Questions tagged [signal-integrity]

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

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2answers
53 views

Controlling a 0-20mA transmitter from an isolated PWM signal

I'm trying to generate a 0-20mA signal for controlling an industrial actuator (the position of a 3-way valve) from a Teensy 3.2 system. Preferably, the mA-output should be galvanically isolated from ...
0
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2answers
44 views

Signal fidelity from fiber optic crosstalk

I was watching a video about tapping fiber optic cables when it brought up some points from an early US govt document describing security concerns about fiber optic cables. The relevant part: ...
1
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1answer
49 views

Impedance Mismatch of LVDS Differential Pairs

A mistake was made when designing a set of mother and daughter PCBs, resulting the daughter board to have its LVDS pairs at ~100Ω differential impedance, while the motherboard ~90Ω. The receiver, ...
13
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4answers
6k views

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 ...
0
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1answer
32 views

Pads reflecting in controlled impedance strip?

Background I'm designing a controlled impedance line for a 1900MHz signal travelling between SIM7000A cellular chip and an antenna. Question Tuning circuits are recommended for antennas with series ...
0
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3answers
70 views

Split hdmi signal the passive way

I would like to know if it's possible to split a HDMI signal (generate by raspberry pi or equivalent) to a deserializer (TFP401APZP) and to a micro HDMI. I have a source going direct to the TFP and ...
0
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2answers
50 views

Problem with transient on power rails

I have an AC to DC converter that outputs 5V. I then run this into 2 regulators on my board. The 4.2V regulator goes into a cellular module, and the 3.3V regulator goes into a microcontroller. I ...
10
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2answers
1k views

How this DIY High-Speed Probe doesn't reflect signals?

I am reading The Art of Electronics, page 809 and 810, where they show this probe: Which is a DIY probe, made out of a RG-178 coaxial cable, in series with a 953 ohms resistor. I wonder why the 953 ...
3
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0answers
65 views

Eliminate reflections on pulse signal transformer

I am trying to isolate an RLC ringdown signal via an RF signal transformer but I'm having trouble maintaining the signal integrity through the transformer. Below is the simple schematic describing my ...
3
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3answers
123 views

PCB design for 50MHz

I'm designing a rather big PCB which will have 64 nokia 5110 LCDs arranged in an 8x8 matrix and will all be controlled by a single microcontroller. Each screen will have an 8-bit shift register as a ...
0
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1answer
38 views

common-mode noise in single-ended parallel wire

As we all know that common-mode voltage is the average of voltages in two lines Vcm = (V1+V2)/2. So as shown in the figure below, a transmission line composed of two parallel wires above a ground ...
3
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1answer
81 views

Need smaller pullups on i2c lines, but design is low power, what is best?

The pullups on my i2c lines are 4.7k. People are afraid of draining the battery by fixing this waveform with smaller pullups, like 2.2k. It doesn't seem much power is wasted considering the short ...
2
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2answers
164 views

SPI signals show overshoot and ringing - does that affect reliability?

Here is MISO in yellow and MOSI in purple. I thought I would use a ferrite bead in series of each signal to filter out the noise. I will be making hundreds of these boards. I'm not sure it is worth ...
0
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0answers
31 views

SGEN amplitude measurement doesn't match oscilloscope

I don't understand the measurements regarding the voltage of the oscilloscope of the JDS6600 signal generator I recently bought. Being the SGEN specified amplitude 5V I'd expect the Vpp on the ...
6
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1answer
178 views

DDR3 Data Errors

I am looking for post layout solutions for DDR3 data errors. I have a PCB with a FPGA and a 2 banks (2 rank) DDR3 ram setup. Data errors occur either when the RAM (FPGA is not confirmed, but could ...
2
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2answers
73 views

What's the suitable wire size for 9VDC @25 Amps line?

I am trying to put together the requirements for a cable and I was wondering what would be the most suitable wire size to load the DUT with 25Amps @ 9VDC. I will have few other high current lines ...
2
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1answer
70 views

Differential pairs or single ended signals for 1m cable

I have one control board and 3 additional boards for the power electronics, that send and receive data from the control board over a distance of ~1m (3ft). All signals are single ended. I have to ...
3
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1answer
338 views

SPI waveform on Raspberry Pi is not clean, and I'm wondering why

I have a Raspberry Pi Zero Wireless and I wish to connect it to an FPGA via SPI. I have done some SPI tests with my 100 MHz oscilloscope and see the images shown below. The Raspberry Pi ...
0
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0answers
63 views

Avoiding signal interference in a cable that carries video signal and sensor signal

I am using a 6 core shielded cable. In this 3 wires are used for a sensor and 3+1(shield) is used for a analog camera. All the cores take DC supply. Sensor(3 wires) (+)24 volt supply, (-)minus, ...
1
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2answers
114 views

what if the two wires of a single twisted pair are different in length?

For example, one wire of a twisted pair is longer than the other wire (imbalance starts from the middle of the twisted pair, everything is balanced before the middle point). What problems will it ...
15
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3answers
2k views

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 ...
2
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2answers
66 views

Considering Moding Issues in High Speed PCB Design

My question is a more generic one. I recently learnt about TE and TM propagation modes in waveguides. This made me think that when designing high-speed PCBs people always talk about matching the ...
0
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1answer
79 views

signal propagates in bending transmission line (unequal length between signal path and return path)

Suppose I have a square wave signal generated from a signal generator and its outputs are connected to the two terminals of a paired PCB traces (left side of the picture below). The other end of the ...
0
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0answers
90 views

Test LVDS signals

I am wondering how I could test LVDS signals on a PCB using a scope. The most straight forward answer would be to measure on the termination resistor points, although this isn't possible, since the ...
4
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2answers
579 views

What makes “quality” analog AV cables better than cheap cables? [closed]

I want to upgrade my retro game setup from a mix of composite and RF to a mix of S-video and component, with some composite for the really old stuff that doesn't support S-video. How can I distinguish ...
0
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0answers
72 views

Power line between data lines

I am finalizing my design which connects a USB Controller (FT601) with the FPGA (MachXO2). There is last thing I am not particularly happy about and I would like your feedback on that. In the ...
0
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1answer
77 views

VCC on surface or inner layer on 4-layer board?

If I can get away with, I will use 6-layer design where I get two dedicated GND planes, L2 and L5, which creates strong reference plane for traces on L1, L3 and L6. When you're working with 4 layers,...
0
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1answer
80 views

Could shielding (not grounded) affect signal integrity?

I'm trying to shield 6 flat cables that give me some communication issues because I thought that there might be cross-talk or other sources of interference that cause the problem. The shielding is ...
1
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3answers
154 views

How do you know if impedance is the same for 2 ICs?

in my last question I got some very interesting answers that made rethink a lot about my design as to whether or not I need termination resistors at all. Additionally, the design proposed in this ...
1
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3answers
130 views

Large number of termination resistors and bi-directional signals

I am designing PCB which has an FT601 for USB communication. No matter how hard I tried, I could not keep the traces short enough in order to avoid reflections and simulation was revealing significant ...
1
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2answers
98 views

How protect analog input connected to thermistor through long wires

I'm developing a data acquisition board for 8 thermistors hooked up through 3 feet wires. The board is gonna be installed inside a package unit air conditioning. In there, we have compressors, fan ...
-1
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2answers
71 views

Reducing noise that grows with frequency

I have a project in university where my professor gave us the following problem: There is a transducer generating an AC signal with amplitude of 7.5mV and a frequency range from 50Hz to 150Hz. This ...
0
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1answer
47 views

Is there a problem connecting PSU grounds to earth for an isolated signal chain in this scenario?

For a precision and simultaneous analog signal data acquisition; several force, temperature and acceleration transducer outputs are coupled to a daq board input channels through signal conditioning ...
1
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1answer
119 views

3 wire signal to 4 core shielded twisted pair

So I have some flow sensors, which have a 3 wire interface. The three wires are 5V, signal, and ground. Signal is pulse output that varies between 5V and ground at a maximum frequency of about 200 Hz....
0
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1answer
122 views

Altium - design rule check does not match with signal integrity for impedance

I have designed a 2-layer PCB with Altium Designer. I placed an impedance rule of 50 Ohm in trace width rule section. When I run the design rule check, there is no impedance error. However, when I ...
0
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1answer
72 views

On-PCB SPI Distance Considerations

I've been reading about ringing and overshooting and all sorts of things, but all without getting a real "feeling" for how likely these things are to affect my circuit. I've got a chip generating an ...
2
votes
2answers
533 views

How to achieve 100ohm impedance for HDMI differential pair on FR4?

I have a 6 layer FR4 PCB, and want to achieve 100ohm impedance on HDMI differential pairs. I am only using top and bottom layer for differential pairs, and following are my parameters: Trace width= 3....
1
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0answers
29 views

Signal Attenuation TVS and series resistor

This question is in regards to signal attenuation on high speed data lines like RS-485 (and any others as well). I'm new to the signal world, so please bear with me here. Are there some useful ...
0
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1answer
39 views

Boosting the Analogue Response of a Sensor

I have a A1308KUATN-9-T Hall Effect sensor with the following sensitivity (from the data sheet): As you can see, the sensitivity comes to about 9mV per Gauss on average. My calculations (see below ...
3
votes
1answer
152 views

Analogue (or digital) signal integrity with multiple sources of noise

tldr: Can I transmit an analog signal through a noisy environment without it being corrupted, or should I use a digital signal instead? My requirement is to transmit a signal from a MA3 absolute ...
0
votes
1answer
41 views

Digital signal integrity & grounding

I have a battery operated device with an old B&W LCD in it. I'm tapping to the display bus and would like to input it into an FPGA for some processing. The bus includes vertical and horizontal ...
0
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3answers
111 views

Tektronix function generator THD

I am confused by the datasheet of the AFG3021C: https://www.tek.com/link-click-count?nid=75006&url=https%3A//download.tek.com/datasheet/AFG3000C-Arbitrary-Function-Generator-Datasheet-75W282817....
0
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0answers
122 views

How do passive boosters/repeaters (such as a HDMI 'booster') work?

I have a HDMI device and I want to connect it to something very far away. I notice you can buy a HDMI booster to do this, but some of them are unpowered (they take no external power). How can a signal ...
9
votes
3answers
899 views

If temperature is not an issue, what can be said about the different ceramic dielectrics

Let’s assume we have a circuit whose operating ambient temperature range is well-regulated to 25+-5C. Besides cost, what would be the use cases for the different ceramic dielectric types? In other ...
4
votes
1answer
185 views

JTAG trace length affecting programming ability

I've recently had a design made that requires a programming port to be located quite far from the device I'm trying to program. This has meant that my cJTAG traces are around 13cm long. I think as a ...
1
vote
1answer
128 views

I2C bus line over different layers in an arc

I have the following board design in mind: It's a 4 layer, ~5cm diameter board where 10 slave PCB's will be soldered to it that are connected over the I2C bus. The trace line you see is roughly 8 cm ...
0
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1answer
63 views

Are digital inputs of data acquisition devices differential or single ended?

I read that in almost all daq board datasheets the analog inputs are specified as single ended or differential inputs. But the same daq have digital I/O ports. How can one understand whether the ...
1
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0answers
114 views

Reducing electromagnetic interference in underwater acoustics cables

Our college underwater robotics team has a passive acoustics system with four hydrophones that provide an analog signal typically between +/- 200 mV corresponding to the sound wave at that point in ...
2
votes
1answer
331 views

Grounding and Signal Integrity of my PCB Layout (ADC, SMPS, SD card, USB)

I am currently designing a battery monitoring system for an 8 cell lithium battery pack. I originally made the device using a STM32 dev board and breadboard, with an SD card to log data. The system ...
1
vote
3answers
428 views

Advice for 25-50 Mbit SPI lines - PCB design

I would like to ask some advice for my layout design. I am working on a layout design. The designed PCB will be a Beaglebone Black (BBB) extension card. It is a four layer PCB with the following ...