Jitter measuring method utilizing A/D conversion and device

A device for measuring jitter in pulse width modulated signals previously recorded on an optical disk in units of cycles and being reproduced therefrom, comprising:

• an optical pickup for detecting a cyclic signal reproduced from said optical disk;
• an analog-to-digital converter for sampling said cyclic signal at a predetermined sampling interval so as to define sampling points, thereby producing sample data corresponding to the signal level of the cyclic signal at each of the sampling points;
• an operation processing means for computing a timebreadth corresponding to a time interval for which the signal level exceeds a slice level;
• said timebreadth being computed by:
• computing a first time point at which the signal level first exceeds said slice level, by interpolating between the sampling point first exceeding said slice level and the previous sampling point;
• computing a second time point at which the signal level first drops below said slice level subsequent to said first time point, by interpolating between the sampling point last exceeding said slice level and the next sampling point;
• computing a first time interval corresponding to the time between said first time point and the sampling point first exceeding said slice level;
• computing a second time interval corresponding to the time between the sampling point first exceeding said slice level and the sampling point last exceeding said slice level;
• computing a third time interval corresponding to the time between said second time point and the sampling point last exceeding said slice level;
• and
• computing said timebreadth by adding the first, second, and third time intervals;
• and
• said operation processing means further calculating a jitter measurement based upon the difference between the computed timebreadth and a cyclic window corresponding to a theoretical timebreadth of the cyclic signal as recorded.