Disk reproducing circuit with automatic gain control

An optical disk apparatus for reproducing data of an optical disk by detecting mark edge, comprising:

• a clamping circuit for clamping a difference between peak level and bottom level of a reproduced signal at a prescribed value;
• a comparator circuit for discriminating a mark using center level of a clamped signal amplitude as a reference;
• and
• a demodulator for demodulating the data on the basis of a pulse signal which conforms to the mark outputted by said comparator circuit.

An optical disk apparatus for reading marks from an optical disk on which data is recorded by absence or presence of marks, and demodulating data from a reproduced signal obtained by reading the marks, comprising:

• discriminating means for discriminating whether a reproduction method used by the optical disk is a first reproduction method of performing reproduction by detecting edge of a mark or a second reproduction method of performing reproduction by detecting center of a mark;
• a clamping circuit for clamping a difference between a peak level and a bottom level of the reproduced signal at a prescribed value;
• a comparator circuit for discriminating marks using center level of a clamped signal amplitude as a reference, and outputting a pulse signal (first mark signal) conforming to a mark and a pulse signal (space signal) conforming to a space;
• a zero-cross signal generating unit for differentiating the reproduced signal and outputting a zero-cross signal when the differentiated signal crosses the zero level;
• means for outputting a data pulse sisal when the zero-cross signal is generated while the first mark signal is being generated;
• and
• a demodulator to which the first mark signal and the space signal are inputted, when the first reproduction method has been discriminated, for reproducing a clock signal from these signals and detecting the edge of a mark, and to which the data pulse signal is inputted, when the second reproduction method has been discriminated, for generating a clock signal from this signal and detecting the center of a mark, said demodulator demodulating data using said clock signal.

An optical disk apparatus for demodulating data from a reproduced signal obtained by reading marks from an optical disk on which data is recorded by absence or presence of marks, comprising:

• a clamping circuit for clamping a difference between a peak level and a bottom level of the reproduced signal at a prescribed value;
• a variable-gain amplifier for amplifying the reproduced signal and inputting the amplified signal to the clamping circuit;
• a comparator circuit for discriminating marks using center level of a clamped signal amplitude as a reference and outputting a pulse signal (gate signal) conforming to a mark;
• a zero-cross signal generating unit for differentiating the reproduced signal and outputting a zero-cross signal when the differentiated signal crosses the zero level;
• data-pulse output means for outputting a data pulse when the zero-cross signal is generated while the gate signal is being generated;
• a demodulator for demodulating data from the data pulse;
• a reference voltage generating circuit for generating a reference voltage which is one to two times a clamp level;
• an amplitude comparator for comparing the reference voltage with the signal amplitude of the differentiated signal;
• and
• a gain control circuit which, on the basis of results of comparison performed by said amplitude comparator, is for controlling gain of said variable-gain amplifier by generating a gain control voltage in such a manner that signal amplitude outputted by said variable-gain amplifier attains a prescribed value which is one to two times the clamp level.