Course Introduction Purpose This course discusses techniques for analyzing and eliminating noise in microcontroller (MCU) and microprocessor (MPU) based embedded systems. Objectives • Learn what EMI is and why it should be minimized. • Understand decoupling capacitors and how they should be used. • Find out how to measure noise currents and near-field emissions. • Discover a way to evaluate the effectiveness of EMI prevention measures. Content 16 pages Learning Time 30 minutes Welcome to the “EMI Analysis and Countermeasures – Part 1” course. To benefit the most from this course, you should be familiar with microcomputers (microcontrollers [MCUs] and microprocessors [MPUs]) and also understand the basic issues related to the design and development of embedded control systems. Because the subject matter is somewhat technical, you should have a good knowledge of electrical theory and electromagnetic waves. This course first briefly reviews what EMI is and why it’s important to take measures to minimize EMI in embedded systems. The course then describes how to use decoupling capacitors and other EMI reduction methods, and explains ways to measure noise currents and noise emissions. Finally, the course shows a technique for evaluating the effectiveness of EMI reduction techniques. The “Part 2” course in this series explores design factors for reducing noise (chip packaging, optimized capacitors, and component placement) and describes how to maximize the results of noise countermeasures. The “Part 3” course covers several advanced, system-level tests as well as IC-level EMI analysis methods that can be used to select the best components for an embedded system. Finally, the “Part 4” course discusses ways to measure the emissions caused by common-mode voltage and describes a way to reduce noise from the supply lines on a printed circuit board and in an IC package.

Design Goal: Reduce EMI EMI reduction is a goal shared by both the semiconductor experts who design MPUs and other LSI devices, and by the engineers who apply those chips in embedded systems - It includes techniques for decreasing the noise generated by a specific system, circuit, or device that might cause problems in other electronic systems, circuits, and devices RADIATION NOISE Let’s begin by stating what perhaps should be obvious. Reducing the problems caused by EMI in a device or circuit is an important goal not only of the semiconductor experts who design MCUs, MPUs and other LSI devices but also of the engineers who apply those devices in embedded systems. Various techniques can be used to reduce the level of EMI produced by internal and external noise sources so that it doesn’t cause problems in other systems, circuits and devices. The methods described in this course are representative of proven good design approaches.

Explanation of Terms Anechoic chamber A room designed to block radiation from the outside and to minimize reflections off the room’s walls, ceiling, and floor Balun A passive electronic device that converts between balanced and unbalanced electrical signals CISPR 25 International Special Committee on Radio Interference (CISPR) publication 25: “Limits and methods of measuring radio disturbance characteristics for the protection of receivers on board vehicles.” CISPR is a sub-committee of the International Electrotechnical Commission (IEC). Core A microcontroller chip is composed of a core, I/O ports, and power supply circuitry. The core consists of the CPU, ROM, RAM, and blocks implementing timers, communication, and analog functions. ECU Electronic Control Unit EMI Electromagnetic Interference Harness Cables (wires) connecting a board and power supply or connecting one unit in a system to another In the discussions that follow, you may encounter electronic design and testing terms with which you are not familiar. The definitions of various terms can be seen on this page. LISN Line Impedance Stabilization Network Power supply Two power supplies are applied to the LSI: Vcc and Vss. The core power supply internal to the LSI is VCL (internal step-down). The Vss-based power supply routed through the LSI is VSL. TEM Cell Transverse Electromagnetic Cell WBFC Workbench Faraday Cage

Why Is EMI Reduction Important? Example: In an automobile, noise radiated and conducted from the ECU to the radio and its antenna can disturb FM reception FM station FM band radio signals Radiated emissions from ECU Antenna Conducted emissions from power wiring Here is a typical application that illustrates why it’s important that embedded systems be designed to generate low levels of EMI. It shows one effect of the noise generated by the electronics in a car — a real-world situation. An FM radio is standard equipment in most automobiles, and unclear reception is a source of annoyance for driver and passengers. One possible cause of bad reception is the pickup of EMI noise by the radio. Such noise might be produced by the automobile’s many onboard microprocessor units, whether they are in the ECU or in any of the vehicle’s many other embedded systems. EMI can be conducted to the radio through the power wiring that connects those devices and the radio to the car’s battery. It can also be radiated to the radio antenna either directly from those systems or from their signal wires. This diagram shows both possibilities. The FM reception problems caused by in-vehicle noise sources become most severe when radio signals are weak, as is often the case when driving in mountainous terrain. Automakers work to minimize EMI throughout their vehicles in order to maximize customer satisfaction, among other reasons, including occupant safety. FM Radio Battery ECU Wiring harness (power line) MPU 4

Use a Decoupling Capacitor One way to reduce EMI is to minimize rapid variations in the current that the main power source has to deliver to the MPU or other LSI device By using a decoupling capacitor (Cdc) to provide the fluctuations of the current drawn by the MPU, the current drawn from the power supply will be more stable and, thus, generate less EMI C = A + B Chip Module Package CPG Measuring point (VDE method) A C B Decoupling capacitor (Cdc) Power supply Vcc* current Vss* current (measured by 1Ω resistor) One of the most basic and effective ways to reduce EMI noise in a system is to use a decoupling capacitor, sometimes also called a bypass capacitor. Installed on the circuit board and connected between a signal trace and ground, it helps filter out noise. Let’s look at how this is done. The operation of MPUs and other digital LSI devices is synchronized with a clock, causing the chip to draw Vss current cyclically. For example, the top trace of the scope photo on the right shows the rapid repetitive variations (AC components) in the current drawn by a device that’s running on a 4MHz clock. The circuit diagram on the left shows currents A, B, and C, where C (the Vss current) equals A + B. If the circuit doesn’t have a decoupling capacitor, current B is zero, so all of the Vss current, including the fluctuations, must come from the main power supply. Those fluctuations are a source of EMI, so they must be minimized. This can be accomplished by adding a decoupling capacitor next to the chip to accumulate energy from and release energy into the power wiring. If the capacitor is sufficiently large, it can provide all or most of the AC part of the Vss current, in which case the main power supply usually has to provide only the DC part of the Vss current. To minimize the AC components drawn from the main supply, the impedance of the decoupling capacitor must be much lower than the impedance of the main power supply loop — where both impedances are measured at the primary frequencies contained in the variations of the Vss current. Thus, as part of the process of selecting the best decoupling capacitor for a system design, design engineers must study the frequency characteristics of the Vss signal, then apply that data to the impedance-versus-frequency characteristics of different types and sizes of capacitors. Main clock 5

Minimize Inductance of Cdc Wires Decoupling capacitor Power supply The external decoupling capacitor (Cdc1) supplies the fast transients in the Vss current flowing into the chip; the main power supply charges this decoupling capacitor gradually Current variations flowing in wiring inductances can produce unwanted induced voltages (V = L x di/dt) Lowering the inductances (Lb, Lbg) of the wiring to the external decoupling capacitor reduces its impedance, enabling it to achieve better EMI suppression On-chip decoupling capacitors (Cchip, etc.) are very effective at suppressing EMI, even if their capacitance is small. 1 2 Lb, Lbg = 10nH In the circuit diagram shown here, the CPU core of the MPU chip has been modeled to include parasitic inductances, capacitances, and resistances. The external decoupling capacitor on the circuit board and its connecting traces are represented by a capacitor (Cdc1, red circle), resistor (R8), and two inductors (Lb and Lbg). The main power supply that gradually charges the decoupling capacitor is represented by two parallel paths, one containing a battery and resistor and the other containing a capacitor and resistor. The long wires from the main power supply are represented by two 50nH inductors (La and Lag.) A SPICE simulation was performed to evaluate circuit behavior with respect to electrical noise. The graphs show measured data for the values shown in the diagram. Because wiring inductances generate induced voltages when the current flowing through them changes rapidly (V = L x di/dt), the inductances in the traces to the decoupling capacitor are important. For this simulation, Cdc1 was 0.05µF (50,000pF) and Lb and Lbg were each 10nH. The upper test result shows current in mA versus time in nanoseconds. The green curve is current A from the main power supply; the pink curve is current B from the decoupling capacitor; and the purple curve is the total current, C. The middle test result shows voltage in mV vs. time in nanoseconds. The blue curve is voltage Vn1g, measured at point 1, going into the chip. The red curve is voltage Vn1, which is measured at point 2 but offset here by 4.9V, so the two graphs can be viewed together. As can be seen, both waveforms have considerable undershoot and overshoot. The bottom test result plots levels in volts or amperes vs. a logarithmic scale of frequency extending from 3MHz to 1GHz. The red portions of the spectrum lines show the spectrum of Vn1, which has a fundamental frequency of approximately 12MHz, harmonics at multiples of 12MHz, and sub-harmonics that begin at about 6MHz. Notice that the harmonics are significant out to about 1GHz. Those high frequencies generate electromagnetic noise. The gray portions of the spectrum lines show the spectrum of current A from the main power supply. Its energy at high frequencies is negligible due to the use of the decoupling capacitor. Decoupling capacitors can be integrated into the MPU. They are very effective at suppressing EMI, even if they’re small. An example is Cchip, highlighted by the blue circle. Internal bypass capacitors will be discussed further on the next page.

Different Design Approaches EMI decreases when . . . - the traces to the external decoupling capacitor are redesigned, reducing the values of Lb and Lbg from 10nH to 1nH - a 3,000pF internal decoupling capacitor is built into the chip Lb and Lbg decreased to 1nH On-chip capacitor = 3,000pF This page provides more details on ways to achieve reductions in EMI. The scope photos on the left show the behavior of the same circuit previously described, except that the traces to the decoupling capacitor were redesigned to reduce inductances Lb and Lbg from 10nH to 1nH. The top graph shows that the overall current (C [= Vss]) does not change. However, the current from the main power supply (A) changes much more slowly than before because the current from the decoupling capacitor (B) changes much more quickly to make up the difference. The reduced impedance of the decoupling capacitor and its wiring traces allows high-frequency current to flow more readily. The middle graph shows that the slower variation in the current from the main power supply eliminates the overshoot and undershoot of voltages Vn1 and Vn1g. The reason for this is that the current from the main power supply has to pass through the relatively large inductors La and Lag. Since most of the rapidly changing current no longer flows through the wires from the main power supply, the di/dt in those wires is much smaller and so are the induced voltages. The bottom graph shows that the spectrum for the voltage and current have both been greatly reduced. Harmonics have now been almost entirely eliminated for frequencies above about 300MHz. The graphs on the right show how well EMI can be reduced when a bypass capacitor is built directly into the chip. In this case, the internal capacitor (Cchip) is only about 3,000pF, much smaller than the external 50,000pF decoupling capacitor. Yet it is very effective in reducing EMI because the package inductances are eliminated and the on-chip inductances are very small. The scope traces show that the current from the main power supply changes relatively slowly (top), and the resulting voltage waveforms don’t have any undershoot or overshoot at all (middle). Moreover, the voltage and current spectra have few components beyond 200MHz (bottom).

Measuring Noise Current Noise current can be evaluated quantitatively (using the VDE method [1Ω], etc.) Efforts to reduce EMI can be evaluated by comparing circuit performance with and without various decoupling capacitors Vcc Vss VDE method measuring point LSI Chip R (1Ω) The noise characteristics of an MPU or other LSI device can be evaluated using the VDE method (IEC61967-4) to measure the noise current. This is done by inserting a special probe between the circuit-under-test and ground, as illustrated in the photograph and the diagram to the right. The circuit diagram below the photo shows that a 1-ohm resistor (R) in the probe is connected to a 49-ohm resistor and a coaxial cable that goes to an RF spectrum analyzer. The high-frequency components in the current that passes through the 1-ohm resistor are converted into voltages and measured by the spectrum analyzer. The low impedance of the probe doesn’t significantly alter the noise current. The ability to qualitatively evaluate the power supply current noise makes it possible to make improvements in MPUs and other LSI devices by revising the chip design. For example, decoupling capacitors (such as the ones highlighted by the green circles) can be added or changed and the resulting effects on EMI can be measured and analyzed. VDE Measurement Method Vcc IC Spectrum Analyzer 49Ω in R=1Ω 50Ω

Measuring Near-field Emissions Probe with sensor coil EMV-200 Details of EMV-200: • Sensor coil (magnetic- field sensor) is at the tip of a probe mounted on a robotic arm that moves with precision in three dimensions. • Sensor coil is directional, so the probe rotates to accurately detect magnetic fields generated by noise currents, as the arm moves in a pattern close above the board without making contact. • Tester accurately maps the magnitude of the circuit’s magnetic-field emissions at a specific measurement frequency. Various types of test equipment can be used to measure the EMI produced by a chip and its support components. This page shows a special test solution that Renesas has developed for visualizing and measuring near-field (NF) electromagnetic emissions from MPUs and other products. The automated system — the EMV-200 shown in the top-left photo — is used in a shielded enclosure (bottom-left photo) that eliminates external sources of noise emissions. This device mounts a magnetic-field sensor coil on the bottom of a probe at the end of a precision robotic arm that moves in three dimensions (top-right photo). Because the response of the coil to magnetic fields is directional, the probe can be rotated around its vertical axis, as shown in the diagram, to ensure that the maximum field strength of the emissions from the chip are measured. Test engineers program the probe to move in a predetermined x-y pattern near but not on the surface of the circuit board. During a test, the semiconductor device is powered up and runs specified programs while the EMV-200 moves the probe systematically to accurately map — at a specific frequency – the magnitude of the electromagnetic field emissions that are produced by the chip and other components on the circuit board. Shielded room

Noise-current Measurement — 1 VDE method (IEC 61967-4) and NF-probe analysis (at 80MHz) Pitch: 2mm Height above board: 5mm Scanned Area The previous discussion explained two ways that an MPU can be evaluated: by putting the device on a circuit board and then measuring the board with a VDE probe attached to a spectrum analyzer, and by using a near-field mapping machine. In the example on this page and the two pages that follow, both of these methods were used to measure the effect of adding decoupling capacitors. The photo on the left shows the chip under test, an SH7055RF RISC MPU, with locations for external decoupling capacitors highlighted. The plots in the middle of the page show the behavior of the circuit board without decoupling capacitors, while those on the right show the behavior when decoupling capacitors were added. The field maps in the upper row reveal that the decoupling capacitors act to confine the magnetic fields inside a geometrical region demarcated by the locations of those capacitors. The VDE test results in the bottom row are spectrum analyzer frequency displays. They reveal that the addition of decoupling capacitors has caused the 80MHz fundamental frequency component to drop by 12dB (from 58dB to 46dB). The data also show a substantial drop in emissions at frequencies below 80MHz. 58dB 46dB MPU: SH7055RF 40MHz (10MHz x 4) program execute Vcc = 3.3V, PVcc = 5.0V FM FM Decoupling capacitors Without decoupling capacitors With decoupling capacitors

Noise-current Measurement — 2 VDE method (IEC 61967-4) and NF-probe analysis (at 80MHz) Pitch: 2mm Height above board: 5mm Scanned Area In another experiment, the LSI was changed to an SH7055SF, an MPU that includes an internal step-down circuit. Also, VCL capacitors were mounted on the circuit board. Measurements were made without decoupling capacitors, and then again after decoupling capacitors were added to the board. The data in the middle of the page show that the VCL capacitors alone produced a 16dB reduction in the noise level at the 80MHz fundamental frequency, reducing it from 58dB to 42dB. The data on the right show that by adding decoupling capacitors to the board, the noise at that frequency was reduced even further, to 24dB. Again, the decoupling capacitors confined the magnetic fields to a smaller area. 58dB 46dB 42dB MPU: SH7055SF 40MHz (10MHz x 4) program execute Vcc = 3.3V, PVcc = 5.0V 24dB FM FM VCL capacitors Decoupling capacitors Without decoupling capacitors With decoupling capacitors

Noise-current Measurement — 3 VDE method (IEC 61967-4) and NF-probe Analysis (at 80MHz) Pitch: 2mm Height above board: 5mm Scanned Area Here is the same experiment described on the previous page, but performed with a different chip, in this case an SH7058FCC MPU. The data show that many of the noise-frequency spikes have disappeared. Again, notice that the addition of the decoupling capacitors causes a reduction in noise at the lower frequencies. 58dB 46dB MPU: SH7058FCC 80MHz (10MHz x 8) program execute Vcc = 3.3V, PVcc = 5.0V 20dB 28dB 22 FM FM VCL capacitors With VCL capacitors, but without decoupling capacitors With VCL capacitors and decoupling capacitors Decoupling capacitors

Evaluating Supply Decoupling Area under device showing pads for decoupling capacitors Typical decoupling capacitor Power supply connections Current measurement points (Vcc, PVcc, Vss) Pads for inductors (ferrite beads) Let’s look now at a special circuit board used for evaluating the effectiveness of power supply decoupling capacitors. Recall that by decoupling the voltage supply from the chip receiving the power, it’s possible to avoid the rapid voltage variations on the supply line that may result in EMI noise. On this evaluation board, the power supply connects to the pads on the right, and the supply traces on the board go the device on the left. The top side of the circuit board, shown in the photo on the left, contains the MPU or other device and Vcc, PVcc, and Vss connectors for monitoring voltages and noise. The bottom of the board, shown in the photo on the right, provides pads for attaching inductors (ferrite beads) and — closer to the chip — an area containing pads for mounting decoupling capacitors. The top photo shows this area in greater detail. Top of evaluation board Bottom of evaluation board

12 bypass capacitors added Evaluation Example Near-field tests* using the evaluation board allow comparisons of levels of RF current in the power supply lines * MPU: SH7055R (40MHz) Measurement frequency: 80MHz No filter components The evaluation board allows the EMV-200 near-field measuring system to be used to generate data for visualizing how well various numbers, types and arrangements of filter components reduce noise. Here, the power-line traces and chip region are highlighted in the middle row of figures, which show the results of scans that mapped the electromagnetic fields. The bottom row of illustrations shows three-dimensional versions of each mapping scan. The middle and bottom figures on the left show the behavior of an SH7055R circuit board without filter components — no decoupling capacitors or ferrite bead. As expected, the field levels are relatively high in the power-line region of the board. The corresponding figures in the middle of the page show how the field levels in that area are reduced when decoupling capacitors are added to the circuit board. The two field-magnitude illustrations on the right show that an additional reduction in field levels was achieved by adding a ferrite bead to the board. Reducing noise on a particular circuit board using the techniques discussed in this course provides benefits not only for that board, but also for the entire embedded system. That’s because the same power supply lines are often shared by multiple subsystems. 12 bypass capacitors added Ferrite bead + 12 caps

Supply Decoupling Test Results Using a ferrite bead and multiple decoupling capacitors is an effective way to reduce EMI Ferrite bead Decoupling capacitors Power plane Ground plane (no slit) Slit (moat) Typical Circuit Board Example 70 f = 80MHz 60 Capacitors added 50 Noise Current (dBµV) 40 30 -20dB Vcc GND Capacitor I/O current Core current The graphic in the upper left shows a recommended design for the area containing the semiconductor device mounted on a multilayer circuit board. The power supply voltage connects to the device and other components via a power plane, rather than wiring traces. That plane can be separated from the chip by a moat bridged by an inductor — specifically, a ferrite bead. Inside the moat, multiple decoupling capacitors, each of which are connected to the board’s ground plane, are placed in parallel near active circuit components to filter out noise. The block diagram below the illustration explains this design. Be aware that many circuit boards obtain adequate performance using just the decoupling capacitors, without the moat and ferrite bead. The blue line of the graph shows how the noise level might decrease as more capacitors are added. In the typical example tested, the level dropped from approximately 58dB when the board had no capacitors installed to 38dB when 12 capacitors were used. If a ferrite bead is inserted into the connection between power plane and the chip, that forms a low-pass L-C filter with the decoupling capacitors. To obtain the data in the green line of the graph, a moat was cut in the power plane and a ferrite bead installed on the circuit board. Again, the test results reveal that the combination of the ferrite bead and bypass capacitors implemented very effective EMI suppression. In this example, the noise level was reduced by 40dB. 20 Target level Capacitors + ferrite bead 10 2 4 6 8 10 12 14 16 18 20 Number of Decoupling Capacitors

Course Summary • Importance of EMI reduction • Decoupling capacitors • EMI measurements • Evaluating EMI reduction techniques This concludes the “EMI Analysis and Countermeasures in Embedded Systems – Part 1” course. In this course, you reviewed the importance of minimizing EMI in embedded systems, then learned about design issues associated with the use of decoupling capacitors. You also learned about ways to measure noise currents and electromagnetic emissions, and saw how to evaluate the effectiveness of power supply decoupling techniques for reducing EMI. We now encourage you to take the other courses in this series, which cover various aspects of noise analysis and reduction. Renesas applies all of the various techniques discussed to achieve excellent EMC performance in the MPUs, MCUs, and other LSI products we produce. Many of these techniques might also prove beneficial to your system designs. Thank you for your interest in Renesas microcomputers. The Renesas Interactive website offers many other free resources, such as courses on various aspects of microcomputers and embedded system design. There are also VirtuaLab setups that you can use to evaluate and experiment with Renesas microcomputers and support tools anywhere/anytime from your PC, without having to buy components and wait for delivery. Please take advantage of these resources and visit us often. For more information about specific semiconductor devices as well as related support products and documentation, please visit the Renesas website. For more information on specific devices and related support products and material, please visit our Web site: http://america.renesas.com