Electromagnetic compatibility (EMC) is a branch of electronics related to identifying and solving problems caused by electromagnetic interference (EMI) between devices. It encompasses both attempting to prevent unwanted emissions from a device and also ensuring that emissions from another device ...

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48 views

Can smd ferrite beads be avoided

I am redesigning an input interface circuit for digital input. Its a basic signal conditioning circuit for reverse polarity protection, EMI ESD protection, and filtering voltage surges. For EMI EMC, ...
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2answers
87 views

3.3V UART over 20cm ribbon cable inside an enclosure - EMC considerations

I am currently designing a device which internally consists of two circuit boards inside a fairly large, grounded metal enclosure. I'm designing one of the boards myself, the other is a bought part ...
0
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1answer
73 views

Long wire PWMed LED lights

so I plan to build a house (at some point in future) and I'd like to implement some sort of home automation. Now one of the things I'd like to have is PWMed lighting. Most of the lights would be 12V ...
6
votes
1answer
92 views

PCB layout for 8-16MHz crystal very near WiFi module AND small DC motor

I'm designing an "Internet of Things" appliance where space and layout are constrained by mechanical and cost requirements. The main processor is a PIC18 and its crystal (probably 8MHz, maybe 16) is ...
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2answers
55 views

Optimal PWM Frequency for EMI & EMC

I am planning to design a 65W power supply which will use a PWM frequency of around 100kHz. I am specifically concerned about conducted EMI (not as much about radiated for now). I am currently ...
6
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1answer
123 views

Tying ground planes together with a non-zero Resistor

I was reviewing the schematic of a motor driver board and noticed that the digital and analog grounds are tied together with a 3.9 ohm 1/4 watt resistor. I am still trying to find the gerber files to ...
6
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1answer
95 views

EMC testing of unenclosed PCB assembly

What is the most common practice in performing EMC tests for PCB assemblies that will be sold without a housing? In my case it is an FPGA development board. Is it possible to design excessive ...
2
votes
1answer
91 views

eeprom data corruption during power failure

I recently found a problem with eeprom of a PIC16F877A which is used to control the speed of a dc motor. The drive is supposed to work on the last set speed even if the power fails. But the problem is ...
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0answers
38 views

How to shield from electro surgical generator in close proximity?

Looking for help EMI hardening a SERDES interface in close proximity to electro surgical instruments. I believe there may be tips or reference designs from existing pacemaker applications that may ...
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0answers
30 views

LED selection for EMI/EMC considerations

For my system, I need to select panel-mount LED indicators which needs to withstand through EMI/EMC tests. Can I use normal panel mount LEDs coming in aluminium threaded sockets for my application? Is ...
2
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2answers
59 views

How does spread spectrum VCXO (voltage controlled oscillator improve EMI on your board?

I have seen people adding spread spectrum voltage controlled oscillator to EMI on the board, How is EMI affected by single spectrum crystal and with spread spectrum crystal.
3
votes
1answer
52 views

Cable shield as ground conductor

I have two circuits connected by a shielded cabled. The cable brings 3.3V DC and LVDS communication between the circuits. The shield is being used as the sole conductor for the reference ground to the ...
0
votes
2answers
71 views

Signal distribution, buffers, rise times and EMC

I am designing a DSP based audio mixer. There are 4 AD/DA converters (AD1939 and AD1974) and a DSP (OMAP L138), which is on a carrier module. I am distributing the frame clock (48kHz) and the bit ...
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1answer
153 views

What's the purpose of this ground connection circuit?

I inherited a power supply circuit design from another engineer, and he used a ground connection method I am not familiar with: The input comes from an external isolated 48 V AC/DC power brick. The ...
3
votes
1answer
99 views

Return Paths of Signals on Flat Flex Cable

I have a 4 layer PCB with a typical stackup (signal-gnd-vcc-signal) and on the top layer there's a CMOS sensor connected with a flat flex cable... I was wondering, since there's no reference plane ...
1
vote
1answer
72 views

TVS Diode Array with EMI Filters on ADC Input

Is there any problem with using this SP6002 TVS Diode Array/EMI filter to protect ADC inputs on a micro-controller? The ADCs will only measure DC voltages. I am a little worried that the filters will ...
3
votes
1answer
179 views

GND plane close to LVDS differential pair?

I have two LVDS differential pairs on my PCB, running from a connector. On the connector, I have the following sequence of nets: GND LVDS+ LVDS- GND LVDS+ LVDS- GND This is as I have seen ...
4
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2answers
233 views

Where to connect shield and ferrites in PCB with isolated planes

I have a device which has two sections of the PCB completely isolated form each other, but connected by an isolator IC (PN: ????). I think I need to shield the whole device for reducing EMI because ...
3
votes
2answers
90 views

Understanding source of EMI

I have a device which contains a USB chip which uses 19.2MHz external oscillator. When I measured the EMI generated from the device, I got series of peaks ranging from 100MHz to 1GHz+. The peaks ...
5
votes
1answer
343 views

EMI Filtering on LVDS lines

This question is slightly related to: What's radiating on my PCB? These are Beckhoff's EtherCAT industrial IO modules. Each module is connected to its neighbours by 100mbps LVDS. Each module contains ...
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2answers
107 views

Smoothing current drawn by PWM load

I have a PWM load which draws its current from a regulated DC supply. The supply and load will be separated by some distance, and I'm worried that the rapid changes in current through the current ...
2
votes
1answer
196 views

Square Wave pulses generating EMI

Following on my unanswered question about bluetooth noise, I have now believe that I have learned a bit more about my problem. I have built a Arduino controlled circuit to replace the pots and ...
5
votes
1answer
239 views

On referencing power planes and return current paths

I recently worked on a 16-layer board design that contained only 2 ground planes, at the outer layers of the board, and several power planes (+1V1, +1V8, +3V0, +5V0) in the middle: Since there are ...
32
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3answers
788 views

What's radiating on my PCB?

I recently did a proper EMC test on a PCB of mine. It failed the test, and seems to be radiating in the 300MHz - 1GHz region, with peaks every 50MHz, and little peaks on the 25MHz. Looking at the ...
4
votes
1answer
121 views

Crystal Harmonics EMC Failed

I have a failed on EMC Test 300MHz and 500MHz due to crystal harmonics. There is a lot of spike with a 25MHz harmonics. The first picture is the Top of the Board and the 2nd is the 2nd layer ...
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2answers
178 views

How to debug emc problem?

First time during my entire engineering career I have been to an emc lab last week. My design has failed to satisfy FCC requirements. The board uses a 25mhz clock and we have failed at 500mhz but I ...
5
votes
2answers
1k views

How does a ferrite core wire terminator work to reduce EMC?

The following question was asked on superuser: What is that cylinder on cables? How does that cylinder work? As far as I can tell, even if you put one on either end of the cable, any HF signal should ...
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2answers
729 views

What is the best way to layout a PCB with crystal oscillators and MCU?

I have heard that the clock circuit is a noise source and that the clock circuit is also sensitive to noise. I believe that keeping the clock circuit close to the MCU and keeping other routes or ...
0
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0answers
38 views

E-textiles EMC/FCC and durability issues

I am trying to build a keyboard sewn into a shirt and I wonder if I need to worry about EMC/FCC issues with the conductive thread to the keys? For each key I use a normal (but very thin) pushbutton, ...
5
votes
1answer
472 views

How can electromagnetic interference from a USB charger cause a capacitive touchscreen to malfunction?

Electromagnetic interference from a USB charger can cause a touchscreen on a mobile device to malfunction, with symptoms such as reduced sensitivity or spurious touches. As an example, see ...
3
votes
1answer
244 views

How to create EMI?

I want to subject my product to large amounts of EMI to see what happens. I figure I need the EMI to be broad-spectrum to be sure it will have the best chance of wreaking havoc. However, I don't ...
4
votes
1answer
206 views

How to identify and remove unintentional PCB antenna?

It has been pointed out to me, more than once, that I might be making a few too many antennas unintentionally on the PCB with the copper pour, an obvious example is this L shaped pour at the edge of ...
4
votes
1answer
205 views

common mode choke inductance question

In a common mode choke, my understanding is that common mode currents will produce fluxes that add together, which increases the effective inductance between them and so attenuating these currents. ...
7
votes
1answer
410 views

Placement/routing of decoupling cap straddling oscillator guard ring on dsPIC

Changes in my design are forcing me to replace my 44-pin dsPIC33FFJ16MC304 with a 64-pin (same package size, finer pin pitch) dsPIC33FJ64MC506. In the datasheets for both chips, Microchip recommends a ...
6
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3answers
715 views

Is it better to have a poor top layer copper pour or no copper at all?

For a few small 2 layers boards I'm doing, I'm using the top layer for parts and signals and a ground pour on the bottom layer with no or very short traces, based on comments and answers to my ...
1
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2answers
128 views

Effect of radiation detectors on electronic components

After the Fukushima nuclear disaster that took place in Japan in 2011, any imports from there are checked for nuclear radiations using radiation detectors. I recently ordered components from Digikey ...
2
votes
0answers
190 views

Digital RGB interface EMI filtering

Consider the following system: where: The motherboard contains a LCD controller (SSD1963 from Solomon Systech) and other components (application processor, solenoid drivers, power supplies, etc.) ...
3
votes
3answers
506 views

TFT LCD pixel clock filtering

I would like to know how to filter the pixel clock in order to reduce emitted radiations. Block diagram The LCD controller is part of a motherboard. A board, connected at the other side of the FFC ...
16
votes
5answers
814 views

Why does a simple conductor start to emit EM waves when carrying a signal?

I understand that on circuit board traces with a clock, if the higher harmonics have sufficient power, it results in electromagnetic waves being emitted from the traces which creates EMI. What I don't ...
1
vote
0answers
39 views

Parallel, low noise motor driver design with L293D [duplicate]

I'm designing a very basic motor driver circuit for 12V DC brushed motors to be connected with my microcontroller. The motor needs to be driven in forward and reverse My objective is to do that with ...
0
votes
2answers
417 views

PWM controller to meet EMI/EMC regulations

I'm designing an application in which the current running into a load is controlled by PWM. A microcontroller generates a PWM cycle at 20kHz and this signal is used to control a MOSFET which is ...
3
votes
2answers
222 views

Return current in 8 Layer stackup

I have to design a multilayer Board (8 Layer). This is a part of 4 PCBs in a product with plastic enclosure. The high speed signal on PCB are Ethernet, USB2, LAN and UMTS integrated modem. Product ...
8
votes
1answer
257 views

Weak internal pullups on microcontrollers and EMI susceptibility

What disadvantages can I run into when using weak internal pullups (100k) on microcontrollers? I'm wondering how susceptible lines (with only parasitic trace/component capacitance) become to EMI ...
5
votes
1answer
2k views

PCB Ground and Power Planes

I am desigining a 4-layer PCB with the following stack-up: Signal Top, Ground Plane, Power Plane, Signal Bottom. This is the first PCB I make like this, which includes a noisy SMPS with a switching ...
4
votes
2answers
217 views

EMC Design Precaution

I'm designing a simple circuit which will charge a big capacitor for 3 seconds, then pass a 5A current for few microseconds, then charge again the big capacitor for 3 seconds, then pump again 5A for a ...
13
votes
2answers
337 views

Best way to group power pins on a connector?

I am designing a little mezzanine PCB that uses Hirose DF12 connectors to connect to the motherboard. Four different voltages are delivered to this PCB: ±10v, 3.3v, 48v (and ground). They go ...
1
vote
1answer
235 views

Running Microwave Oven interupts Wifi connection. Should I worry about it? [closed]

Every time I turn on microwave oven, Wifi connection to my computer is disconnected. When the oven's done, Wifi recovers. This means the microwave somehow floats in my home when it's running. Should I ...
3
votes
1answer
165 views

What EMC considerations need to be made with RF bias-t with 3-4A of current consumption?

After getting a great answer on how to couple a signal on to a DC line, I wonder what EMC considerations that has to be done with using a bias-T circuit used for communications with a ~130kHz QPSK ...
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3answers
215 views

Wrapping data cable around ferrite rod

I am trying to do some high quality audio recording using a fire wire interface. Currently I have a naked firewire cable. I was looking on eBay for some ferrite cores and that got me thinking about ...
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0answers
144 views

Different ringing patterns on flyback output

A modified version of the PCB that I discussed on this post was implemented. It is still 2-layer with all components on top and the ground on the bottom layer. The transformer windings were directly ...