Podręcznik Nauczania

Podręcznik Nauczania

EMI / EMC Trainer

ST2206

www.hik-consulting.pl

An ISO 9001 : 2000 company

Learning Material

Ver. 1.1

94, Electronic Complex, Pardesipura

Indore - 452 010 India

Tel : 91-731 4211100

Fax : 91-731-2555643 e mail : [email protected]

Websites: www.caddo.bz

www.scientech.bz

ST2206

www.hik-consulting.pl

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EMI / EMC Trainer

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Table of Contents

Features

Technical Specifications

Electromagnetic Interference

Sources of EMI

Receptors of EMI

Electromagnetic Compatibility and Interference

Other Helpful Guides

Use of Ferrites in EMI Suppression

Tips for Noise Reduction Techniques when Designing with Clocks

Experiments

Experiment 1

To observe the effect of high frequency signals over the low frequency signals

Experiment 2

To identify the sources of electric and magnetic field

Experiment 3

Finding the trace carrying high frequency current

Experiment 4

To observe ferrite suppressing High Frequency signal

Experiment 5

To observe the effects of shielding

Experiment 6

Observe waveforms of high frequency signals using an

Oscilloscope

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Warranty

List of Accessories

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Features

Self contained and ready to use

Gives hands on experience of electromagnetic emission

Helps to diagnose and troubleshoot emission problems

Compact and lightweight

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RoHS Compliance

Scientech Products are RoHS Complied.

RoHS Directive concerns with the restrictive use of Hazardous substances (Pb, Cd, Cr,

Hg, Br compounds) in electric and electronic equipments.

Scientech products are “Lead Free” and “Environment Friendly”.

It is mandatory that service engineers use lead free solder wire and use the soldering irons upto (25 W) that reach a temperature of 450°C at the tip as the melting temperature of the unleaded solder is higher than the leaded solder.

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Crystal frequency

Signal source

Power supply

Dimensions

ST2206 EP probe :

Field

Frequency range

Self indication

Speaker

Output

Sensitivity

Batteries

ST2206 MP probe :

Field

Frequency range

Self indication

Speaker

Output

Sensitivity

Batteries

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Technical Specifications

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20MHz

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625 KHz

+12V, -12V

W269 x H64 x D170

Electric

2MHz … 2GHz

5 Colour LED level bar

Tone pitch proportional to field strength

AC and DC

-10dBm/ (V/m)

1.5×2

Magnetic

1MHz upto 1GHz

5 colour LED level bar

Tone pitch proportional to field strength

AC and DC

- 10dBm/mT

1.5×2

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Electromagnetic Interference

Electromagnetic Interference (EMI) is defined as the influence of unwanted signals on devices and systems, making the operation of the device difficult or impossible. www.hik-consulting.pl

Figure 1

The three elements shown in Figure 1 are used to describe and understand disturbance problems. An electromagnetic signal must have a “Source” or origin. The source then needs a “coupling path” to facilitate the transmission of the disturbance signal to the

“Victim”. If one of these three elements is removed from the system, the disturbance problem is solved. The coupling path between source and victim does not have to be a conducting medium such as an electric conductor or dielectric. It can be coupled through the atmosphere as well. In most instances, the coupling path is a combination of conduction and radiation. One technique that can be used to minimize EMIproblems is to keep the disturbance signals from the source and across the coupling path below a certain level.

EMI is the electronic equivalent of automotive smog and is emitted by any electronic system that has changing voltages and currents.

Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI) are usually caused by the rapid switching action of semiconductors, relays, etc. resulting in undesirable currents and voltages (electronic pollution). These affect the reception of broadcasts and can lead to the malfunctioning of other sensitive electrical and electronic equipment.

Electromagnetic Interference refers to noise spread over the whole electromagnetic spectrum.

EMI can be propagated in two ways; conducted interference along input and output cables; and radiated through direct transmission, capacitive and inductive coupling etc.

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Sources of EMI

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Figure 2

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Figure 3

Natural EMI sources :

Sources those are associated with natural phenomena. They include atmospheric charge/discharge phenomena such as lightening and precipitation static and extra-terrestrial sources including radiation from the sun and galactic sources such as radio stars, galaxies, and other cosmic sources. As shown in the above diagram, all natural sources are classified as broadband, incoherent, radiated, and unintentional.

Man-made EMI sources :

Sources associated with man-made devices such as power lines, auto-ignition, fluorescent lights, etc.

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Broadband EMI :

Electromagnetic conducted and radiated signals whose amplitude variation as a function of frequency extends over a frequency range greater than the bandwidth of the receptor.

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Narrowband EMI :

Electromagnetic conducted and radiated signals whose amplitude variation as a function of frequency extends over a frequency range narrower than the bandwidth of the receptor.

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Coherent broadband signals :

Neighbouring components of the signal (in the frequency domain) has a welldefined amplitude, frequency, and phase relationship.

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Neighbouring components of the signal (in the frequency domain) are random or pseudo-random (bandwidth limited) in phase or amplitude.

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Conducted EMI :

Noise signals transmitted via electrical conduction paths (i.e. wires, ground planes, etc.).

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Radiated EMI :

Electric and magnetic fields transmitted through space from source to receptor.

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Intentional radiating emitters :

Emitters whose primary function depends on radiated emitters. Examples include electronic licensed communication systems. These include communication, navigation, and radar systems.

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Unintentional (incidental) radiating devices :

Devices that radiate radio frequencies but is not considered their primary function.

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Restricted radiating devices :

Devices that intentionally use electromagnetic radiation for purposes other than communication or data transfer. (i.e. garage door operating systems, wireless microphones, etc.)

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Receptors of EMI

Any EMI situation requires not only an emission source but also a receptor. A receptor is also called a “victim” source because it consists of any device, when exposed to conducted or radiated electromagnetic energy from emitting sources, will degrade or malfunction in performance. Many devices can be emission sources and receptors simultaneously. For example, most communication electronic systems can be emission and receptor sources because they contain transmitters and receivers.

Figure 4 shows taxonomy of different receptors that are susceptible to EMI. Similar to the emission source taxonomy, receptors can be divided into natural and man-made receptors. A brief description of each category will be given below. www.hik-consulting.pl

Figure 4

There are many design considerations that need to be taken into account. While it is not the point of this manual to give detail explanations about EMC design techniques, brief descriptions will be given simply for an overview.

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Cable wiring and harnessing is a significant EMI concern. Cables are required to distribute electrical power and transmit electrical signals for the operation of various systems. Since cables are usually routed to accommodate its function, it is often difficult to quantify its environment and it usually varies over both frequency and electric and magnetic field amplitudes. Cables can be EMI radiating sources if they act as radiating antennas, or be susceptible to EMI if they are receiving antennas. Cables can also be coupling paths. In addition, cables are sometimes harnessed together, so interference can also be between two cables that are close in proximity. Therefore, their performance is very difficult to predict. Many specifications classify wiring or cable types into four to six categories but these classifications are generally qualitative in nature.

More quantitative classifications should look at levels of power transmitted, or susceptibility of termination.

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Connectors are contacts that either link or separate two cables or other equipments. There may be anywhere from several to hundreds of individual wire-pins or coaxial sheaths making simultaneous contact via a connector. EMI problems from connectors are usually related to poor contact which may result in arcing, or overheating that leads to arcing.

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Grounding is one of the least understood EMC subjects, despite the fact that it seems straightforward. Improper grounding is the source of many EMI problems. Grounding is necessary to prevent shock hazard, which occurs when a wiring or component insulation in an equipment frame or housing breaks down.

Grounding also protects against lightning damage. Grounding is also necessary to reduce EMI due to electric field flux coupling, magnetic field flux coupling, and common impedance coupling. There are two reasons why grounding is not understood well. One reason is that shock and safety control requirements existed before the electronics and high frequency area, so traditional grounding techniques were developed to satisfy those requirements. A second reason is that sometimes a conflict occurs between requirements for safety grounds and EMI control.

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Different considerations must be taken into account with shielding. Shielding is www.hik-consulting.pl

Usually, the theoretical attenuation offered by materials to electric, magnetic, and electromagnetic waves does not match that achieved in practice. This is because a shielded enclosure or housing is not completely sealed. Any shielding application has some kind of penetrations and apertures like meter windows, cover plates and access cover members, and push buttons. These apertures cause leakage and therefore compromise the integrity of the shielding material.

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The previous design considerations dealt with topics that represent problems between sources and receptors. There are also EMI control techniques that are applied at the component, circuit, and equipment levels. The problem with resistors, inductors, and capacitors is that they do not behave at their stated values, especially at high frequencies due to the effects of parasitic inductance and capacitance. Under certain conditions, their performance degrades at frequencies as low as 1MHz. Inductive devices like transformers, solenoids, and relays produce low-impedance fields that are sources of EMI if they are uncontrolled.

Radio-frequency interference (RFI) is a serious EMI problem today due largely to the large number of radio transmitters that exist. Radio transmitters range from large, high-power transmitters such as broadcast, communications, and radar to small, low-power equipments such as handheld radios and cellular telephones. The problem with radio transmitters is twofold, as equipment can cause interference to nearby radio and television receivers, and equipment can be upset by nearby transmitters. Radio and television receivers can be very vulnerable to RFI pollution from nearby computers. Repetitive digital signals contain harmonics that can extend into the GHz range. This unwanted energy can be radiated through cables and wiring acting as antennas, or conducted through the AC power system. If the levels are high enough, the receivers can be damaged. It was this emissions problem that caused countries around the world to pass EMI regulations. In the U.S., complaints from consumers about interference with television disruption in the 70's drove the FCC to initiate mandatory EMI testing of personal and commercial computers in the 1980's.

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Digital circuits are usually the primary source of emissions, and analog circuits are more vulnerable to RFI than digital circuits. In protecting equipment against

RFI, it is important to start at the circuit level. Filters can be used and sometimes multistage filters are needed. Slots and seams cause the most problem in RFI shielding, so high-quality shields and connectors are needed for adequate RFI protection

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Electrostatic discharge (ESD) is also an EMI problem. An ESD event starts with a very slow buildup of energy, followed by a very rapid breakdown. It is this fast breakdown that causes EMI problems in modern electronic systems. The energy discharge yields EMI frequencies in the hundreds of megahertz. The high speed and frequency of the ESD energy can damage circuits, bounce grounds, and cause upsets through electromagnetic coupling. Good protection against ESD problems starts at the circuit level through the use of filters and www.hik-consulting.pl

ESD cable protection. The length-to-width ratio for grounds should be less than

3 to 1. Thin materials are adequate for shielding and special attention must be paid to slots and penetrations.

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In addition to the design considerations above, there are other EMC issues in the design of embedded systems. One is the compatibility among transmitters that are designed to work together. For example, when every car has forwardpointing smart cruise control radar, and they are either next to each other or coming head-on at each other, the transmitters must be designed that there is not interference. Another problem to consider is what happens when a component is inserted in an integrated system and causes EMI. For example, computer motherboards are designed with empty slots for different cards to be plugged into. In particular, video cards are FCC certified to ensure that they are compatible with whichever motherboard they are plugged into.

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There are also issues concerning EMC when humans are the receptors. A scare that has not yet been proven deals with cellular phone emissions. A source cited that radiation emitted from cellular phones has shown to cause short-term memory loss and lapses in concentration. However, this is not a proven fact yet.

There was also an early brain cancer scare with cell phones that actually led to the FCC limiting the transmitting power of handheld cell phones to 0.3 watts.

Electromagnetic interference (EMI) is increasing as a result of higher clock speeds in today’s PCs and workstations. This radiation, mainly produced by fundamental and low order harmonics, unfortunately coincides and interferes with many popular radio FM bands. This has forced the regulatory agencies to place limits on electromagnetic radiation produced by PCs and any electronic instrumentation that might use clocks and generate emissions

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Electromagnetic Compatibility and Interference

Electronic devices operating normally in their intended environment, without conducting or radiating excessive amounts of electromagnetic energy, or being susceptible to such energy from internal or external sources, are in the state of electromagnetic compatibility, or EMC. Electromagnetic interference, EMI, is radiated or conducted energy that adversely affects circuit performance, and thus disrupts a devices EMC.

Electromagnetic Fields

Radiating electromagnetic waves consist of both an E-field (electric) and an H-field

(magnetic) oscillating at right angles to each other, as illustrated in Figure 5. E-fields are created from voltage sources, such as logic chips or clocks switching between their zero and 5-volt states. H-fields result from current sources, such as motors and transformers. www.hik-consulting.pl

Figure 5

Electromagnetic Interference Analysis

Almost any electrical transitions with sharp edges, such as clocks, data, address and control, produce electromagnetic radiation. As performance requirements increase, clock speeds have also increased. The transition edge, or in engineering terms, the slew rate, has become faster and faster as the need for meeting set up and hold time has become harder to meet. Set up is the time needed for a data pulse to be stable before the rising edge of the clock, and hold time is the time for the data pulse to remain stable after the edge of the clock. Clocks are no longer fed to only one or two devices on circuit boards. Rather, they are being distributed all over the circuit board.

Also, increased memory requirements, and other loads on the clock lines, have significantly contributed to electromagnetic radiation. EMI is linearly proportional to current, the area of the current loop, and with the square of frequency. EMI is defined

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as EMI = kIAf2 where I is the current, A is the loop area, f is the frequency, and k is the constant depending on PCB materials and other factors. There are two types of

EMI radiation: Differential Mode and Common Mode. Current loops formed between traces and the ground plane on PC add-in cards and motherboards cause the

Differential Mode. These loops act as antennas and radiate EMI that may exceed FCC limits. Localized ground noise injected into the PC’s I/O traces and cable causes

Common Mode radiation. Since these cables and traces are long, they act as antennas.

In the past, shielding was the most prevalent method used to decrease EMI. Within the system, the relationship between the various signals can create a potential source of disturbance. A simple way to understand the combinations is to examine the effects of pairs of signals in terms of their common-mode voltage and differential-mode voltage relationships. Although, EM disturbances are caused by current sources, this voltage example is helpful in clarifying definitions and terminology. This simplistic approach will identify a majority of the EM disturbance sources in the circuit. These www.hik-consulting.pl

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The independent voltages V1 and V2.

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The voltage VDM the differential-mode voltage, is the difference voltage between V1 and V2,

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The voltage VCM. VCM is the difference of the voltage between the middle of

V1 and V2 and the reference VREF. The ideal voltage for VREF is zero.

Differential currents flow from V1 to V2. When the connection between V1 and V2 is ideal, which is nearly impossible, common-mode currents do not occur.

Figure 6

The radiation from a circuit can come from two different relationships between two or more current sources, common-mode radiation currents and differential mode

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currents. The differential-mode radiation currents in a circuit are a natural consequence of the physical layout. They occur as a result of separate PCB traces with differing current densities. The resulting phenomena from these currents are a differential-mode H-field radiation. Likewise, common-mode radiated currents are created as a result of losses due to cables and traces of the printed circuit boards.

Common-mode currents create radiated signals that are predominately E-fields. www.hik-consulting.pl

Figure 7

Other Helpful Guides

To combat EMI, designers have also adhered to a series of guides and methods. Here are some of these methods: We highly recommend that solid ground and power planes be used in the design. Partitioned ground and power planes must be avoided. These ground and power partitions may create complex current loops. In this example, the larger the current loops the higher the magnitude of radiation. Routing any channel lines, especially clocks, over a segmented ground plane must be avoided. Place the clock drivers near the center of the PCB rather than at the periphery. A periphery location increases the magnetic dipole moments. For clock traces that are routed on the surface plane, to further reduce EMI, it is better to route parallel ground traces on either side of the clock trace. However, it is even better to place the clock traces in the layer in between Ground and the Vcc plane. Use 4 to 8 mil traces for clock signals since narrow signal traces tend to increase high frequency damping and reduce capacitate coupling between traces. In general, right angles or ‘T’ crosses should be avoided. Right angles increase trace capacitance and also add an impedance discontinuity that effect signal degradation.

Impedance must be matched as closely as possible. Usually cases impedance mismatches cause emissions. Signal integrity mainly depends on impedance

Matching. Do not run long clock traces parallel to each other because they effect crosstalk that contributes to EMI. It is a good idea to make sure that the spacing between traces is at least equal to the trace width.

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As system operating frequencies, data path widths, and output drive requirements increase, guaranteeing EMI compliance is becoming a difficult task for design engineering and manufacturing. As shown in Figure 8 the conventional methods used to meet EMI standards require metal shielding, multi-layer printed circuit boards, special casing, and passive components. As a result, the system’s bill of materials and manufacturing costs increase but no value is added to the product in terms of features and competitiveness. In addition, using conventional methods of reducing system

EMI requires a “trial and error” approach and results in longer time to market. In the worst case, a system must be entirely redesigned in order to satisfy EMI requirements.

When a design is constructed using EMC guide-lines it is possible that the EMI is still to high. Further action can be taken to reduce these signals with shielding (Faraday shielding) around the housing. Shielding will help to reject emission and improve immunity. In the most cases the metal housing of the device will work as a shield. In www.hik-consulting.pl

housing with a conductive coating or place a conductive foil against the cover.

At lower frequencies, only ferromagnetic materials offer the properties needed for shields at a practical thickness. At higher frequencies, decreases in both the shield thickness requirement and the magnetic response of ferromagnetic materials make copper a good alternative. Even the copper layer of a ground plane becomes an effective magnetic shield.

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Figure 8

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Use of Ferrites in EMI Suppression

Introduction :

Ferrites are a class of ceramic ferromagnetic materials that by definition can be magnetized to produce large magnetic flux densities in response to small applied magnetization forces. Originally referred to as "magnetic insulators," ferrites were first used as replacements for laminated and slug iron core materials in low loss inductors intended for use above 100 kilohertz (KHz). At these frequencies, laminated and slug iron are plagued by excessive eddy current losses whereas the high volume resistivity of ferrite cores limit power loss to a fraction of other core materials. Today, ferrites are the core material of choice for modern high density switch mode power supply and pulse transformer design.

Fundamental Properties :

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ferrites are actually well understood magnetic components. Ferrites intended for EMI applications above 30 MHz are mixtures of iron, nickel and zinc oxides that are characterized by high volume resistivity (107 ohm-cm) and moderate initial permeability (100 to 1500).

Figure 9

Ferrites are most frequently used as two terminal circuit elements, or in groups of two terminal elements. The unique high frequency noise suppression performance of ferrites can be traced to their frequency dependent complex impedance, as shown in

Figure 9. At low frequencies (below ~10 MHz), ferrite bead presents a small, predominately inductive impedance of 10 ohms or less. At higher frequencies, the impedance of the bead increases to over 100 ohms, and becomes essentially resistive above 100 MHz. When used as EMI filters, ferrites can thus provide resistive loss to attenuate and dissipate (as minute quantities of heat) high frequency noise while presenting negligible series impedance to lower frequency intended signal components. When properly selected and implemented, ferrites can thus provide significant EMI reduction while remaining "transparent" to normal circuit operation

For high frequency applications, ferrites should be viewed as frequency dependent resistors. Since they are magnetic components that exhibit significant (and useful) loss over a bandwidth of over 100 MHz, ferrites can be characterized as high frequency, current operated, low Q series loss elements. Whereas a purely reactive (i.e., composed only of inductors and capacitors) EMI filter may induce circuit resonances and thus establish additional EMI problem frequencies, lossy ferrites cannot. In fact, ferrites are often used in high frequency amplifier design and power supply design to prevent or significantly reduce unintended high frequency oscillations.

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Ferrite Noise Suppressors :

As shown in Figure 10 below, the Ferrite noise suppressors are beads surrounding the conducting material. www.hik-consulting.pl

Figure 10

Ferrite suppressors add inductance in series with the line. The added impedance is a function of frequency.

Figure 11

Common-mode current signals can cause unwanted radiation. The radiation can be reduced by placing a choke or clamp in the path of the current. The low pass filter or choke is easy to implement. The low pass filter can be designed using an RC combination. If this approach is not feasible, the choke can be constructed by winding wire a few turns around a ferrite core or bead. The choke will act to restrict high frequency dI/dt signals through the conductor. As the frequency in the line increases so does the influence of the choke.

Figure 12

Digital ribbon cables can also present a problem in terms of radiated signal due to common-mode currents. When a ferrite bead is not feasible a ferrite clamp can be used instead. It is important to note that differential-mode currents are not affected by this technique of radiated noise reduction. 3.9

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Tips for Noise Reduction Techniques When Designing with Clocks

If there are Op Amps in the design, terminate unused op-amps in dual and quad packs by grounding the positive input and connecting the negative input to the output.

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Filter all signals leaving a noisy environment and filter all signals entering the board.

Place I/O drivers near where they leave the board.

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Place the crystals flush to board and ground them.

Place the clock at the center of the board, however, if the clock goes off the board, place the clock near the connector.

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Divide the circuits on the board based on their frequency and current switching levels.

Separate digital and analog lines and route the signals away from each other.

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Clock and digital signal lines must be placed as far away as analog input and voltage reference pins.

Clock circuit must be placed away from I/O cables.

Length of sensitive leads such as decoupling capacitors must be as short as possible.

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Use all power and ground pins of an IC.

To cancel mutual coupling, twist noisy lead together.

Place a ground lead between low-level signal leads and noisy leads in the same connector like a ribbon cable.

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Keep high-speed lines short and direct.

Avoid running trace under Crystal.

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Sensitive traces should not be run in parallel with high current, fast switching signals.

Critical traces should be wide, and must be guarded with a ground on each side of the trace.

Better to reduce the EMI at the source :

Two methods to reduce EMI :

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Enclosing the EMI (traditional):

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Additional shielding

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c.

Special coating

Filtering equipment

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At the source (Spread Spectrum):

a.

Choosing the right components

Recommended instruments for experimentation :

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Oscilloscope

2.

Spectrum Analyzer

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Experiment 1

Objective :

To observe the effect of High frequency signals over the low frequency signals.

Interference is main problem when designing a PCB. Circuits working on bread board may not work on PCB.

Therefore, while designing PCB utmost care should be taken not to pass a HF and an

LF tracks near each other, or over each other as PCB material are transparent to emissions.

Procedure :

1.

Connect power supply from ST2509 to switch it ‘On’.

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with the help of Patch cords and

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signal of 625 KHz approximately See figure 13

Also observe the output at tp7. It is a high frequency signal of 20 MHz flowing through the track between tp7 and tp8. See figure 14

4.

Now connect the output of signal source to tp5, which is the nearest test point to the tp7. You can see the 20 MHz signal being superimposed over the low frequency signal. The same effect can be seen at tp9 also. See figure 15

5.

In the same way you can connect the signal source output to tp3 & tp1 and observe that as the distance between high frequency carrying track (tp7 – tp8) and low frequency increases, the interference decreases.

Signal source out put (Low frequency)

Figure 13

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High frequency signal at tp7

Figure 14

Interference of high frequency over low frequency at tp5

Figure 15

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Experiment 2

Objective :

To identify the sources of electric and magnetic field.

Electric fields are generated by presence of voltages and Magnetic fields are produced by presence of currents. Hence one should use both

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EP and MP probe not to miss possible sources of emission.

Procedure :

1.

Connect power supply from ST2509 to switch it ‘On’.

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with the help of Patch cords and

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3.

Adjust Level dial of both

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EP and

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MP probes such as only green LED should be lit by taking the probes away from the board.

Bring the tip of www.hik-consulting.pl

number of lit LEDs indicating the high level of E field emission due to the presence of voltage at 10 pin box type connector.

4.

Now take the

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MP probe near the 10 pin connector and observe that less number of LEDs are lit. The reason being there is no current coming through the connector.

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Experiment 3

Objective :

Finding the trace carrying high frequency current.

Magnetic fields are highly directional. Its direction relates with the direction of current in the conductor of trace.

Procedure :

1.

Connect power supply from ST2509 to switch it ‘On’.

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with the help of Patch cords and

2.

Adjust Level dial of

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MP probe such as only green LED should be lit by taking the probe away from the board.

3.

Bring the probe over the white line between tp1 & tp2 and slide it through out www.hik-consulting.pl

Repeat the same procedure for every white line.

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5.

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The highest number of lit LEDs and highest pitch of sound at tp7 & tp8 indicate that this trace carries the HF current.

When you hold the probe vertically over the trace at any fixed point and turn the probe around in clockwise direction, a direction can be noted in which the detection will be high.

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Check the signals at tp5 & tp7 on both CRO in time domain as well as on

Spectrum Analyzer in frequency domain by connecting the ‘BNC to BNC’ cable to the probe.

Check and observe the magnitude of signal to compare the signal strength on both CRO and Spectrum Analyzer.

Signal at tp5 in time domain

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Figure 16

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Signal at tp5 in frequency domain

Figure 17

Signal at tp7 in time domain

Figure 18

Signal at tp7 in frequency domain

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Figure 19

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Experiment 4

Ferrites are used to reduce HF contents of signal. Ferrites introduce losses for HF signals by converting current to heat.

Objective :

To observe ferrite suppressing HF signal

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4.

5.

6.

Procedure :

1.

Connect power supply from ST2509 to switch it ‘On’.

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with the help of Patch cords and

2.

Adjust Level dial of

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MP probe such as only green LED should be lit by taking the probe away from the board.

Take the probe over the right hand side trace leading to ferrite. www.hik-consulting.pl

Now move the probe to the other side of the ferrite without readjusting the dial.

Observe the LEDs, less number of LEDs are lit indicating that the signal is much weaker after attenuation by ferrite.

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Switch on the buzzer, and compare the sound at both sides of the ferrite.

Also connect ‘BNC to BNC’ cable to the BNC socket of the

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MP probe and observe the signal on CRO as well as on Spectrum Analyzer to see the suppressing of HF signal by ferrite core. ( photograph)

Signal at right hand side of the ferrite in time domain

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Figure 20

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Figure 21

Signal at left hand side of the ferrite in time domain

Figure 22

Figure 23

Signal at left hand side of the ferrite in frequency domain

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Experiment 5

Objective :

To observe the effects of shielding.

Shielding is the conventional way of reducing emission. Conductive materials such as copper, is generally used for shielding.

2.

3.

4.

Procedure :

1.

Repeat experiment number 3 by holding the shielding material in between the probe and the white line for tp7 & tp8.

Slide the probe over the shielding material and observe the number of lit LEDs.

Less number of glowing LEDs demonstrate how shielding reduces emission.

You can observe the emission level over a spectrum analyzer with and without www.hik-consulting.pl

Signal at tp7 without shielding

Figure 24

Signal at tp7 with shielding

Scientech Technologies Pvt. Ltd.

Figure 25

26

ST2206

Experiment 6

Objective :

Observe waveforms of high frequency signals using an oscilloscope.

The HF signals are difficult to observe on oscilloscope as the conventional probe may load the signal and distort the signal. Some observations say that the circuit functions properly when probe is connected to it.

That’s why it is recommended to use tools that do not load/ affect the signal you are measuring. Hence the

ST2206

EP probe is very useful tool as it does not physically touch your circuit.

2.

3.

4.

5.

Procedure :

1.

6.

7.

8.

Connect power supply from ST2509 to

ST2206

with the help of Patch cords and switch it ‘On’. www.hik-consulting.pl

Adjust level knob of

ST2206

EP probe at min. position such that no LED glows.

Switch ‘On’ the power supply.

Connect

ST2206

EP probe to 100MHz Oscilloscope.

Place the tip of probe over the ferrite; observe the waveform of signal on an oscilloscope.

Connect a regular scope probe to ferrite, and observe the waveform.

A conventional probe loads the circuit and alters it. Hence

ST2206

EP probe is of great use as it does not touch the circuit and load it.

Similarly, you can observe the current waveform on an oscilloscope by using

ST2206

MP probe.

Example :

Observe the waveform of composite color TV signal with the help of these probes, you will see them like never before.

Figure 26

Signal at right hand side of ferrite Signal at left hand side of ferrite

Scientech Technologies Pvt. Ltd.

27

1.

2.

3.

4.

5.

ST2206

1.

Warranty

We guarantee this product against all manufacturing defects for 24 months from the date of sale by us or through our dealers. Consumables like dry cell etc. are not covered under warranty.

2.

The guarantee will become void, if

a)

The product is not operated as per the instruction given in the Learning

Material

The agreed payment terms and other conditions of sale are not followed.

b) c) d)

The customer resells the instrument to another party.

Any attempt is made to service and modify the instrument.

3.

The non-working of the product is to be communicated to us immediately giving www.hik-consulting.pl

type, serial number of the product and date of purchase etc.

4.

The repair work will be carried out, provided the product is dispatched securely packed and insured. The transportation charges shall be borne by the customer.

List of Accessories

Patch cord 16"......................................................................................... 3 Nos.

Shielding Material................................................................................... 1 No.

BNC – BNC cable ..................................................................................1 No.

Power Supply ST2509 ............................................................................1 No.

Learning Material (CD) ..........................................................................1 No.

Scientech Technologies Pvt. Ltd.

28

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