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7 Electromagnetic Interference
Published in C. Sankaran, Power Quality, 2017
The common mode rejection ratio (CMRR) is the ratio (usually expressed in decibels) between the common mode noise at the input of a power handling device and the transverse mode noise at the output of the device. Figure 7.3 illustrates the distinction between the two modes of noise. Common mode noise is typically due to either coupling of propagated noise from an external source or stray ground potentials, and it affects the line and neutral (or return) wires of a circuit equally. Common mode noise is converted to transverse mode noise in the impedance associated with the lines. Common mode noise when converted to transverse mode noise can be quite troublesome in sensitive, low-power devices. Filters or shielded isolation transformers reduce the amount by which common mode noise is converted to transverse mode noise.
Multistage Amplifiers
Published in Amir M. Sodagar, Analysis of Bipolar and CMOS Amplifiers, 2018
Another measure is defined for a differential amplifier which states how it discriminates between the useful differential mode component and the nonuseful common-mode component. Common-mode rejection ratio (CMRR) is defined as the absolute value of the ratio of the differential-mode gain to the common-mode gain: () CMRR=|AV,DMAV,CM|.
Application of Operational Amplifiers
Published in Bogdan M. Wilamowski, J. David Irwin, Fundamentals of Industrial Electronics, 2018
Carlotta A. Berry, Deborah J. Walter
The differential amplifier has a differential input mode defined as the difference between the two input voltages. The second feature of a difference amplifier is the common mode input, the average of the two input voltages. Ideally, the common mode gain should be zero and only the differential input should be amplified. Typically, the common mode signal represents the noise found in most electric signals, which should be suppressed at the output. To design for this feature, the resistors used in the op amp must be well matched. The common mode rejection ratio (CMRR) is used to measure how well a difference amplifier performs. The CMRRR is the ratio of the differential mode gain to the common mode gain.
Application of Behavioral Psychology in Clothing Design from The Perspective of Big Data
Published in Applied Artificial Intelligence, 2023
The common mode rejection ratio of the single op amp differential amplifier circuit is affected by the resistance matching accuracy of the external circuit. Where, the perfect op-amp has an infinitely low input resistance. It establishes the degree of output voltage reduction caused by the application of a load. When a differential signal needs to be amplified in the presence of a potential substantial common-mode input, such as significant electromagnetic interference, a high CMRR is necessary (EMI) and the common mode rejection ratio of the amplifier itself. Signals or noise that flows in a pair of lines in the same direction are referred to as the common mode. The voltage shared by both input terminals of an electrical device is known as a common-mode voltage. Whereas, signals or noise that travel along a pair of lines in the opposite directions are said to be in the differential mode voltage. A differential voltage between two conductors is used to convey the signal in the majority of electrical circuits. In practice, the total common-mode rejection ratio cannot reach the ideal state, so the circuit structure needs to be improved. Either raising differential voltage gain or reducing common mode voltage gain will help us increase the CMRR. Emitter resistance RE should be raised to increase CMRR. CMRR should ideally be unlimited. CMRR would typically have a value of 100 dB. The use of a buffer stage in series with a differential amplifier with an in-phase parallel structure is the pre-stage design scheme that is often selected.