Patent ID: 7345468

Claim:
A signal processing circuit disposed in a rotation sensor, the rotation sensor including two sensing elements disposed in a confronting relationship with a rotor to produce detection signals having different phases in accordance with rotation of said rotor, and detecting a rotational speed and a rotational direction of said rotor based on said detection signals, said detection signal processing circuit comprising: pulse signal generating means for generating pulse signals in response to a change occurring in a level of the detection signal produced from at least one of said two sensing elements; forward/reverse judging means for generating a judgment signal based on the pulse signals from the pulse signal generating means, the judgment signal showing whether the rotational direction of said rotor is a forward direction or a reverse direction; and potential changing means comprising: a path connecting a power source line to a predetermined power source and an earth line; a constant current source generating a constant current, and being disposed in the path; and a switch disposed in the path, and being controlled to be selectively switched between on/off states to connect or disconnect the constant current source and the earth line, wherein the potential changing means changes an electric potential supplied to the signal processing circuit via the power source line on the basis of a voltage drop caused in response to the selectively switching between the on/off states of the switch so that the changed electric potential shows the rotational direction of the rotor, and controls the switch in accordance with said judgment signal of said forward/reverse judging means.