Automotive System ASIC, ASSP and Electromagnetic Compatibility (EMC) Design

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Automotive System ASIC, ASSP and Electromagnetic Compatibility (EMC) Design [Copy link]

The increasing number of electronic devices in modern cars has led to an increasing need for good design to meet the requirements of major electromagnetic compatibility standards. At the same time, the increasing integration level has also made automotive designers urgently need system-on-chip application-specific integrated circuits and application-specific standard product solutions that can replace multiple discrete components. This article explores some of the electromagnetic compatibility and integrated circuit (IC) issues facing automotive designers.

Electronics in modern cars continue to advance at a rapid pace - engineers are developing increasingly complex solutions for comfort, safety, entertainment, powertrain, engine management, stability and control applications. And advanced electronics are becoming more common. As a result, even the most modest cars today are equipped with electronics that were only available in high-end cars a few years ago.

In the past, non-critical applications such as comfort and convenience drove the growth of automotive electronics. Like power windows or central locking, these electronic applications simply replaced existing mechanical systems. More recently, the scope of automotive electronics has expanded to support critical applications such as engine optimization, active and passive safety systems, and advanced infotainment systems including GPS.

We are now entering the third phase of automotive electronics development. In this phase, electronics not only support critical functions, but also control them - whether it is providing important driver information and controlling the engine, or collision detection and prevention, brake-by-wire and steering, and intelligent climate control. As you can imagine, these applications require low-cost, easy-to-install electronic solutions with increasing intelligence and robustness.

Speed and cost factors have led to the emergence of "universal" embedded hardware electronic platforms. These platforms provide basic or common hardware functions and can be customized with specialized application software to provide the functions required by different models in the same car series, or even customized for different car manufacturers. System-on-Chip (SoC) semiconductor solutions integrate multiple functions into a single integrated circuit, which reduces component count and space requirements while ensuring long-term reliability, which is extremely important for developing successful general-purpose embedded electronic platforms.

Electromagnetic Compatibility

As automotive electronics continue to increase and complex electronic modules are used more and more in various parts of the vehicle, electromagnetic compatibility issues are becoming an increasing design challenge for engineers. Three major issues are:

(a) How to minimize electromagnetic sensitivity so that electronic devices are not affected by electromagnetic emissions from other electronic systems such as mobile phones, global positioning systems or infotainment devices.

(b) How to protect electronic devices from the harsh automotive environment, including transients in the power supply system and interference when switching large or inductive loads such as lights and starter motors.

(c) How to minimize electromagnetic emissions that can affect other automotive electronic circuits.

Moreover, these issues become more challenging as system voltages increase, more vehicle electronics increase, and frequencies rise due to more high-frequency electronic devices. In addition, many electronic modules now also interface with low-power, inexpensive sensors with poor linearity and large zero offsets. These sensors rely on small signals, and electromagnetic interference can be catastrophic to their normal operation.

Compliance testing, pre-compliance testing and standards

These issues mean that automotive EMC testing has become an essential element of vehicle design. Compliance testing has been standardized between car manufacturers, their suppliers and the various legislative bodies. The later an EMC problem is discovered, the harder it is to identify its root cause and the more limited and expensive the solution may be. It is therefore essential to consider EMC issues at all stages of the process - from IC design and PCB layout to module mounting and final vehicle layout design. To simplify this process, pre-compliance testing that considers EMC issues at the module and IC stage has been standardized.

Designing ICs and modules for EMC requirements

For ICs, there are three main EMC standards:

Electromagnetic emissions standards - IEC 61967: Standard for measuring radiated and conducted electromagnetic emissions in the range of 150 kHz to 1 GHzElectromagnetic

susceptibility standards - IEC 62132: Standard for measuring transients in electromagnetic immunity in the range of 150 kHz to 1 GHz

- ISO 7637: Electrical disturbances caused by conduction and coupling in road vehicles.

So how can system designers ensure that their system chips and final modules meet these standards? Traditional SPICE models, etc., are useless at this point because electromagnetic fields are not compatible with the SPICE simulation environment. Because the size of the chip and the entire assembly is much smaller than the wavelength of the electromagnetic signal (the wavelength is 30 cm at 1 GHz, which is much larger than the size of the integrated circuit), at the integrated circuit level, electromagnetic fields are accurately enough to be modeled using only electric fields. It is worth noting that radiated emissions and susceptibility are not the main issues for integrated circuits; the main issues are conducted emissions and susceptibility to effective antennas on the printed circuit board and wiring harness.

Designers should use several techniques to ensure that electromagnetic compatibility requirements are met. We will look at electromagnetic emissions and electromagnetic susceptibility one by one.

Electromagnetic emissions

Electromagnetic emissions are generated by high-frequency currents in external loops that act as antennas. The sources of these high-frequency currents include the toggling of core digital logic such as digital signal processing and clock drivers (synchronous logic produces large, sharp current peaks with a lot of high-frequency content), the action of analog circuits, switching digital input/output pins, and high-power output drivers that provide high current peaks to the printed circuit board and wiring harness. To minimize the impact of these factors, designers should use low-power circuits whenever possible, which may include reducing or using adaptive power supply voltages or architectures that distribute clock signals across the frequency domain. The number of switching elements in a clock cycle can also be reduced by turning off unused parts of the digital system. In addition, controlling the rising/falling slope of the clock and driver signals to slow down the switching edges and provide soft switching characteristics can also help reduce electromagnetic emissions. Finally, designers should also carefully study external and chip layout methods. For example, differential output signals using "twisted pair" wires generate less electromagnetic emissions and are less sensitive to electromagnetic emissions. Ensuring that the power supply and ground are close to each other and using efficient power supply decoupling are also simple ways to reduce electromagnetic emissions.

Electromagnetic sensitivity

Rectification/pumping, parasitic devices, current and power consumption are the three most serious interference effects of low electromagnetic sensitivity. High-frequency electromagnetic power is partially absorbed by the integrated circuit, which can cause some interference, including outputting high-frequency high voltage to high-impedance nodes and outputting high-frequency high current to low-impedance nodes.

An important way to minimize the impact of electromagnetic sensitivity is to make the circuit symmetrical to avoid the possibility of rectification. The method is to use differential circuit topology and layout. Even if small signals are required in applications (such as using sensors), topologies that can handle large common-mode signals can help the system remain linear in the case of a wide range of electromagnetic signals. Limiting the frequency input range of sensitive devices by filtering is another approach often used, especially with on-chip filters. Designing with high common-mode rejection ratios (CMRR) and power supply rejection ratios (PSRR) can also prevent rectification from occurring in the circuit, as can reducing internal node impedance and placing all sensitive nodes on the chip. Finally, it is important to use protection devices to limit the level of electromagnetic susceptibility that is exceeded in order to avoid or control parasitic devices and currents. This helps to avoid rectification and keep signal levels symmetrical, and it is also important to minimize substrate currents and discharge currents in critical locations. The

Latest Semiconductor Technology

Many designers are using mixed-signal semiconductor technology to provide the system-on-chip solutions needed for today's automotive applications. The latest high-voltage mixed-signal technology is particularly suitable for designs that require high-voltage outputs - such as driving motors or starting relays - combined with analog signal conditioning functions and complex digital processing.

The I2T and I3T families developed by Ammann Semiconductor (AMIS) are examples of the latest high-voltage mixed-signal ASIC technology. I3T80 is based on a 0.35-micron CMOS process and can handle a maximum voltage of 80 volts, making it possible to integrate complex digital circuits, embedded microprocessors, memory, peripherals, high-voltage functions and various interfaces into one integrated circuit.

Figure 1: Several functions integrated into a single chip manufactured using the I3T80 process.

Figure 1 illustrates several functions integrated into a single chip manufactured using the I3T80 process, including sensor analog interfaces (one of the most common requirements for automotive applications), high-voltage drivers for motors and transmissions, and digital processing circuits using an embedded 16/32-bit ARM(tm) processor core. For low-power processing needs, an 8-bit embedded R8051 processor is also available. As shown, other 'standard' IP blocks available from AMIS include timers, pulse width modulation (PWM) functions, JTAG for simplified device testing, interfaces, and communication transceivers including CAN bus and LIN bus communication options. Finally, it should be noted that the I3T technology contains built-in protection features to protect the ASIC from damage due to overvoltage or incorrect battery connection.
Figure 2: Comparison of electromagnetic interference performance of AMIS-30660 with other competitive products.



AMIS has used this mixed-signal technology and many of the EMC sound design methods described in this article to develop a variety of application-specific standard products (ASSPs) for the automotive industry, including the AMIS-41682 standard-speed, AMIS-42665, and AMIS-30660 high-speed CAN transceivers. These devices provide an interface between the CAN controller and the physical bus, simplifying design and reducing component count in 12-volt and 24-volt automotive and industrial applications that require CAN communication at a maximum rate of 1 megabit baud. For example, the AMIS-30660 fully complies with the ISO 11898-2 standard and provides differential signaling capabilities for the CAN bus through the transmit and receive pins of the CAN controller. The integrated circuit provides designers with a choice of 3.3-volt or 5-volt logic-level interfaces, ensuring compatibility with existing applications and the latest low-voltage designs. Carefully matched output signals minimize electromagnetic emissions, eliminating the need for common-mode chokes, while the large common-mode voltage range (±35 volts) of the receiver inputs ensures high electromagnetic susceptibility (EMS). Figure 2 shows the electromagnetic immunity performance of the AMIS-30660 compared to other competitive products.

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