Hi Stomp, As you saw in the application note ( Improving CMR Using the RLD ), component tolerance is one of the biggest factors that can worsen CMR performance. By replacing the common-mode caps with a differential cap, you remove the CMRR loss due to the capacitor tolerance. Of course, you still have the resistor tolerance to deal with, but it's easier to get lower value resistors at a reasonable cost (typically 1% or better is used). The differnetial cap should not have any negative impact on the signal quality. Simply size the cap to set the desired signal bandwidth while keeping the resistors large enough for patient protection. 1 kHz to 10 kHz is usually low enough for antialiasing, so 470 pF is a good start. Even if you keep the 47 pF common-mode capacitors, the differential filter will roll off about 1 decade earlier in frequency, which will mitigate some of the CMRR loss due to common-mode capacitor mismatch. Best Regards,
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