Questions regarding how to properly ensure Signal Integrity, protection from noise, shielding, proper pcb layout.
Questions regarding how to properly ensure Signal Integrity, protection from noise, shielding, proper pcb layout.
Questions tagged [signal-integrity]
441 questions
49
votes
3 answers
Why are vias placed this way on a PCB?
I used to check complex commercial PCBs specially those of graphics cards to see how professional PCB designers do their layout and learn from their techniques.
When I checked the card shown below I noticed two things regarding the placement of…
Abdella
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41
votes
8 answers
Why put a resistor in series with signal line?
A lot of times in circuits I see a resistor placed in series in a signal line and sometimes even in series with an MCU's VDD line. Is the intention of this to smooth out noise in the line? How is this different from using a small cap, like a .1µF to…
PICyourBrain
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29
votes
3 answers
Why does VGA have so many ground pins (compared to DVI-I for example)?
If you look at the pinout for VGA, there are several ground pins:
I was curious as to why, and I found this answer. To sum it up, the extra ground pins are so that each pin has its own ground in order to prevent interference in the analog…
user112513312
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25
votes
4 answers
Short Distance Board to Board Communication
My MCU runs a SPI bus with about 4 devices. I'd like to extend this bus to be off board as well i.e. have some PCBs connect to the "main" board and extend the functionality. The "pad to pad" distance would be:
trace length of main board + Cable…
Saad
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24
votes
5 answers
How termination resistors work; what happens if I use lower values?
I am going to try to interface low-speed 8bit DDR2 chip to FPGA, and I've got some questions crucial to make it work :-)
Is that correct that the idea of termination resistor is to sink most of the signal to GND, so that only small part of it…
BarsMonster
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21
votes
1 answer
PCIe, diagnosing and improving an eye diagram
I have implemented a design that uses PCIe. It is somewhat different in that the PCIe interface is used as a chip-to-chip communication lane on a single PCB (e.g. no PCIe connector).
The root complex device is a Freescale i.MX6 which is PCIe Gen 2…
Funkyeah
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19
votes
2 answers
PCB routing: EMI and signal integrity, return current questions
If there's any EMI/SI lesson I've taken in, it's to minimize return loops as much as possible. You can work lots of EMI/SI guidelines from that one simple statement.
However, not having or ever even seen Hyperlynx or any sort of full RF simulation…
darron
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18
votes
1 answer
Why are PCIE's coupling capacitors so large
I was looking at the PCIE specification, and I don't understand the
requirement for coupling capacitors. For 2.5GT/s, the standard requires
AC coupling capacitors of 75nF to 265nF. I tried to analyze the number
like in this article in
High-Speed…
7efkvNEq
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18
votes
5 answers
Physics behind signal reflections and series termination
I have been looking for cause of signal reflections in transmission lines. Everywhere it is concluded that the reason is impedance mismatch. I can understand if the impedance changes in the path of the signal travels, then reflection will occur, but…
Vignesh C
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18
votes
3 answers
What problems could occur when chaining 40 shift registers?
I'm planning on chaining together 40 x 74HC595 shift registers. The whole chain of 74HC595s will be controlled by a 5 V microcontroller, which will generate the SDI, CLOCK & LATCH signals.
Each shift register and the microcontroller will have its…
m.Alin
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17
votes
3 answers
Why am I Seeing A Weird "Notch" on the Data Line For Some Logical 1s?
I'm attempting to build a Z80 homebrew computer for some retrocomputing fun and to teach myself the basis of electronic design. For proof-of-concept, I've already assembled a basic system on breadboards successfully in the previous weeks.
The…
比尔盖子
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16
votes
2 answers
How to transmit high current (2.6A) with low voltage (1.2V) for a long distance?
I want to supply a DSP with 1.2V. This DSP needs 2.6 Amps of current at full load. The minimum supply based on the electrical specs of this DSP is 1.16V, which means that the maximum voltage drop caused by power planes, traces and connectors should…
Abdella
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14
votes
1 answer
Why does reflection off a PCB via look like this?
My question is related to http://mobius-semiconductor.com/whitepapers/ISSCC_2003_SerialBackplaneTXVRs.pdf.
On the page 18 there are a few figures of "TDR off Diferent Types off Vias". I am confused regarding the capacative, inductive and L-C-L…
quantum231
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14
votes
2 answers
What is the purpose of the positive feedback in this opamp circuit?
Consider:
Attached schematic is from a broken sampling scope that I have in the lab.
During the reverse engineering the module, I noticed that it uses positive feedback around U2. I understand that positive feedback is often used to implement a…
Emm386
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13
votes
4 answers
What to do with excess co-ax cable
These days light aircraft come with lots of instruments that require thin co-ax cable for GPS antennas, transponders, collision avoidance systems, tracking and navigation systems.Like this GPS antenna as an example.
Whats the best way (from the…
ConanTheGerbil
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