EMC Analysis During PCB Layout

Catch Issues Earlier

If your electronic product design fails EMC compliance testing for its target market, that product can’t be sold. That’s why EMC analysis is such an important step. In this article, Craig shows how implementing EMC analysis during the design phase provides an opportunity to avoid failing EMC compliance testing after fabrication.

By Craig Armenti,
Mentor, A Siemens Business

Electromagnetic Compatibility (EMC) is generally defined as the ability of a product to function in its environment without introducing electromagnetic disturbance. EMC compliance is a necessary condition for releasing products to market. Simply stated, if a product does not pass EMC compliance testing for the target market, the product cannot be sold. Regulatory bodies around the world define limits on the radiated and conducted emissions that a device is allowed to produce. Automotive and aerospace manufacturers can set even stricter standards for their suppliers. Design teams are well aware of the importance of ensuring their product is EMC compliant. All that said, many do not attempt to perform EMC analysis during design.

There is a perception that EMC analysis during PCB layout can be a time-consuming task that is challenging to set up and properly configure, with difficult-to-interpret results. Historically, the focus of analysis during design has been on Signal Integrity (SI) and Power Integrity (PI). Manual EMC “analysis” typically is performed post-fabrication, based on the results of testing the actual product. What is often overlooked is that implementing EMC analysis during the design phase provides an opportunity to avoid failing EMC compliance testing after fabrication.

Figure 1
EMC analysis implemented during PCB layout

The current generation of ECAD tools offers EMC analysis functionality that is easy to use, with well-documented rule checks that often include an explanation for each principle and advice on how to address issues. Implementing EMC analysis at appropriate points during PCB layout, prior to fabrication, can mitigate the need for redesign(s) that affect both product development cost and overall time to market (Figure 1).

EMC Simplified

EMC can be a confusing topic, especially for new engineers and designers or those not well versed in the subject matter. Furthermore, there is often confusion as to the difference between electromagnetic compatibility (EMC) and electromagnetic interference (EMI). Although this article is not intended to be an in-depth tutorial on EMC and EMI theory, a quick review of the definitions is appropriate.
As previously stated, EMC is generally defined as the ability of a product to function in its environment without introducing electromagnetic disturbance. Specifically, the product must:

• Tolerate a stated degree of interference
• Not generate more than a stated amount of interference
• Be self-compatible

EMI is generally defined as disturbance that affects an electrical circuit, due to either electromagnetic induction or electromagnetic radiation.

To further simplify the two definitions: EMC is how vulnerable the product is to the environment, and EMI is what the product introduces into the environment (Figure 2).

Figure 2
The four basic EMC/EMI coupling mechanisms relative to the source and victim

The complexity of the topic contributes to the perception that implementing EMC analysis during PCB layout can be a time-consuming task that is challenging to set up and properly configure, with results that are difficult to interpret. The alternative, however, foregoing automated in-design analysis and waiting to test the actual product post-fabrication, has the potential to be significantly more time consuming and costly. Although EMC test labs are not required to provide the average EMC testing pass rate, several studies suggest that the first time pass rate is approximately 50%. Furthermore, EMC compliance failure has been cited as the second cause for redesigns in the automotive industry. Given that an EMC failure will require one or more redesigns that affect both product development costs and overall time to market, performing EMC analysis during PCB layout (designing for EMC compliance) is essential.

Left-Shift to Layout

The term “left-shift” within the engineering space is often used to describe the act of moving (or shifting) a task that would normally occur toward a later phase of the design process, to occur also during an earlier phase. . …

Read the full article in the July 336 issue of Circuit Cellar

Mentor | www.mentor.com

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July Circuit Cellar: Sneak Preview

The July issue of Circuit Cellar magazine is coming soon. And we’ve rustled up a great herd of embedded electronics articles for you to enjoy.

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Here’s a sneak preview of July 2018 Circuit Cellar:

TECHNOLOGIES FOR THE INTERNET-OF-THINGS

Wireless Standards and Solutions for IoT  
One of the critical enabling technologies making the Internet-of-Things possible is the set of well-established wireless standards that allow movement of data to and from low-power edge devices. Here, Circuit Cellar’s Editor-in-Chief, Jeff Child, looks at key wireless standards and solutions playing a role in IoT.

Product Focus: IoT Device Modules
The rapidly growing IoT phenomenon is driving demand for highly integrated modules designed to interface with IoT devices. This Product Focus section updates readers on this technology trend and provides a product album of representative IoT interface modules.

TOOLS AND TECHNIQUES AT THE DESIGN PHASE

EMC Analysis During PCB Layout
If your electronic product design fails EMC compliance testing for its target market, that product can’t be sold. That’s why EMC analysis is such an important step. In his article, Mentor Graphics’ Craig Armenti shows how implementing EMC analysis during the design phase provides an opportunity to avoid failing EMC compliance testing after fabrication.

Extreme Low-Power Design
Wearable consumer devices, IoT sensors and handheld systems are just a few of the applications that strive for extreme low-power consumption. Beyond just battery-driven designs, today’s system developers want no-battery solutions and even energy harvesting. Circuit Cellar’s Editor-in-Chief, Jeff Child, dives into the latest technology trends and product developments in extreme low power.

Op Amp Design Techniques
Op amps can play useful roles in circuit designs linking the real analog world to microcontrollers. Stuart Ball shares techniques for using op amps and related devices like comparators to optimize your designs and improve precision.

Wire Wrapping Revisited
Wire wrapping may seem old fashioned, but this tried and true technology can solve some tricky problems that arise when you try to interconnect different kinds of modules like Arduino, Raspberry Pi and so on. Wolfgang Matthes steps through how to best employ wire wrapping for this purpose and provides application examples.

DEEP DIVES ON MOTOR CONTROL AND MONITORING

BLDC Fan Current
Today’s small fans and blowers depend on brushless DC (BLDC) motor technology for their operation. In this article, Ed Nisley explains how these seemingly simple devices are actually quite complex when you measure them in action. He makes some measurements on the motor inside a tangential blower and explores how the data relates to the basic physics of moving air.

Electronic Speed Control (Part 1)
An Electronic Speed Controller (ESC) is an important device in motor control designs, especially in the world of radio-controlled (RC) model vehicles. In Part 1, Jeff Bachiochi lays the groundwork by discussing the evolution of brushed motors to brushless motors. He then explores in detail the role ESC devices play in RC vehicle motors.

MCU-Based Motor Condition Monitoring
Thanks to advances in microcontrollers and sensors, it’s now possible to electronically monitor aspects of a motor’s condition, like current consumption, pressure and vibration. In this article, Texas Instrument’s Amit Ashara steps through how to best use the resources on an MCU to preform condition monitoring on motors. He looks at the signal chain, connectivity issues and A-D conversion.

AND MORE FROM OUR EXPERT COLUMNISTS

Verifying Code Readout Protection Claims
How do you verify the security of microcontrollers? MCU manufacturers often make big claims, but sometimes it is in your best interest to verify them yourself. In this article, Colin O’Flynn discusses a few threats against code readout and looks at verifying some of those claimed levels.

Thermoelectric Cooling (Part 1)
When his thermoelectric water color died prematurely, George Novacek was curious whether it was a defective unit or a design problem. With that in mind, he decided to create a test chamber using some electronics combined with components salvaged from the water cooler. His tests provide some interesting insights into thermoelectric cooling.

 

LED Lighting Controller for Automotive

Texas Instruments has introduced the first 3-channel high-side linear automotive light-emitting diode (LED) controller without internal MOSFETs that gives designers greater flexibility for their lighting designs. The TPS92830-Q1’s novel architecture enables higher power and better thermal dissipation than conventional LED controllers, and are particularly beneficial for automotive LED lighting applications that require high performance and reliability.

TPS92830-Q1Conventional LED drivers integrate the MOSFET, which limits designers’ ability to customize features. With that type of driver, designers often must make significant design modifications to achieve the desired system performance. The TPS92830-Q1 LED controller’s flexible on-board features give designers the freedom to select the best MOSFET for their system requirements. With this new approach, designers can more quickly and efficiently optimize their lighting power designs for automotive system requirements and desired dimming features.

The on-chip pulse-width modulation (PWM) generator or PWM input enables flexible dimming. Designers can use either the analog control or PWM to manage an output current of more than 150 mA per channel, to power automotive rear combination lamps and daytime running lights.

By pairing the LED controller with an external MOSFET, the designer can achieve the required high power output while distributing the power across the controller and MOSFET to avoid system overheating. By retaining linear architecture, the TPS92830-Q1 provides improved electromagnetic interference (EMI) and electromagnetic compatibility (EMC) performance.

Advanced protection and built-in open and short detection features help designers meet original equipment manufacturer (OEM) system reliability requirements. The output current derating feature protects the external MOSFET under high voltage conditions to ensure system reliability.

Support tools include the TPS92830-Q1 3-Channel High-Current Linear LED Controller evaluation module. Engineers can jump-start automotive lighting systems designs using the TPS92830-Q1 with the EMC Compliant Automotive Daytime Running Light and Position Light Reference Design with LED Thermal Protection. The TPS92830-Q1 is now available through the TI store and authorized distributors. Offered in a thin small outline package (TSOP), it is priced at US$1.96 in 1,000-unit quantities.

Texas Instruments | www.ti.com

AD-DC Power Supplies for Medical Designs

CUI’s Power Group has announced five new open frame series, ranging from 180 W up to 550 W, to its line of internal ac-dc medical power supplies. Certified to the medical 60601-1 edition 3.1 safety standards for 2 x MOPP applications and 4th edition EMC requirements, the VMS-180, VMS-225, VMS-275, VMS-350, and VMS-550 series feature high efficiency up to 94% and high power densities up to 30 W/in3. The new models are housed in 2 x 4 inch (50 x 101 mm) and 3 x 5 inch (76 x 127 mm) packages with profiles measuring as low as 0.75 inches (19 mm), providing a compact, high density solution for medical diagnostic equipment, medical monitoring devices and dental applications.

high-density-medical-printAll of the new VMS series provide output voltage options from 12 VDC to 58 VDC, feature wide universal input voltage ranges from 80 to 264 VAC and offer no-load power consumption as low as 0.5 W. The 180 W to 550 W models also carry an input to output isolation of 4200 Vac with leakage current ratings as low as 0.3 mA at 230 VAC. Operating temperatures range at full load from -40°C up to +50°C with forced air cooling, derating to 50% load at +70°C.

Additional features include protections for over voltage, over current, and short circuit, power factor correction, and a 12 VDC / 500 mA fan output. These medical power supplies further meet EN 55011 Class B limits for conducted and radiated emissions and achieve an MTBF of 3.37 million hours, calculated per Telcordia SR-332 Issue 3. The VMS series are available immediately with prices starting at $108.94 per unit at 25 pieces through distribution.

CUI | www.cui.com

Pre-Compliance EMC Probe Kits

Saelig Company recently announced the availability of the TBPS01-TBWA2 EMC Probe Kit (Singapore-based Tekbox Digital Solutions), which includes investigative near-field probes and a wideband amplifier to increase the versatility of economical spectrum analyzers to identify EMC issues. The TBPS01-TBWA2 EMC Probe Kit comprises four rubber-handled near-field probes (three H-field and one E-field), a 20- or a 40-dB wideband amplifier, and associated cables. The shielded probes have built-in ferrites and insulated rubber handles to insure that measurements are insensitive to the human hand.    Saelig-emcprobekit

The H- or E-field probes are useful for detecting radiated emissions when placed near potential sources of electromagnetic radiation, and can help locate and identify interference issues in electronic assemblies and PCBs. Scanning the probe over the surface of a PCB assembly or housing quickly identifies locations which emit electromagnetic radiation. The probes act as wide bandwidth antennas, picking up radiated emissions from components, PCB traces, housing openings, or gaps—and from any other parts that could be emitting unwanted RF signals. The probes are usually connected to a spectrum analyzer but may also be used (less effectively) with the FFT capability of a digital oscilloscope. By changing to a probe with smaller size, the origination of the emissions can be further narrowed down.

Engineers usually have to rely on experience and best-practice methods in order to design an EMC-compliant product. But when it comes time for compliance testing at an authorized test house many products fail first time through. Failing is expensive, and retesting costs are high too. The project schedule gets delayed and market introduction targets are missed. Therefore, it is essential for an engineer to do pre-compliance testing in-house to increase the chances of success when it comes time to book space in an anechoic chamber. One of the key components of an in-house pre-compliance test set-up is a spectrum analyzer. Entry-level models are now very affordable but the near-field antennas often are not. The TBPS01-TBWA2 EMC Probe Kit is an affordable antenna kit and amplifier that will enable any spectrum analyzer to be used to localize the origin of emissions or immunity compromises. Scanning the board with these hand-held probes will help identify problem areas, as well as the subsequent effectiveness of experimental solutions. An additional use of the probe kit with a signal generator is to identify PCB areas that are susceptible to RF interference by locally transmitting signals from the probes.

The included USB-5V-powered TBWA2 Wideband Amplifier, housed in a compact metal box (1.9″ × 2.6″ × 1″) provides either 20- or 40-dB amplification (depending on model) with a flat response from 10 MHz to 3 GHz, increasing the sensitivity of near-field probe measurements when attached to a spectrum analyzer.

Applications include radiated EMC measurements,  contactless (load free) relative measurement of RF signal chains, contactless (load free) relative measurement of oscillators, modulators, RF immunity testing (by feeding a RF signal into the probe and radiating it into potentially susceptible circuit sections), noninvasive measurement of RF building blocks such as modulators or oscillators, and more.

Source: Saelig

EMC Measurement Technology

LangerSX near-field probes enable electromagnetic compatibility (EMC) analyses of interferences emitted by electronic boards, components, and IC pins with high internal frequencies. The SX-R3-1 magnetic H-field probe is designed to detect high-frequency magnetic fields with a high geometrical resolution. The field orientation and distribution can be detected by moving the probe around conductor runs, bypass capacitors, EMC components, and within IC pin and supply system areas. The SX-E03 E-field probe detects bus structures and larger components.

The probes have a 1-to-10-GHz frequency range. Their high resolution (the SX R3-1 achieves 1 mm and the SX E03 covers up to 4 mm × 4 mm) enables them to pinpoint RF sources on densely packed boards or on IC pins. The magnetic-field probe heads are electrically shielded. The probes are connected to a spectrum analyzer input via a shielded cable and SMA connectors during measurement. High clock rates of 2 GHz, for example, may result in fifth-order harmonics of up to 10 GHz. These harmonics are coupled out by RF sources on the board (e.g., conductor-run segments, ICs, and other components). They may stimulate other structural parts of the board to oscillate and emit interferences.

Contact Langer for pricing.

Langer EMV-Technik
www.langer-emv.com

Electromagnetic Compliance Protection (EE TIP #115)

Electromagnetic compatibility (EMC) compliance is one of the last processes before a device may be released to the public. EMC goes hand-in-hand with electromagnetic immunity (EMI), but immunity is only needed for critical devices. With EMC, it is very important to find a good EMC company to deal with. With most circuits, the weak point for EMC is any external leads. By adding a few inexpensive parts, EMC protection can be added and the EMC filtering can be adjusted by changing the values of the parts. In the figure below, the 1 µH inductors act as chokes to block any external voltage spikes above a certain frequency. The 1 nF capacitor also acts as a shock absorber to reduce any sharp voltage spikes. Effectively, this is a second-order filter and the cutoff frequency may be reduced by increasing the inductance and capacitance.

EMC ProtectionEditor’s Note: This EE Tip was written by Fergus Dixon of Sydney, Australia. Dixon, who has written two articles and an essay for Circuit Cellar, runs Electronic System Design, a website set up to promote easy to use and inexpensive development kits. Click here to read his essay “The Future of Open-Source Hardware for Medical Devices.”

Ultra-Compact 50-W DC-DC Converter

CUIThe PQA50-D is an ultra-compact 50-W DC-DC converter that reduces board space and costs in telecommunications, industrial and IT equipment applications. The DC-DC converter family features a 2“ × 1“ (50.8-mm × 25.4-mm) footprint and incorporates six-sided metal shielding for improved electromagnetic compatibility (EMC) performance and efficiency up to 93%.

The single-output isolated DC-DC converter modules feature a 2:1 input range and are available with an 18~36 VDC or 36~75 VDC input voltage range and 3.3-, 5-, 12-, 15-, or 24-VDC output. The series features 1,500-VDC I/O isolation and protections for output over voltage, short circuit, over load, and input under voltage.

The series offers precise voltage regulation, featuring load regulation of ±1% maximum from 10% to 100% load and line regulation of ±0.5% maximum. The PQA50-D converters’ additional features include a –40~85 °C operating temperature range, remote on/off control, and ±10% voltage adjustability.

Pricing for the PQA50-D series starts at $85.12 in 100-unit quantities.

CUI, Inc.
www.cui.com

Six-Channel RS-422 Line Driver/Receiver

ic-HausThe iC-HF provides six RS-422 line drivers for 3-to-5.5-V encoder applications. The device contains reverse polarity protection for a safe sensor-side supply of up to 60 mA.

The iC-HF is pin configurable. A safe external signal sequence at two complementary line driver outputs activates the Encoder Link state. In the Encoder Link state, nine pins are connected from the sensor side to the field side. With this low-impedance bypassing, internal analog sensor signals and digital communication signals (e.g., BiSS, SPI, I²C, etc.) can be accessed at the line driver output pins.

With the integrated Encoder Link function, the line drivers can be deactivated and A/D signals can be directly accessed through the line driver output pins. Conventional sensors can be calibrated or programmed through the usual RS-422 outputs via the Encoder Link function. Extra contacts, pins, control lines, or signals are not needed. For differential RS-422 line driver operation, six differential complementary drivers are implemented.

Each push-pull driver stage can drive up to 65 mA maximum at 5 V and operate at up to a 10-MHz output frequency with RS-422 termination. The driver stages are current limited, short-circuit proof, and over-temperature protected. The current limitation also reduces electromagnetic compatibility (EMC).

The device provides under-voltage detection and on-chip temperature monitoring to switch the driver stages to high impedance on demand. A sensor error signal is combined with the iC-HF error states. When a fault occurs, the open-drain error output NERR is activated. All inputs are CMOS- and TTL-compatible and ESD protected.

The iC-HF’s operating temperatures range from –40°C to 125°C. The device is available in a 5-mm × 5-mm 32-pin QFN package. The design-in process is supported by ready-to-operate demonstration boards including the Encoder Link signal sequence generator.

The iC-HF costs $3.65 in 1,000-unit quantities.

iC-Haus GmbH
www.ichaus.com

Prevent Embedded Design Errors (CC 25th Anniversary Preview)

Attention, electrical engineers and programmers! Our upcoming 25th Anniversary Issue (available in early 2013) isn’t solely a look back at the history of this publication. Sure, we cover a bit of history. But the issue also features design tips, projects, interviews, and essays on topics ranging from user interface (UI) tips for designers to the future of small RAM devices, FPGAs, and 8-bit chips.

Circuit Cellar’s 25th Anniversary issue … coming in early 2013

Circuit Cellar columnist Robert Lacoste is one of the engineers whose essay will focus on present-day design tips. He explains that electrical engineering projects such as mixed-signal designs can be tedious, tricky, and exhausting. In his essay, Lacoste details 25 errors that once made will surely complicate (at best) or ruin (at worst) an embedded design project. Below are some examples and tips.

Thinking about bringing an electronics design to market? Lacoste highlights a common error many designers make.

Error 3: Not Anticipating Regulatory Constraints

Another common error is forgetting to plan for regulatory requirements from day one. Unless you’re working on a prototype that won’t ever leave your lab, there is a high probability that you will need to comply with some regulations. FCC and CE are the most common, but you’ll also find local regulations as well as product-class requirements for a broad range of products, from toys to safety devices to motor-based machines. (Refer to my article, “CE Marking in a Nutshell,” in Circuit Cellar 257 for more information.)

Let’s say you design a wireless gizmo with the U.S. market and later find that your customers want to use it in Europe. This means you lose years of work, as well as profits, because you overlooked your customers’ needs and the regulations in place in different locals.

When designing a wireless gizmo that will be used outside the U.S., having adequate information from the start will help you make good decisions. An example would be selecting a worldwide-enabled band like the ubiquitous 2.4 GHz. Similarly, don’t forget that EMC/ESD regulations require that nearly all inputs and outputs should be protected against surge transients. If you forget this, your beautiful, expensive prototype may not survive its first day at the test lab.

Watch out for errors

Here’s another common error that could derail a project. Lacoste writes:

Error 10: You Order Only One Set of Parts Before PCB Design

I love this one because I’ve done it plenty of times even though I knew the risk.

Let’s say you design your schematic, route your PCB, manufacture or order the PCB, and then order the parts to populate it. But soon thereafter you discover one of the following situations: You find that some of the required parts aren’t available. (Perhaps no distributor has them. Or maybe they’re available but you must make a minimum order of 10,000 parts and wait six months.) You learn the parts are tagged as obsolete by its manufacturer, which may not be known in advance especially if you are a small customer.

If you are serious about efficiency, you won’t have this problem because you’ll order the required parts for your prototypes in advance. But even then you might have the same issue when you need to order components for the first production batch. This one is tricky to solve, but only two solutions work. Either use only very common parts that are widely available from several sources or early on buy enough parts for a couple of years of production. Unfortunately, the latter is the only reasonable option for certain components like LCDs.

Ok, how about one more? You’ll have to check out the Anniversary Issue for the list of the other 22 errors and tips. Lacoste writes:

Error 12: You Forget About Crosstalk Between Digital and Analog Signals

Full analog designs are rare, so you have probably some noisy digital signals around your sensor input or other low-noise analog lines. Of course, you know that you must separate them as much as possible, but you can be sure that you will forget it more than once.

Let’s consider a real-world example. Some years ago, my company designed a high-tech Hi-Fi audio device. It included an on-board I2C bus linking a remote user interface. Do you know what happened? Of course, we got some audible glitches on the loudspeaker every time there was an I2C transfer. We redesigned the PCB—moving tracks and adding plenty of grounded copper pour and vias between sensitive lines and the problem was resolved. Of course we lost some weeks in between. We knew the risk, but underestimated it because nothing is as sensitive as a pair of ears. Check twice and always put guard-grounded planes between sensitive tracks and noisy ones.

Circuit Cellar’s Circuit Cellar 25th Anniversary Issue will be available in early 2013. Stay tuned for more updates on the issue’s content.