My question is somewhat similar to this one asked here before. I have the following circuit:
simulate this circuit – Schematic created using CircuitLab
The input signal is being fed to two (possibly three) inverting operational amplifier circuits. The positive input of each opamp is used to adjust the input offset to a desirable value. Resistor R11 is added because the input is a voltage drop from the 50Ω resistor. Another thing I should mention is that the input signal scale is approximately from 0 V to 10 mV.
The problem is that these circuits affect each other. This behaviour is explained in the answers to mentioned question, so I'm trying to design a different circuit. I have read this tutorial by AD and a similar by TI. So, there are several methods of adjusting the input offset. I'm using the one for the inverting opamp circuit and the impedance of my voltage source is not low enough so these circuits don't work correctly together. I thought of the following solutions:
- Use a non-inverting circuit. Offset adjustment can be done like this:
However, I'm worried about connecting multiple opamps together. In the above circuit, R2 changes the input signal; will multiple opamps with inputs connected together affect each other in this case?
- Simulate the whole circuit and optimize resistor values so all the opamps will have a correct gain. This method would produce a lot of optimization goals which would be difficult to achieve. How stable a circuit built like this would be?
Best Answer
The simplest way to eliminate your problem is to reduce the effective impedance of the source, and a voltage follower will do nicely
simulate this circuit – Schematic created using CircuitLab
The choice of buffer op amp is left to you, depending on the frequency response you need.