Integrated circuit for optical disc
View Patent ↗An integrated circuit for optical disc comprising for each of light-receiving surfaces: an operational amplifier including inverting and noninverting input terminals receiving first and second input voltages, and output terminal receiving output voltage; a feedback resistor connected between the inverting input and output terminals; a photodiode connected between one power supply line of the first and second power supply lines and the inverting input terminal to generate current corresponding to reflected light; a capacitor connected between the one power supply line and the noninverting input terminal; and an input resistor connected between reference power source and the noninverting input terminal, further comprising: an adder adding voltages corresponding to the output voltages to generate RF signal, capacitance of the capacitor and resistance value of the input resistor being determined in accordance with capacitance of parasitic capacitor connected in parallel with the photodiode and resistance value of the feedback resistor.
1. An integrated circuit for optical disc, outputting an RF (Radio Frequency) signal for reproducing information recorded on an optical disc, based on reflected light of a laser beam applied to the optical disc, the reflected light being received by a plurality of light-receiving surfaces of a photodetector,
the integrated circuit comprising, between a first power supply line and a second power supply line whose voltage is lower than that of the first power supply line, for each of the plurality of light-receiving surfaces:
an operational amplifier including a positive power supply terminal connected to the first power supply line, a negative power supply terminal connected to the second power supply line, an inverting input terminal for receiving application of a first input voltage, a noninverting input terminal for receiving application of a second input voltage, and an output terminal for outputting an output voltage;
a feedback resistor connected between the inverting input terminal and the output terminal;
an input resistor connected between the noninverting input terminal and a reference power source providing a variable reference voltage value, a resistance value of the input resistor equal to a resistance value of the feedback resistor,
a photodiode connected between one power supply line of the first power supply line and the second power supply line and the inverting input terminal, the photodiode to generate a current corresponding to the reflected light of the laser beam, the photodiode having a first parasitic capacitance that varies in accordance with variations in the reference voltage;
a capacitor connected between the one power supply line and the noninverting input terminal; and
the integrated circuit further comprising:
an adder adding voltages corresponding to the output voltages of the operational amplifiers of the respective light-receiving surfaces, to generate the RF signal,
wherein a capacitance of the capacitor is an intermediate capacitance in a range of the first parasitic capacitance of the photodiode varying in accordance with variations in the reference voltage so as to at least alleviate an effect of fluctuations of the one power supply line on the RF signal.
2. The integrated circuit for optical disc of claim 1 , wherein:
the one power supply line includes an inductor component,
a second parasitic capacitor exists between a signal line for transmitting the RF signal and a ground, and
fluctuations of the one power supply line are generated by a current flowing through the inductor component when the second parasitic capacitor between the signal line and ground is charged or discharged.