Dropout detection circuit and optical disc apparatus
View Patent ↗The dropout detection circuit of the invention includes: a high-speed envelope detection circuit for detecting an envelope of a reflection signal of a light beam with a first time constant; a low-speed envelope detection circuit for detecting an envelope of the reflection signal with a second time constant larger than the first time constant; a differential circuit for generating a difference signal indicating the difference between the envelopes detected by the envelope detection circuits; and a comparator for converting the difference signal to a binary value according to a predetermined binary criterion. The high-speed envelope detection circuit makes the first time constant larger during recording than during reproduction, to enable stable dropout detection irrespective of during reproduction or during recording.
1. A dropout detection circuit comprising:
first envelope detection means for detecting an envelope of a reflection signal of a light beam converged on an optical disc for irradiation of the optical disc with a first time constant;
second envelope detection means for detecting an envelope of the reflection signal with a second time constant larger than the first time constant;
differential means for generating a difference signal indicating a difference between the envelope detected by the first envelope detection means and the envelope detected by the second envelope detection means; and
comparator means for converting the difference signal generated by the differential means to a binary value according to a predetermined binary criterion,
wherein the first envelope detection means sets the first time constant to be larger during recording than during reproduction.
2. The dropout detection circuit of claim 1 , wherein the first envelope detection means and the second envelope detection means set the first time constant and the second time constant to be identical to each other at the time of switching from reproduction to recording or from recording to reproduction.
3. The dropout detection circuit of claim 2 , wherein the first envelope detection means and the second envelope detection means set the first time constant and the second time constant to be identical to each other for a predetermined time period from the time of switching.
4. The dropout detection circuit of claim 1 , further comprising variable gain means for changing the amplitude of the reflection signal of the light beam converged on the optical disc for irradiation of the optical disc to a predetermined amplitude at a predetermined gain,
wherein each of the first and second envelope detection means detects an envelope of the reflection signal changed by the variable gain means.
5. The dropout detection circuit of claim 4 , wherein the first envelope detection means and the second envelope detection means set the first time constant and the second time constant to be identical to each other at the time of switching from reproduction to recording or from recording to reproduction, and
the variable gain means uses different values of the predetermined gain between during recording and during reproduction.
6. The dropout detection circuit of claim 4 , wherein the first envelope detection means and the second envelope detection means set the first time constant and the second time constant to be identical to each other at the time of switching from reproduction to recording or from recording to reproduction, and
the comparator means uses different values of the binary criterion between during recording and during reproduction.
7. The dropout detection circuit of claim 4 , wherein the first envelope detection means and the second envelope detection means set the first time constant and the second time constant identical to each other at the time of switching from reproduction to recording or from recording to reproduction,
the variable gain means uses different values of the predetermined gain between during recording and during reproduction, and
the comparator means uses different values of the binary criterion between during recording and during reproduction.
8. An optical disc apparatus comprising the dropout detection circuit of any of claims 1 to 7 .