Questions tagged [signal-integrity]

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

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28 views

Signal line current estimation and impedance matching

As far as I know, the input pins to ICs are typically just the gate of a MOSFET. I have always just take stuff for granted (like if you want to control a logic pin, just put a source voltage on it), ...
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1answer
31 views

How to make sure you have “adequate” ground in a self-enclosed portable circuit?

How to make sure you have "adequate" ground in a self-enclosed portable circuit? I read that a good ground ensures steady signals. But, if you run a circuit from a battery it is not connected to ...
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1answer
18 views

RS-485 device to RS-232 adapter MUXing not working as expected

I have a RS-485 device that returns serial ASCII constantly. As the device might near very high voltage or electromagnetic areas, I need to ensure the RS-485 to RS-232 adapters I've been supplied with ...
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3answers
78 views

How do bypass capacitors recharge in high-frequency if the PCB can't deliver high-frequency currents?

I understand the whole theory behind bypass capacitors, how they are necessary to deliver high-frequency currents to the IC, as the PCB in general has high-inductance, thus high-impedance in high-...
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1answer
15 views

Touching MOSI on RJ45 connector cleans bus noise

I am using a STM32F767ZI-Nucleo development board from ST. i'm using it to communicate by SPI with a UM7 orientation sensor board. There a register to read in the FW version. Normally I only receive ...
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1answer
58 views

When to Remove the Ground Plane under SMD components for High-Speed Signals?

I'm reading TI's recommendations on routing high-speed signals. Most of the guidelines are common sense, but there's one guideline that I haven't read before: It recommends completely removing the ...
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1answer
38 views

Self solder 8-pin din cable

a bit of specific question. I want to build my own cable based on pins stated in the manual of an old camera, so I can capture the video (composite video) and audio signal. Question: Is there ...
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1answer
69 views

Is it a good idea to connect ethernet cable's shielding to PCB GND?

Background My project is split over two PCBs for convenience. The first PCB adapts an input signal and converts it to a low-voltage differential signal. There are 4 channels to be measured, so 4 ...
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2answers
59 views

ADC signal conditioning circuit

I have a circuit that is fed into a ADC chip (adc128s022), that I am trying to understand. The sensors are inferred gas sensors. Could you please criticise my analysis. The way I am reading it: ...
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0answers
36 views

Quadrature Encoder output overshoot

I have a Faulhaber 1717T006SR DC motor with a build-in quadrature encoder. Here is the relevant bit of the datasheet for the encoder. The encoder outputs are 5V. I want to interface this with an ...
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3answers
90 views

Signal return path between circuits with separate full-bridge rectifiers

Edit: I think I've figured out WHY this is happening (see my answer below), but I still would love to hear ways to mitigate this issue. I've got two microcontrollers that are powered by the same dc ...
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1answer
134 views

Is it better to route Ethernet on the top layer, or to use vias?

I'm making a circuit board with Ethernet (PoE if that makes a difference) coming in through an M12 connector, passing through magnetics and a PHY and going to a micro. I've always heard that there are ...
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5answers
1k views

Detection of signals buried in noise

This is more of a general question to see which methods are the most common to improve the detection of a signal which is buried in noise. Currently, we are building an optical system for medical ...
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1answer
44 views

phy chip straping pins

as you can see options strapping pins are multiplexed with RXD# pins .. which are MII interface pins. this will make the PCB have "stubs" (connected to MAC + pullup resistors) which is not good in ...
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4answers
119 views

Why longer stubs cause more intense ringing?

Why connection of longer stub lengths cause more intense ringing in a Communication Network like CAN? As stub lengths increase won't the attenuation increase and lead to less ringing? Also the time ...
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4answers
124 views

Why is the amplitude of ringing in square wave independent of frequency of square wave?

Reflections in a transmission line is causing ringing in square wave because certain frequencies are getting enhanced, but when frequency of the square wave changes won't the amplitude of those ...
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1answer
67 views

Does the standard termination of 120 ohm really suppress reflections in recessive state in CAN?

Suppose we have a multi-node CAN network with the ends of transmission line terminated with the standard 120 ohm. When the recessive state is on the transmission line, the voltage on both CAN_H and ...
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5answers
2k views

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 ...
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0answers
60 views

Questions on ringing over square wave in transmission line

Considering a transmission line with open circuit termination at one end and a square wave voltage source with impedance not matching the characteristic impedance at the other end. Because of ...
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1answer
40 views

How will the proper termination at one end while the other end is kept open avoids reflections in transmission line?

Consider a transmission line which is terminated with characteristic impedance at one end but other end is kept open, the reflections are not observed. I don't understand the mechanism behind. Please ...
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1answer
46 views

9-pin micro-d connector for LVDS signals

Has anyone utilized 9-pin micro-d connectors for driving and receiving LVDS signals? I am running the LVDS at 100 Mbps for 20-30 inches. I am using a vertical pcb mounted connector 380-009-213 from ...
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1answer
63 views

Using DB9 connectors for LVDS signals

Has anyone utilized 9-pin DB9 connectors for driving and receiving LVDS signals? I wanted to use Micro-D connectors on a board I am developing but they take too long to get. Since DB9 connectors are ...
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4answers
259 views

How do reflections of a square wave cause ringing in transmission lines?

When a square wave is applied to a transmission line which is not terminated with its characteristic impedance, reflection and ringing occur. I don't understand how sinusoidal ringing occurs when I ...
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0answers
39 views

Unexpected values from insertion loss calculation in IEEE P802.3cg documentation

I'm looking at the insertion loss calculations from an IEEE document on P802.3cg (10SPE Ethernet). On pages 6 and 7 they talk about insertion losses over the cabling in a multi-drop scenario. I'm ...
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2answers
111 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 ...
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2answers
54 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: ...
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1answer
67 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, ...
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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 ...
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1answer
35 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 ...
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3answers
89 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 ...
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2answers
51 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 ...
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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 ...
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0answers
67 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 ...
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3answers
128 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 ...
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1answer
41 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 ...
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1answer
90 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 ...
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2answers
323 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 ...
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0answers
32 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
251 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 ...
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2answers
79 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
98 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
386 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 ...
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0answers
67 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, ...
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2answers
119 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 ...
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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 ...
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2answers
79 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 ...
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1answer
83 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 ...
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2answers
580 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 ...
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0answers
83 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 ...
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1answer
97 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,...

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