Patent ID: 7586081

Claim:
An output impedance varying circuit for adjusting an output impedance of a photo detector IC having an output terminal connected to a flexible printed circuit board in an apparatus for optically recording/playing back information, without causing attenuation of a required signal bandwidth while suppressing occurrence of peaking, the output impedance varying circuit comprising: an output circuit of the photo detector IC, an impedance varying circuit provided between an output of the output circuit and the output terminal, a first NPN transistor having an emitter connected to the output of the output circuit and a collector and a base connected to a first variable current source, a first PNP transistor having an emitter connected to the output of the output circuit and a collector and a base connected to a second variable current source, a second NPN transistor having a base connected to the base of the first NPN transistor and an emitter connected to the output terminal, a second PNP transistor having a base connected to the base of the first PNP transistor and an emitter connected to the output terminal; and a resultant resistance of an emitter resistance of the second NPN transistor and an emitter resistance of the second PNP transistor is adjusted by current values of the first and second variable current sources.