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

The analog-to-digital conversion circuit for use in an information reproduction apparatus comprising:

• an envelope generation means for extracting an upper-side envelope signal and a lower-side envelope signal from a reproduced signal reproduced from a recording medium;
• a first circuit for subtracting the extracted lower-side envelope signal from the reproduced signal and producing a first output signal;
• a second circuit for subtracting the extracted lower-side envelope signal from the extracted upper-side envelope signal and producing a second output signal;
• and
• an analog-to-digital converter for converting the first output signal from the first circuit into digital data by using a reference voltage obtained from a difference between an upper-side reference voltage and a lower-side reference voltage,
• wherein one of the upper-side reference voltage and the lower-side reference voltage is set to a level of the second output signal from the second circuit and the other reference voltage is set to a predetermined fixed level.

An analog-to-digital conversion method, comprising the steps of:

• (a) extracting an upper-side envelope signal from a reproduced signal, reproduced from a recording medium;
• (b) extracting a lower-side envelope signal from the reproduced signal;
• and
• (c) converting the reproduced signal into digital data using the extracted upper-side envelope signal and the extracted lower-side envelope signal, step (c) including the substeps of, and the extracted lower-side envelope-signal,
• (c1) generating a plurality of secondary reference voltages from a difference between the extracted upper-side envelope signal and the extracted lower-side envelope signal,
• (c2) comparing the reproduced signal with each of the plurality of generated secondary reference voltages and generating a plurality of respective outputs, and
• (c3) converting the plurality of respective outputs into digital data.