Filter circuit, filtering method and disc rotation control method and apparatus

A filtering method comprising the steps of:

• selectively outputting an input signal or an output signal;
• amplifying a selectively output signal at a first amplification factor;
• adding together a signal amplified at said first amplification factor and another signal amplified at a second amplification factor;
• delaying an addition signal by a first delay time, and outputting a delayed signal as said output signal;
• delaying said output signal by a second delay time, and outputting a delayed signal;
• amplifying said delayed signal delayed by said second delay time at a second amplifying factor, and outputting an amplified signal as said another signal to be added to said signal amplified at said first amplification factor;
• and
• controlling selection between said input signal and said output signal in accordance with an order of a filtering operation.

A disc rotation control apparatus comprising:

• control signal input means for inputting a control signal relating to rotation of a disc;
• selective output means for selectively outputting said control signal or an output signal;
• first amplifying means for amplifying an output of said selective output means at a first amplification factor;
• first delay output means for delaying a received signal by a first delay time, and for outputting a delayed signal as said output signal;
• second delay output means for delaying said output signal as output from said first delay means by a second delay time, and for outputting a delayed signal;
• second amplifying means for amplifying an output of said second delay output means at a second amplifying factor;
• adding means for adding together an output of said first amplifying means and an output of said second amplifying means, and for supplying an addition signal to said first delay output means;
• and
• control means for controlling selection of said selective output means in accordance with a drive mode of said disc.

A disc rotation control method comprising the steps of:

• selectively outputting a control signal relating to rotation of a disc or an output signal;
• amplifying a selectively output signal at a first amplification factor;
• adding together a signal amplified at said first amplification factor and another signal amplified at a second amplification factor;
• delaying an addition signal by a first delay time, and outputting a delayed signal as said output signal;
• delaying said output signal by a second delay time, and outputting a delayed signal;
• amplifying said delayed signal delayed by said second delay time at a second amplifying factor, and outputting an amplified signal as said another signal to be added to said signal amplified at said first amplification factor;
• and
• controlling selection between said control signal and said output signal in accordance with a drive mode of said disc.