AUTOMATIC CALIBRATION FOR A CAPACITIVE PICKUP CIRCUIT.

摘要

A calibrating pickup circuit detects, using primary and secondary pickups, the primary and secondary voltages of an ignition coil of know turns ratio. The pickup circuit includes a programmable gain amplifier, responsive to the detected secondary voltage waveform signal and to a gain control feedback signal for generating an amplified secondary voltage waveform signal wherein the feedback signal has an initial predetermined value in calibration mode and has a calibration value in signal monitor mode. A waveform multiplexing circuit is selectively operable in calibration mode to alternately sample the primary and the amplified secondary voltage waveform signals over a predetermined period to generate single interlaced waveform signal. Waveform comparison is then performed by evaluating the single interlaced waveform signal and a secondary-to-primary ratio calculated representative of the signal strength difference between analogous portions of the primary and the amplified voltage waveform signals. A calibration value is then determined on the basis of the secondary-to-primary ration and the know turns ratio of the ignition coil.