Optical disc reproduction apparatus

1. An optical disc reproduction apparatus, comprising:

a signal reproduction circuit configured to reproduce a wireless frequency signal from an optical disc, and convert the wireless frequency signal to a digital signal including a plurality of digital values in synchronization with a predetermined sampling clock;

a demodulation circuit configured to perform demodulation to the digital signal; and

a jitter detection circuit configured to detect an absolute jitter value to be an index of signal quality of the digital signal in parallel with the demodulation by the demodulation circuit,

wherein the jitter detection circuit includes

an instantaneous jitter information detection section configured to detect, based on first and second digital values of the digital signal which indicate different polarities relative to a predetermined reference value, an instantaneous gradient value corresponding to a difference value between the first and second digital values, and an instantaneous deviation value corresponding to a difference value between an intermediate value between the first and second digital values and the reference value,

an information conversion section configured to convert, based on an inversely proportional conversion table showing a correspondence relationship between the instantaneous gradient value and an inversely proportional value which is inversely proportional to the instantaneous gradient value, the instantaneous gradient value detected by the instantaneous jitter information detection section to the inversely proportional value,

an arithmetic section configured to detect an instantaneous variance value by multiplying the instantaneous deviation value detected by the instantaneous jitter information detection section and the inversely proportional value obtained by the information conversion section together, and squaring a value obtained by the multiplication, and detect an integrated value by accumulating the instantaneous variance value, and

a standard deviation detection section configured to detect a square root of a mean value of the integrated value as the absolute jitter value, and

the information conversion section limits the inversely proportional value so that the inversely proportional value is smaller than a predetermined value.

2. The optical disc reproduction apparatus of claim 1 , wherein a time distance between the first digital value and the second digital value corresponds to one cycle of the sampling clock.

3. The optical disc reproduction apparatus of claim 1 , wherein a bit width of the inversely proportional value obtained by the information conversion section is different from a bit width of the instantaneous gradient value.

4. The optical disc reproduction apparatus of claim 1 , wherein the instantaneous jitter information detection section discerns a rising edge at which the second digital value is larger than the first digital value, and a falling edge at which the second digital value is smaller than the first digital value, and detects the instantaneous gradient value and the instantaneous deviation value, when only one of the rising edge and the falling edge is generated.

5. The optical disc reproduction apparatus of claim 1 , wherein the jitter detection circuit further includes an asynchronous transfer section provided between the arithmetic section and the standard deviation detection section, and configured to hold the integrated value detected by the arithmetic section with a timing corresponding to an operation of the arithmetic section, and transfer the held integrated value to the standard deviation detection section with a timing corresponding to the operation of the standard deviation detection section.

6. The optical disc reproduction apparatus of claim 1 , wherein the optical disc is any one of a CD, a DVD, a DVD-RAM, and a BD.