Common-mode rejection ratio (CMRR) is the measure of rejection by the device of unwanted input signals common to both input leads, relative to the wanted difference signal.
Questions tagged [cmrr]
44 questions
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Why is noise is considered to be a "Common Mode Signal"?
I learnt that the magnetic interference due to the Earth causes noise in the cable but I wonder why this is considered to be a 'Common Mode Signal' and why differential amplifiers are used to eliminate it?
Dhiraj Dhakal
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Why does this op amp input stage have single ended output?
Looking at the internal diagram of LM324:
I see that the output of the the input stage, which is a differential pair, is single ended rather than being a differential output.
How does then this input stage block common mode signals? As I understand…
Jonathan Wick
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Why do some laboratories use a multimeter on top of an aluminum plate connected to ground?
I was reading a laboratory to study some backgrounds about common mode rejection (CMR), when I saw this image:
Does the aluminum plate connected to ground under the multimeter increase the reading precision or does it do something else?
This is the…
Jjeico
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Should I connect ground for differential measurement with oscilliscope?
Suppose I need to view voltage between two arbitrary points of a circuit with an oscilloscope. For that I can use two probes and A-B math, but should I connect the ground lead to the circuit? How to maximize CMRR?
user54579
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1 answer
Calculate output voltage using the CMRR
Im trying to calculate the output of an opamp, the data is
Closed loop gain = \$20dB\$
CMRR= \$90dB\$
Common signal applyed = \$-60dBV\$
so the idea is to use the next…
avelardo
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What actually is the differential gain of an operational amplifier and why does its value change when we consider the common-mode gain?
Okay, this may be a stupid question, but at the beginning of my Applied Electronics course they taught us that the differential gain \$A_d\$ of an operational amplifier is ideally infinite; however, in real op amps, we get a limited bandwidth. Which…
Maurizio Carcassona
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Why is CMRR effect multiplied by gain in this non inverting op amp configuration?
In this document Vout of a non inverting op amp is given as follows:
But why \$\frac{V_{in}}{CMRR} \$ is also multiplied by the gain?
I would write it as:
\$ V_{out} = \big[1 + \frac{R2}{R1} \big] \big[V_{in} \big] + \big[\frac{V_{in}}{CMRR} \big]…
GNZ
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Why is CMRR defined differently in open loop and closed loop configuration of opamp?
I have recently been studying "Linear Integrated Circuits" and I am currently studying about opamp circuits. The books I am referring are Microelectronic Circuits (Seventh Edition) by Sedra Smith, and Op-Amps and Linear Integrated Circuits (Fourth…
Anubhav
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First principles modeling of op amp CMRR
Introduction
I'm trying to analyze an op amp circuit from first principles (i.e. without using the two rules of ideal op amp analysis -- virtual short circuit and infinite input impedance). The circuit itself is complicated but, for the purposes of…
swineone
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ECG / EEG Amplifier design tricks
First of all, sorry, I missed the links / images where I have found the solutions mentioned below (I hope, if you are familiar with this topic, you know them):
I have to design an ECG / EEG analog amplifier with a gain around 1000. Sigma-Delta is…
moravas8051
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How can I calculate CM and DM gains for this model?
Regarding the second page of this document, in the first example it calculates the DC CMR due to line imbalance Rs and an explanation is given in the first paragraph below (ignore the second example):
I don’t understand where the numbers 0.9990 and…
cm64
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operational amplifier CMRR measurement
I am trying to measure CMRR of an op-amp and I found an application note from Analog Devices, that suggests the circuit below. I understand what CMRR means, but I can't understand why in the formula they use \$V_{IN}\$, although the common mode…
isam
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Why does CMRR degrade in an instrumenation amplifier when the feedback resistor is increased?
Why does CMRR degrade in an instrumenation amplifier when the feedback resistor is increased, keeping all other resistances constant at a fixed value? What mathematical relationship links the feedback resistor and CMRR?
user172541
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1 answer
How can the CMRR of an opamp be negative?
I was reading a paper from 1977 regarding the analysis for the CMRR of a three opamp instrumentation amplifier, I got the paper through my Unviersity but I cant post the paper since its copyrighted, however here is the link to download it legally…
S.s.
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PSRR and CMRR in a diffferential amplifier
Please, can anyone help me how to find the PSRR and CMRR in this simple differential amplifier circuit as shown below in figure 1?
I have searched on the internet and I decided to follow this methodology to find it:
First of all, I calculate the…
gr1
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