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Questions tagged [common-mode]

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3
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2answers
103 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/...
1
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1answer
50 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 ...
4
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1answer
57 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 ...
0
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1answer
54 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 ...
1
vote
1answer
64 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 ...
0
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1answer
32 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 , ...
0
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2answers
43 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 ...
0
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1answer
62 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 ...
1
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1answer
63 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 ...
0
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1answer
53 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 ...
0
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2answers
43 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 ...
1
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0answers
42 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 ...
0
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2answers
73 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 ...
0
votes
1answer
70 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 ...
0
votes
1answer
25 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 ...
0
votes
1answer
96 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 ...
1
vote
1answer
60 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 ...
7
votes
3answers
429 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....
1
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2answers
101 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 ...
0
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3answers
114 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: ...
0
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1answer
79 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?
1
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3answers
61 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 ...
1
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1answer
56 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 ...
0
votes
1answer
143 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 ...
0
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1answer
31 views

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 ...
0
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1answer
266 views

maximum possible common mode voltage for npn

First I would like to thank everybody here for providing the help. This great resource allows me to understand things beyond what my textbook only offers. I have the question below: Here is the ...
0
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2answers
592 views

Why is the MCP601 better suited than the LM833 for single supply applications?

Still not answered, please need some help. If you guys don't know the answer don't be afraid to admit it, but I want to generate discussion around potential solutions/calculations and not semantics ...
0
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2answers
79 views

Noise on the whole board after USB connection

I designed a device on which there is a HUB, FT232 , two external USB port and some periphery. I wanted to check the noise on the power bus. And I saw only white noise. But after I connect the USB ...
0
votes
1answer
116 views

Common mode range and DC common mode interference

Here is my basic understanding of common mode range for diff input amplifiers: As far as I understand the common mode voltage is nothing but the offset at which the diff signal is travelling above a ...
0
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2answers
61 views

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 ...
0
votes
1answer
71 views

Common mode problem with floating sensor

So I'm trying to measure the signal from a potentiometric sensor, that has a working and reference electrode. Electrically it can be summarized with the picture below. Note that my circuit is intended ...
0
votes
1answer
325 views

USB chokes for USB power

We are designing a ultra low noise USB 2.0 hub. I am thinking to add a common mode choke to + and - of the USB connector, in addition to the D+ and D- choke to remove the common mode noise. I am ...
2
votes
1answer
63 views

Which diagram is better for common mode noise rejection?

I want to us this sensor(107LN type) as in the following signal chain with differential-input DAQ board and a STP CAT6 cable as below: Above the GND of the power supply is local/near to the DAQ. ...
0
votes
1answer
45 views

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 |...
1
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2answers
126 views

Avoid in-amp common mode and ADC input protection

I'm designing a temperature measuring circuit using a PT100 on a wheatstone bridge. In the temperature range I'm measuring (0-45C) I should get 0-25.5mV from the bridge and then amplify the signal to ...
1
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2answers
186 views

Why is common-mode noise on a power line bad?

I've always been intrigued by common-mode noise, as it seems to be such a pertinent issue when it comes to op-amps, chokes, etc. used as solutions to remove it. I understand from a digital signal ...
1
vote
1answer
36 views

Isolation of voltmeter via DC->AC->DC conversion

I bought a combination ammeter/voltmeter which has the restriction that the measurement/display circuitry must be powered from a different source than the measured voltage. What is the underlying ...
0
votes
1answer
83 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 ...
3
votes
3answers
346 views

Commonmode voltage and measurement with voltmeter and an instrumentation amplifier

I'm trying to compare a voltmeter and instrumentation amplifier which both measures voltage. Below in Figure 1, Figure 2 and Figure 3 I made these diagrams to ask my question. Basically a device(on ...
0
votes
1answer
93 views

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 ...
0
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0answers
190 views

Common Mode Noise in Isolated System

I am working with an isolated system (battery powered with no GND connection), but am seeing common mode noise (40-85MHz) on cables during radiated EMI testing. Cable ferrites reduced levels ...
3
votes
1answer
496 views

Instrumentation amplifier noise amplified

I built a simple circuit with an instrumentation amplifier (PGA204AP) in order to clean a differential signal from noise. The signal is generated few meters away from the acquiring point and the cable ...
0
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2answers
426 views

DM and CM noise filter

I have this long cable which is carrying two differential voltage signals (around 300kHz maximum frequency) through a very "noisy" environment. I need to acquire this signal through a differential op ...
0
votes
2answers
41 views

Truncating negative results of Op amp by rail limiting

I have a signal that will swing from -5v to 5v. I am interested in the 0 to 5v part only. I will set a reference voltage and give it and the signal into a comparator. The comparator's rails are 0, and ...
1
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0answers
49 views

Question about noise effects of parasitic common-mode coupling in a single ended system

This question is related to a previous question. Now I'm trying to understand a bit deeper about the phenomenon I will present. (to see bigger view please left click) To make it clear enough I used ...
0
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2answers
204 views

Why is a common mode bias required for this differential amplifier? [closed]

TI makes the ADS1118 which is an ADC with a programmable gain amplifier (PGA). In one of their application examples (page 4), they indicate that small differential input voltages (1-2mV) must have a ...
0
votes
1answer
465 views

common mode choke placement in smps

I am designing a hi end SMPS and I have 1 CMC on the input (ac line) and a second on the DC output. My question is where to place this second CMC. Usually its best to place filters right at the ...
0
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2answers
356 views

common mode choke on DC line

usually common mode chokes are used on AC lines to take care of common mode noise. If I am using a CMC on a DC line ..would the inductance degrade ?
0
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1answer
76 views

How to explain this solution to the common-mode voltages?

One of my previous question revealed that a variable voltage test device's power supply which is an AC/DC adapter, and is SMPS type which causes common-mode voltages. A solution given by tying the ...
0
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2answers
139 views

Is this definitely common-mode interference and how can I model and filter it?

A test device which can output voltage between 0 to 10V by a knob is powered by a DC adapter which converts 220V rms(meaning 311V amplitude) 50Hz AC to DC. Device is not a commercial and its adapter ...