Wobble detection circuit corresponding to a plurality of media having different pre-formats and optical disk apparatus having reduced size

A wobble detection circuit, comprising:

• an optical system having a plurality of photodetector (light receiving) elements corresponding to several kinds of media having different pre-formats, the optical system receiving reflectional light from a medium at the photodetector elements, each of the photodetector elements being divided at least into two parts by a line tangential to a track formed on the medium;
• a plurality of subtracting amplifiers, each subtracting amplifier obtaining a difference between a set of outputs of the corresponding one of the photodetector elements;
• a plurality of second amplifiers, each changing a gain of an output of a corresponding one of the subtracting amplifiers depending on a pre-format of a reproducing or recording medium;
• a selector selecting an output from outputs of the plurality of the second amplifiers;
• and
• a binary circuit converting an output of the selector into a digital signal,
• wherein the selection of the output from the outputs of the plurality of the second amplifiers depends on the pre-format of a reproducing or recording medium.

A wobble detection circuit, wherein:

• a signal is detected by a common photodetector (light receiving) element from several kinds of media having different pre-formats;
• and
• a gain for amplifying the signal in a wobble signal detection process is changed depending on the pre-format of a reproducing or recording medium to obtain a wobble signal,
• wherein a filter circuit having variable frequency characteristic is provided, and the frequency characteristic of the filter circuit is changed depending on wobble frequency to be detected, the filter circuit having:
• the frequency characteristic determined according to a frequency of a provided reference signal;
• and
• a divider circuit dividing a channel clock signal to obtain a reference signal for reproducing or recording data,
• wherein an output of the divider circuit is regarded as the reference signal of the filter circuit, and the frequency characteristic of the filter circuit is changed by changing a dividing ratio.

A wobble detection circuit, wherein:

• a signal is detected by a common photodetector (light receiving) element from several kinds of media having different pre-formats;
• and
• a gain for amplifying the signal in a wobble signal detection process is changed depending on the pre-format of a reproducing or recording medium to obtain a wobble signal,
• wherein an inversion circuit inverting polarity of the wobble signal and a selector selecting noninversion or inversion are provided, and the polarity is selected depending on the pre-format of the reproducing or recording medium.