Questions tagged [common-mode]

A common mode signal is a signal that is common (i.e. has the same magnitude and phase) to both inputs of an electrical device, as opposed to a differential mode signal. It is often desirable to reject common mode signals, in which case the common mode rejection ratio (CMRR) is an important metric.

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Why feed a V_OCM outpin pin of a FDA?

The Analog Devices reference design CN0540 (see diagram below) shows an AD7768-1 ADC together with a fully-differential ADC driver ADA4945-1. I am wondering why the common-mode voltage pin V_COM of ...
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SVPWM: space vector generation star point shifting - effects?

I keep seeing that the space vector generation (as a part of a FOC) is generated around DC Link / 2. What effects would be expected if the (in this case isolated) star point were permanently shifted? ...
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How are SPICE files created compared to S4P files generated from a VNA?

When measuring impedance versus frequency using the same data in both SPICE and S4P formats, why do I obtain different results? COMMON MODE IMPEDANCE Common mode impedance 10514 Ohm at 79.1 MHz S4P ...
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Radiated Emissions problem

This is regarding some Radiated Emissions testing unintentional radiator. We did a pre-scan of our product and we got the following EMI signature. Critical frequency is at 314.986 MHz Polarization is ...
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Input common-mode range vs output voltage (INA826) interpretation

I'm starting a new design using INA826 and analyzing the input common mode limitation, I do not understand the differences between this curves; I mean, why in figures 11 and 12, gain and VS is not ...
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Input common mode voltage in differential amplifier used for high-side current sensing

I am confused about the input common mode voltage seen by an op amp configured as a differential amplifier for high side current sensing. Assuming that the op-amp and the load for sensing share the ...
Jackson's user avatar
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Difference between current and voltage expressions in fully differential circuits

This is an old, unimportant question. I am adding a bounty on it to effectively raise the bounty of the question linked below. Please answer the linked question for the bounty. Both bounties will be ...
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Common-mode capacitance of operational amplifiers as defined in datasheet

The common-mode input capacitance is modeled as Ccm/2 on each operational amplifier input in https://www.allaboutcircuits.com/technical-articles/input-capacitance-analog-circuits-how-to-compensate-...
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Multiple 4-20mA Transmitters from Common Referenced Analogue Inputs

I'm trying to come up with a scheme for multiple loop powered 4-20mA transmitters controlled from seperate analogue voltages, which all have a common 0V reference. My inital thought was to use an ...
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What is a Fast-Stat Commonmaker actually doing?

Trying to get an Ecobee thermostat to work in my old house where I only have two wires going to my thermostat. Ecobee needs a common, and the remedy they suggest is a Fast-Stat Commonmaker, which has ...
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Differential Amplifier small signal analysis

I am having trouble doing the analysis the small signal model of this circuit: So far, I have come up with this this circuit for the small signal analysis: However, I can't come up with a formula ...
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Inferring common mode impedance for a given CMRR

In the figure below, the common mode impedances of the line driver and receiver are represented by RCM+ and RC-: (What I understand by the phrase CM impedance is that it is the resistance or ...
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Trying to view CM and DM components of a signal on a two channel digital scope screen

I want learn how to view the CM and DM components of a signal on a usual two channel scope. The reason for this to be able to verify whether a noise superimposed on a signal is CM orDM. Regarding my ...
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Homemade EEG circuit common mode feedback

I am currently building a DIY EEG circuit using this guide. This guide is for when there are two inputs. How can I modify this so that I can also input two EMG signals too? It is common knowledge that ...
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Accuracy of a single to differential ended circuit

I have single-ended senors/transducers which are hooked up to a DAC in single-ended configuration. The transducers are calibrated by another company with certificates and they can output from -10V to +...
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Is this a suitable common mode choke?

I've got a system here where I get 12V DC from a laptop charger which is connected to the wall. That 12V gets stepped down to 5V using the TPS56221 buck converter (running this at 500 kHz, with an ...
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Common mode error formula from TI seems counter intuitive

I'm working on an application to measure current in a buck converter using a current sense amplifier. According to this video from Texas instriment, the equation for common mode error is same as eqn 1 ...
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How to write \$V_{\text{a0}}\$, \$V_{\text{ab}}\$ and \$V_{\text{cm}}\$ for the three-phase three-level inverter in terms of the switching signals?

How to write \$V_{\text{a0}}\$, \$V_{\text{ab}}\$ and \$V_{\text{cm}}\$ for the three-phase three-level inverter in terms of the switching signals? For the three-phase two-level inverter, the values ...
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Common mode voltage with configurations of Opamp

I am reading this article (https://www.analog.com/media/en/training-seminars/design-handbooks/designers-guide-instrument-amps-complete.pdf) in order to understand more how traditional instrumentation ...
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Transfer Function of Differential opamp with common mode voltage

When we consider the relationship between Vout and Vin of the differential amplifier, we connect one of its inputs each time to the ground to ignore that input voltage in the calculation, in order to ...
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Differential Amplifier with unbalanced differential signal

The circuit topology of figure 1a corresponds to a differential amplifier with resistor load. Since the signal generator available in lab does not have a differential output, a balanced differential ...
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Need of Cmfb in fully differential amplifiers

Instead of using cmfb circuit to set output dc common mode voltage Why can't we put at dc bais voltage at inverting or non inverting inputs of differential amplifier that way Vocm is set through ...
mahmoud esmail's user avatar
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How does INA 290 reduce voltage level from 120V to ICMR range of the corresponding op-amp?

How 120 V is in the Input Common Mode Range of the op-amps?
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Bias common mode and Impendence in relation to ASD1299

I was wondering if anyone would be able to help me understand the Bias common mode and Impendence in relation to ADS1299. If someone has a ADS1299 for dummies that would be great Thanks
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Effects of Improper Grounding on Common Mode Noise

In a DC power system like the one shown below in the diagram, a resistor is placed between the return wire and chassis to limit fault currents in the scenario where there is a high side to chassis ...
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Common mode voltage suppression for low side high bandwidth current sensing

I want to measure current of short duration high amplitude pulses using a low side shunt resistor. The test pulses are up to 400ns (2.5Mhz) with amplitude up to 3000V, depicted in the picture below. ...
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Ethernet RJ45 Mg Jacks - CMC placement

Ethernet RJ45 Mg Jacks. Some have common mode chokes on the PHY side and some have chokes on the cable side. What's the difference? Some examples: https://www.sparkfun.com/datasheets/Prototyping/...
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DM EMI filter components calculations

I'm attempting to design a passive DMEMI filter according to the paper titled "guideline for a simplified differential mode EMI filter design". Two formulas are presented in this paper to ...
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What is the standard common mode voltage of Media Dependent Interface MDI[0:3]± signals?

I am working on the selection RJ45 connector for MDI interface between PHY and the link-partner. I am planning to use this PHY for my SGMII interface application. From various online readings, I ...
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How to simulate this circuit for common mode voltage effect?

Regarding my previous question and this paper, I wanted to simulate the circuit below to see whether it is rejecting common mode voltage as claimed. The paper says that sharing DAC's Vref with non-...
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EMI analysis for low power low voltage AC/DC

I've designed an 80W 220V-IN 400V-OUT PFC Boost converter in order to analyze its conductive EMI and design the proper active EMI filter for it. but as this is my first implementation project, working ...
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Can someone help me understand why in this datasheet the Vcm vs Vout curve(or the 'diamond curve') is specified for 'all gains'?

From what I read so far and from the equations used for deriving the diamond plot for instrumentation amplifier, the shape of the plot changes with gain. Following is an example: However, in the ...
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Why do I keep blowing this current shunt amplifier?

I'm using an INA293B3-Q1 current shunt amplifier in the standard high-side configuration as shown below. The supply is a variable DC power supply (0-20V). Rsense = 1 mOhm. And, the load is a ...
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Does a rail-to-rail input fully-differential amplifier need Common mode feedback at Output nodes?

I am designing an Op-amp with rail-to-rail inputs and the operation being fully differential in nature. I am trying to understand whether I will still need a CMFB (common-mode feedback) circuit to fix ...
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Common-mode voltage on the body

In the attached figure, input impedances of the right hand, right leg and left hand are respectively \$20k,50k\$ and \$10k\$ Ohms. The input impedance of the opamp is also assumed to be \$1M\, \Omega\$...
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Finite CMRR even with ideal tail current source (body effect)

In Razavi's Design of Analog CMOS Integrated Circuits 2nd edition page 123, the diff-pair below is included with a comment about how even if the tail current source is infinite, if the transistor pair ...
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What is the correct way to bias a floating instrumentation amplifier?

Im designing a voltage measurement circuit that needs to measure differential signals in the order of mV in the presence of high voltage common mode noise. Im using a isolated DC/DC converter that is ...
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Reducing Common Mode Voltage at the ADC input

I need some help from you expert engineers. I have to automatically measure VCE / IC and VBE / IB of a big bunch of transistors under specified collector and base voltages. Since Vcin and Vbin can ...
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Common mode and differential mode noises

I want to understand common mode and differential mode noise more intuitively. I have read this article. But I would like some analogy or experience with real circuits with some example to understand ...
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Can I use cumulative winding in common mode chokes?

I have been designing a common mode choke for common mode noise filtering at the input of my SMPS. I have chosen the capacitance value to be 6.6nF on both Line to Ground and Neutral to Ground. I am ...
Jaacs Job Pottas's user avatar
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Netfilter (230VAC) without protective earth (PE)

I need to filter my mains input, but I don't have any protective earth (PE). Will a mainsfilter (schaffner for example) still be usefull? I think so. I think the mains filter despite of not being ...
Weaverworm's user avatar
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Understanding a common mode signal conditioning module

As far as I understand, normally an ideal differential amplifier(or an instrumentation amp) can reject common mode(CM) voltages up to around its rail voltages. Let's say the rails of the diff. amp ...
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Would any voltage be induced in this scario due magnetic coupling?

Imagine a source with a 100 Ohm source impedance is coupled to an amplifier/receiver which has 1Meg input impedance and the transmission is done by using two parallel wires signal and return |XA| and |...
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Common Mode feedback in EEG systems

EEG signals (potential from brain) contain 'noise' due to EMG signals (potential from muscles). I was thinking of using the EMG as a common mode feedback prior to the amplification of the EEG signal. ...
Nathan Le's user avatar
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How do non-flowing common mode or bias currents cause common mode range to exceed/float?

Below is a very simplistic view of differential ended inputs of a data-acquisition channel's inAmp which measures a floating battery voltage V. To make concepts and explanations simpler I use two ...
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Measuring impedance of wire/cable

I'm working on an audio project where I'd like to install common-mode filters consisting of a cm choke and 2 caps to chassis at each of the input connectors in order to shunt common-mode noise picked ...
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Common mode range?

I managed finding the \$A_{cm},A_d\$ both in b and c (both sections yielded \$A_d=1,A_{cm}=0\$), but I have no idea how to determine the limitation on the range of the input common-mode signal and ...
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Single-ended common mode gain

In the following circuit, what would be the single-ended \$A_{cm}\$? I realise that there would be no current through \$R_e\$ in common mode and that this is a CE (Common Emitter). However, I am not ...
peripatein's user avatar
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How do I find CMRR?

How do I find the common-mode rejection ratio, CMRR for this circuit? I know I have to find differential gain and common-mode gain as 'differential mode gain/commonmode gain' but with current mirrors ...
jessie's user avatar
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How does common mode voltage surges couple in wires

From doing some research and with the assistance of a user on this platform, I would like to know if my understanding of this concept is correct. Please note this post is an add-on to this post. A ...
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