Asahi Kasei Microsystems Co., Ltd.

Koji Tomioka

Tamotsu Nagashima

Makoto Kobayashi

Kazunari Sasaki

A spread spectrum clock generator is provided which improves the spread spectrum effect with little increasing the circuit cost by modifying the shape of a triangular wave used for frequency modulation by a simple method. The output signal of the modulation waveform generating circuit has such a modulation waveform as indicated by solid lines in FIG.A. The modulation waveform is input to a VCO (voltage-controlled oscillator). In response to the modulation waveform, the oscillation frequency of the VCO is modulated, and the output clock that varies its frequency as illustrated in FIG.B is obtained. The frequency transition of the output clock involves such temporal variations as indicated by solid lines in FIG.C.

Waveform generating circuit and spread spectrum clock generator

A mark S/H circuit () samples, for example, a signal A generated as a photodetector () detects a return beam from marks of an optical disk (), a space S/H circuit () samples a signal A generated through detection of a return beam from spaces, and amplifiers (and) justify amplitudes of the sampled A signals from the marks and spaces. A mark/space selector switch () selects alternately and combines the mark and space signals whose amplitudes have been justified. After A, B, C, and D signals Ato Dare subjected individually to a series of processes up to the combination process, a wobble processing circuit () adds them in predetermined combinations, finds differences among the added signals after justifying the amplitudes of the added signals, and thereby reproduces a wobble signal ().

Optical disc device, circuit for optical disc device, wobble signal reproduction method, and land pre-pit signal reproduction method

A waveform generating circuit is provided which generates a modified triangular wave signal suitable for being input to a frequency modulation circuit such as a voltage-controlled oscillator (VCO). The waveform generating circuit includes a triangular generator, an offset generator for generating first and second offset component signals, a combiner for adding the triangular wave signal generated by the triangular wave generator and the offset component signals, and an output for delivering an output signal resulting from the addition by the combiner.

In a slew rate limiter, a slew rate is limited so as not to pass a signal varying more abruptly than a wobble signal included in a difference signal generated by a differential amplifier, and this limited slew rate is used to process the difference signal to be outputted. That is, the slew rate limiter removes a signal varying more abruptly than a wobble signal included in a difference signal DIFO, and then outputs only the wobble signal. A DAC generates an offset voltage. An adder is used to add this offset voltage to the wobble signal from the slew rate limiter. The signal obtained by this addition as a slice level is compared by a comparator with the difference signal, thereby reproducing an LPP signal.

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Tokyo, Japan

Koji Tomioka