| 摘要 |
PURPOSE:To obviate skipping of sound, etc. owing to the loss of a tracking function by providing a multiplier circuit for variable magnification which multiplies the variable magnification by the output from at least one of photoelectric converting elements so as to make approximately equal the two inputs to a differential circuit in the reference circuit of an object to be detected of the position thereof. CONSTITUTION:A variable gain amplifier circuit 7 having voltage gains Ga, Gb is inserted between the sections 1a, 1b of a bisected sensor 1 and the respective input terminals of an operational amplifier circuit 2. The error voltage Verr in the just focusing state can be made zero simply by making Va', Vb' equal if the voltages to be inputted to the respective input terminals of the circuit 2 are designated respectively as Va', Vb' in this stage. The adjustment of the gain Ga, Gb of the variable gain amplifier circuit is simply required for making said voltage Verr zero. The light reflectivity rho of the disk and the deviating distance (DELTAL) of the light spot in the just focusing state do not affect the voltage Verr at all. The skipping of sound is thus obviated even if the light reflectivity changes sharply as a result of flaws and stains on the disk. |
