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| Generating a bipolar offset for an op amp |
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| netdudeuk:
Hi I have the below circuit (courtesy of Louis, Scullcom Hobby Electronics). It is a work in progress but adjusting RV7 does indeed allow a positive / negative offset to be added to the output. The problem is that I'm using a precision trimmer to do this and even if I used a regular pot, it would probably be a bit hit and miss in terms of what the offset actually is. So, what I would like to do is either drive the junction of C21 / R15 with a DAC or the like (so that I get to say exactly what the output voltage / offset is) or use a regular pot with an ADC to read in the value at that junction. The preferred option would be to do the former. It wouldn't matter if I needed to use a relay to switch the polarity. Any thoughts please ? Thanks |
| cvanc:
I'm not quite sure what your goal is? Are you trying to just null this circuit to have a low DC offset? (If yes, consider an op-amp based DC servo loop.) Or are you trying to *modulate* the DC offset like it was a signal? |
| ledtester:
It's for controlling the DC offset of a function generator circuit. I imagine the OP wants to control it digitally. Schematic is attached. Relevant part of the circuit is bottom left of center. |
| netdudeuk:
--- Quote from: ledtester on August 16, 2019, 02:31:20 pm ---It's for controlling the DC offset of a function generator circuit. I imagine the OP wants to control it digitally. Schematic is attached. Relevant part of the circuit is bottom left of center. --- End quote --- Thanks guys. Yes, that's where I have taken that block of hardware from and yes, I would like to drive it digitally. However, I am using my own DDS device. |
| MarkF:
I found that I could replace the adjustment pot and series with just a DAC and an op-amp to shift the +4V output to +/-2V output. |
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