Precise schematics are generally classified as NI Confidential. Here is some public information which may help you:
- 40 mVpk-pk to 40 Vpk-pk input range
- 1 MΩ input impedance
- AC, DC and GND coupling
Sorry that this is maybe an oversimplified answer to your request.
If you can be more specific in your questions about the input circuit, I may be able to provide some more detailed answers.
The spec additionally tells :
Input impedance 1MOhm || ~17pf
AC cutoff 12 Hz (3db) ...
Hook up a NVA and you can measure all properties you migth need 😉
However a bit more documentation as can be found in other digitizer/scope devices from NI should be standard!