Disc data reproducing apparatus and signal processing unit for preventing underflow and overflow

An apparatus for reproducing a plurality of information data stored on a disc, the plurality of information data capable of being classified into at least one of a first type data and a second type data, the apparatus comprising:

• means for designating information data to be read among the plurality of information data and for designating one of the first and second types of data;
• pickup means for reading information data designated by the designating means;
• means for generating a first clock signal synchronous with the information data read from the disc;
• means for generating a second clock signal derived from constant clock signal;
• storing means for storing information data read from the disc;
• and
• control means for controlling an operation of writing the information data read from the disc to the storing means in synchronism with the first clock signal and for controlling a reading operation from the storing means in synchronism with a second clock signal;
• wherein, when the designated information data is the first type data, the second clock signal is derived with a frequency according to an amount of information data stored in the storing means, and when the designated information data is the second type data, the second clock signal is derived with a frequency independent of the amount of data stored in the storing means.

A signal processing circuit for use in processing in processing information data read from a disc, comprising:

• a first clock circuit for generating a first clock signal synchronous with a digitized signal generated by quantizing the information data in accordance with a rotation of the disc;
• a demodulator for demodulating the digitized signal in synchronism with the first clock signal and to output a demodulated data;
• a second clock circuit for generating a second clock signal derived from a constant clock signal, the second clock circuit comprising a plurality of clock generating means for generating a plurality of clock signals of different frequencies from the constant clock signal, and selecting means for selecting the second clock signal from the plurality of generated clock signals;
• a buffer memory for storing the demodulated data:
• and
• a control circuit for controlling a writing operation to the buffer memory in accordance with the first clock signal and a reading operation from the buffer memory in accordance with the second clock signal, wherein the second clock signal is selected in accordance with an amount of data stored in the buffer memory.

A method for reproducing information data stored on a disc comprising:

• reading out information data from a rotating disc on which the information data is stored:
• generating a digitized signal by quantizing the information data in accordance with a rotation of the disc:
• generating a first clock signal synchronous with the digitized signal;
• demodulating the digitized signal in synchronism with the first clock signal and outputting demodulated data;
• generating a plurality of second clock signals having different frequencies;
• storing the demodulated data in synchronism with the first clock signal to a memory;
• selecting one of the plurality of generated second clock signals;
• reading the demodulated data stored in the memory in synchronism with the selected second clock signal;
• and
• changing the selection of the one of the plurality generated second clock signals in accordance with an amount of the demodulated data stored in the memory.

An apparatus for reproducing information data stored on a disc comprising:

• an optical pickup for reading out information data from a rotating disc on which the information data is stored;
• a digitized signal generator for generating a digitized signal by quantizing the read out information data in accordance with a rotation of the disc;
• a first clock signal generator for generating a first clock signal synchronous with the digitized signal;
• a demodulator for demodulating the digitized signal in synchronism with the first clock signal and to output a demodulated data;
• a buffer memory for storing the demodulated data;
• a second clock signal generator for generating a second clock signal from a constant clock, the second clock signal having a frequency controlled in accordance with an amount of data stored in the buffer memory, the second clock signal generator including a plurality of clock dividers for generating a plurality of divided clock signals of different frequencies and a selector for selecting one of the divided clock signals as the second clock signal according to the amount of data;
• and
• a controller for controlling a writing operation to the buffer memory in synchronism with the first clock signal and to control a reading operation from the buffer memory in synchronism with the second clock signal.

A signal processing circuit for use in processing information data read from a disc, comprising:

• a first clock circuit for generating a first clock signal synchronous with a digitized signal generated by quantizing the information data in accordance with a rotation of the disc;
• a demodulator for demodulating the digitized signal in synchronism with the first clock signal and to output a demodulated data;
• a second clock circuit for generating a second clock signal from a constant clock signal, the second clock signal including a plurality of clock dividers for generating a plurality of divided clock signals of different frequencies and a selector for selecting one of the divided clock signals as the second clock signal;
• a buffer memory for storing the demodulated data;
• and
• a control circuit for controlling a writing operation to the buffer memory in accordance with the first clock signal and to control a reading operation from the buffer memory in accordance with the second clock signal,
• wherein the selector selects the one of the divided clock signals as the second clock signal based on an amount of data stored in the buffer memory so that a frequency of the second clock signal is controlled in accordance with the amount of data stored in the buffer memory.

A signal processing circuit for use in reproducing designated information data to be read from a plurality of information data stored on a disc, the plurality of information data capable of being classified into at least one of a first type data and a second type data, the signal processing circuit comprising:

• a first clock circuit for generating a first clock signal synchronous with the designated information data read from the disc;
• a second clock circuit for generating a second clock signal derived from a constant clock signal;
• a buffer memory for storing the designated information data read from the disc;
• and
• a control circuit for controlling writing the designated information data read from the disc to the buffer memory in synchronism with the first clock signal and to control a reading operation from the buffer memory in synchronism with the second clock signal,
• wherein when the designated information data is the first type data, the second clock signal is derived with a frequency according to an amount of the first type data stored in the buffer memory, and when the designated information data is the second type data, the second clock signal is derived with a frequency independent of an amount of the second type data stored in the buffer memory.