we don't care about the CMRR at 64 kHz. We care about it at up to 10 kHz, but not above.
In this case, the conner frequency for the lowpass filter would be around 100kHz in order to satisfy the requirement.
>>And doesn't the value depend on the resistors?
Yes, it does. The error in the resistor (typically 0.1%) is much smaller than that of the capacitor (10%). Since the resistor error propagates in the same as the capacitor,
we can ignore it.
Note that we only specify the conner frequency (=1/RC) instead of R and C specifically from the tolerance analysis, we still need to choose appropriate
values for R and C with the conner frequency fixed to be around 100kHz, for which we need to consider the output impedance of port 1 and port 2.
