Asymmetry correcting circuit and information reproducing apparatus using the same

An asymmetry correcting circuit for correcting a vertically asymmetric distortion of an input signal waveform in an analog-to-digital converter which quantizes the input signal waveform in accordance with a quantization reference voltage and converts the quantized waveform into a digital signal of predetermined bits, said asymmetry correcting circuit comprising:

• a first envelope detection circuit for detecting the envelope of a positive peak of the input signal waveform;
• a second envelope detection circuit for detecting the envelope of a negative peak of the input signal waveform;
• an adding circuit for outputting a sum voltage of the positive peak voltage obtained from said first envelope detection circuit and the negative peak voltage obtained from said second envelope detection circuit;
• a smoothing circuit for smoothing the sum voltage obtained from said adding circuit;
• a multiplying circuit for multiplying the smoothed sum voltage, which is obtained from said smoothing circuit, by a predetermined offset adjustment coefficient;
• and
• a quantization reference voltage control circuit for shifting, in response to the output signal of said multiplying circuit, the median of the quantization reference voltage of said analog-to-digital converter DC-wise in conformity with the offset derived from the asymmetry of the input signal, and controlling the upper limit and the lower limit of the quantization reference voltage to the values that correspond to the offset quantity.

An information reproducing apparatus for reproducing, as digital data, information recorded optically on an optical recording medium, comprising:

• an optical reading means for optically reading, from said optical recording medium, a signal corresponding to the recorded information;
• an analog-to-digital converter for quantizing the read signal waveform, which is obtained from said optical reading means, in accordance with a quantization reference voltage whose at least upper and lower limits are settable to desired values, and converting the quantized waveform into a digital signal of predetermined bits;
• and
• an asymmetry correcting circuit including:
• a first envelope detection circuit for detecting the envelope of a positive peak of said read signal waveform;
• a second envelope detection circuit for detecting the envelope of a negative peak of said read signal waveform;
• an adding circuit for outputting a sum voltage of the positive peak voltage obtained from said first envelope detection circuit and the negative peak voltage obtained from said second envelope detection circuit;
• a multiplying circuit for multiplying the sum voltage, which is outputted from said adding circuit, by a predetermined offset adjustment coefficient;
• and
• a quantization reference voltage control circuit for shifting, in response to the output signal of said multiplying circuit, the median of the quantization reference voltage of said analog-to-digital converter DC-wise in conformity with the offset derived from the asymmetry of the read signal, and controlling the upper limit and the lower limit of the quantization reference voltage to the values that correspond to the offset quantity;
• wherein said asymmetry correcting circuit is capable of correcting a vertically asymmetric distortion of the read signal waveform in said analog-to-digital converter.

An information reproducing apparatus for reproducing, as digital data, information recorded optically on an optical recording medium, comprising:

• an optical reading means for optically reading, from said optical recording medium, a signal corresponding to the recorded information;
• an analog-to-digital converter for quantizing the read signal waveform, which is obtained from said optical reading means, in accordance with a quantization reference voltage whose at least upper and lower limits are settable to desired values, and converting the quantized waveform into a digital signal of predetermined bits;
• and
• an asymmetry correcting circuit including:
• a first envelope detection circuit for detecting the envelope of a positive peak of said read signal waveform;
• a second envelope detection circuit for detecting the envelope of a negative peak of said read signal waveform;
• an adding circuit for outputting a sum voltage of the positive peak voltage obtained from said first envelope detection circuit and the negative peak voltage obtained from said second envelope detection circuit;
• a smoothing circuit for smoothing the sum voltage obtained from said adding circuit;
• a multiplying circuit for multiplying the smoothed sum voltage, which is outputted from said smoothing circuit, by a predetermined offset adjustment coefficient;
• and
• a quantization reference voltage control circuit for shifting, in response to the output signal of said multiplying circuit, the median of the quantization reference voltage of said analog-to-digital converter DC-wise in conformity with the offset derived from the asymmetry of the read signal, and controlling the upper limit and the lower limit of the quantization reference voltage to the values that correspond to the offset quantity;
• wherein said asymmetry correcting circuit is capable of correcting a vertically asymmetric distortion of the read signal waveform in said analog-to-digital converter.