Knock sensor signal conditioner

This paper describes a knock sensor signal conditioning circuit, which is appropriate for monolithic implementation, thus providing a low-cost option for such an important part of electronic control units of cars. Knock signal is an undesirable effect in spark-ignition engines, which can be detected by recognizing the occurrence of vibrations at well-established frequencies. The usual sensor for this kind of vibration is a piezoelectric element, whose signal is amplified, filtered and integrated in time. The ECU acts correcting the detonation instant whenever the amplitude of the accumulated variable exceeds a pre-established level. The circuit herein described contains the necessary circuit blocks to implement a fully integrated system to perform these functions. Experimental prototypes of the circuit blocks have been fabricated in 0.6 μm CMOS and exhaustively characterized. Results are presented and discussed.