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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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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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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How can I improve this Ethernet differential pair?

This is my first 100 Mbit/s Ethernet project (I am doing it to learn more about differential signals). I did two things that I don't know if are good or bad in this particular case. One is to route ...
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Differential Signals - Why is having an equal impedance an advantage?

I lately heard in a course that a main advantage of differential signals is that both signals show the same impedance, whereas a single-ended signal, which is measured against ground, has a high ...
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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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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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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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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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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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Impedance of differential inputs on AD converters

I'm currently trying to attach a rather fast ADC/DAC-converter chip to an FPGA to receive and transmit RF in the future, but getting the converter to run and attaching a signal generator and an ...
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Generating a differential signal

I was given a small task (actually it's part of a much larger task) where the requirement is to generate a signal which looks like it came from a microphone. The following requirements needs to be ...
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How does this BJT transistor circuit works?

I just wanted to know a little more about this circuit about how it works a more in depth analysis I mean. I know there's some kind of differential amplifier and a Zener diode for voltage regulation ...
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Voltage and current measurement of battery Single ended or differential?

I am trying to measure battery's current and voltage for a battery charging/monitoring project. I have read all about current sensing (including high side & low side sensing). And i have decided ...
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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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458 views

Designing my own Bus

This question is further to my previous question: Alternatives to SPI because of EMI. I am toying with the idea of designing my own communication bus. I would be grateful if someone could cast their ...
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Is it worth going to so much trouble with Ethernet differential tracks?

I am laying out a PCB containing an Ethernet connector with integral magnetics, and a Micrel KSZ8051MNL Phy. This is for a 100mbps application. In an attempt to reduce EMI, and make the Ethernet data ...
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Differential amplifier with differential output and common-mode shift

Summary: I would like to build a differential amplifier with differential output, but shift the common mode to a different level from the original. My current knowledge takes me this far: Take the ...
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Can anyone explain this balanced driver circuit to me?

I'm looking to generate a differential signal to control a laser projector's galvos, and as I understand it needs to be +5V/-5V (10Vpp). I've found this circuit for a laser harp, but I'm confused ...
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Impedance Matching Differential Signals

I'm designing a circuit with RFICs using differential signaling. I'd like to keep noise to an absolute minimum. Let's use the mixer (LT5560) as an example. All of the reference schematics match to 50 ...
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Do USB Data Wires (D+/D-) have 90 ohm differential impedance and single ended 45 ohm impedance to ground and if so how is this made?

I understand that USB data transmission is done over various speeds where transmission line effects could come into play(max 480Mbps which means a max frequency that is much higher considering the ...
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Is there a preferred placement of termination resistor for a differential clock line?

Looking at a reference design board from Xilinx, we noticed the placement of the termination resistor for a differential clock line (~300 MHz): The resistor is placed not at the closest possible ...
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Where are small-signal differential amplifiers used?

I am teaching students about the differential pair (see circuit below). I addressed many issues like the difference between differential and common mode gain, taking arbitrary vb1 and vb2 signals and ...
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833 views

Are the currents that travel on the outside of coax really “common mode”?

Consider a ladder-line transmission line. Given any currents on the two conductors, we can describe those currents as the current on each conductor individually, or: currents that flow one way on one ...
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535 views

Running JTAG chain over busy backplane

We are busy designing a large system with around four PCBs slotting into a backplane. Each PCB could contain a DSP as well as a large FPGA. We would like to run 2 JTAG chains through the system, one ...
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Transmitting HDMI/DVI over an FPGA with no support for TMDS

I'm hoping to be able to output HDMI/DVI-D for my next FGPA project but my FPGA doesn't have native support for TMDS outputs. The FPGA is a Spartan 3E and I believe it only has support for LVDS ...
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1answer
614 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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6k 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? ...
7
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1answer
8k views

How to use common mode choke inductors? (differential vs common mode)

I have yet to undestrand exactly how to use common mode chokes inductors, according to the datasheet they have 2 operation modes like in the picture common mode and differential mode, however im ...
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Do I need biasing resistors on the +/- lines for RS485?

I know I should have a terminating resistor on RS 485. Do I need biasing resistors on the +/- lines of an RS485 differential signal?
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Comprehension problems with op-amps

The common differential amplifier takes two signals and amplifies the difference between these two signals. I am aware that this difference usually is around a few millivolts or microvolts so, to put ...
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3answers
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Differential to single ended

I have a differential signal ranging from 0 to 2 MHz and need to transform it into a single-ended signal. I found out that there are 3 methods: Transformer Amplifier simply ground the negative part ...
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4answers
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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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3answers
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Ethernet 100 ohm differential pair layout

I'm finishing off the layout of a board in Eagle which has a LAN8710A 100Mbps Ethernet PHY on it. The SMSC documentation is really pretty good but I'm stuck on the important detail of how to do the ...
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2answers
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GND plane close to LVDS differential pair?

I have two LVDS differential pairs on my PCB, running from a connector. On the connector, I have the following sequence of nets: GND LVDS+ LVDS- GND LVDS+ LVDS- GND This is as I have seen suggested: ...
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1answer
98 views

GPS L5C Differential? Max Update Rate(bits/s|Hz)?

The differential GPS chips use L1 and L2C to calculate the ionospheric interference. With the new GPS satellites, the new band L5C is being deployed, and I am wondering about the following things: ...
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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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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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1answer
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+ and - meaning in Tx+ and Tx- in cable pairs?

Tx and Rx are required in Computer networking, used in Cat5 or Cat5e or Cat6 cable? What does +(plus) and -(minus) sign mean in cable pairs for RJ45
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287 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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4answers
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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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1answer
217 views

MOSFET differential amplifiers - difference between configurations

Consider the following differential amplifiers: In the first picture, we have a basic differential amplifier configuration and we can assume that it's symmetrical (meaning M1=M2 and resistances are ...
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1answer
485 views

Difference Amplifier with 3 Op. Amp. How to analyze it?

I have to demonstrate, in the following circuit, that \$ V_o= \left( 1+\frac{2R_2}{R1}\right)(V_2-V_1) \$ if the Pot is in the halfway. I know that the circuit inside the pink block its a Buffer for ...
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4answers
8k views

Differential analog signal conversion using Arduino Uno

I need to perform a A/D conversion for a differential signal using Arduino Uno. I have tried a software method where I connect one input to A0 and another to A1, read ADC for both channels and then ...
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2answers
3k views

Differential to single ended circuit

I have a differential signal up to 1.5 MHz and have to transform it to a single ended signal. I have found this amplifier which has a BW of 2.2 MHz and should therefore be okay for this task. The ...
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1answer
180 views

sizing a DC bias RF choke for a differential antenna + PA

Trying to figure an antenna for the Si4012 RF chip. Page 26 of https://www.silabs.com/documents/public/application-notes/AN639.pdf talks about feeding the two sides of the loop antenna through two ...
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544 views

Inner layer routing of LVDS traces in between ground vias

I have ground vias underneath an ADC on a multi-layer board for thermal relief. I am using inner layers to route the LVDS signals for the ADC. The image shows diff pairs on layer 4, which is in ...
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1answer
845 views

Why are there so many signal grounds for PCI Express?

PCIe connections have one to two ground contacts per differential signal pair. Why is this the case? On the boards that I have been studying, all of these pins are tied together onto the same ground ...
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Op-amp subtractor: problems supplying a fixed base voltage to be subtracted

The context is that of a simple sound-level meter. An electret mike, pre-amp (transistor), amplify with a 386 op-amp, detect the envelope of the waveform, and the output the level to an ammeter. (...