I'm working on a project for school that involves a configurable input stage (AC/DC coupling and variable input impedance) connected to an instrumentation amplifier. I am wondering whether I will experience any major DC offset issues if I connect an analog switch to the in-amp's inputs, or if I would be better of using relays.
A few notes on the design:
- The 1.3k resistor pair provides protection for the input stage
- The resistor network connected to the switch is designed to allow be to select the input impedance
- The options are infinite, 50ohm single-ended, 75ohm single-ended, 100ohm differential, and 150ohm differential.
- To the left (out of image), there is a mechanical relay-based AC/DC coupling selection circuit
- I realize that the analog switch will have no protection, but I'm hesitant to use diodes due to leakage currents
- I do not need fast switching
This question is mainly about leakage current: is the leakage of a CMOS switch (such as the ADG409) low enough that it won't produce a significant DC offset at the output? Or would I be better off using relays?
Edit: something like the MAX14778 would be a better option, assuming that the leakage currents are common-mode. The only problem is that it comes in a 5x5mm QFN package, which is not ideal for prototyping.