Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-04-05
2001-02-13
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S2140LS, C369S044320
Reexamination Certificate
active
06188060
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a signal reproduction apparatus of an optical disk player, for example a compact disk (CD) player, and more particularly, to an optical signal conversion apparatus in which peaking detected from an RF signal read from a disk is compensated in order to reproduce a stable output signal.
2. Description of the Related Art
In general, a CD player includes a preamplifier, a data strobe portion, a digital signal processor, an analog-to-digital (A/D) converter, and an analog circuit portion. The preamplifier amplifies a signal sensed by a photodiode, removes noise and distortion from the signal using a waveform equalizer, and then transmits the signal to the digital signal processor following waveform-shaping. The preamplifier commonly includes an adder, an automatic gain controller (hereinafter “AGC”), a waveform equalizer and a data slicer circuit.
The data slicer circuit shapes the signal waveform equalized by the waveform equalizer and converts the signal into a rectangular pulse. Since a slice level should be set at the center of an eye pattern, if the slice level is set at a level beyond the center of the eye pattern, an error is generated in the pulse width of the positive and the negative and accordingly a data error is generated. This asymmetry phenomenon commonly occurs when the degree of asymmetry in the CD data pits is greater than 20%.
The data slicer circuit commonly includes a correction circuit for correcting the asymmetry phenomenon. The eye pattern may have a defect due to a pin-hole generated during the disk manufacturing process. When the eye pattern is applied as an input to an eight-to-fourteen modulation (EFM) circuit and then passed through a passive high pass filter (hereinafter “HPF”), a peaking phenomenon of the eye pattern occurs wherein the eye pattern is not integrated instantaneously in the defect interval. Thus, in EFM slicing, since the EFM input does not trace DC offset instantaneously, it is sliced at an incorrect DC level thereof. The incorrect DC level causes troubles in error correction (hereinafter “ECC”).
The EFM signal conversion apparatus used for the conventional optical disk reproduction system including a high frequency slicer, or an RF slicer, converts an RF signal into a digital EFM signal. A typical EFM signal conversion apparatus slices an RF signal received by a photodiode.
FIG. 11
is a circuit diagram showing a conventional EFM signal conversion apparatus. The EFM signal conversion apparatus includes a capacitor C, a comparator
110
, operational amplifiers
112
and
114
, resistors R
1
, R
2
, R
3
, and R
4
, resistors R
5
and R
6
and capacitors C
1
and C
2
constituting a two-stage low pass filter (LPF)
116
, and invertors I
1
and I
2
constituting a MOS buffer
118
.
In the operation of the EFM signal conversion apparatus having an eye pattern of a CD player as a non-inverting input of the comparator
110
, a DC offset is extracted by passing the output of the comparator
110
through the two-stage LPF
116
. The extracted DC offset is fed back as an inverting input of the comparator
110
. The comparator
110
corresponds to the above-described data slicer circuit. As the eye pattern is applied as the input of the comparator
110
, the eye pattern passes through an HPF differentiator.
The capacitor C shown in
FIG. 11
as receiving an RFO signal output from the photodiode removes a DC component from the RFO signal and outputs the RFI signal removed of the DC component to the non-inverting input terminal of the comparator
110
. Here, the comparator
110
compares the RFI signal input to the non-inverting input terminal thereof with the signal output from the operational amplifier
112
and outputs the comparison result as a digital EFM signal via an output terminal OUT. After being buffered in the MOS buffer
118
, the digital EFM signal passes through the LPF
116
, where DC offset is detected, and an asymmetry buffer and an asymmetry amplifier, and finally is fed back to the comparator
110
. Here, the asymmetry buffer corresponds to the operational amplifier
114
of an emitter-follower type and the asymmetry amplifier consists of the resistors R
1
, R
2
, R
3
, and R
4
and the operational amplifier
112
.
In the conventional EFM signal conversion apparatus, since the asymmetry phenomenon occurring due to manufacturing deviation cannot be removed with only an AC coupling, it is used when the probability of generation of
1
or
0
according to the digital EFM signal is 50%. However, when a defect occurs such as a scratch or pin-hole, this technique is time consuming, as long as the external time constant, for example approximately 5 ms, in order that the slice reference level for the eye pattern tracks an accurate DC level for the eye pattern following the defect interval.
Accordingly, during the period of an input signal where there is no eye pattern or wherein the eye pattern is defective, when the abnormal signal portion is differentiated, the DC level of the eye pattern may instantaneously peak. Since it normally takes a long time to extract a DC offset, the eye pattern cannot be sliced during this brief period. Namely, in the conventional EFM signal conversion apparatus, when an optical disk contains a scratch or pin-hole defect, it is a problem that it takes a time as long as the external time constant for the slice reference level output from the operational amplifier
112
to trace an accurate DC level of an RF signal.
Further, since the asymmetry of the RF signal is not appropriately compensated during the period where defects exist, an error correction portion connected to the rear end of the EFM signal conversion apparatus is prevented from accurately correcting errors.
SUMMARY OF THE INVENTION
To solve the above problem, it is an object of the present invention to provide an optical signal conversion apparatus in an optical disk reproduction system which prevents peaking of an analog signal input to a data slicer to accurately reproduce a conversion signal, for example an EFM signal.
It is another objective of the present invention to provide an optical signal conversion apparatus, for example an EFM signal conversion apparatus, of an optical disk reproduction system for detecting a stable EFM signal which detects peaking of an analog input signal according to the pulse width of an EFM output signal and controls the signals input to the data slicer according to the state of detection.
Accordingly, to achieve the first objective, there is provided an optical signal conversion apparatus, for example an EFM signal conversion apparatus, for converting an RF input signal read from a disk into an EFM signal, the apparatus comprising: a peaking prevention portion which detects peaking of the RF input signal and outputs a predetermined reference voltage, if the peaking is detected, or alternately the input signal, if the peaking is not detected; and a waveform processing portion which extracts a high frequency component from the signal output from the peaking prevention portion, slices the extracted signal as a predetermined level, and outputs the sliced signal.
The peaking prevention portion preferably comprises: a peaking detector which detects peaking of the input signal and outputs a control signal according thereto; and a selector which receives a predetermined reference voltage and the input signal and selects and outputs the reference voltage if the peaking is detected, or the input signal if the peaking is not detected, in response to the control signal.
The peaking detector preferably comprises: a bottom envelope detector which amplifies the input signal and outputs the same, if the input signal is higher than a predetermined threshold voltage, and otherwise, outputs the threshold voltage; an envelope hold circuit which responds rapidly to rise of an output signal from the bottom envelope detector and slowly to fall of the output signal from the bottom envelope detector; and a comparator which compares the output signal
Jang Young-wook
Kim Je-kook
Le Que T.
Samsung Electronics Co,. Ltd
Samuels , Gauthier & Stevens, LLP
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