Hello, i am trying to use an differential ADC to measure voltages quite similar to using a multimeter. But to achieve this, i have to extend the common mode input range of the ADC. The CMIR of the ADC used is approximately 10V. But this is not sufficient for my application. So my question is very simple, how can i enlarge this CMIR. It should be possible to measure voltages accross all kinds of components, just like a multimeter.
I thought of using a differential amplifier with high common mode voltage. But the problem with these are that the common mode rejection ratio is highly dependent of the value of the shunt resistor between the two input terminals. Even the slightest input imbalance can cause a large decrease in common mode rejection. So if i want to measure voltage across a high impedance load this would lead to problems.
I have also considered isolated ADC's, but i wanted to know if there is a solution to this problem using non-isolated differential ADC's.
Can anyone help me, or supply me with some reading material concerning this problem?