A thorough understanding of common mode input signals of differential mode and input signals

A thorough understanding of common mode input signals of differential mode and input signals

For A differential amplifier, the input signal A at the left end is equivalent to input A/2 + A/2 at the left end and input-A/2 + A/2 at the right end. It is equivalent to inputting the differential mode signal + A/2-A/2 and the input common mode signal + A/2 respectively at both ends of the input differential mode. Input B at the right end, which is equivalent to input-B/2 + B/2 at the left end, and input B/2 + B/2 at the right end, it is equivalent to inputting the differential mode signal-B/2 + B/2 and the input common mode signal + B/2 respectively at both ends. The two are combined, which is equivalent to A and B When both ends of the current and current sides input signals at the same time. Therefore, from the input port on the right, the total difference modulus signal is [(+ A) + (-B)]. (Why not [(+ A)/2 + (-B)/2]? When the difference mode inputs C, + C/2 and-C/2 are input respectively, and the total common mode signal is [(+ A)/2 + (+ B) /2] (why not [(+ A) + (+ B)]? Because C is input at both ends of the definition common mode input C ,). In summary, the difference mode is the difference, and the common mode is the average value.

Common Mode signal of differential mode signal

In fact, this is an understanding of the knowledge in the analog circuit, regardless of the difference mode signal or common mode signal, the output is a difference. The common-mode rejection ratio refers to the difference between two ports that input the same signal at the same time, for example, noise signal ,, so the average value of the common mode signal is incorrect. You can understand that, after a difference-mode amplifier (for example, composed of two peering transistors), the common mode signal can be output as a difference-mode signal, the output is a common-mode signal of 0.

Differences between common mode and Differential Mode

Common Mode Signal
Common Mode signals are the same signals used at the same phase and reverse phase input ends of a differential amplifier or instrument amplifier. For example, the noise voltage is introduced to two balancing ends in the balancing line center. Another example is the DC voltage added to the balancing line (for example, the DC level produced by the ground potential difference between the signal source and the receiver ).
The ideal differential amplifier can completely eliminate common-mode signal output because the differential input (same phase and reverse phase) offsets the same input component. The parameter used to measure this feature is referred to as the common mode rejection ratio or CMRR.
Differential Mode Signal
It is also known as the norm, serial mode, inter-line induction, and symmetric signal. In the two-line cable transmission circuit, each line of ground voltage is expressed by symbols V1 and V2. The difference mode signal component is VDIFF. All the differential current (IDIFF) flows through the load. Differential Mode Interference intrude into two signal lines, with the same direction as the signal current direction. One is generated by the signal source, and the other is generated by electromagnetic induction during transmission, it is in the same phase as the signal string, which is difficult to suppress.