Embedded Flash enables new sensor interface applications in vehicles
Single-chip sensor interface solutions that also incorporate Flash memory offer great potential to automotive designers who are adding more and more electronic content across their increasingly comprehensive and complex vehicle ranges.
Herve Branquart, AMI Semiconductor
Single-chip sensor interface solutions that also incorporate Flash memory offer great potential to automotive designers who are adding more and more electronic content across their increasingly comprehensive and complex vehicle ranges. Single-chip sensor interface ASICs that incorporate Flash give the designer greater reliability, shorter development time and significant cost savings.
New features and systems relating to vehicle safety, comfort and convenience, and powertrain are being developed and implemented as quickly as possible by the big car manufacturers. In addition to the development and implementation of new features, we are now also seeing established systems such as multiple airbags, ABS, traction control, and air conditioning appearing as standard features on much smaller ‘entry-point’ vehicles. The key effect of this has been to put pressure on the price of the systems in question.
At their “sharp end” most automotive electronic systems employ sensors. Depending on the specific application, these may be required to measure any one of a host of conditions, for example: temperature, pressure, acceleration, or perhaps linear and angular position changes.
Different systems require different quantities of sensors. For example, an anti-lock braking system needs four wheel-speed sensors, whereas a brake fluid level monitor may require just one. In some cases, more advanced derivatives of once revolutionary but now commonplace features see an increased call for sensors. A good example of this is an airbag. Early vehicles that included airbags in their specification typically had just one – a driver’s airbag – that used a single accelerometer and a braking sensor. Now, multiple airbags are commonplace and for some of them a whole host of extra information is being fed into the electronic control unit (ECU) to determine not just whether the airbag should deploy, but also how much it should inflate. This involves sensors to detect seat position, occupant weight and position, presence of child seats, vehicle speed and position, direction, and force of impact. The end result is that the overall sensor count and system complexity increases.
Before the electronic output from sensors can be interpreted and used by the relevant ECU, conditioning, conversion and processing of the signal must take place to get it into the correct format for analysis - this is where sensor interfaces come in.
Sensor interfaces chip with Flash
A single-chip solution is the optimal approach for an automotive sensor interface. A sensor interface module comprising numerous discrete components may create a number of headaches for the automotive manufacturer that could include use of valuable space, reliability and cost.
By using the latest mixed-signal design and manufacturing techniques, the integration of complex digital circuitry, embedded microprocessors and high-voltage (up to 80V) functionality required for an automotive sensor interface can be combined on a single IC. One example is an 80V modular SmartPower technology based on a 0.35µm CMOS core. It combines the ability to handle high voltage with CMOS logic making it capable of working in the harsh electrical and environmental conditions found in automotive applications.
More recently, by using a high injection MOS (HiMOS™) split gate transistor, it has also become possible to incorporate non-volatile Flash memory into the high-voltage, mixed-signal process. The addition of Flash needs just three extra mask layers when applied to the 80V modular SmartPower base set. This keeps solutions with Flash as cost effective as possible.
Typical sensor interface IC Flash memory sizes range up to 64kBytes with 100 erase cycles for code storage. An emulation of EEPROM for data storage (up to 512 bytes) can also be provided on-chip, using the same IP with a higher endurance rate (up to 100K erase cycles).
Key features of the non-volatile Flash include a sector and multiple sector erase time of 0.5s and page programme in 20µs (32 pages per sector). Random access read time is 100ns for either 8-bit or 16-bit words. Flash IP can be offered in any size from 2kbytes up to 64kbytes upon request, thanks to a memory compiler, thus avoiding silicon waste. The memory can retain data for up to 15 years.
The Flash IP consists of the matrix of Flash hard cells and the digital wrapper that provides the needed timing for erasing, programming and reading the Flash. The wrapper includes built in self-test (BIST) capability to screen completely the devices before shipping to the customer and error correction code (ECC) logic, to guarantee the quality levels required by the automotive market. The Flash wrapper is designed to interface with 8-bit and 16-bit embedded microcontrollers (8051, ARM).
Flash – not just the obvious benefits
Using Flash allows designers to take a more modular approach to the way they develop and apply a sensor interface IC for their application. Because many of the basic functions of many sensor interface designs are the same, it makes sense to re-use already proven blocks of functionality rather than re-design them, with all the issues that brings. Flash memory can be used just to take care of functional requirements that are unique to that one sensor interface.
Programming in Flash is a pure software task so therefore it is a lot faster and less expensive than putting down a part of the design in new silicon.
Complex model ranges
A new vehicle model may have five, ten or more variations: different engine sizes and types, different safety and convenience specification levels and various body shapes all add to the matrix of choices offered to the end customer. Some of the sensor interface requirements may vary subtly between these different vehicles. This is often something that can be addressed through changes in the Flash programming rather than having to produce a complete new chip.
Economies of scale are very important to vehicle manufacturers. With all the common blocks of functionality put down in hardware and the differences being covered in software by Flash, sensor interfaces with a block of non-volatile memory can help avoid this problem. The car maker can then continue to enjoy the economies brought by higher volume purchasing of a single common sensor interface chip.
Reliability is essential to any car manufacturer. It only takes the malfunction a single component to cause a system to fail, so every component is important. Proven, previously-used components generally give the highest levels of reliability. There is always risk attached to do something new whether it be leading edge technology or not. It therefore makes sense to, wherever possible, re-use sensor interface ASICs that have shown over time that they stand up to the long-life and difficult operating conditions unique to automotive applications. By putting the most volatile elements – in terms of likelihood to need changing on a new design – of the initial sensor interface chip into Flash, this can often be avoided, and therefore reliability enhanced.
About AMI Semiconductor
AMI Semiconductor (AMIS) is a leader in the design and manufacture of silicon solutions for the real world. As a widely recognised innovator in state-of-the-art integrated mixed-signal and structured digital products, AMIS is committed to providing customers with the optimal value, quickest time-to-market semiconductor solutions. Offering unparalleled manufacturing flexibility and dedication to customer service, AMI Semiconductor operates globally with headquarters in Pocatello, Idaho, European corporate offices in Oudenaarde, Belgium, and a network of sales and design centres located in the key markets of North America, Europe and the Asia Pacific region. For more information please visit the AMIS website at www.amis.com.