What does it mean by common mode for a non differential circuit?

[sys_eng]

What does it means by common mode for a non differential circuit?

for differential circuit, it has two inputs, +, - inputs. Common mode refers to something that common to both inputs.


But for non differential circuit, it doesn't not have two inputs and still it use the term common mode.
like the diagram listed. Common mode means what? Here, Vcm is common mode voltage.
So what the are two voltages it trying to compare.

 

[d123]

Re: What does it means by common mode for a non differential circuit?

Hi,

Hard to guess, for me. Perhaps it just means that the voltage referred to ground before the shunt, from ground to the resistor positive terminal, is the full supply voltage, the "Vcm - Vshunt" means the voltage referred to ground minus the shunt resistor's voltage drop when measured at the resistor negative terminal.

Presumably the difference inferred is the voltage across the resistor to measure the current Iload. So maybe it's trying to explain current shunt measurement, e.g. measuring the voltage across the resistor based on V1 - V2/R = I(load).

 

[sys_eng]

Re: What does it means by common mode for a non differential circuit?

Hi,

Hard to guess, for me. Perhaps it just means that the voltage referred to ground before the shunt, from ground to the resistor positive terminal, is the full supply voltage, the "Vcm - Vshunt" means the voltage referred to ground minus the shunt resistor's voltage drop when measured at the resistor negative terminal.

Presumably the difference inferred is the voltage across the resistor to measure the current Iload. So maybe it's trying to explain current shunt measurement, e.g. measuring the voltage across the resistor based on V1 - V2/R = I(load).

hi,
I try to find a general definition for common mode for a non differential circuit.

 

[asdf44]

Re: What does it means by common mode for a non differential circuit?

It is a differential circuit. The voltage across the shunt tells you the current across the shunt. That's a differential measurement.

Common mode refers to the absolute voltage of the shunt with respect to ground. The diagram captures it well. The + and the - are the differential measurements. The voltage source shown is common to both of them.