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22 votes
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USB differential signal from single pin?

USB is not always differential. There are signalling states that require both D+ and D- to be low. Additionally D+/D- are used for other purposes, such as performing reset and speed detection which ...
Tom Carpenter's user avatar
22 votes
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Trace impedance ohm meaning

Ohms has dimensions volts/amps. When applied to a resistor, it's the ratio of applied voltage to current through the resistor. When applied to the behaviour of transmission lines, it's the ratio of ...
Neil_UK's user avatar
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17 votes
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How can I improve this Ethernet differential pair?

If I were to suggest how to route this I would propose something more like this:
Michael Karas's user avatar
17 votes
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How to do low pass filtering on a differential signal

how would I do a simple RC low pass filter on this differential signal? The simplest method: - Source. This circuit only filters differential signals; if there is an in-phase signal (or interference)...
Andy aka's user avatar
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16 votes
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Differential Signals - Why is having an equal impedance an advantage?

The same impedance is good because capacitively coupled noise is inversely proportional to the impedance. Usually differential signals are arranged so that both are subjected to the same noise. ...
Olin Lathrop's user avatar
16 votes
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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?

USB cables do require some precision engineering. There are stringent requirements on value of differential impedance, quality of interconnects, and amount of losses per cable. The high-speed part of ...
Ale..chenski's user avatar
  • 40.8k
16 votes

Review request: DIY DC to 50MHz differential oscilloscope probe

After actually building the thing I can finally answer my own question in hindsight. I've built the circuit as featured in the question, with a 1:10 attenuator. Could I get away without ...
jms's user avatar
  • 8,651
15 votes
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What is the difference between PN- and PM- Differential pairs?

No. Some people prefer Plus/Minus as identifiers, others prefer Positive/Negative, and some use +/-.
Simon Richter's user avatar
13 votes
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Do you have to use an instrumentation amplifier to measure voltage across a 0.01 ohm shunt?

You don't have to use a differential amplifier providing you are careful about the voltage drops that occur along the grounds. If you return the bottom end of the 500 ohm resistor to the same point as ...
Kevin White's user avatar
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13 votes

Do you have to use an instrumentation amplifier to measure voltage across a 0.01 ohm shunt?

You have an amplifier with a gain of about +2000 and an offset voltage of as much as +/-3mV at room temperature. It might typically be +/-2mV (onsemi datasheet). Since the output swing with no load ...
Spehro Pefhany's user avatar
12 votes
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USB (low speed) on stripboard: can it work?

If you keep the USB strips adjacent and as short and neat as possible and you'll likely have no problems for a prototype. For USB low speed, the 1.5Mbps is so low that you don't really need to put any ...
Tom Carpenter's user avatar
11 votes
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Differential to single ended

1.Transformer If your signal is a single, or narrow band, frequency this method is fine. However, anything else and you introduce the transformers frequency response into your signal. 3.simply ...
Trevor_G's user avatar
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11 votes
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Why don't I get the right values for Vout=Gain(v1-v2) for this differential BJT amplifier?

Large-Scale Result Assuming you already know the value for the current in \$R_{_\text{E}}\$ (which, by the way, you do not) and also assuming the BJTs are matched (and in a simulator they probably are)...
jonk's user avatar
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10 votes
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Maximum slope of a sine wave

The maximum slope for a sine wave that has no offset and an ampliutde \$A_0\$ occurs exactly during the zero crossings. Its value is simply \$A_0 \omega\$ The derivation is $$ \frac{d}{dt} A_0 \sin (...
Mario's user avatar
  • 8,195
10 votes

Resistor between differential lines

The purpose is to match the characteristic impedance of the twisted pairs that carry the differential signals. By matching the impedance, reflections from the termination can be minimized, which ...
Spehro Pefhany's user avatar
10 votes
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Differential probe design ground copper pour

The designer probably did that to reduce the capacitance of the probe. If you filled that area with ground, when you contacted the probe points to your circuit under test, you'd be connecting a ...
The Photon's user avatar
  • 130k
10 votes

Differential probe design ground copper pour

What would happen if i pour ground copper at that area as well. The PCB legend implies it's good for 1 GHz. At 1 GHz a 1 pF capacitor has an impedance of 159 ohms. Do you really want to spoil the ...
Andy aka's user avatar
  • 460k
10 votes
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Why do differential signals need an inverse wave?

why does a differential signal need an inverse input They don't. What makes "differential" signals work is that the impedance of both wires is equal (balanced) which is necessary for noise ...
bobflux's user avatar
  • 78.4k
10 votes

Differential probe input impedance 1Meg, but 50ohm oscilloscope mode recommended

The probe itself is an active device which has input and output, each one with its characteristics (given in the manual): Impedance matching, like with a standard signal generator with 50 Ohm output, ...
devnull's user avatar
  • 8,527
10 votes
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Differentiator and integrator - without op-amp

You don't need the opamp, in theory. A simple, passive, RC circuit gives you am integrator or differentiator (otherwise known as first order low pass/high pass filter). One problem is output impedance ...
danmcb's user avatar
  • 7,147
10 votes
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Why common-mode choke on differential-signal serial lines?

Wouldn't the common-mode noise simply be cancelled in the receiver? A lot of noise would be heavily cancelled in a differential receiver but, high frequency stuff can cause problems and, of course a ...
Andy aka's user avatar
  • 460k
10 votes

What is the difference between PN- and PM- Differential pairs?

P and M are Plus and Minus. P and N are Positive and Negative. Some manufacturers just use plus and minus signs such as for USB you might see D+/D-, DP/DN, or DP/DM, and they all mean the same thing. ...
Justme's user avatar
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9 votes
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Amplify difference between two photodiodes

For my application, the only relevant data is the difference in luminosity between these photodiodes. If both photodiodes are the same, wire them antiparallel to a single TIA. Wiring them ...
Andy aka's user avatar
  • 460k
9 votes

Amplify difference between two photodiodes

simulate this circuit – Schematic created using CircuitLab Andy's anti-parallel diode idea works nicely in a transimpedance amplifier. The dynamic range is maximized so long as the opamp doesn't ...
glen_geek's user avatar
  • 26.3k
8 votes

Differential Signals - Why is having an equal impedance an advantage?

Is it because "environmental" noise affects both signals the same way? It is entirely for that very reason. Impedance balance to earth (or earth impedance balance) it is called and, in the presence ...
Andy aka's user avatar
  • 460k
8 votes
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How does the resistor at the tail act as a current source in a differential pair?

An ideal current source has infinite output impedance (i.e. \$dV/dI = \infty\$). A real current source is equivalent to an ideal current source in parallel with some finite output impedance Ro. A ...
τεκ's user avatar
  • 4,279
8 votes
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Should Ethernet MDI Pairs all be Length Matched (Inter-Pair) before going into magnetics?

There is no need to have the pair lengths balanced. The standard for 1000base-T (IEEE Std 802.3-2008) states: 40.7.4.2 Link delay skew The difference in propagation delay, or skew, between ...
asdfex's user avatar
  • 3,064
8 votes
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What value series resistor should I use for USB data lines when two ICs require different impedance values?

The TUSB tells you to use a 90 Ω impedance for the differential pair of tracks. The ADuM tells you to use series 24 Ω resistors from the chip to connect to the tracks. Both are correct. The numbers ...
Neil_UK's user avatar
  • 168k
8 votes
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Where does one find the minimum voltage above the negative rail an op-amp can output in their datasheets?

DKNguyen’s answer addresses limitations on the input voltage swing, but I believe you asked about the output swing. That’s generally specified fairly directly in the data sheet as “output voltage ...
td127's user avatar
  • 3,097
7 votes

Capacitor between grounds: Reason and how to decide the value

Its a NL\switchable part that is used for identification only (almost definitely). It appears that they use a capacitor to indicate what kind of board it is visually. On other boards, if the grounds ...
Voltage Spike's user avatar
  • 83.4k

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