In the past few years, the number of mobile devices such as smart phones, tablets, and wearable devices has increased significantly. At the same time, wireless communication has increased due to higher data rates. Will more and more wireless devices increase EMC problems? Can today's industry meet the EMC requirements prepared for us by the Internet of Things?
If more devices must interact with each other and their EMC quality remains at the current level, then from a statistical point of view, this will lead to more EMC problems. In addition, even if the conformance test has been passed, the equipment may not be compatible in practice. For example, suppose that electronic equipment has passed the emission compliance tests of IEC 61000-6-3 and IEC 61000-6-4. Contrary to testing, in practice, electronic devices may be located near metal objects (such as housings). This may cause field coupling, which in turn leads to a higher emission than in the test. In this case, the size of the metal object is essential. This field may excite standing waves suitable for the size of metal objects, and then cause additional emission.
This means that in the future, there will be not only wireless transmission problems, but also equipment radiation problems.
Stricter equipment standards may not solve this compatibility problem.
The above example shows that current conformance tests usually do not consider any field coupling mechanism. The field coupling mechanism may give rise to some useful ideas on how to solve the problem.
It remains to be seen whether the measurement principles stipulated in the current standard are sufficient or whether new measurement principles need to be developed.
In addition, the EMC standard of the IC (IEC 61967 and IEC 62132) New requirements have emerged in the field. In the future, specific IC EMC parameters will be required as input values for EMC development tools/PCB simulation programs. It is wise to obtain these EMC parameters from measurements in accordance with IC EMC standards. Unfortunately, the current standard measurement results are not enough to achieve this goal.
This program will become more important in future IC development.
This is why consideration should be given to adapting standard measurement test methods to this task. The following will illustrate the IC by taking conduction emission as an example.
The interference suppression strategies currently used in electronic development have encountered their limitations. Until the first development sample is completed, the IC as a potential source of emissions will not be considered a troublemaker. Developers encounter them when taking interference suppression measures on devices or PCBs. Near-field probes are used to locate radio frequency sources in electronic devices. These do not identify the IC itself as a source of interference, but instead feed the IC into the PCB traces of the interference current and interference voltage. The electronic equipment will then be modified using additional components, copper foil, or other methods. Last but not least, EMC measurements are performed to confirm whether the interference suppression measures taken after the PCB is redesigned are successful.
This method is very time-consuming and expensive. A big problem here is that selective EMC measures cannot be taken until the first functional development sample is completed. When it's too late, gain insights that are critical to EMC. The results of EMC testing are not considered when making important decisions during the development process. The problem is almost inevitable, because the EMC test results were obtained at such a relatively late point in time.
However, the industry needs faster and more efficient development that complies with EMC. This can only be achieved by adopting a completely new approach. This must start early in the development process and delve into the chain of action of emissions. Only the knowledge of actual emission sources can allow developers to follow this path. Once the IC is more accurately described as a potential radiation source, appropriate measures can be taken earlier and more effectively to stabilize the EMC of the entire equipment.
Appropriate EMC parameters are a prerequisite and are therefore highly required. They must describe the EMC problem area of the IC for practical use in industry. This means that they must be suitable for the development of PCBs that meet EMC requirements. In addition, the EMC parameters of the IC must be linked to actual measures and strategies.
This method should define electronic development in accordance with EMC. Due to the extreme miniaturization, today's equipment development field is more sensitive to electromagnetic interference. Equipment manufacturers are increasing their efforts to solve these problems to suppress interference in the equipment and meet corresponding standards.
The problem described in the example above makes the situation worse. An important requirement of the Internet of Things is that devices operate normally and reliably in their environment.
It remains to be seen to what extent equipment manufacturers can continue to grasp the EMC situation that has deteriorated due to miniaturization and suppress interference in equipment by spending more time and money on this work. Development that meets EMC requirements will account for an increasing share of equipment development costs. It is doubtful whether this goal can be fully achieved. This problem can be alleviated by providing better EMC parameters in the field of IC research and IC development in the future. However, this means that more time and money must also be spent here. Of course, this is related to wireless devices. German industry has begun to cope with this increasing pressure.
The company now cooperates with EMC consultants to use new EMC technologies to solve EMC-related problems in the development of equipment and complex systems from the beginning of the development process.
Main part
Due to the operation of internal functions, the IC generates radio frequency voltage, current, and field. Different physical mechanisms are responsible for these entering the cable harness in the form of emission or entering the surrounding open space in the form of radiation. The IC may have the following effects：
Conductive: Transmit RF current and voltage to the PCB trace through the IC pin，
Capacitance/inductance: emits E and H near field from the connection of the chip or IC，
Radiation: Directly emits electromagnetic waves. For ICS with very high clock frequencies in practice, direct transmission is usually only in the gigahertz range, which is essential.
The following sections describeItems 1 and 2: Conductive, capacitive, and inductive effects in PCB.
Emissions follow a closed loop. The driving RF current and RF voltage sources are located inside the IC. They drive RF into PCB traces through junction wires, lead frames, and pins, where current generates a near-magnetic field and voltage generates a near-electric field. If the PCB traces are freely positioned in space, the near-field of the electric and magnetic fields will be established undisturbed. These fields are similar to the E-field and H-field of the antenna. The electric field is closely coupled to the magnetic field through the antenna element, its current and voltage. This electric field mode leads to the emission of electromagnetic waves. The PCB trace acts as a transmission antenna.
However, the situation on the PCB is usually very different. The PCB contains a metal surface. These metal surfaces usually extend to the entire PCB and have a ground or power supply voltage potential. The gap between these metal surfaces and PCB traces is usually less than 1 mm. These grounding surfaces will affect the distribution of the electromagnetic field of the trace. Taking a loop antenna as an example, this effect can be best described. If placed freely in space, the loop antenna can emit electromagnetic radiation. If the loop antenna is placed on the ground, this will prevent the emission of electromagnetic radiation. This is because the corresponding conductive metal surface will block the magnetic field when the loop is opened, which is the cause of the current/field displacement effect (skin effect). The loop antenna's magnetic field is no longer established around the antenna and actually no longer exists. Therefore, the radiation emission of the loop antenna is greatly reduced (Figure 2).
。 When the magnetic field is blocked, the near-field of the loop antenna can stimulate the metal plate's radiation emission (other radiation characteristics). If the gap between the loop antenna and the metal plate is zero, the H-field is also zero.
The PCB traces react in exactly the same way. Once the ground surface in the PCB is large enough, direct radiation from the traces can be prevented. Before a certain distance from the ground, the launch of the trace will not increase. The distance required depends on the length of the trace. Practical experience has shown that the gap must be > 0.5cm to cause any effective emission (frequency range 10 cm.
This means that the PCB is discharged in other ways, that is, through its near field.
These near-fields cause emission by interacting with metal parts (Vdd/Vss surfaces, large metal parts, cables and lines, metal structural parts).
The relationship between IC voltage and emission
What we refer to below is PCB routing. The traces inside the IC follow the same principle. Therefore, the declaration of PCB traces can be transferred to the traces inside the IC. The pin voltage of the PCB trace or the internal trace of the IC will establish an electric field around the trace (Figure 1). Most field lines lead to the GND surface of the PCB. Only a few field lines leave the PCB vertically upward and penetrate into the open space. The closer the trace is to the edge of the GND system, the more field lines will pass through the space.
These field lines (excitation field lines) leave the GND system of the PCB and transmit displacement current through space, thereby stimulating the entire metal system (PCB with cables and metal structural components) to produce electrical vibration (Figure 3).
Standing waves on metal systems may cause emissions.
The electrical excitation field can reach the metal parts (cables, structural parts, shielding plates) located on the opposite side of the PCB.，Figure 4), and these components can be excited by the transferred displacement current to produce electrical vibration.
The relationship between IC current and emission
The current loop of the IC can be located inside the chip or formed by the pins of the IC. These loops pass through the grounding system of PCBs, pins, lead frames, welding wires, and chips. For example, this type of loop can be formed through the Vdd or Vss pin. The Vdd/Vss loop penetrating to the outside may be much larger than the loop located inside the chip. A larger outer ring can produce a stronger magnetic field, which is usually the cause of the highest emissions.
What we refer to below is PCB routing. The traces inside the IC follow the same principle.
Therefore, the declaration of PCB traces can be transferred to the traces inside the IC.
The pin current flowing into the PCB trace will establish a magnetic field H2 (Figure 5). The return pin current also generates a magnetic field H1 in the GND system (Figure 6). Suppose the PCB ground is a metal surface, which extends over the entire PCB. The trace is very close to the ground and usually only produces insignificant emissions, as in the loop antenna example above. The field H1 of the return current induces the inductive voltage U Err。 On the GND plane (metal surface) of the PCB. This voltage drives the cable and the structural components connected to it, such as the antenna. Therefore, cables and structural components emit electromagnetic waves.
The magnetic field of the trace H2 (Figure 5) Will not produce any radiation in the open space. This is because the trace is close to the ground plane, similar to the loop antenna example above, thereby preventing radiation. There is another chain of interaction that causes the emission of magnetic field radiation. This is similar to the one described above for field H1. For this, metal parts must be inserted into area H2. If the magnetic field surrounds the metal part, the excitation voltage is induced there only by mutual induction. The excitation voltage stimulates the metal part to act as an antenna. The metal part emits electromagnetic waves. Take the steering column, metal pillar or cable near the PCB in the automobile as an example.
EMC parameters of IC pins
IC pin current and IC pin voltage are the EMC parameters related to IC pin. The electrical near field and magnetic near field of the IC are the field-related EMC parameters of the IC. All four parameters of the IC (u, i, E, and H) must be tested by suitable measuring equipment.
The electrical near field of the PCB trace is proportional to the pin voltage, and the magnetic field near field of the PCB conductor loop is proportional to the pin current of the IC. The pin current and pin voltage depend on the load that the pin bears through the connected PCB trace.
The IC parameters must use the values of the conditions that produce the highest pin voltage and the highest pin current.
The current and voltage of the trace depend on the driving voltage in the IC and the impedance of the PCB trace load.
If the pin is operating under short-circuit conditions, the maximum possible pin current is measured. If the pin is operating under no-load conditions (open circuit), the maximum possible pin voltage is measured. Therefore, the maximum possible value has been determined, and all values in actual operation (determined in a large number of measurements on different PCBs) are equal or smaller.
Under special circumstances, the PCB traces have the highest voltage and electrical near field under open circuit conditions. Then the emission potential is greatest.
The corresponding EMC parameter of the IC is its open circuit voltage Urise(F).
The near field of the magnetic field is proportional to the current flowing through the trace. The current depends on the driving voltage of the IC and the load of the trace. Under special circumstances, a short circuit may occur. The current, magnetic field, and the resulting emissions are maximized.
The EMC parameter corresponding to the IC is its short-circuit current I k (f).
Maximum pin current and pin voltage value (U l (f), I k (f)) Is generated in the case of a short circuit or an open circuit of the pin. In these cases, the highest emissions are generated through the above-mentioned coupling mechanism.
Therefore, each pin of the IC has its own conduction and radiation EMC parameters. The EMC parameters of the IC pin are its open circuit voltage and short circuit current.
Through measurements close to open circuit and short circuit conditions, the open circuit voltage and short circuit current of most pins of the IC can be determined. For example, two spectra for each pin result in 128 spectra for a 64-pin IC. In addition, the pins can have different switching states (input, output H, L, and high impedance). Internal functions can also be in different states (Clk-PLL OFF/ON).
The current in the power supply pin is measured according to the 1 ohm method. If the resistance of 1 ohm is too large, a measured resistance of 0.1 ohm is used. This measurement can be performed in Vdd and Vss. The corresponding high impedance probe and decoupling capacitor can be used to measure the RF open circuit voltage on the crystal oscillator pin. The filter capacitor of the crystal oscillator can be used as a decoupling capacitor.
Measurements can generate a lot of data and become difficult to manage. The 3D representation provides a clear overview of the results (Figure 8). Custom-developed measurement settings with corresponding software (ChipScan ESA) allow semi-automatic recording of needle spectra. The results are displayed in 3D. For the selected pin, the representation can be switched to 2D (Figure 12).
Use of IC parameters
The 3D spectrum clearly reveals the cause of the problem in practical applications. The open circuit voltage in the range of 80 dBµV can cause it to exceed about 10 mm (especially problematic in automobiles). The critical frequency range can be read from the 3D–2D spectrum.Figure 12The crystal oscillator pin 15 shows this. The critical frequency range is extended to 600 MHz. The layout and design can be guided in the right direction according to the EMC parameters of the IC pins to save time and money. In some ICS, individual pins show high values in terms of the transmitted conduction EMC parameters. These values provide useful suggestions on how to use the ICS on the PCB in a compatible manner. Therefore, it is not necessary to exclude these ICS from development. IC users should determine the EMC parameters of the IC before starting to develop the PCB.
If the IC is integrated without this information (because it is still a common practice today), there will be no problem until the first development sample is measured. This leads to the high cost of time-consuming interference suppression measures (layout changes, design modifications, etc.). This method also allows the selection of ICS from a range of alternatives, because it is likely to lead to lower emissions, so it will be easier and cheaper to make its PCB components comply with EMC standards.
Two new useful tools for electronic development can be created based on the EMC parameters of the IC：
Pin-related open circuit voltage and short circuit current spectra (3D / 2D)
Layout and design skills and EMC parameters of IC pins
EMC experts can derive such design techniques (countermeasures) from the pin spectrum, interaction (items 1 and 2), and the characteristics of special applications. However, in practice, it is best to provide design tips and techniques in the form of pin information. EMC parameters of IC pins U l (f), I k (f) Can be grouped into frequency-related level ranges with different risk potentials. Certain barriers to design measures must be established based on potential risks. This strategy will form the basis of EMC's activities in the coming years.
Examples of pin selectivity countermeasures for open circuit voltage：
In Figure 8The static port pins 16 to 35 show a high open circuit voltage. If multiple port conductors are connected to the PCB trace, this will cause emission through an electric field. As a countermeasure, the traces should be well surrounded by GND, not on the edge of the PCB.
Examples of pin selectivity countermeasures in terms of short-circuit current
Port pins 16 to 35 also provide relatively high short-circuit values (Figure 9). Filter capacitors that are far away will generate critical current loops. As a countermeasure, the filter capacitor should be located near the IC or a series resistor should be inserted.
The power supply pins 12 and 13 obtain high values in the lower frequency range (
IC pin EMC parameter measurement system
Figure 10Shows the measurement settings for pin current and pin voltage measurements.
The test IC (DUT) is placed on a test board embedded in the ground plane. This provides a continuous GND surface as a prerequisite for measuring up to the GHz range.
A (voltage or current) measuring probe, the tip of which can be easily moved to contact each pin, is placed on the GND plane. The measurement path (IC-needle contact-probe) is only a few millimeters long, so it can be measured within a short electrical distance. The IC is powered and controlled by the connecting board through a filter (Figure 10). The connecting plate is integrated in the ground plane
Case analysis of IC EMC measurement
The limit of 24 dB is exceeded at 120 MHz. Reason: The electric field is coupled out of the trace connected to IC 02
Figure 11The measurement results of vehicle components are summarized. Due to the E field, a 24 dB limit violation occurred at 120 MHz. This problem was not discovered until after the prototype was developed and tested. The open circuit voltage U of the IC pin as one of the IC EMC parameters l (f) The measurement reveals the reason.
An abnormally high voltage was measured on the IC pin of the crystal oscillator in the 40 MHz grid (approximately 80 dBµV at 120 MHz) (Figure 12Displayed in black).
All lines and metal parts connected to these pins emit electric fields, such as physical mechanismsChapter 1As described in the item. The electric field is extremely powerful, which can cause electrical vibration of the PCB and wiring harness.
This means that the field is coupled in the following ways：
Welding wire and lead frame leading to the IC pin of the crystal oscillator，
15 mm PCB routing from IC to crystal oscillator，
Crystal oscillator housing and crystal oscillator wiring 3 x 0603 SMD assembly.
In this case, a suitable remedy is to reduce the surface of these metal parts, that is, to shorten the traces and embed them in the GND to use a smaller crystal oscillator housing. However, in our example, these countermeasures are not enough. The open circuit voltage of the pin U l (f) So high that the metal surface of the bonding wire and lead frame is large enough to cause the limit to be exceeded during the component measurement process. Filter capacitors cannot be used to reduce the voltage on the crystal oscillator. The electric field shielding directly above the IC can be used as a final remedy.Figure 13It shows the positive results achieved as a result of these countermeasures. Meet the limit value.
Today, it is already possible to determine the EMC characteristics of the IC. It is useful if the obtained values are entered into the product data sheet. This information allows developers to have planned the EMC measures required for the PCB during the development process so that in principle they can use any IC.
The test method for determining the EMC parameters of the IC enables IC manufacturers to develop the IC more effectively.
Due to the continuous miniaturization of modules and a large number of very complex electronic equipment, the EMC evaluation of ICS is an important prerequisite for the future development of electronic equipment.
The use of IC EMC parameters will also have a positive impact on the development of the Internet of Things
- Creation date: July 7, 2021
- Revision date: July 2, 2024