Capacitor Placements

Question

I have been studying the effects of using capacitors in different locations and one I have come across is split caps across a signal output. I've re-created the design in LTSPICE and screen-cap'd it:

Let's assume for the sake of argument that the Signal In and Signal Out are already balanced to be half of Vcc, (24V_Ref in the screencap). Is there anything gained by using the above capacitor layout compared to the following simple RC filter? My gut tells me that if the signal is already balanced to half Vcc, then it IS useful, but playing with it in LTSPICE doesn't show any difference between these two layouts.

Lars Hankeln · Answer

Since in small signal analysis all DC sources are shorted, both circuits would result in the same small signal equivalent circuit. Connecting both capacitors to Vcc would also be equivalent. So for the signal it doesn't matter if the capacitances are connected to GND or the supply voltage.
It also doesn't really matter if the signal is balanced to half Vcc or not. There is no DC biasing done in those circuits. You might imply that there is some sort of voltage divider created by the capacitors which is not the case for DC.

Capacitor Placements

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