Photocurrent amplifier circuit and optical pick-up device

An optical pick-up device which is capable of (a) reading information from or (b) reading information from and writing onto plural types of optical disc media by using lights having different wavelengths, said optical pick-up device comprising

• a photocurrent amplifier circuit which includes:
• a differential amplifier circuit which is configured to have an input unit including amplifier devices which are connected in parallel;
• device selector switches, each of which is connected to an input of an associated one of said amplifier devices and is operable to apply an input voltage to said associated amplifier device, the input voltage inactivating said associated amplifier device;
• gain resistors each of which is connected between an input of an associated one of said amplifier devices and an output of said differential amplifier circuit;
• and
• light receiving devices, each of which is connected to an input of an associated one of said amplifier devices and is operable to cause a photocurrent in accordance with an amount of received light,
• wherein the photocurrent flowing from each of said light receiving devices into an associated one of said gain resistors is amplified into a voltage signal by said differential amplifier circuit, and
• wherein said light receiving devices in said photocurrent amplifier circuit receive the lights having different wavelengths.