Digital automatic gain control of a multilevel optical disc read signal
View Patent ↗A system and method are disclosed for providing a gain control signal for a multilevel read signal. In one embodiment, maximum automatic gain control marks are periodically inserted amongst a series of data fields. The automatic gain control marks include a series of high level marks such that the maximum signal detected in the interior portion of each maximum automatic gain control mark is not reduced by intersymbol interference. Minimum automatic gain control marks are also periodically inserted amongst a series of data fields. The automatic gain control marks include a series of high level marks such that the maximum signal detected in the interior portion of each minimum automatic gain control mark is not reduced by intersymbol interference. In another embodiment, multilevel signals are encoded to facilitate automatic gain control. The effect of a plurality of candidate merge symbols on the residual running total power associated with a current data block is determined. A preferred merge symbol is selected based on a residual running total power minimization criteria. The preferred merge symbol is added to the current data block.
1. A method of determining a gain control signal for a multilevel read signal comprising:
detecting a maximum signal in an interior portion of a maximum automatic gain control mark wherein the automatic gain control mark includes a series of high level marks such that the maximum signal detected in the interior portion of the maximum automatic gain control mark is not reduced by intersymbol interference;
detecting a minimum signal in an interior portion of a minimum automatic gain control mark wherein the automatic gain control mark includes a series of low level marks such that the minimum signal detected in the interior portion of the minimum automatic gain control mark is not reduced by intersymbol interference;
determining the envelope of the signal from the maximum signal and the minimum signal; and
computing a gain control signal such that variance in the envelope of the signal over time is reduced.
2. A method of determining a gain control signal for a multilevel read signal as recited in claim 1 wherein the gain control signal controls a digital gain amplifier.
3. A method of determining a gain control signal for a multilevel read signal as recited in claim 1 wherein the gain control signal controls an analog variable gain amplifier.
4. A method of determining a gain control signal for a multilevel read signal as recited in claim 1 wherein the maximum automatic gain control mark and the minimum automatic gain control mark are combined so that the DC value of the combined mark is zero.
5. A method of determining a gain control signal for a multilevel read signal as recited in claim 1 wherein an average maximum is determined over a plurality of maximum signals and an average minimum is determined over a plurality of minimum signals and wherein the envelope of the signal is determined using the average maximum and the average minimum.
6. A method of determining a gain control signal for a multilevel read signal as recited in claim 5 wherein the average maximum is determined using a sliding window.
7. A method of determining a gain control signal for a multilevel read signal as recited in claim 5 wherein the average minimum is determined using a sliding window.
8. A method of determining a gain control signal for a multilevel read signal as recited in claim 1 wherein the multilevel read signal is read from an optical disc.
9. A method of encoding a multilevel signal comprising:
periodically inserting a maximum automatic gain control mark amongst a series of data fields wherein the automatic gain control mark includes a series of high level marks such that the maximum signal detected in the interior portion of the maximum automatic gain control mark is not reduced by intersymbol interference; and
periodically inserting a minimum automatic gain control mark amongst a series of data fields wherein the automatic gain control mark includes a series of high level marks such that the maximum signal detected in the interior portion of the minimum automatic gain control mark is not reduced by intersymbol interference.
10. An automatic gain control circuit comprising:
an envelope detector configured to compute a gain control signal by:
detecting a maximum signal in an interior portion of a maximum automatic gain control mark wherein the automatic gain control mark includes a series of high level marks such that the maximum signal detected in the interior portion of the maximum automatic gain control mark is not reduced by intersymbol interference;
detecting a minimum signal in an interior portion of a minimum automatic gain control mark wherein the automatic gain control mark includes a series of low level marks such that the minimum signal detected in the interior portion of the minimum automatic gain control mark is not reduced by intersymbol interference; and
determining the envelope of a read signal from the maximum signal and the minimum signal; and
a variable gain amplifier controlled by the gain control signal such that the variance of the envelope of the read signal over time is reduced.
11. A multilevel write channel comprising:
a data source; and
a symbol merger configured to insert a maximum automatic gain control mark wherein the automatic gain control mark includes a series of high level marks such that the maximum signal detected in the interior portion of the maximum automatic gain control mark is not reduced by intersymbol interference and to insert a minimum automatic gain control mark wherein the automatic gain control mark includes a series of low level marks such that the minimum signal detected in the interior portion of the minimum automatic gain control mark is not reduced by intersymbol interference.
12. A multilevel medium comprising:
data fields containing data;
maximum automatic gain control marks wherein the automatic gain control mark includes a series of high level marks such that the maximum signal detected in the interior portion of the maximum automatic gain control mark is not reduced by intersymbol interference; and
minimum automatic gain control marks wherein the automatic gain control mark includes a series of low level marks such that the minimum signal detected in the interior portion of the minimum automatic gain control mark is not reduced by intersymbol interference;
wherein the minimum automatic gain control marks and the maximum automatic gain control marks are periodically inserted between the data fields.