Electromagnetic compatibility design and EMC standard of automobile Soc system

As engineers develop increasingly complex solutions to meet the needs of comfort, safety, entertainment, powertrain, engine management, stability, and control applications, the number of modern automotive electronic products will continue to grow steadily. In addition, with the increasing popularity of very complex and sophisticated electronic products in automotive applications, even the most basic vehicles are equipped with electronic equipment that was only available in high-end vehicles a few years ago.

In the past, the growth drivers of automotive electronics were safety-related applications such as comfort and convenience. Usually, such as the use of electric lifting windows or central control locks, these products just replace the existing mechanical systems. Recently, the scope of automotive electronics has expanded to support safety-related applications such as engine optimization, active and passive safety systems, and advanced infotainment systems including GPS.

Now, we are welcoming the third revolution in the development of automotive electronics. Automotive electronics no longer only supports key functions, but also penetrates into the control of the car, providing important driver information, controlling the engine, collision avoidance monitoring and collision avoidance, performing wire-controlled braking and steering, or implementing intelligent control of the interior environment of the vehicle .

For general embedded hardware electronic platforms, speed and cost are well-known issues. These platforms have basic or common hardware functions. Through application-oriented software design, they can be customized for various models of the same model series or different car manufacturers. System-on-chip (SoC) semiconductor devices integrate various functions into a single chip, reducing the number of components and space requirements. While ensuring long-term reliability, it is essential for the successful development of a universal embedded electronic platform. Important.

Electromagnetic compatibility

With the increase in the number of automotive electronic products and the increase in the distribution of complex electronic modules throughout the vehicle, engineers face increasingly severe electromagnetic compatibility design challenges. The problems mainly exist in three aspects:

1. How to minimize electromagnetic susceptibility (EMS)? To protect electronic products from the harmful electromagnetic radiation of other electronic systems (such as mobile phones, GPS or infotainment systems).

2. How to protect electronic products from the harsh automotive environment? Including the transient changes of the power supply voltage, the interference caused by heavy or inductive loads (such as car lights and starters).

3. How to minimize the EME that may affect other automotive electronic circuits?

As the system voltage, the number of vehicle electronic devices and the frequency increase, these problems will become more challenging. In addition, many electronic modules will interface with inexpensive, low-linearity, large-offset low-power sensors. These sensors work in a small signal state, and the impact of electromagnetic interference on their working state may be catastrophic.

Compliance and standards

The above problems show that automotive EMC compliance testing has become a major element of automotive design. The standardization of compliance testing has been carried out in automakers, automaker suppliers and different legislative bodies. However, the later the EMC problem is discovered, the harder it is to find the root cause of the EMC problem, the higher the cost of the solution, and the greater the limitations that may be experienced. Because of this, it will be the basic design method to consider EMC issues in the entire process from IC design, PCB mass production, module implementation to vehicle design. To facilitate this process, module-level pre-compliance testing and IC-level testing have been standardized.

Design EMC-compliant ICs and modules

The following are the EMC standards that IC design should follow:

EME standard IEC 61967: Measurement of radiated and conducted electromagnetic emissions in the range of 150kHz to 1GHz.

EMS standard IEC 62132: Measurement of electromagnetic immunity (anti-electromagnetic interference) in the range of 150kHz to 1GHz.

Transient standard ISO 7637: Measurement of conducted and coupled electrical interference caused by road vehicles.

How can system design engineers ensure that their SoCs and final modules meet the requirements of the above standards? The traditional SPICE model (an analog circuit emulator that focuses on integrated circuit design) does not work here because the electromagnetic field is not compatible with the SPICE-based simulation environment. At the IC design level, the electromagnetic field can only be modeled by the electric field, because the size of the chip and package is much smaller than the wavelength of the electromagnetic signal (the wavelength of the 1GHz signal is 30cm, which is much larger than the size of the IC). The key point to note here is that radiated emission and susceptibility are not the main problems of ICs, and the effective antennas on printed circuit boards and cables are the main causes of conductive emission and susceptibility.

Design engineers need to adopt several techniques to ensure EMC compliance. Let's examine EME and EMS in turn.

EM launch

EME (Electromagnetic Emission) is generated by high-frequency currents in an external loop like an antenna. Such high-frequency currents include:

-Switches of core digital logic, such as DSP and clock drivers (synchronous logic generates a large number of current spikes containing many high-frequency components);

-The action of analog circuits;

--Switch for digital I / O pins;

--High-power output driver that transmits large current spikes to the circuit board and wiring harness;

In order to minimize the impact of these factors, design engineers should use low-power circuits as much as possible, including lower voltage, adaptive power supply voltage, and spread-spectrum clock signal architecture in the frequency domain. When some parts of the digital system are not working, they should be turned off to reduce the number of component switches on a single clock cycle. In addition, by reducing the slope of the switching edges of the clock and drive signals and providing soft switching characteristics, it also helps reduce EME. Finally, the design engineer should carefully design the layout of the exterior and the chip. For example, a differential output signal using twisted pairs produces a lower EME and is less susceptible to EME. VDD and VSS close to each other and effective power supply decoupling is also a simple technique to reduce EME.

EM susceptibility

Rectifier / pump, parasitic elements, current, and power consumption are too large are the four main interference effects of EMS (electromagnetic susceptibility). High-frequency electromagnetic power is partially absorbed in the IC, so it may cause interference. These disturbances include the introduction of large high-frequency voltages to high-impedance nodes and large high-frequency currents to low-impedance nodes.

The main way to reduce the EMS effect to a minimum is to make the circuit design symmetrical, thus avoiding the possibility of rectification. This can be done using differential circuit topology and layout design. Even for sensors that require small signals in applications, a topology that can handle larger common-mode signals may help keep the system linear over a wide range of electromagnetic signals. Filtering can limit the frequency range into sensitive devices, which is another commonly used technique, especially when on-chip filtering can be used. Adopting high common mode rejection ratio (CMRR) and power supply rejection ratio design (PSRR) will also protect the circuit from rectification interference, and keep the internal node impedance low and all sensitive nodes on-chip. Finally, in order to avoid or control parasitic elements and currents, it is important to use protection devices to clamp parts that are larger than the required EMS suppression level. This technique helps to avoid rectification interference and maintain the protection level and signal symmetry. It is also critical to keep the substrate current to a minimum and concentrate these currents in controlled points.

The latest devices provided by AMI

Many design engineers are looking for mixed-signal semiconductor technology to provide SoC solutions for today's automotive applications. The latest high-voltage mixed-signal technology is particularly suitable for designs that require higher voltage output, such as driving motors or stimulating relays, in order to adjust analog signal conditioning functions with Combining complex digital processing.

As for high-voltage and mixed-signal ASIC technology, AMI's I2T and I3T series are excellent examples. The design handles voltages up to 80V, and the I3T80 based on 0.35μm CMOS technology integrates complex digital circuits, embedded processors, memory, peripherals, high-voltage functions and different interfaces in a single chip.

AMIS uses mixed-signal technology and many of the above-mentioned excellent EMC design methods to develop a series of ASSPs for automotive applications, including AMIS-41682 standard speed, AMIS-42665 and AMIS-30660 high-speed CAN transceivers. For 12V and 24V automotive and industrial applications requiring a CAN communication rate of up to 1Mbps, these devices provide an interface between the CAN controller and the physical bus and simplify design and reduce the number of components. For example, AMIS-30660 fully complies with the ISO 11898-2 standard, and provides differential signaling capabilities to the CAN bus through the CAN controller's transmit and receive pins; this chip provides design engineers with a choice of 3.3V or 5V logic level interfaces To ensure compatibility with existing applications and upcoming low voltage design requirements. By carefully matching the output signal, the common-mode choke required to minimize EME can be omitted, and the wide common-mode voltage range (± 35V) that receives the input also ensures high EMS performance.

The importance of EMC design

With the increase of electronic equipment in modern automobiles, more and more good design is required to ensure compliance with electromagnetic compatibility standards. At the same time, with the increase in integration, automotive design engineers need system-on-chip ASIC and ASSP solutions to replace multiple discrete components.

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