To buffer or not to buffer that is the question.

[TUBESMAN]

Fellow humans:

I need a voltage reference with Rs about 1 ohms or less. This is to drive a simple Instrumentation Amplifier using a general purpose FET op-amp. I need to use a simple IA because their will be four of them and space and cost are factors. A simple IA is affected by the Rs in the two legs. So, to reduce gain errors I need a reference with low Rs to match the Rs of the leg I am measuring.

My question is, can I simply use an LT1004-1.2 straight into my FET IA + input through its 16.5k resistor, (I need gain in my IA their is a FB r as well) or should I buffer it with a unity gain op-amp THEN into my IA ? This is all at DC, AC behavior is not really important. Thank you for your help.

 

[rayma]

can I simply use an LT1004-1.2 straight into my FET IA + input through its 16.5k resistor

The reference's impedance is less than an ohm, so unbuffered should be fine.

 

[TUBESMAN]

I figured it would be. I just needed a second opinion. Thank you!

 

[rayma]

I figured it would be. I just needed a second opinion. Thank you!

If you needed even lower noise, an RC filter on the reference, followed by a buffer, would work.
A shunt capacitor alone wouldn't do enough.

 

[TUBESMAN]

Yeah, if the source impeadance is 1 Ohm, it would need a really huge cap to knock down the noise. But, the noise from this device is already low enough for my needs. I just need a really low Rs to avoid major gain errors. I MIGHT put a build out resistor in the line to match the other input but I have to look into that.

 

[rayma]

I just need a really low Rs to avoid major gain errors. I MIGHT put a build out resistor
in the line to match the other input.

Maybe you should post the schematic.

 

[TUBESMAN]

yeah, but not now. It's still only in my head. Worst possible place!!