Absolute shaft position sensing circuit

摘要

An absolute shaft position sensing circuit uses a magnetic sensor and a toothed wheel to produce two pulse trains which are used to determine the absolute position of a shaft which is coupled to the toothed wheel. One pulse train includes regularly spaced pulses which are fed to a phase locked loop to produce an oscillating output signal. A counter counts this signal and produces an output count which is representative of the relative angular position of the shaft. A second pulse train includes an irregularly spaced pulse. Circuitry is provided to detect the occurrence of this irregularly spaced pulse and to reset the counter in response to that occurrence, thereby making the count representative of the absolute angular position of the shaft.