Digital Knock Signal Conditioning using Fast ADC and DSP

The increasing legal requirements for safety, emission reduction, fuel economy and onboard diagnosis systems is pushing the market for more innovative solutions with rapidly increasing complexity. Hence, the embedded systems that will have to control the automobiles have been developed at such an extent that they are now equivalent in scale and complexity to the most sophisticated avionics systems. The former analogue filter design is now replaced by digital signal processing. This paper will demonstrate the key elements to provide a powerful, scalable and configurable solution that offers a migration route to evolve and even revolutionize automotive electronics.

To illustrate this migration toward digital processing the knock function has been developed. A simple RC filter is used as external anti-aliasing. To get the maximum flexibility the signal is very early converted and processed digitally. The micro-controller has been developed using a three-layered solution. The lowest layer “peripheral layer” is having a programmable differential amplifier, a very fast A/D converter which can sample the signal up to 3,5 Mega-sample per second, this layer use a decimation filter to compress the flow of information. The second layer is the “transport layer”, it allows moving and preprocessing the data to reduce the load of the main processor. The highest layer is the “application layer”, it runs the very sophisticate DSP algorithm in real time to measure the energy of the knock phenomena and to decide the appropriate correction. A very effective interrupt engine supports this architecture for high real time performance. The high data throughput has been enhanced by the optimization of this three-layer architecture. This implementation is providing an improved Knock Detection functionality and enhances the flexibility across a large platform of engines and vehicles.