Hello,
We are using the ADS4149 as a digitizer for unipolar PMT pulses and therefor would like to bias the inputs towards one end of the range. We are presently using some op-amps (well filtered outputs) to provide a stiff voltage both above and below Vcm. These bias voltages are couple to the ADC inputs through 50ohm "termination" resistors, while the input is AC coupled. We see 60MHz noise (1/4 sampling freq. and dominant FPGA noise) that is proportional to the amount of DC offset applied (up to ~10LSB rms). I am about to reconfigure the DC bias network to be referenced off of Vcm, but wondering if others have used DC biasing or know of any "gotchas" with using the Vcm pin as a reference for a symmetric DC bias.
Thanks for any insight!
-Perry