How to share a single gain resistor among multiple op-amps in a circuit

Question

I'm currently designing a circuit where I need to implement multiple op-amps, each configured with the same variable gain resistor using a single digital potentiometer.

To simplify the design and reduce component count, I'd like to use the same gain resistor (which is a digital potentiometers in my case) across all op-amps. However, I'm unsure about the best approach to achieve this.

Here is my drawing:

From my understanding, instrumentation amplifiers share a single gain resistor (R1 in the picture below) with two input buffers in the first stage before feeding into a differential amplifier (green box):

Image source: Electronics Tutorials - High Input Impedance Instrumentation Amplifier

This is exactly what I need, but I couldn't find any way to extend this configuration for more than 2 op-amps (I need for 4 op-amps at the moment).

I'm wondering if there are any techniques or best practices for ensuring that the gain resistor is properly matched and that the gain remains consistent across all op-amps.

If anyone has experience or insights into efficiently using the same gain resistor among multiple op-amps, I would greatly appreciate any guidance or suggestions.

Answer 1

My hacked solution: Source: https://www.youtube.com/watch?app=desktop&v=NoNgQpbj77Y&ab_channel=EngineeringProf

Use one of these circuits, you should be able to parallel the current mirror. by doing this:

^{simulate this circuit – Schematic created using CircuitLab}

Simulate it and see if it's a solution for your application.

Answer 2

The instrumentation amp single-resistor gain set works because both input amps are processing aspects of the same signal. You want to have currents from four different signals go through one resistor (capacitor, inductor, digi-pot - whatever) without interacting, and that won't work.

If you use integrated programmable gain amplifiers, then you can send the same binary code to all four of them while maintaining complete isolation of the four inputs and four outputs. This is a minor variation of having four digi-pots and four opamps.