I'm working on a battery-powered piece of instrumentation and ran into a problem that so far has resisted my efforts.
We're using an AD736 to measure the RMS voltage of a signal. The 736 needs a symmetric supply, so it's powered from the 0V and 12V battery terminals and the "ground" at midpoint (6V) is established with a voltage divider that has ample overhead to meet the needs of this circuit. The RMS output signal from the 736 ranges from 0-1Vdc and is referenced to this midpoint 6V "ground". Therefore, with respect to the negative battery terminal. the RMS signal ranges between 6 and 7Vdc.
I need to feed this signal into a 0-5V ADC which is powered from a separate supply but must have its 0V reference tied to the negative battery terminal.
Usually, I just use op-amp sum or subtraction circuits, but this time I'm running into problems because I'm trying to shift the level by 6V--from the midpoint "ground" level down to the bottom rail. I wouldn't be surprised if I have to give up some resolution on my ADC, but it'd be handy to hear if there are some well-known solutions for this.
We're using an AD736 to measure the RMS voltage of a signal. The 736 needs a symmetric supply, so it's powered from the 0V and 12V battery terminals and the "ground" at midpoint (6V) is established with a voltage divider that has ample overhead to meet the needs of this circuit. The RMS output signal from the 736 ranges from 0-1Vdc and is referenced to this midpoint 6V "ground". Therefore, with respect to the negative battery terminal. the RMS signal ranges between 6 and 7Vdc.
I need to feed this signal into a 0-5V ADC which is powered from a separate supply but must have its 0V reference tied to the negative battery terminal.
Usually, I just use op-amp sum or subtraction circuits, but this time I'm running into problems because I'm trying to shift the level by 6V--from the midpoint "ground" level down to the bottom rail. I wouldn't be surprised if I have to give up some resolution on my ADC, but it'd be handy to hear if there are some well-known solutions for this.