10 µA sensor excitation

Question

I need to measure cryogenic temperatures using a silicon diode type temperature sensor. This has a 4 wire interface. Two wires for a 10 µA current excitation for the sensor and 2 wires for the voltage output which I connect to the ADC pins of a microcontroller. What circuits or ICs are typically used to generate this 10 µA current?

Answer 1

You'd best be using an op-amp with some kind of transistor most likely. And a precision voltage reference and a few precision resistors. You will only need a few volts of compliance since the Si diode won't drop more than that, and the drop across the high-resistance cryostat wiring should be negligible at 10uA.

Plus another op-amp or two to buffer and amplify the voltage to your ADC, in this case an instrumentation amplifier with +/- supplies would be a good idea to return the signal to ground reference and amplify/buffer/signal condition. And some more precision resistors.

And likely some circuitry to make sure the amplifier output does not exceed the input bounds of your ADC and protect it from damage.

Or just buy an instrument designed for the task from Lakeshore or whoever.

Answer 2

The circuits you'd be looking for would be called "precision current sources".

You would first sit down and do the engineering thing where you start by stating requirements, which you so far forgot to do.

Accuracy and noise need to be stated, as well as well as maximum voltage.

Then, you'd go ahead, pick an appropriate opamp configuration, select an opamp with sufficient specs, and build your current source.

Answer 3

Something as this could be used ...