Sharp Kabushiki Kaisha Corporation

Hiroshige Hirajima

Hiroshi Fuji

Yukio Kurata

Takeshi Yamaguchi

Keiji Sakai

Tetsuo Ueyama

Tsuneo Fujiwara

Katsushige Masui

Renzaburo Miki

Noboru Fujita

Naotaka Otsuka

An optical pickup can be provided, the optical pickup being capable of recording and playback of a plurality of optical disks having different specs by using light beams of different wavelengths, and further being suitable for integrating the semiconductor lasers and light receiving elements into a single package, by including: first and second semiconductor lasers adjacently disposed; a three-beam diffraction grating for generating three beams for tracking control; a second hologram element for diffracting light of the second semiconductor laser to guide it to a photosensor; a complex polarization beam splitter (PBS) for reflecting only light from the first semiconductor laser; and a first hologram element for diffracting light of the first semiconductor laser to guide it to the photosensor.

Optical pickup

An information reproducing apparatus which includes: pickup section for converting information recorded in a recording medium into an electrical signal; preprocessing section for amplifying a signal output from the pickup section; automatic gain control circuit for receiving a signal output from the preprocessing section as an input signal and for eliminating an amplitude change component other than the information from the input signal; and digital signal reproducing section for reproducing a digital signal corresponding to a signal output from the automatic gain control circuit, the automatic gain control circuit including: amplifier section for amplifying the input signal so as to be output as an output signal, and for receiving a control signal for controlling a gain; and control section for controlling the gain of the amplifier section, the control section including: amplitude detector for detecting an amplitude of the output signal; control signal generator for generating a control signal corresponding to the amplitude of the output signal; memory section for storing the control signal; and interpolation section for detecting an error signal caused by an input signal in an impulse form from the control signal and replacing the error signal with an interpolation signal.

Interpolating gain amplifier for information reproducing apparatus

A recorded signal reproduction circuit in an optical disc information reading and recording apparatus converts a recorded signal recovered from an optical disc to PR (1, 2, 1) characteristics through a equalizer circuit, digitizes it through an A/D converter and at the same time also generates a clock signal synchronized in phase with the equalizer circuit output signal by using a binary edcoder circuit and a PLL circuit. This clock signal is then provided to an A/D converter as the sampling clock. The A/D converter output signal is then decoded to the original channel bit stream based on the clock signal. Because the equalizer circuit output signal is provided to both the binary encoder/PLL circuit and the A/D converter together, additional circuity for converting signals into a binary series of pulses is unnecessary and reduction of circuit scale is possible. Moreover, in case of a change-over in the frequency characteristics of the equalizer circuit, due to a change in recording and reproduction frequency, the change-over will not affect the phase relationship between an input signal to the A/D converter and a sampling clock. In addition, it becomes simple to adjust this phase relation.

Readback circuit for an optical information reading and recording

An A/D conversion circuit for use in an information reproduction apparatus, includes an envelope generator for extracting an upper-side envelope signal and a lower-side envelope signal from a reproduced signal read out from a recording medium, and an A/D converter for converting the reproduced signal into digital data by using a reference voltage that is obtained from a difference between an upper-side reference voltage and a lower-side reference voltage. In the analog-to-digital conversion circuit, the upper-side reference voltage is set to the level of the upper-side envelope signal, while the lower-side reference voltage is set to the level of the lower-side envelope signal. With this arrangement, the difference between the level of the upper-side envelope signal and the level of the lower-side envelope signal fluctuates together with an amplitude fluctuation component and a low-frequency superimposed component in a fluctuation of the reproduced signal. The reproduced signal is converted into digital data by using the difference as a reference voltage. This makes it possible to cancel the fluctuation of the reproduced signal. Thus, this arrangement makes it possible to obtain digital data free from deviations, as well as ensuring a proper response even to a quick fluctuation in the reproduced signal.

Analog-to-digital conversion circuit for use in information reproduction

An information reproducing circuit for reproducing digital information from a signal read by scanning an optical disk comprises an HPF 1 inputting the read signal and removing a low-frequency component from the input signal for outputting the same, an adder 2 inputting the signal outputted from the HPF 1 and adding a feedback signal having an amplitude matching with half that of the input signal to the input signal for outputting the same, a comparator 3 inputting the signal outputted from the adder 2 and converting the input signal to a binarized signal through a threshold value signal for outputting the binarized signal, a compensation circuit 5 inputting the binarized signal outputted from the comparator 3 and outputting the input signal while compensating the same through a compensation signal for compensating the low-frequency component of the read signal, and an LPF 6 inputting the signal outputted from the circuit 5 and removing a high-frequency component from the input signal for supplying the same to the adder 2 as the feedback signal.

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Tenri, Japan

Hiroshige Hirajima