Greetings to everyone in the engineer zone.
I'm an electronic hobbyist, and I'm currently looking for some advice about a circuit I'm working on. I would like to digitally control the gain of a certain dual-supply operational amplifier, but I'm having a difficult time finding the correct digital potentiometer to act as a voltage divider over the negative feedback loop.
I have a +5VDC supply line (vs. GND) that could be used to power the digpot, and a +/-9VDC dual voltage supply that I use to power the operational amplifier. The circuit is currently on a breadboard, and the amplifiers are using 100K physical potentiometers that I want to replace with digital variants, but I am having a tough time finding an appropriate model.
So what's my problem here? Well it seems that it's the voltage on the A, B and W terminals of any digipot I've tried so far. Why do digital potentiometers limit their A/B/W terminal input voltage to their supply voltage range (i.e. 0 to +5.5V), and where can I find digipots that do not? I always believed that the A, B and W terminals were supposed to be galvanically isolated from the rest of the circuitry. Let me show you an image to get a better idea of what I mean.
What can I do to solve this, and if isolated digipots aren't an option what other solutions do you propose?
Thanks in advance