Compensation circuit for an automotive ignition sensing system

Abstract

In a vehicle having an engine and an ignition system, a sensing circuit is provided for sensing the ignition voltage and providing this sensed signal to various operating modules of the vehicle. The sensing circuit includes a diode/resistor filter that provides a filtered voltage signal at a first output node. A compensation circuit is provided that compensates voltage errors introduced by the filter circuit. The compensation circuit includes a second diode that has substantially identical electrical performance characteristics as the first diode, and that is preferably mounted on a common substrate. A voltage signal at a second output node between the second diode and the filter circuit is indicative of the voltage drop across the second diode, which is further representative of the voltage error introduced by the filter circuit. In one embodiment, the operating module receiving the ignition voltage signal is configured to receive voltage signals at the first and second output nodes. The operating module can include a microprocessor that receives the A/D converted voltage signals and subtracts the signal at the second output node from the signal produced by the filter circuit according to a predetermined relationship. The result of this subtraction is then utilized by other software functions of the operating module that depend upon the ignition voltage signal.

Dependencies are inferred from the claim text.