Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By pulse width or spacing
Reexamination Certificate
2002-02-20
2003-12-30
Le, Dinh T (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By pulse width or spacing
C327S551000
Reexamination Certificate
active
06670831
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a signal processing circuit and a signal processing method, and more particularly, to a signal processing circuit and a signal processing method that convert a frequency modulation signal into digital data.
2. Description of the Related Art
FIG. 6
is a block diagram showing the structure of an optical disk drive.
The optical disk drive
100
shown in
FIG. 6
is a CD-R drive, for example, on which a CD-R disk
40
is set. Information is recorded in, and read out of, the CD-R disk
40
.
The optical disk drive
100
is configured by an optical system
41
, a spindle motor
42
, a sled motor
43
, a laser driver
44
, a front monitor
45
, an auto laser power control (ALPC) circuit
46
, a recording compensation circuit
47
, a wobble signal processing unit
48
, an RF amplifier
49
, a focus/tracking servo circuit
50
, a radial servo circuit
51
, a spindle servo circuit
52
, a CD encoding/decoding circuit
53
, a D/A converter
54
, an audio amplifier
55
, RAMs
56
and
58
, a CD-ROM encoding/decoding circuit
57
, an interface/buffer controller
59
, and a CPU
60
. The optical disk drive
100
performs recording and reading out of data in response to a command sent by a host computer
61
.
The spindle motor
42
controlled by the spindle servo circuit
52
rotates the optical disk
40
at a predetermined rotational speed. The optical system
41
is facing the optical disk
40
. The optical system
41
records data by emitting a laser beam to the optical disk
40
, or reads out the data by detecting a reflectional laser beam from the optical disk
40
. The sled motor
43
and the focus/tracking servo circuit
50
control the position of the laser beam emitted to the optical disk
40
.
The sled motor
43
, which is controlled by the radial servo circuit
51
, actuates a carriage, part of the optical system
41
, in the radial direction. The focus/tracking servo circuit
50
controls a focus actuator and a tracking actuator (both not shown) of the optical system
41
.
The read signal outputted from the optical system
41
is provided to the RF amplifier
49
. The RF amplifier
49
amplifies the read signal. The read signal, after being separated into servo signals of different kinds, is provided to the CD encoding/decoding circuit
53
as a main signal. The servo signals are provided to each servo circuit.
The CD-ROM encoding/decoding circuit
57
performs operations such as encoding and decoding of the error correction coding (ECC) that is unique to the CD-ROM, and detecting a header. The RAM
56
provides the CD-ROM encoding/decoding circuit
57
with a working memory area. The interface/buffer controller
59
exchanges data with the host computer
61
and controls a data buffer. The RAM
58
provides the interface/buffer controller
59
with a working memory area.
In the case that the optical disk
40
is an audio disk, the read signal decoded by the CD encoding/decoding circuit
53
is transferred to the D/A converter
54
for the conversion into an analog signal, and amplified by the audio amplifier
55
.
The CPU
60
controls the entire operation of the optical disk drive.
FIG. 7
is a schematic sectional view showing the structure of an optical disk.
As shown in
FIG. 7
, a wobble
40
b
is formed along each track
40
a
on the CD-R disk
40
in advance. A wobble signal is obtained by detecting the wobble
40
b
. The wobble signal, which is modulated in FM, contains control information of different kinds, such as an address indicating a position in the optical disk
40
. The control information is obtained by demodulating the FM signal obtained by detecting the wobble
40
b
. In order to obtain correct information such as an address, it is necessary to convert the wobble signal modulated in FM into digital data.
FIG. 8
is a block diagram showing a conventional signal processing circuit as an example.
FIGS. 9
(A)-(D) are waveforms of the conventional signal processing circuit.
The signal processing circuit
500
shown in
FIG. 8
is configured by a rise/fall edge detecting circuit
501
, a counter circuit
502
, a latch circuit
503
, and a digital low pass filter (LPF)
504
.
The rise/fall edge detecting circuit
501
is provided with an FM signal shown in
FIG. 9
(A) inputted through an FM signal terminal
505
. The rise/fall edge detecting circuit
501
compares the FM signal with the zero level, and generates an FM pulse signal shown in
FIG. 9
(B) that is at a high level if the FM signal is higher than the zero level, and at a low level if the FM signal is lower than the zero level. The rise/fall edge detecting circuit
501
further generates a rise/fall edge signal shown in
FIG. 9
(C) by detecting rise edges and fall edges of the FM pulse signal. The rise/fall edge signal is provided to the counter circuit
502
, the latch circuit
503
, and the digital LPF
504
.
The counter circuit
502
is cleared in response to reception of the rise/fall edge signal sent from the rise/fall edge detecting circuit
501
, and counts the clock signals provided through a clock signal terminal
506
. The count of the counter circuit
502
changes as shown in
FIG. 9
(D), and is provided to the latch circuit
503
.
The latch circuit
503
is provided with the count of the counter circuit
502
and the rise/fall edge signal of the rise/fall edge detecting circuit
501
, and latches counts Q
1
-Qn in response to the rise/fall edge signal. The counts latched as Q
1
-Qn are sent to the digital LPF
504
.
The digital LPF
504
is provided with the counts of the latch circuit
503
and the rise/fall edge signal of the rise/fall edge detecting circuit
501
. The digital LPF
504
eliminates noise in the FM signal as a digital low pass filter based on the counts provided by the latch circuit
503
. A digital FM signal, after being processed by the digital LPF
504
, is outputted from digital FM signal terminal
507
. The digital FM signal is demodulated and the control information contained in the digital FM signal is extracted.
However, the actual FM signal contains significant noise.
With reference to
FIGS. 10
,
11
(A)-(D), and
12
(A)-(C), the operation of the conventional signal processing circuit is further described.
As shown in
FIG. 10
, the actual FM signal crosses across the zero level several times as it passes through the zero level region due to the noise. If the actual FM signal is converted into an FM pulse signal without any countermeasure for noise reduction, undesirable pulses, or chattering noise, is generated before and after the true FM pulse signal, as shown in
FIG. 11
(A). Because of the generation of these undesirable pulses (chattering noise), a plurality of undesirable rise/fall edges are generated as shown in
FIG. 11
(B). The counter circuit
502
counts, in response to these undesirable rise/fall edges, the clock signal. It is impossible to obtain an accurate FM pulse signal in this situation.
[Conventional Technique]
A method for detecting the rise/fall edges of the FM pulse signal, by excluding time periods in which chattering noise is generated, has been proposed. The method will be described with reference to
FIG. 12
below.
FIG. 12
is waveforms showing a conventional method for eliminating the noise.
FIG. 12
(A) is a waveform of an inputted FM pulse signal;
FIG. 12
(B) is a waveform of the FM pulse signal after noise-reduction; and
FIG. 12
(C) is a waveform of the rise/fall edge signal of the pulse signal after noise reduction.
In a conventional technique, an edge is identified subject to the level of an FM pulse signal remaining at the same level for a predetermined time period T
3
. The FM pulse signal rises to a high level at time t
1
, but it falls to a low level within the predetermined time period T
3
. It is assumed in this conventional technique that the rise edge of the FM pulse signal at time t
1
is generated by noise, and accordingly this rise edge is ignored. However, the FM pulse signal rises to a high level at ti
Anderson Kill + Olick P.C.
Le Dinh T
Lieberstein Eugene
Meller Michael N.
Teac Corporation
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