I have extreme confusion in figuring out common mode voltage related topics. I would like to illustrate my understanding first: Below opamp has two inputs V+ and V- as usual. And lets say the differential voltage is:
Vd(t) = (V+) - (V-) = sin(w*t)
And lets say there is DC common mode voltage. When we measure the voltage between V+ input and the system GND(could be earth) the oscilloscope shows this difference signal as: (V+) + Vcm. When we measure the voltage between V- input and the system GND(could be earth) the oscilloscope shows this difference as: (V-) + Vcm. So the above circuit can be modelled as below??:
Is the above model only valid when the - input is not system or earth grounded?
Now imagine we have a single ended system with a floating signal source like a battery powered transducer. At the differential amplifier end the GND of the transducer is wired to the system ground as below(you see - input of the opamp is earth grounded here):
In this case when we measure the voltage between V+ input and the system GND(could be earth) the oscilloscope shows this difference signal as: (V+) + Vcm. When we measure the voltage between V- input and the system GND(could be earth) the oscilloscope shows this difference as: 0V since - input is wired to GND/earth. So can the above system can be modelled as in below?
And in a book I read the following about this configuration:
Here is a paragraph from the book for this configuration:
What does that mean here? Is common mode offset error higher in this configuration than in differential signalling. Im completely lost.