We are currently using an INA116 for a precision bio-medical measurement. The current prototype implementation is a dead bug and thus the general concerns about layout were avoided We are getting ready to fabricate an initial PCB and I have two questions.
1 - For our application we are measuring across a high-Z load but 10s of fA input bias up to possibly a 100s of fA or so would be tolerable. Is there a part anyone would recommend as a replacement?
2 - If we stick with the INA116 there is of course the guard ring guidance that mist be considered. We will have the amplifiers close to the point of measurement but reading the section on input connections I was looking at the coaxial configuration and wondered if the shields indicated in the top Fig. 5 (see below) are tied together at the source or if they are floating as seems to be indicated. The latter seems like it would be susceptible to EMI and such.
Thanks in advance for your consideration,