Say I have 2 or 3 PWM channels coming out of a FPGA or microcontroller or something, and I want to filter and sum them into one analog output.
Is there any advantage to using 4 or 6 output lines and using an opamp in a differential summer/two pole filter configuration, over using a single ended summer/filter?
Maybe ground loop supression, if you care about millivolts. FPGAs can have terrible grounds.
The best thing to do is buffer the PWMs outside of the FPGA, with some small cmos gates, where you can control the analog situation better.
The extreme would be to come out LVDS, and drive an LVDS-to-CMOS receiver.
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