Electrostatic voltage detecting device

Claim 1

An electrostatic voltage detecting device comprising: detecting means provided with a semiconductor member arranged movably along the surface of a recording medium to detect electrostatic voltage generated by the surface charge of said recording medium, and a metal electrode connected to part of said semiconductor member to form a depletion layer in the semiconductor member, the width of the depletion layer changing in accordance with a voltage detected by the semiconductor member; first inductance means connected to the metal electrode and combined with said detecting means to form a resonance circuit whose resonance frequency changes in accordance with the width of the depletion layer formed in said semiconductor member; signal generating means including second and third inductance means inductively coupled with the first inductance means, an oscillating circuit for supplying an oscillating output signal of predetermined frequency to the second inductance means, and a detector circuit connected to the third inductance means to detect a voltage signal excited through the third inductance means; and bias means for applying a DC bias voltage to the semiconductor member through the metal electrode and the first inductance means, the DC bias voltage being superposed on a voltage detected by the semiconductor member to determine the width of the depletion layer formed in said semiconductor member.