Servo circuit for use in reproducing PCM signal discs

Claim 2

A servo circuit for use with an apparatus for reproducing a disc on which a pulse code modulated signal modulated by a run length limited code is recorded at a constant linear velocity, the servo circuit comprising: a circuit (6) for detecting the time during which a playback signal is inverted and producing an output corresponding to the detected time; a peak value hold circuit (8) for receiving and holding the peak value of the output from said detecting circuit (6); a bottom value hold circuit (12) downstream of said peak value hold circuit (8) having a time constant larger than the charge time constant of said peak value hold circuit (8) and for producing an output which follows the output of said peak value hold circuit (8); and a comparator (9) for receiving an output of said bottom value hold circuit (12) and a reference voltage and producing a signal to control a disc driving motor (10) such that a maximum or minimum time during which said playback signal is inverted equals the time when the linear velocity is the reference value, whereby the velocity upon playback becomes equal to said reference value.

Claim 3

A servo circuit for driving a disc drive motor (10) for a disc upon which a pulse code modulated signal with a run length limited code is recorded at a constant linear velocity, the servo circuit comprising: an optical detector (1) for scanning said disc and producing an output signal; a differentiating circuit (5) for receiving an output of said optical detector (1); a sawtooth signal producing circuit (6) for receiving the output of said differentiating circuit (5) and the level of said sawtooth signal varying as a function of the output of said differentiating circuit (5); a peak value hold circuit (8) with a first time constant receiving the output of said sawtooth signal producing circuit (6); a first diode (12D) for receiving the output of said peak value hold circuit (8); a fixed-voltage source (+V ); a first resistor (12R) and a first capacitor (12C) connected between ground and said fixed-voltage source (+V ) and having a second time constant substantially more than said first time constant; a comparator (9) connected to said first diode (12D) and to the junction point between said first resistor (12R) and said first capacitor (12C); and a reference voltage source (E S ) connected to said comparator (9); said disc drive motor (10) receiving the output of said comparator (9).

Claim 4

A servo circuit for driving a disc drive motor (10) for a disc upon which a pulse code modulated signal with a run length limited code is recorded at a constant linear velocity, the servo circuit comprising: an optical detector (1) for scanning said disc and producing an output signal; a differentiating circuit (5) for receiving an output of said optical detector (1); a sawtooth signal producing circuit (6) for receiving the output of said differentiating circuit (5) and the level of said sawtooth signal varying as a function of the output of said differentiating circuit (5); a peak value hold circuit (8) with a first time constant receiving the output of said sawtooth signal producing circuit (6); a first diode (12D) for receiving the output of said peak value hold circuit (8); a fixed-voltage source (+V ); a first resistor (12R) and a first capacitor (12C) connected between ground and said fixed-voltage source (+V ) and having a second time constant substantially more than said first time constant; a comparator (9) connected to said first diode (12D) and to the junction point between said first resistor (12R) and said first capacitor (12C); and a reference voltage source (E S ) connected to said comparator (9); said disc drive motor (10) receiving the output of said comparator (9).

Claim 5

A servo circuit according to claim 2 wherein said peak value hold circuit (8) includes a second diode (8D), and a second resistor (8R) and a second capacitor (8C) connected in parallel and with said first time constant.

Claim 6

A servo circuit according to claim 3 wherein said second time constant of said first resistor (8R) and said first capacitor (8C) is ten or more times said first time constant.

Claim 7

A servo circuit according to claim 4 including a buffer amplifier (11) connected between said first and second diodes (12D, 8D).