Light-receiving amplifier circuit and optical pick-up device using the same

An optical pick-up device which outputs a voltage in accordance with an intensity of reflected light from an optical disc medium, comprising:

• a light-receiving amplifier circuit comprising
• a photodiode which converts an optical signal into a current signal;
• an operation amplifier circuit which converts and amplifies the current signal into a voltage signal, and outputs the voltage signal;
• a clipping circuit which clips the voltage signal outputted by said operation amplifier circuit to a predetermined value by clipping an input voltage of an output amplifier stage of said operation amplifier circuit, when the voltage signal outputted by said operation amplifier circuit reaches the predetermined value;
• a plurality of conversion resistances;
• and
• a conversion resistance switching circuit which selectively connects one of said conversion resistances to an output terminal of said operation amplifier circuit,
• wherein the current signal is converted into the voltage signal through a conversion resistance connected between the output terminal and an inverting input terminal of said operation amplifier circuit,
• said clipping circuit clips the input voltage of said output amplifier stage to a different voltage in accordance with switching of said conversion resistances by said conversion resistance switching circuit,
• when the optical disc medium is being reproduced, said conversion resistance switching circuit connects one of said conversion resistances to the output terminal of said operation amplifier circuit, and clips the input voltage of said output amplifier stage at a voltage which is high enough to keep said operation amplifier circuit from being saturated, and
• when the optical disc medium is being recorded, said conversion resistance switching circuit connects one of said conversion resistances, which has a lower resistance value than said conversion resistance connected when the optical disc medium is being reproduced, to the output terminal of said operation amplifier circuit, and clips the input voltage of said output amplifier stage at a voltage which is low enough to allow said operation amplifier circuit to perform normal operation.

A light-receiving amplifier circuit comprising:

• a photodiode which converts an optical signal into a current signal;
• an operation amplifier circuit which converts and amplifies the current signal into a voltage signal, and outputs the voltage signal, said operation amplifier circuit comprising a first transistor connected to an output of the operation amplifier circuit;
• a clipping circuit which clips the voltage signal outputted by said operation amplifier circuit to a predetermined value by clipping an input voltage of an output amplifier stage of said operation amplifier circuit, when the voltage signal outputted by said operation amplifier circuit reaches the predetermined value, said clipping circuit comprising a second transistor connected to a base of the first transistor;
• a plurality of conversion resistances;
• and
• a conversion resistance switching circuit which selectively connects one of said conversion resistances to an output terminal of said operation amplifier circuit,
• wherein the current signal is converted into the voltage signal through a conversion resistance connected between the output terminal and an inverting input terminal of said operation amplifier circuit,
• said clipping circuit clips the input voltage of said output amplifier stage to a different voltage in accordance with switching of said conversion resistances by said conversion resistance switching circuit,
• said clipping circuit includes a plurality of voltage sources and a clipping voltage switching circuit which is connected selectively to one of said voltage sources, and
• said clipping circuit selects one of said voltage sources in accordance with switching of said conversion resistances by said clipping voltage switching circuit, and clips the input voltage of said output amplifier stage in accordance with the selected voltage.