I need to drive AD6649 with AD8370 for a narrow band application in the frequency range 20-500MHz. Taking the examples as a guideline, I took out anti-aliasing filters, as the filtering is already done in the RF, and came up with the attached scheme.
At the input of the VGA, impedance is matched using the parallel resistor. At the output, Capacitors are for decoupling, 100ohm is load of AD8370 and 33 ohm resistors are for isolation of the switching currents from the ADC. Shunt capacitor is included for kick back currents. The VCM is also supplied. My questions are:
1) Do you see any problem with the impedance matching?
2) Do I need pull-up at the output of VGA?
3) Can the VCM inputted this way? Output common mode voltage of the VGA is ~1.65V whereas input CM Voltage of the ADC is 0.9V.
4) I would be grateful for any other improvements.