Questions tagged [signal-integrity]

Questions regarding how to properly ensure Signal Integrity, protection from noise, shielding, proper pcb layout.

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7
votes
2answers
2k views

Returning Currents for two side boards and returning current questions

I have some questions these are I am not sure: I have designed a board that has classical 2 side PCB design. Frequency is not a big issue for me but with ESD my CPU resets itself. (CPU clock 20 Mhz, ...
5
votes
2answers
366 views

Can I slow a CMOS output through an RC filter?

Is it good practice to slow down the slew rate of a CMOS output by putting an RC filter on it? What happens with impedance matching after I do this? Or can I just set the RC filter with such a low cut-...
4
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1answer
1k views

When scoping the CLK and DATA lines of a PS/2 keyboard it looks… rather odd

Normally if I look at a digital signal I see a nice, relatively sharp pulse train on the screen, but when scoping the outputs of a PS/2 keyboard things get a little weird and I'm not sure what it ...
2
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1answer
3k views

Does transmitting break over FTDI chipset yield a binary 0 received on the receiving end?

I send breaks (using Tx) over FTDI FT232R chipset using two ways: ...
6
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2answers
6k views

False Positives on Arduino Input

I've used analog and digital input for a multitude of applications with the Arduino Uno board. It has continuously given extremely non reliable readings, where the analog input is always fluctuating, ...
5
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2answers
3k views

Packet loss in CAN

How susceptible is a CAN bus to packet loss, and what are the sources of packet loss in CAN? I realize the answer may depend heavily on the application, so here are some details: bus length: about 1 ...
18
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3answers
7k views

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,...
3
votes
3answers
5k views

The resistance between the 1.2V rail and GND is 40 Ohms, is it safe?

I have a power supply board that supplies a DSP, FPGA, CPLD and other components of a system. When I measure the resistance between power rails and GND using a multimeter I get the following readings: ...
3
votes
2answers
497 views

Determining parity or FEC (Forward Error Correction) requirements from percent error

I am very new to signal processing and my background is in physics. I would like to know if it is possible to determine the number of parity bits needs to theoretically get 100% transmission from a ...
9
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4answers
1k views

Why do some of my signals 'shiver' (have jitter)?

I have a 2 MHz SPI bus but one thing I've noticed that is that some of my signals often 'shiver'. Yes my trigger is setup properly so I don't think the issue lies there. You can see what I mean here: ...
45
votes
3answers
30k views

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 ...
4
votes
2answers
2k views

Signal integrity at 40 MHz with parallel signals

I have to design a board with an 8 bit parallel port that carries 40 MHz signals. It is not possible to wire them very short and in parallel (I am sure the wires will be about 7 cm long), so I have to ...
5
votes
2answers
2k views

Routing considerations of analog signals on twisted pairs

I'm designing a part of a system that will receive 4 analog signals carried on 4 twisted pair cables which are input to an ADC. These signals are low speed (probably in KHz) bipolar ranging from -10V ...
0
votes
1answer
674 views

How to reduce voltage from a high speed buffer?

I am using this buffer to connect signal between 2.5 V and 5.5 V to a 3.3 V microcontroller. The problem is I will get a 5 V output and my microcontroller doesn't have 5 V tolerant inputs so I have ...
2
votes
2answers
570 views

How can I meet these PCB design conductivity/isolation requirements?

The specifications required are as follows: The resistance between ground pins on a connector and the case (chassis) ground should be less than 3 Ohms. The resistance between any other signal on the ...
24
votes
4answers
10k views

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 ...
11
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3answers
2k views

SDRAM Prototype vs Production Woes

I have a design using an LPC1788 together with a SDRAM module from ISSI (IS42S32800D). This is a 32bit interface. I have routed this design out and had a prototype made with a PCB manufacturer that ...
1
vote
4answers
276 views

Sinusoidal Waveform Induced on Long (~15m) Wire

I have about 72 of the following circuits on my board. The MOSFET and R2 comprise of the output stage and the pull up resistor is my input stage. The long length of wire in-between is the wire under ...
6
votes
3answers
2k views

Increasing Fall/Rise Times for Signal Integrity

I have a board that tests a wiring harness' continuity by outputting a set of test vectors onto the harness and reading it back. The wires in the harness can be as little as 1 m and as large as 10 m. ...
1
vote
2answers
3k views

Highly asymmetrical rise and fall times

I'm using a MOSFET to buffer my signals from a CPLD. The signals travel external to the PCB using long (from 1m to 10m) wires and then come back to the same PCB - the wires are actually the component ...
2
votes
2answers
2k views

System Clock Ringing

I have a 8 MHz oscillator that I run to two CPLDs on my board. The trace lengths are less than 1.5 inches. The traces do you have vias in them, so they do change their impedance. But I was hoping that ...
4
votes
2answers
3k views

Why the measured voltage increases when I change ground reference?

The following image shows my connections: The grounds of all devices are connected to a common PCB. When I measure the 1.2V referenced to the ground on my PCB, it reads 1.201V which is great. But ...
2
votes
4answers
3k views

What's the Actual Speed in GHz of RapidIO or RocketIO serial interfaces?

When reading about high speed serial interfaces like RapidIO or RocketIO, I find data rates of 3.125 Gigabits/second and more. My question is: 3.125 Gb/s = ?? GHz What's the relation between Data ...
16
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2answers
1k views

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 ...
7
votes
3answers
1k views

Want my PCB design to work right the first time!

Just finished a design of a 8-Layer PCB, the highest frequency is 125MHz. I want this design to work right the first time, how should I revise the design and what should I take care of? Something ...
10
votes
2answers
5k views

Poor eye diagram, where to start looking?

I'm trying to debug a 100Mbit ethernet board and I'm running up against a problem I'm having trouble trying to resolve. This is the eye diagram for the transmit pair. The receive pair is very similar....
9
votes
3answers
4k views

DDR1 Layout Considerations - DOs and DONTs

I am novice to high speed design. Before getting in to DDR, I recently learned about impedance matching and how it is done, likewise I learned about length matching and how it is done.(Baby steps ...
6
votes
4answers
3k views

Best way to learn Signal Integrity [closed]

I am currently working on ECAD. Just to add more technical values to my work, I want to learn Signal Integrity and Thermal Analysis. What are the books,links you would suggest me to learn it? I am ...
9
votes
1answer
3k views

How Signal Integrity check in Altium Designer compares to HyperLynx?

I've finally discovered how to simulate high-speed signals propagation on PCB using Altium Designer, and it looks easy to use & convinient. I wonder, how close to reality results from Altium ...
2
votes
3answers
5k views

PCB and trace design for high-speed TTL

I am designing high-speed TTL-based processor. I will be using only fast AC, ACT and LVC series, so switching frequencies will be in 100Mhz range with 1-3ns fronts. I plan to use homemade 2-sided ...
7
votes
2answers
8k views

SPI Signal Integrity

A couple of days ago I had an issue where I was unable to read data from an SPI slave. I finally fixed and I'm now able to read data quite well. However, I found another interesting issue today. If I ...
7
votes
2answers
2k views

PCIe over a short cable

For a new project I need to connect two boards via PCI express. For space reasons a custom cable assembly would be the best solution. But I'm not sure what is the best way to go here. I've seen Riser-...
12
votes
7answers
10k views

Trace crossing splitted power plane

Most sources on the internet discuss routing signals over a split power plane and how to do this properly. The main solution here is to create a short return current path. I'm wondering whether ...
19
votes
2answers
5k views

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 ...
4
votes
1answer
2k views

Polygons pours under BGAs?

Is it a good practice to put polygon pours on the top layer underneath a BGA? I've occasionally got several GND or VCC pins in a row/column, and I'd like to pour around them all. I've got the same ...
8
votes
2answers
2k views

What kind of effects does a relay have on signals?

Currently I'm working on a DDS based function generator. The idea is to use an AD9834 chip that will generate a triangle/sine or square wave. With some amplification electronics I want a configurable ...
24
votes
5answers
60k views

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 ...
35
votes
8answers
67k views

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 ...

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