27
votes
Accepted
How do I lay out PCB traces for a given "differential impedance"
I'll try to answer this briefly, but a great resource for this type of question is Eric Bogatin's Signal and Power Integrity -- Simpified.
You've listed and described several very high speed ...
- 6,096
27
votes
USB signal routing - Swap data lines using vias?
As an addition to Armandas' answer:
If you want to use vias, there is a simple trick to swap the lines: Rotate the vias by 90 degrees, i.e. put them "above" each other. If you enter both vias from ...
- 2,380
21
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 ...
- 56.6k
21
votes
Accepted
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 ...
- 140k
16
votes
Accepted
How does this BJT transistor circuit works?
The zener with series resistor R3 has about 10V on the anode wrt ground. It is seeing 50mA so the actual voltage will be a bit higher than the 10V nominal, maybe one percent on average.
That voltage ...
- 328k
16
votes
Accepted
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. ...
- 306k
16
votes
Accepted
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 ...
- 37.3k
15
votes
Accepted
How can I improve this Ethernet differential pair?
If I were to suggest how to route this I would propose something more like this:
- 55.1k
15
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 ...
- 8,314
15
votes
Accepted
What is this circuit called, and what is it used for?
This is a capacitance multiplier: It behaves like a capacitor to ground with a capacitance of C*(1+R2/R1). This means you can use it to "simulate" very large capacitors without actually ...
- 7,198
14
votes
Accepted
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)...
- 380k
13
votes
Accepted
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 ...
- 29.2k
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 ...
- 328k
12
votes
Accepted
What does pseudo-differential mean?
Pseudo-Differential means that the AN+ and AN- are not being sampled simultaneously. Therefore dynamic common mode rejection is not improved, but DC common mode rejection is. Also, the different ...
- 4,089
11
votes
Accepted
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 ...
- 45.7k
11
votes
Accepted
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 ...
- 5,136
11
votes
Accepted
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)...
- 69.1k
10
votes
Accepted
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 ...
- 121k
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 ...
- 380k
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, ...
- 6,138
10
votes
Accepted
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 ...
- 380k
9
votes
Accepted
How to characterize SNR for an amplifier with extreme low input signal?
Your amplifier has average noise characteristics, the problem is that your signal is very, very weak. The amplifier is responsible only of the noise part of the SNR, so it has not a "poor SNR", but a "...
- 15.6k
9
votes
Accepted
USB signal routing - Swap data lines using vias?
Since it's hard to describe it in the comments, I'll put it as an answer.
If space permits, you can route your signals like so:
- 7,450
9
votes
Accepted
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 (...
- 7,965
9
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 ...
- 328k
9
votes
Accepted
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 ...
- 57.7k
9
votes
Accepted
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 ...
- 380k
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 ...
- 18k
8
votes
Accepted
Transmitting HDMI/DVI over an FPGA with no support for TMDS
Good questions. I have been researching this topic myself recently, and will try to provide some brief answers here.
what exactly is TMDS vs LDVS?
LVDS (low-voltage differential signaling) is ...
- 164k
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 ...
- 380k
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