I need to convert a differential pair into a single ended signal and would like to use a differential amplifier to do this.
Using the above circuit and the ADA4850 I was hoping to achieve this but of course, the DC from each differential pair branch cancel one another out so only the AC components from each remain (which are centred around 0V). We cannot have a -ve supply and have connected VEE to GND. Because of this, whilst this is a rail to rail op amp, the DC bias cancel one another out and the -ve portion of the AC signal at the diff pair hits the GND floor/ limit.
If adding a DC bias to one input so the DC is passed through the op amp as show below (Diff pair input 200mVpp (peak to peak)):
Then the output DC bias is 50% of the input DC Bias with the peak to peak voltage being a quarter (100mVpp) of the expected (400mVpp) output voltage as shown below:
Why in the second circuit is the AC peak to peak voltage a quarter of what was expected?
What is the best way to convert this diff pair into a single ended signal (a transformer is not suitable in this case, nor is dumping the -ve and only using the +ve signal)?