Abstract: In a phase error detecting circuit used in a synchronous clock extracting circuit for extracting a clock which is synchronized with reproduced data, a cross reference value generator 72 inputs, as a rising cross reference value S5, rising phase error data S3 calculated in a phase error calculator 71 to a rising cross detector 70a and inputs, as a falling cross reference value S6, falling phase error data S4 similarly calculated to a falling cross detector 70b. Each of the cross detectors 70a and 70b calculates a difference value between the value of the reproduced data at a sampling point and the inputted cross reference value (cross offset value) S5 or S6 and outputs a rising or falling cross detection signal when one of two difference values at consecutive sampling points is negative and the other thereof is positive. Accordingly, a capture range is enlarged.

Abstract: In a playback signal processing device for extracting, from an analog playback signal, playback data and a clock synchronized with the playback data, a digital equalizer 2 is disposed outside a clock extraction loop formed by an interpolator 3, a timing recovery circuit 4, and a control circuit 5. The digital equalizer 2 is provided between an AID converter 1 and the interpolator 3 and performs equalization processing on digital playback data from the A/D converter 1 in accordance with the timing of a fixed clock CLK from a synthesizer 7. The coefficients of the digital equalizer 2 are updated by the control circuit 5 by using a coefficient setting device 6 according to frequency ratio information 4a from the timing recovery circuit 4. Accordingly, the clock extraction capability is enhanced in spite of the equalization processing on the playback signal by the digital equalizer.

Abstract: A digital analog converter includes a current conversion section and a voltage conversion section. The current conversion section has a first output terminal and a second output terminal. The first output terminal outputs a first current and a second output terminal outputs a second current, the first current varying in value according to inputted digital data, the sum of the first current and the second current becoming a constant current. The voltage conversion section converts the first current to a corresponding first voltage and produces an offset voltage on the basis of the constant current and outputs the sum of the first voltage and the offset voltage as an output voltage.

Abstract: In a phase error detecting circuit used in a synchronous clock extracting circuit for extracting a clock which is synchronized with reproduced data, a cross reference value generator 72 inputs, as a rising cross reference value S5, rising phase error data S3 calculated in a phase error calculator 71 to a rising cross detector 70a and inputs, as a falling cross reference value S6, falling phase error data S4 similarly calculated to a falling cross detector 70b. Each of the cross detectors 70a and 70b calculates a difference value between the value of the reproduced data at a sampling point and the inputted cross reference value (cross offset value) S5 or S6 and outputs a rising or falling cross detection signal when one of two difference values at consecutive sampling points is negative and the other thereof is positive. Accordingly, a capture range is enlarged.

Abstract: An unusual waveform detection circuit is a digital-type unusual waveform detection circuit that arbitrarily sets a threshold used for determining an unusual waveform and produces an unusual waveform determination signal by comparing an input signal with the threshold. In producing the unusual waveform determination signal, one of a configuration where a voltage at each of all sampling points is compared with a reference voltage and a configuration where a continuously changing gradient of signal waveform peaks is calculated and is compared with a reference gradient is selectively employed. The unusual waveform detection circuit can easily and accurately detect various unusual waveforms.

Abstract: For the purpose of achieving reproduction of data recorded in an optical disc, or the like, with high accuracy and hence increasing the recording density, a digital filter is provided at a position between an A/D converter and an adaptive equalizing filter and between the A/D converter and a PLL circuit. Basically, an analog filter has only a low pass function. In a learning period prior to reproduction, a controller section sets various tap coefficients in the digital filter to determine a tap coefficient such that a jitter value detected in the PLL circuit is minimum. In a reproduction operation, the determined tap coefficient is set in the digital filter to perform optimum pre-equalization, and as a result, reproduction of data is performed with high accuracy.

Abstract: In a state where a PLL circuit is not locked, a gain control signal according to the difference between a peak value of a reproduced signal and the upper or lower limit value of the dynamic range of an A/D converter is given to a variable gain amplifier. In a state where the PLL circuit is locked, a gain control signal according to the difference between the reproduced signal and a reference value that corresponds to a level to which the reproduced signal belongs is given to the variable gain amplifier for each sampling point of the A/D converter. The variable gain amplifier amplifies the reproduced signal with a gain according to the gain control signal.

Abstract: An unusual waveform detection circuit of the present invention is a digital-type unusual waveform detection circuit that arbitrarily sets a threshold used for determining an unusual waveform and produces an unusual waveform determination signal by comparing an input signal with the threshold. In producing the unusual waveform determination signal, one of a configuration where a voltage at each of all sampling points is compared with a reference voltage and a configuration where a continuously changing gradient of signal waveform peaks is calculated and is compared with a reference gradient is selectively employed. The unusual waveform detection circuit can easily and accurately detect various unusual waveforms.

Abstract: In a state where a PLL circuit is not locked, a gain control signal according to the difference between a peak value of a reproduced signal and the upper or lower limit value of the dynamic range of an A/D converter is given to a variable gain amplifier. In a state where the PLL circuit is locked, a gain control signal according to the difference between the reproduced signal and a reference value that corresponds to a level to which the reproduced signal belongs is given to the variable gain amplifier for each sampling point of the A/D converter. The variable gain amplifier amplifies the reproduced signal with a gain according to the gain control signal.