Patent ID: 7149232

Claim:
A laser noise cancel circuit for reducing laser noise in a reproduction system for an optical disk device comprising: a gain-variable amplifying noise cancel circuit for amplifying a monitor output signal for laser light irradiated to an optical disk; a first low-pass filter for extracting low frequency signal components of a monitor output signal; a second low-pass filter for extracting low frequency signal components of a reproduced high frequency signal from said optical disk; a negative return loop circuit for controlling a gain in said amplifying noise cancel circuit based on the low frequency signal components of the monitor output signal extracted by said first low-pass filter as well as the low frequency signal components of the reproduced high frequency signal extracted by said second low-pass filter; and an arithmetic circuit for generating said reproduced high frequency signal with laser noise components cancelled by canceling the laser noise components extracted from said monitor output signal; wherein said negative return loop circuit comprises a differential amplifier for gain control based on comparison of a lower frequency signal component of the monitor output signal with respect to a low frequency signal component of said reproduced high frequency signal, and out putting a gain control signal to said amplifying noise cancel circuit to control a gain in said amplifying noise cancel circuit; wherein said amplifying noise cancel circuit comprises a non-inverting amplifying circuit comprising a differential amplifier using a resistance value variable MOS resistor element as the return resistor element and a resistance value of said MOS resistor is controlled according to said control signal for changing the gain.