Questions tagged [common-mode]

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160 views

How many / which electrodes should I use as input for an RLD (right leg drive)?

When reading through the datasheet of the ADS1298 (an analog Front-End for Biopotential Measurements) I noticed the schematic on page 42 (see below): It is possible to select or deselect the positive ...
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37 views

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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1answer
47 views

Ground offset or common mode noise voltage

This is just a small doubt I would like to clear. Suppose I have a buck regulator providing output at 5V and 1A. Suppose I measure the output voltage at the ground pad of the output capacitor and it ...
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1answer
37 views

Common mode noise mitigation in two pin smps

How does a 2 pin (no earth ground connection) SMPS offer common mode protection? Is it safe to power appliances over it?
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33 views

Purpose/Difficulties of having a common mode choke

This question is related to common mode choke. I know I have asked this question a couple of times in this forum and I have also read related questions and answers. But I am not able to get the total ...
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1answer
32 views

Balanced impedance CM and DM stages EMI Filtering

Here is the following assertion : I would like to understand why line impedance imbalance can cause CM noise to get converted into DM noise ? Thank you very much !
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22 views

Cutoff frequency of Common mode part of EMI Filter?

Anybody knows how we can determine the cutoff frequency for the common mode parts of EMI Filter? I know for the differential mode we use FFT to find the highest harmonics of input current and then ...
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2answers
90 views

Can this be CM related noise?

In a single ended data acquisition system a DAQ board is sampling channels in a multiplexed way. The DAQ is single ended as well as the input signals. When I use two analog transducers coupled to two ...
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1answer
102 views

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, ...
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1answer
50 views

Using common mode choke in differential configuration for differential mode EMI filtering

Why is it not popular using common mode chokes in differential mode configuration for differential mode noise filtering? Mostly when using fly-wire type chokes with filters, where the chokes are ...
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1answer
60 views

How is the differential mode noise suppressed by adding a capacitor across the Lines

I was reading about the common mode noise and differential mode noise. I don't understand how a differential mode noise gets coupled and how adding a capacitor across the line will help. I ...
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1answer
56 views

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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1answer
50 views

Understanding Common mode voltage

I am trying to understand common mode voltage a little bit fundamentally (only with electronic devices and no math). I watched this Youtube Video to understand common mode and differential mode ...
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2answers
57 views

Is this way proper to create differential inputs from a function generator for this setup?

I have soldered an RS485 to TTL converter on a board and want to test it. The thing for a test, I need differential inputs as DATA+ and DATA- and I don't have a sensor which outputs differential ...
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3answers
278 views

Is there a practical method to verify whether the noise have CM component in this setup?

An SMPS power supply unit namely Vsupply output can be composed of its desired DC output Vdc, differential mode noise Vdm and common-mode noise Vcm. If we have such a power supply and an earth ...
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1answer
53 views

Does input impedance of an isolation amplifier or a transformer have impact on common mode to differential mode conversion?

I have a question where I can only explain it clearly by an example. It is about conversion of common-mode interference to differential mode due to overall system imbalance. I will use below two ...
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32 views

Question about a common mode feedback circuit

I'm studying fully differential op-amps. I know from the theory that with fully differential op-amps, unlike the single-ended op-amp, the output common mode is not stable because of unavoidable ...
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1answer
39 views

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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1answer
80 views

Question about the common mode

After introducing the two-stages op-amp and frequency compensation for this circuit, during lecture the Professor asked us to find as an exercise a possible polarization of the following circuit: in ...
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63 views

What is Common Mode Noise [duplicate]

I have read this before asking this question. I understand somewhat, but I couldn't get clarity. Can someone help me understand the difference between common mode noise and differential mode noise ...
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1answer
159 views

Testing spice model for common mode rejection ratio?

I've been trying to create a circuit to simulate common mode rejection ratio of an op amp to test the spice model's accuracy. While I've seen online that being able to use exact resistors only a ...
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3answers
110 views

Opamp input offset voltage…common mode?

Looking at the datasheet for an OPA197 opamp, I see this: What is the circled expression trying to tell me? The common mode voltage is equal to the voltage at the non-inverting input minus 1.5 V ...
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1answer
34 views

Does swapping the inputs cause increase in the common mode noise in this scenario?

This is a question I wanted to ask after I have observed much more noise when I swap a filtered traducer's output to a single ended data acquisition board. A transducer outputs Vs1 signal. The ...
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25 views

Where does the (even-mode) interference come from?

I have a question regarding the differential connection of a surface acoustic wave (SAW) delay line element. When I connect the filter asymmetrically, i.e. at each port one half of the interdigital ...
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1answer
58 views

Can the ADS1118 ADC converter accurately read a voltage close to GND?

1. About the ADS1118 ADC converter I'm using the ADS1118 ADC converter from Texas instruments to measure a voltage. You can find the datasheet here: http://www.ti....
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1answer
81 views

Common mode input impedance

I was looking at the datasheet of the THAT 1510 mic preamp IC, they suggest the following application circuit: In the datasheet it says that the T network formed by R1, R2, and R7 gives a common mode ...
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2answers
214 views

How does placing cap between signal GND and earth GND solve common mode noise?

Thanks in advance for your time. I am reading several articles about differential mode noise and common mode noise. Among which I found the below 2 pretty instructive: https://www.murata.com/~/media/...
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1answer
60 views

Common mode filters effectiveness

As we know, there are many types of common mode filters that can be implemented. One of this type is a single element topology where this element can be a series impedance element (usually R or L or ...
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1answer
306 views

Ground planes disposition in Ethernet connection

I am designing a board that will have sensible analog signals and a processor communicating with the external word via Ethernet and I want to avoid that common mode currents couple into my analog ...
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1answer
90 views

Tail resistor in differential gain

Why doesn't the tail resistor feature in the denominator for differential gain (whereas it does for common mode gain) in the differential amplifier below? (Fig 5N.28 from Learning the Art of ...
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1answer
137 views

Op Amp Input Offset Voltage vs Common Mode Voltage

I would like to use an op amp AD8618 for a design, and need the input offset voltage to be low. For this op amp it seems fine with maximum of 65uV, but looking at the charts on page 6 etc, it seems to ...
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1answer
38 views

dual rail DC/DC convertor and CMC

I have a DC/DC convertor that tales 5V and makes + 15V and -15V rails My question is how to place common mode chokes to reduce common mode noise. Should I place 3 of them (1 on the negative to Gnd , ...
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2answers
74 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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1answer
130 views

How to quantify the cable impedance for common mode voltages?

Since a coaxial cable is not twisted, in the case of a common-mode interference the positive and negative lines will pick up different voltages. This unbalanced impedance nature of the cable can be ...
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1answer
101 views

Common Mode and differential Mode gain of this Cmos diff Amp inverter

This is one of questions our prof gave to students in recent years and im preparing myself for this exam. What is Common Mode and differential Mode gain of this Cmos diff Amp inverter? i understand ...
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1answer
79 views

Trouble with instrumentation and simulation of the common-mode response of a filter

I have been struggling to obtain the Bode plot of common-mode response of a filter. I first simulated it using LTspice, then I used a USB network analyzer. Both do not match each other and to the ...
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2answers
50 views

Interpreting some functions of an optoisolator from its datasheet

I cannot interpret couple of things from the datasheet of this optoisolator. 1-) Is there and hint in the datasheet regarding the maximum CM voltage interference it can handle at its inputs? 2-) The ...
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0answers
61 views

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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2answers
194 views

A question about oscilloscope and common mode noise

To ask this question I needed to simulate two circuits as an example. Imagine we want to measure the voltage across a device output. Call the differential voltage across its terminals Vd. And imagine ...
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1answer
147 views

Opamp input from transformer

Is it possible to connect the circuit like this. The circuit is from the resolver input circuit, It takes the sine (or cosine) signal from the output of resolver and reduce to appropriate voltage for ...
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1answer
29 views

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 ...
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1answer
203 views

Common Mode Voltage Range with Negative Feedback

In section 3.1 of AN21 from Apex Microtechnology it mentions to make sure to accomodate the common mode voltage requirements. But does the common mode voltage range mean anything if one of the inputs ...
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1answer
75 views

Does impedance balancing in the far end make no sense?

Below shows a conversion of unbalanced line to a balanced one: My question is about: if the unbalanced line is very long which means the signal source and the isolation amplifier is apart from each ...
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3answers
545 views

Is star grounding sources necessary for this data acquisition system?

Several single ended output and PSU powered transducers are tens of meters apart from each other outputting 0 to 10V DC like voltages. Some are temperature transducers some are force transducers ect....
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2answers
143 views

How does common mode range include the negative rail?

How do the devices like AD8220 handle the common mode voltage equal to the negative rail or even lower voltage (Take a look at figure 30 of AD8220 datasheet) ? Does the operation of the amplifier ...
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3answers
253 views

Common-mode voltage outside the specified range

I'm reading the datasheet of TL331. Here a summary of the relevant specification for my question: ...
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1answer
122 views

Why does LVDS (or any differential signaling for that matter) use a common mode voltage of 1.2V instead of 0V?

Why does LVDS (or any differential signaling for that matter) use a common mode voltage of 1.2V instead of 0V? Is there an easy way to shift the common mode voltage to 0V?
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3answers
95 views

Isolate low power i2c ADC

I'm using the MCP3421 to read voltages from thermocouples on battery power. I would like to get this working over USB but I think the low common-mode range of the ADC could be problem so I am ...
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1answer
82 views

x2y caps and common mode chokes (using both)

I am designing a ultralow noise PCB board. Common mode noise has to be minimized, so I have a question I am planning to use a CMC on power input and to further decrease the common mode noise I also ...
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1answer
172 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 ...