If breakpoint F is too high and you won't get much image noise rejection.
If breakpoint F is too low, you get ISI or phase shift in passband or group delay or attenuation of desired passband.
Any signals above 1/2 Fs create errors as these do not satisfy the Nyquist sampling criteria. If you need additional rolloff on noise above this point, you can choose C to equal the breakpoint in this LPF.
The bandwidth limitation of Op Amps also serves to limit signal harmonic distortion above the 1/2 sample rate. (32MHz here)
Overall you have to decide what your signal range and bandwidth is and what noise rejection you need.
If you had stringent filtering requirements, you might consider a digital filter.
But if not critical just choose C for your breakpoint to be near or below 32MHz by converting the differential equiv cct to a single-ended value for calculations.
Also your choice of a transformer affects your HPF response above DC. YOu might be able to choose an appropriate Video Amp to forego the need for a transformer. But the sharing of grounds often adds to the conversion noise and XFMR's have much high CMMR at 30MHz than Op Amps.
It all depends what what you are sampling and need for accuracy.
Addendum - unrelated to this design. but important for new designers using ADC's.
A good test of your design is use a generator with a time base sweep synchronized with a SA or use a VNA. Or failing that, perform a frequency response test at low levels and high levels and check for harmonic content.
Otherwise with DC response performing a low frequency triangle signal test and using a scope compare A-B with DC coupling or use in X-Y mode with AC coupling. The compare out-in of analog signals should give a difference of +/- LSB at all times through the range. (if conversion lag is small) Often it is not ! so be warned. Analog ground, Vref, missing codes all contribute to this error.
First, that question should be clearly answered in the datasheet for the device. The absolute maximum section will tell you what voltage range the inputs can tolerate without damage to the part, and the operational spec will tell you what input voltage range it can sense.
Second, it is very unlikely that the A/D can sense voltages outside its power supply range. Again though, read the datasheet for the definative answer.
Most likely you will need to put a resistor divider in front of your A/D. That attenuates signals, so the signal level into the resistor divider can be larger than the native signal range the A/D can convert. Note that the second resistor of the divider (the one your input signal is not attached to) doesn't have to go to ground. In your case, you may want to connect it to the positive supply, or some other fixed voltage source.
Best Answer
In the dual supply schematic, there's no reference for the input voltage. Just as a for-instance, if there's no reference to ground on the input side, then you could be sending in 1000V+1*sin(x) which would result in the op-amps being railed for the entire time. Once it's got a good reference, it will be just sin(x) and shouldn't be railed so long as the resistors are chosen well.
The single supply also has this issue. The input is AC coupled which is fine, but the only place current to go is into or out of the output of the op-amp. If you've already railed it, then it won't be able to move from the rail.
You'll want both circuits to have some kind of path to ground so that when the signal is 0V input, it will level out to 0V output.
RT should be split into two resistors with GND sent to the middle of it. CM on the single supply should likely be connected to ground probably through a resistor.