Questions tagged [differential]

Differential refers to any kind of signaling where the signal information is carried by two or more paths and both are required to properly reconstruct the signal. For example, USB D+ and D-

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Difference between differential op amp and comparator

What is the difference between a differential op amp and a comparator? I know a comparator can only give me two values (the supply values). The differential op amp amplifies the difference between ...
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How do I lay out PCB traces for a given "differential impedance"

This is an attempt to craft a good general question and answer for a topic that's been asked before, but only in specific situations. Could you describe what I need to know, prior to laying out a PCB ...
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Difference between natural response and forced response?

Reference Second post on EdaBoard.com Time response of a system is the time evolution of the variables. In circuits, this would be the waveforms of voltage and current versus time. ...
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17 votes
2 answers
8k views

USB signal routing - Swap data lines using vias?

I'm making my second USB design, but the D+/D- pins on the MCU (atemga16u2) aren't in the right order for the micro B connector. What's the best practice for routing these to go the right way? My ...
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How do I measure differential signals (like RS-485 or DMX) on an oscilloscope?

I've encountered differential signals in a few places, such as a differential output audio amplifier and now in a project working with DMX which is similar to RS-485. (Here's a similar question about ...
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9 votes
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Length Matching Differential Pairs

I am routing a PCB with an Ethernet connection and I am having a bit of trouble deciding on how best to route the TX and RX differential pairs. I have done the impedance calculations to figure out the ...
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578 views

Efficiency of obtaining differential signalling from a single-ended manufactured transducers

This will be a conceptual question. I'm sometimes dealing with data-acquisition of transducers, like strain gauges, accelerometers ect. sort of sensors. Most of these sensors have their own precision ...
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4 votes
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Battery monitor for a camper van electrical system

As one of my first DIY projects, I'm going to build a battery monitor for the DC battery/solar/inverter system in my camper van. The van has 440 Ah of lead acid batteries and DC currents up to 200A ...
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18 votes
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How critical is the layout of USB data lines / how does my layout look?

I'm laying out the USB data lines on my board at the moment, and I'm just trying to get an idea of how well off my design is gonna fare. Here are the particulars: 4 layer board (from the top: signal,...
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9 votes
3 answers
10k views

Ground connection in differential signals

Do I need a ground connection when connecting differential signals between two systems? I was thinking this should not be needed, but how will common mode voltage at the receiving end behaves? ...
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3 votes
4 answers
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Question about differential signals as input of an operational amplifier

I'm studying the circuits which are used to implement operational amplifiers. For example, I've studied the two stages amplifier (in which the first stage is a differential amplifier with differential ...
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7 votes
6 answers
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How does the resistor at the tail act as a current source in a differential pair?

Here is a version of differential pair: I can understand the working principle of differential pair above. When Ic1 increases Ic2 decreases that's the thing. And for that to happen the tail current ...
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4 votes
2 answers
658 views

Why the common-mode gain of the differential pair is almost zero?

If you think of a better title, please do edit or let me know to edit, but this is how I thought I could word the question. I am finding difficulty in understanding how a differential pair exactly ...
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2 votes
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Differential pair biasing by current sources

I'm having a problem understanding of how can a current be injected into emitter and pulled into collector via base, using only current sources at emitters and collectors of differential pair and not ...
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1 vote
2 answers
988 views

Measure Battery Current via Shunt

I'm working on a project where I'm measuring the current into/out of a battery (currents may be as high as approximately 150A, and I'm not aware of any hall effect devices that are continuously rated ...
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3 answers
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Splitting of a differential signal

Can the Ethernet Tx and Rx signals (Using all 4 pairs; RGMII interface) be split into 2 so as to connect to 2 RJ-45 connectors, but only 1 will be used at a time. In general, can we split any ...
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What is i(t) from circuit with differential equation?

When t<0 Components in circuit are Jt = 4 A, R1 = R2 = 2 Ω, R3 = 4 Ω ja L = 10 H At t=0 switch K will be closed and i need to figure out what iL(t) is when t=4 So i tried to figure out iL(t) ...
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Strange Behaviour Using LM358 Op-Amp as Wheatstone Bridge Difference Ampliflier

I've been working on building a circuit which uses a wheatstone bridge to find the value of a resistance temperature sensor (Danfoss AKS 21) and then passes that to a differential amplifier the output ...
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3 answers
395 views

Differential Pairs and GND

I have some doubts about different configurations of differential pair I have seen in many cases: In these schemes, biasing network for the gate is not shown for simplicity. All of them are excited ...
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22 votes
2 answers
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Review request: DIY DC to 50MHz differential oscilloscope probe

Given the cost of proper differential probes, i've decided to make my own. The requirements are: DC to 50 MHz 3db bandwidth A few selectable input voltage ranges, from 3V pk-pk to 300 V pk-pk ...
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13 votes
4 answers
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USB differential pair length

I am routing a PCB that uses a USB connection. The differential pair traces are 10 mil distant from each other, and they are about 1mm different in length. Is it going to be a problem? What is the ...
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12 votes
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Can I use differential I/O pins of FPGA as high speed comparator?

High speed comparators are rather expensive and speed is what FPGAs are very good at. On the other hand, FPGAs (in my case: XC3S400) have paired differential pins in each bank that their voltages are ...
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5 votes
4 answers
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How to specify 100 ohm impedance on a pcb gerber

I've been using Altium for several years when I've needed to designed boards. However it's all been for simple analog designs and never anything too technical. I'm now trying to take a jump into a ...
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4 votes
2 answers
2k views

Ground loops with balanced connections?

Different articles and tutorials provide somewhat contradictory information about ground loops. For a balanced (differential) connection, the return path is "the other wire" in the ...
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3 answers
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How are differential inputs setup in a differential amplifier?

I was struggling to understand what common mode voltage and CMRR is. I think eventually I understand what it is about. Before posing my new question I will briefly write about my drawing. On the left ...
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6 votes
4 answers
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Why does this current limiter circuit oscillate?

I'm trying to make a 0-25 mA current limiter. I want to take a control voltage of 0-5 V as input and have it control a current of 0-25 mA through a restive load (the restive load may vary between 0-...
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5 votes
5 answers
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Why does differential signaling send complementary signals instead of just pairing the input and ground voltage?

I'm very new to EE, so please excuse me if this question is bad or has an obvious answer. After reading an overview of differential signalling, it left me wondering: Why does differential signalling ...
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4 votes
2 answers
2k views

Is the ground necessary with an opto-isolated RS422 signal

I have 8 opto-isolated RS422 ports to install. All of them are coming from a single PC card. It provides the opto-isolation for every RS422 port. Every signal is opto-isolated from the PC ground and ...
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3 votes
5 answers
523 views

Common ground in low side current sensing

I've asked this question a while back and user/Transistor told me that the circuit will be floating and drift without a common ground, he suggested a virtual ground. but in this case we already have a ...
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3 votes
2 answers
9k views

Floating charge pump for high side N-channel MOSFET bias

This question is derived from this one. I'd like to keep gate on for an indefinite period of time (100% Duty cycle) and for that I'd like to use charge pump since idea with relay is not attractive. ...
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2 votes
1 answer
2k views

Current mirrors as active loads in BJT differential amplifier, what does that mean?

I have seen current mirrors being used as current source in differential stage of an amplifier design. The reason given is that the current mirror has a very high output impedance and behaves like an ...
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2 votes
2 answers
211 views

Question about differential signals and feedback

Let's consider, for example, this circuit: During lessons, our professor always assumed perfect differential input (two signals with the same dc value and with equal and opposite amplitudes). As a ...
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1 vote
1 answer
3k views

Current Consumption of CANbus (CANH and CANL)

I'm looking to use the SN65HVD230 CAN transceiver but had a question about the current consumption. Datasheet: http://www.ti.com/lit/ds/symlink/sn65hvd230.pdf In table 8.3 Recommended Operating ...
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1 vote
2 answers
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Virtual Short Concept in an Op-Amp

By virtue of the open-loop gain being infinity for an ideal op-amp, the two input terminals are said to be virtually shorted. Yet, the virtual short concept is only applied to op-amps in negative ...
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0 votes
1 answer
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PCB Routing of CANH and CANL

Continuation from an earlier question: Current Consumption of CANbus (CANH and CANL) I understand how to specify my power supply for multiple CAN transceivers but I am now wondering about the details ...
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7 votes
1 answer
765 views

Preferred balun location? (Are differential microstrips preferrable to single-ended?)

I'm designing a PCB with a transceiver that has differential signal pins for rf. These differential signals travel to a balun, which transforms them into a single-ended signal (50-Ohm characteristic)....
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5 votes
3 answers
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How to set up an experiement to measure SNR for an EEG amplifier?

I have built an EEG amplifier with gain of 2000 and bandwith at 1~40Hz. I use an Instrument Amplifier for pre-Amp and a non-inverting opamp as post-amp and finally bandlimit at 40Hz using a 4th-order ...
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  • 137
3 votes
4 answers
1k views

Where does return current flow for a differential signal?

As far as I understand, return current flows the "negative" channel for a differential signal connection. Only if it is not balanced well, there might be unwanted return current in reference GND or ...
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1 vote
2 answers
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What are the effects of single ended signals on twisted pair conductors?

I'm currently using a cable that has multiple twisted pair conductors. I'm attempting to send a several single ended signals down some of these conductors at a frequency of 12.5MHz. Essentially, I'm ...
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1 vote
3 answers
489 views

Bipolar signal used in differential ADC

I'm trying to find a way to convert a bipolar signal from a load cell (Futek) to an input for a differential ADC on a TIVA microcontroller(TI TM4C123GH6PM). The load cell's amplifier outputs a bipolar ...
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1 vote
2 answers
465 views

Some issues modeling a "two terminal source" coupled to a differential amplifier in LTspice

Below is a circuit where on the left there is a floating single-ended source which directly couples as an input to a DC differential amplifier: So the idea is to be able to simulate a real scenario ...
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1 vote
0 answers
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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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0 votes
1 answer
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A question about differential measurement system

Below represents a differential measurement system for a data-acquisition: As far as I understood, in a differential measurement system neither the outputs of the signals nor the inputs to the ...
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0 votes
2 answers
691 views

Ground, common, and Earth ground confusion

I am learning on transmitters and input modules nowadays. But the usage of word 'ground' is confusing me. What does 'ground' mean there (earth or power supply common)? If it is earth ground, why we ...
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0 votes
1 answer
399 views

Adding multiple differential signal

As I asked in "Adding multiple analog signal" before, I got that: for adding some signal together, we can only use op-amp, instead of lovely integrated circuit (ough). But the question arise because ...
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0 votes
1 answer
193 views

Effects of increasing current on external noise and SNR for analog transmission

This is a conceptual question about long analog signal transmission exposed to capacitive coupling and EMI noise as shown in below figures: simulate this circuit – Schematic created using ...
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4 votes
2 answers
303 views

Why don't I get the right values for Vout=Gain(v1-v2) for this differential BJT amplifier?

I am trying to use the formula that they have mentioned Vout=Gain(v1-v2), in my simulator I have placed one signal at 0.001V and the other one at 0V. The gain that they have found is 192, so I expect ...
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3 votes
2 answers
432 views

Locally hatched ground plane to increase differential impedance

I am designing a flexible PCB to carry two types of differential signals. One is about 1.2Gbps 100R differential impedance, while the other is only 3Mbps, with much more tolerance on the impedance. ...
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3 votes
3 answers
629 views

Is single ended amplifier a subset of differential amplifier?

The reason I'm asking this is that when I read about CMRR issue in amplifiers I only see differential amplifiers as if it is only a diff. amp. issue. But isn't a single ended amplifier also a ...
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2 votes
2 answers
84 views

Differential capacitive transducer

I would like to design a differential capacitive transducer to measure the capacitance change in an accelerometer. I cant seem to understand, how to demodulate the signal and keep the actual DC value....
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