Variable reluctance sensor interface using a differential input and digital adaptive control

摘要

In accordance with the teachings of the present invention, an adaptive threshold circuit is provided which develops a series of square-wave voltage pulses from an alternating differential voltage that is produced in response to the rotation of a wheel. The adaptive threshold circuit includes an input circuit for providing an input voltage in response to the alternating differential voltage. A first voltage comparator compares the input voltage with an adaptive analog threshold voltage and produces an output in response thereto which causes a rising edge of the square-wave voltage pulse. A second voltage comparator compares a selected portion of the input voltage with the adaptive analog threshold voltage and produces an output in response thereto. The adaptive threshold circuit further includes a binary counter having a reset input for receiving the first voltage comparator output and an enable input for receiving the second voltage comparator output and provides a plurality of binary outputs. The second voltage comparator output thereby enables the counter so as to detect a peak input voltage. A digital-to-analog converter receives the binary outputs from the binary counter and generates the adaptive analog threshold voltage as a function of a selected percent of peak voltage.