Hi,
What circuits would you want to measure the difference voltage?
For example the output voltage of a bride mode amplifier, but you didn´t understand. It is a voltage measurement, and no distortion measurement, and you can use it even if both amplifier stages are not matched.
--> and you (alomst) gave an answer to your questions: LVDS signals for example, or RS422/RS485. Quadrature encoded sine signals. Professional differential analog audio lines. BLDC motor control signals.
I have built an Xray sensor with virtual ground. There are a lot of applications.
The differential measurement will display on the oscilloscope the cross-over region only.
I don´t know how you want to do this....
If you mean to measure the difference between input and output, then you usually have the problem caused by the amplifiers gain and phase shift.
If there is cross over distortion between the two cycles you can measure the difference of voltage and just measure the cross over distortions peak to peak voltage. Positive cycle goes to ch1 and negative ch2, add mode and invert ch2 leaving the difference between the channels. This will only display the crossover distortion.
What do you mean with "cycles"?
Do you mean the two power stages? Ther is no "positive cycle to´ch1" and no "negative cycle to ch2". One stag is inverting, the other is not.
Often bridge mode amplifiers use a single power supply. this means both amplifiers produce positive voltage only.
Your description is more like displaying the "sum" (insted of "difference") of both inputs.
The result is by far not the distortion only. It includes DC offset, gain error, phase error .... Maybe on first sight it looks like distortion only, but it´s surely not.
I agree with audioguru.
Klaus