Offset adjusting circuit for optical disc and offset adjusting method

An offset adjusting method for an optical disc apparatus, comprising the steps of:

• outputting a direct current component of an output signal of an offset-adjustment differential operational amplifier having an input terminal to which an output signal of an optical pickup is input and another input terminal to which a control voltage is applied, in the optical disc apparatus;
• outputting a digital signal based on the direct current component;
• and
• varying the control voltage applied to the offset-adjustment differential operational amplifier based on the digital signal so as to remove an offset.

An offset adjusting circuit for an optical disc, comprising:

• a plurality of offset-adjustment differential operational amplifiers corresponding to a plurality of optical pickup output signals output from an optical pickup, each offset-adjustment differential operational amplifier having an input terminal to which the respective optical pickup output signal is input and another input terminal to which a respective control voltage is applied;
• a plurality of sample-and-hold circuits corresponding to the plurality of offset-adjustment differential operational amplifiers, each of the sample-and-hold circuits providing the respective control voltage to the corresponding offset-adjustment differential operational amplifiers;
• an A/D converter that outputs digital signals based on output signals of the plurality of offset-adjustment differential operational amplifiers;
• a control voltage adjuster that varies the control voltages applied to the plurality of offset-adjustment differential operational amplifiers based on the digital signals;
• a single common D/A converter that converts the control voltages applied to the plurality of offset-adjustment differential operational amplifiers from the control voltage adjuster into respective analog signals;
• and
• a first selector that selects one of the plurality of sample-and-hold circuits according to the analog signal from the D/A converter and supplies the analog signal to the selected sample-and-hold circuit.