| 摘要 |
PURPOSE:To make an excellent servo operation for tracking or focus easy, by obtaining an error signal with an output signal in response to a voltage across a resistor connected so as to flow an output current of at least two photodetectors in common. CONSTITUTION:Cathodes of photodiodes 1a and 1c, and 1b and 1d are connected mutually, and anodes 1a and 1b, and 1c and 1d are connected. Signals V1 and V2, V3 and V4, and V5 and V6 led out via resistors R5-R10 provided between the connecting points and a power supply Vcc and between the connecting points and ground are applied to noninverting and inverting inputs of differential amplifiers 18, 8, 17, respectively. Pulse generating circuits 12, 13 transmit pulses to sampling and holding circuits 10, 11 in the timing of zero cross of the rise and fall of an output signal V7 of the differential amplifier 18, an output V8 of the differential amplifier 8 is sampled and held, a tracking error signal is outputted via a differential amplifier 14 and a focus error signal is outputted from the differential amplifier 17. |
