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Suggested op-amp for HV mux buffer?

Question asked by gbredthauer on Jul 29, 2014
Latest reply on Aug 25, 2014 by AnnaFeB

I'm working on a data acquisition system that's selecting among 30 inputs (0 to 30V range) via muxes and digitizing them to an accuracy of about 100 uV.   Each input has an RC filter (10k / 0.1uF) before the mux, and then an op-amp buffer follows the mux.


The settling time between samples is adversely impacted by the comparatively fast slew rate of the output of the mux versus the slew rate of a 30V rated precision op amp - most op amps have input protection diodes that activate in this scenario, which drains the filter capacitor a bit during slewing requiring a long settling period to recover.


Are there suitable Analog Devices amplifiers (op-amp of in-amp) for this application?  In particular, the amplifier inputs need to remain high impedance even with a sudden large differential input voltage (no back to back input protection diodes, for instance).  For 100 uV accuracy, bias currents need to be < 10 nA, offset voltage < 100 uV, and the supply voltage needs to be >= 30V.