By Scott Hunt, System Applications Engineer, Analog Devices
I have an instrumentation amplifier, but I need wider dynamic range than I can get with a single gain. Can I multiplex gain resistors to get programmable gain?
To maximise dynamic range in precision sensor measurements, it may be necessary to use a programmable gain instrumentation amplifier (PGIA). Because most instrumentation amplifiers (in-amps) use an external gain resistor (RG) to set the gain, it would seem the desired programmed gains can be achieved with a set of multiplexed gain resistors. While this is possible, there are three major considerations to make before implementing a system this way with a solid-state multiplexer: supply and signal voltage limitations, switch capacitance and on resistance.