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Questions tagged [cmrr]

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.

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How can I model/understand this isolation module's CMR rejection ability?

Before asking the question here I have to show how I was demonstrating the CMR simply: The first circuit above represents a 100dB CMRR and the second circuit shows how the 1k Ohm source impedance ...
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Variance in ECG lead resistance ; its effect ; CMRR

We are designing custom ECG electrode with flexible printed wires as to reduce wires clutter from different electrode. The manufacturer has made the patch but the resistance variation between all the ...
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35 views

Is it possible to very roughly estimate the CMRR degredation of a differential amplifier due to source imbalance given its datasheet

In the datasheets of differential input amplifiers there is a figure of merit called CMRR. This is normally experimentally measured at a particular frequency like 60Hz and presented in the datasheet ...
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104 views

CMRR of Comparators

I have been looking around for the Common mode rejection ratio value on the datasheets for comparators but there don't have one. Why is this? This ratio is crucial in terms of choosing a particular ...
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142 views

Why CMRR degrades in instrumenation amplifier?

Why CMRR degrades in instrumentation amplifier when R3 (only the feedback resistor) is increased keeping all other resistances constant at a fixed value? What mathematical relationship links R3 and ...
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68 views

Effect of bias resistor value on common-mode rejection in a differential or instrumentation amplifier

In the below schematics a source is coupled to a differential amplifier. Rb is a bias resistor for bias currents to flow: Since in instrumentation amplifiers it is a remedy to add resistors for bias ...
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330 views

High-side current sensing with a rail-bound instrumentation amplifier?

I know that current shunt monitor ICs and high common-mode voltage differential amplifiers like the INA117 and AD629 exist but I'd like to know if it's possible to use a regular instrumentation ...
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1answer
671 views

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, ...
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192 views

Measuring Transformer CMRR

I am wondering how to properly measure the CMRR vs. frequency of a(n) (audio) transformer circuit. I have found a couple of methods but not sure I understand them entirely. The main idea I am going ...
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1answer
283 views

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 ...
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2k views

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 ...
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437 views

Divide Sequencial Parameter Step in Spice

I've been designing a (very) simple MOSFET op-amp for school, and one of the things I need to do is determine the CMRR from my simulations. For the assignment, I'm just going to use the value at 1kHz, ...
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190 views

Minimum CMRR design requirement

I've just started studying op amps recently and I am having trouble with the following problem from my textbook: Design the difference amplifier circuit to realize a differential gain of 1000, a ...
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84 views

Scenario in which the opamp Input offset voltage is more than inverting input?

we are designing a circuit with inverting inputs in the order of millivolts. The aim is to build an amplifier so that the signal can be raised to a digital level (3.3V) Now, the question is this: ...
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117 views

Common mode choke to boost cmrr of transformer input

I was wondering, can a common mode choke be used to enhance the CMRR of a transformer coupled amplifier Even further? What are the drawbacks?
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1k views

Op Amp CMRR problem

I'm studying on my own for an exam. I bumped into this problem that really got me. My answer just doesn't match. Find the CMRR of the operational amplifier above, consider Ad = 1000000 (Answer CMRR= ...
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248 views

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 ...
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234 views

How to quantify the error introduced by CMRR given in dB?

Here is the extract from the manual: I want to have an idea about how much voltage error occurs when applied 10V signal. And is this CMRR zero if differential ended configuration is used? How can I ...