1. Introduction to automotive analogue chips

What exactly is an analogue chip? Unlike digital chips, which can only perform arithmetic and logic operations on discrete digital signals, an analogue chip is an analogue integrated circuit built from capacitors, resistors and transistors. It converts real world information such as sound, light, temperature and pressure into voltage or current and performs amplification, filtering and conversion of electrical signals. By application and function, analogue chips fall into several categories: operational amplifiers and comparators, audio power amplifiers, analogue switches, A/D and D/A converters, voltage references, logic chips and interface chips.

Figure 1. Classification of analogue chips

Taking a grade B vehicle as an example, a conventional combustion model uses about 160 analogue chips, an electric model more than 400, and a grade C electric vehicle more than 650.

According to IC Insights, automotive is the second largest application market for analogue chips. Automotive analogue chips accounted for about 24 percent of the whole analogue chip market in 2022, and by 2027 the value of analogue chips per vehicle will reach 300 US dollars, a compound annual growth rate above 10 percent. Beyond automotive, industry, energy and consumer sectors also use analogue chips in large volumes, so prospects are broad.

In the global automotive analogue IC market, Texas Instruments, ADI, Infineon, NXP, onsemi and Renesas are strongly competitive. Domestic companies started later in automotive-grade products and generally lag well behind in both product breadth and technical level.

The future of automotive analogue chips lies in higher integration and higher reliability. To raise design power density, vehicle makers and component suppliers prefer analogue ICs with higher integration and more complete functionality. High reliability and high consistency have always been goals of the automotive industry, and chip reliability is an area domestic analogue IC companies must focus on improving.

Figure 2. Comparison of analogue and digital chips

2. Operational amplifiers

An operational amplifier is a high gain voltage amplifier with AC and DC coupling, differential input and usually a single ended output. It was first used in analogue computing circuits for addition, subtraction, differentiation and integration, and can amplify and transmit signals. Operational amplifiers generally work in the linear region and offer high gain, high input resistance and low output resistance.

Operational amplifiers are used very widely in vehicles, anywhere a signal is sampled or fed back. Different products impose different requirements, so parameter differences between amplifiers can be very marked.

Figure 3. Operating principle of an operational amplifier

3. Comparators

A comparator compares two or more data items to determine whether they are equal, or to establish their order and relative magnitude. A circuit or device that performs this comparison is a comparator, which compares an analogue voltage signal with a reference voltage. Both inputs are analogue and the output is a binary zero or one. When the difference between the input voltages grows or shrinks while the sign stays the same, the output remains constant.

In automotive circuits, comparators are often used for signal measurement and over-limit alarms so that a circuit is not damaged when something goes wrong. They must respond fast enough to ensure the protective action happens quickly and to send an alarm to the MCU in time for the next step.

4. Audio power amplifiers

An automotive amplifier selects and pre-processes the audio input and amplifies the power so that the electrical signal can drive loudspeakers. It differs slightly from the amplifier in a home theatre system: because many head units already integrate power amplification and provide pre-amplification, the automotive amplifier is sometimes called a post amplifier, meaning it can accept an already amplified high level input.

5. Analogue switches

When the main goal of module development is to maximise channel count, board space becomes precious. Switches are key to increasing system channel count, but as the number of switches grows, the switches themselves, the logic traces and the devices needed to generate the logic signals consume a lot of board space and reduce what remains. Ultimately the achievable channel count is limited by the constraints of controlling the switches themselves.

Multiplexers are used mainly for signal switching. Integrated analogue switches have become the leading product in small signal applications. Compared with earlier mechanical contact switches, integrated electronic switches offer many advantages: fast switching, no bounce, low power, small size, reliable operation and easy control. They also have some drawbacks, such as higher on resistance, limited input current capability and a small dynamic range. Integrated analogue switches are therefore used mainly where switching is fast and system size must be small. At lower frequencies, below 10 MHz, they are usually made in CMOS; at higher frequencies, above 10 MHz, bipolar transistor processes are widely used.

Automotive analogue switch families address the fast growing demand for signal switching in in-vehicle intelligent communication, infotainment, advanced driver assistance systems, advanced diagnostics and engine control modules, traction and stability control modules, and electric windows, locks and mirrors. These applications need audio, video, bus and communication interface switches to bridge and route signals.

6. A/D and D/A converters

(1) Application areas. Automotive data converters are divided into D/A and A/D converters. They convert between analogue and digital signals and are general purpose devices for signal acquisition and control, acting as the bridge between physical and digital quantities. Typical automotive applications include battery management systems, electric drive and control, on-board chargers, lidar, infotainment, instrument clusters, current sensors and pressure sensors.

(2) Role of automotive data converters. Automotive A/D converters mainly acquire the various electrical signals in a vehicle, working with sensors to monitor physical quantities. Main uses:

Sampling every voltage node in the system and converting it to a digital signal, including high and low voltage, single ended or differential. High voltages can be reduced to a suitable range by resistive division.

Sampling the current in a path together with a shunt resistor and converting it to a digital signal, usually differential, or converted to single ended by an amplifier before reaching the A/D converter.

Sampling supply rail current together with an analogue output current sensor and converting it to a digital signal.

Acquiring physical quantities such as sound, light, pressure and temperature together with sensors and front end amplifier circuits, and converting them to digital signals.

Automotive D/A converters mainly generate analogue control signals. Main uses:

Generating adjustable voltage signals, low or high voltage, single ended or differential. High voltages can be produced by a low voltage D/A converter combined with an external step-up circuit.

Generating adjustable current signals.

Working with driver circuits and the corresponding drivers, photodiodes or microphones to control physical quantities such as temperature, displacement and rotation, or to generate sound and light.

7. Voltage references

A shunt voltage reference has its output pin connected in parallel with the load, much like a Zener diode, but the principle is quite different. A Zener diode stabilises output voltage by Zener breakdown once a certain voltage is reached. A shunt reference contains internal negative feedback forming a feedback loop that continuously adjusts the sink current to keep the output voltage stable.

Voltage references are used very widely in vehicles, including on-board chargers, traction motor drives and battery management systems in the powertrain, and also in body electronics and lighting, infotainment and navigation, instrument clusters, autonomous and assisted driving, and airbags, in short anywhere a voltage reference is needed. Consumption per vehicle is therefore very large, reaching several dozen chips.

8. Logic chips

Logic chips mainly comprise small logic gates such as AND, OR and NOT gates, and level shifting circuits.

(1) Logic gate chips. Logic gates are basic building blocks of integrated circuits. Simple gates can be made from transistors whose combination makes high or low levels representing two signals produce a high or low output. High and low can represent logical true and false, or one and zero in binary, enabling logic operations. The most basic logic relations are AND, OR and NOT, and the most basic gates are the AND, OR and NOT gates. In automotive applications gates are often used in protection circuits: since the driver circuits of power devices need protection, which in turn protects the power devices themselves, gates are often combined with drivers to prevent shoot-through and false switching.

(2) Level shifting chips. A level shifting circuit converts the level of one voltage to that of another. Vehicles use many ECUs, and different ECUs often need to communicate to exchange information, but their supply systems differ so their output signal levels differ. Level shifting circuits must therefore be added to the communication path so that ECUs with different supplies can communicate reliably.

Logic chips, including small logic and level shifting, are used mainly in body control modules and telematics boxes. Small logic chips are also widely used in power conversion products such as on-board chargers and motor drives for logic protection.

9. AEC-Q100 qualification required for automotive analogue chips

1. AEC-Q certification is the entry threshold for automotive electronics. AEC stands for Automotive Electronics Council. It was founded in 1994 by Chrysler, Ford and General Motors, and its membership now spans major vehicle makers, automotive electronics companies and semiconductor manufacturers worldwide. Components that comply with AEC specifications can be adopted by all three manufacturers at the same time, which encouraged part makers to exchange product characteristic data, drove standardisation of automotive parts and laid the foundation for the rapid growth of the automotive parts market. AEC-Q is the automotive reliability test standard issued by the AEC and an important passport for part makers entering automotive electronics and tier one supply chains.

AEC-Q100 was the first AEC standard, a set of stress test specifications designed for integrated circuits in automotive applications. It is important for improving product reliability and quality assurance. AEC-Q100 confirms the quality and reliability of each chip against possible conditions and latent failure states, with standardised tests of product function and performance in particular.

2. Automotive ICs required to pass AEC-Q100. Analogue chips: operational amplifiers and comparators, audio power amplifiers, analogue switches, A/D and D/A converters, voltage references, logic chips and interface chips. Beyond analogue chips, the standard also covers control, driver, computing, memory, sensor, communication, power, power supply and security chips.

3. AEC-Q100 operating temperature grades for integrated circuits.

▸ Grade 0: ambient operating temperature -40℃ to 150℃
▸ Grade 1: ambient operating temperature -40℃ to 125℃
▸ Grade 2: ambient operating temperature -40℃ to 105℃
▸ Grade 3: ambient operating temperature -40℃ to 85℃

4. AEC-Q100 validation flow for automotive IC products.

5. AEC-Q100 test groups.

Group A, accelerated environmental stress tests (PC, THB/HAST, AC or UHAST or TH, TC, PTC, HTSL): 6 tests
Group B, accelerated lifecycle simulation (HTOL, ELFR, EDR): 3 tests
Group C, package assembly integrity (WBS, WBP, SD, PD, SBS, LI, BST): 7 tests
Group D, die fabrication reliability (EM, TDDB, HCI, BTI, SM): 5 tests
Group E, electrical verification (TEST, HBM, CDM, LU, ED, FG, CHAR, EMC, SC, SER, LF): 11 tests
Group F, defect screening (PAT, SBA): 2 tests
Group G, cavity package integrity (MS, VFV, CA, GFL, DROP, LT, DS, IWV): 8 tests

6. NTEK chip testing capability and AEC-Q100 requirements.

About NTEK

NTEK Group was founded in 2009 and is headquartered in Shenzhen. The group provides quality research and technical services covering R&D verification, inspection and testing, failure analysis, simulation and market access for intelligent connected vehicles, electronic communications and new energy.

NTEK has extensive experience in automotive-grade electronic certification and has helped more than 100 companies pass AEC-Q series certification, confirming the quality and reliability of each chip case against AEC-Q100.

Driven by the need of vehicle makers to localise automotive-grade chips and supported by the domestic semiconductor industry, NTEK provides comprehensive testing and certification services, applying AEC-Q100 automotive standards to control the safety and quality of automotive chips, supporting the growth of domestic automotive-grade chips and adding new momentum to the intelligent vehicle safety system.