Abstract: An input selection circuit using a plurality of bidirectional analogue switches disclosed which is constituted such that a feedback circuit is installed between the input terminals of a bidirectional analogue switch device and the output terminal of an amplifier, characterized in that the directional conduction deviations of bidirectional switches provided in the bidirectional switch device can be reduced during the transmission of signals. Therefore, the input selection circuit according to the present invention can reduce the signal distortions due to the directional conduction deviations.

Abstract: This invention relates to a grating adjustment apparatus of 3-beam type optical pick-up for the compact disk player and, more particularly, to an apparatus automatically and readily adjusting a grating to the angle where the target value of a tracking error signal is obtainable. Sub-beam currents from the optical pick-up is, through current-voltage transducing amplifiers, converted into voltage signals, which are applied to a differential amplifier. The differential amplifier puts out the tracking error signal mixed with noise, which passes through a band pass filter removing said noise. So only pure tracking error signal is obtained, which is, after its phase is compensated by the low frequency lag compensator, applied to a differentiator. This signal is applied to a discriminator.