JP2621231B2 - Mirror surface detection circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mirror surface detection circuit that detects a mirror surface from a high-frequency signal detected using light from an optical disk as a detection medium.

[Conventional technology]

FIG. 3 shows a track jump control unit in an optical disc reproducing apparatus for reproducing music information and the like recorded on an optical disc such as a CD (compact disc).

An optical disk (hereinafter referred to as a CD) 2 is rotated by a motor 4, and the motor 4 is controlled at a constant _{linear velocity} by a control output _DCLV of a linear velocity (CLV) servo (not shown).

The pickup 6 is armed by the rotation of the feed motor 8.
The laser light 14 emitted from the laser light source 12 can be moved to an arbitrary position in the diameter direction of the CD 2 through the laser beam 10, and the laser light 14 as a detection medium is focused by passing through an optical system including a half mirror 16 and an objective lens 18. By letting CD2
, And the reflected light 20 from the CD 2 is received by the light receiving elements 22, 24, and 26, and is converted into an electric signal. Then, the optical system adjusts the focus of the laser light 14 by the focus coil 28,
Laser light on track by tracking coil 30
Make 14 focuses.

The light receiving element 22 is a main beam of the laser light 14 and the light receiving element.
Reference numerals 24 and 26 convert the reflected light 20 of the sub-beam of the laser light 14 into an electric signal. The light receiving element 22 obtains a high-frequency (RF) signal by the main beam.

By the way, in the case of a track jump, for example, as shown in FIG. 4, a spot 32 of the main beam is scanned in a direction indicated by an arrow Y with respect to a CD 2 rotating in a direction indicated by an arrow X. In this case, 34 represents a pit (non-reflective surface) on the track, and 36 represents a mirror surface.

Then, the RF signal converted into an electric signal through the light receiving element 22 and obtained by passing through the preamplifier 38 is represented by A in FIG.
As shown in FIG. 5, the envelope representing the passage of the mirror surface 36 between the tracks, that is, the low frequency signal component Lf as the mirror surface information and the high frequency signal component Hf representing the passage of the pit 34, Has become.

Conventionally, a mirror surface detection circuit 40 for detecting a base track from a mirror surface between the tracks in the case of counting the number of passing tracks when the CD2 skips tracks using this RF signal is provided.

In that case, as shown in A of FIG. 5, detects the upper limit level is peak (Peak) level V _P of the RF signal, the RF signal by detecting the which is the lower limit level bottom (Bottom) level V _B after extracting the upper level and lower level of the envelope, set by the reference level setting circuit 42 to the reference level V _M in the middle. That is, the peak level detection circuit 44 for detecting a peak level V _P of the RF signal, npn
Type transistor 48 constitutes with a constant current source 50 and capacitor 52, constant tau _P when long corresponding to the peak level V _P in the capacitor 52 is set. Bottom level detection circuit for detecting a bottom level V _B of the RF signal 46, pnp-type transistor 54 constitutes with a constant current source 56 and capacitor 58, constant tau _B short time corresponding to the bottom level V _B at the capacitor 58
(<Τ _P ) is set. Then, the peak level detecting circuit 44, the output level V _P of the bottom level detection circuit 46, added from both ends of the series circuit of the V _B resistance 60 and 62, the reference level V from the midpoint by the ratio of resistors 60 and 62 _M is set.

Further, a low-frequency component detection circuit 66 for detecting a low-frequency signal component Lf indicating passage of the mirror surface 36 between tracks is provided,
The low-frequency component detection circuit 66 includes a pnp transistor 68, a constant current source 70, and a capacitor 72.
Sets a time constant τ ₀ (smaller than the time constant τ _B corresponding to the bottom level V _B ) corresponding to the low frequency signal component Lf.

The reference level V _M thus obtained and the low-frequency signal component Lf are added to a comparator 74 and compared with each other.
The mirror surface detection signal V _mr shown in FIG.

This mirror surface detection signal V _mr is added to the control unit 76 as track count information, and determines whether or not the set required number of tracks has been reached. The rotation of the feed motor 8 is performed until the control signal for skipping tracks output from the control unit 76 is applied to the drive unit 78 and the required number of tracks is reached, and the detection point of the pickup 6 is located on a predetermined track. It is set.

[Problems to be solved by the invention]

By the way, in such a mirror surface detection circuit 40,
When the time constant τ ₀ set in the low-frequency component detection circuit 66 is set to a specific value to increase the track jump speed of the pickup 6 (high-speed access), the mirror surface information is displayed as shown in FIG. 6A. Since the time constant τ ₀ is constant while the frequency of the low-frequency signal component Lf as a signal is high, the mirror surface detection signal V _mr obtained from the comparator 74 is temporally delayed from the original mirror surface 36. (Delay of phase), or the pulse width may be so narrow that detection of the mirror surface 36 becomes difficult.

When the time constant τ ₀ of the low frequency component detection circuit 66 is shortened in order to follow the above speed, the pickup 6
When the track jump speed is slow, the effect of the longest pit having a length of 11T becomes a problem. For example, in FIG. 7 of the A, appears as S _1, the envelope by S _2, etc. noise low-frequency signal component Lf within one track, as shown in B of FIG. 7, the low frequency by S _1, S ₂ Signal component Lf
Is detected as the mirror surface detection signal V _mr , and an error (chattering) occurs in the detection of the mirror surface 36.

Thus, the present invention is designed to accurately detect the mirror surface 36 even during high-speed access.

[Means for solving the problem]

As shown in FIG. 1, the mirror surface detection circuit according to the present invention uses an upper limit level (peak level _VP ) and a lower limit level (peak level VP) of a high-frequency signal (RF) detected from the optical disk 2 using light (laser light 14) as a medium. detecting a bottom level V _B) and a reference level setting means for setting an intermediate level of both the reference level V _M (the reference level setting circuit 42), with a constant tau ₀ at a specific time as a starting point the lower limit level of the high-frequency signal Low frequency component detection means for obtaining low frequency signal component Lf (low frequency component detection circuit
And 66), comparing means for comparing the low-frequency signal component Lf and the reference level V _M having passed through the low-frequency component detecting unit (comparator 74)
In the mirror surface detection circuit 40 that obtains a mirror surface detection signal V _mr representing the mirror surface 36, a low-pass filter 80 that removes high frequency components from the signal representing mirror surface information is provided on the output side of the low frequency component detection means. Install this low pass filter 80
The low-frequency signal component Lf ₀ that has passed through is added to the comparison means.

[Operation] With this configuration, the time constant τ ₀ of the low-frequency component detecting means is set to a value corresponding to the high-speed access speed. In this case, the mirror surface appearing on the output side of the low-frequency component detecting means is set. The components in the high-frequency band unnecessary for the mirror surface detection in the signal representing the information can be cut off by the low-pass filter 80, thereby realizing the accurate mirror surface detection.

〔Example〕

FIG. 1 shows an embodiment of a mirror surface detecting circuit according to the present invention.

In this mirror surface detection circuit 40, the configuration of the reference level setting circuit 42 is the same as that of the mirror surface detection circuit 40 shown in FIG.
At 72, a time constant τ ₀ enabling high-speed access is set.
The low-frequency component detection circuit 66 includes an npn-type transistor 68, a constant current source 70, and a capacitor 72, and the capacitor 72 has a time constant τ ₀ (bottom level) corresponding to the low-frequency signal component Lf.
V _B is smaller than the time constant τ _B corresponding to V _B ).

A low-pass filter (LPF) 80 for cutting off a signal component in a high-frequency band unnecessary for detecting a mirror surface and extracting a necessary low-frequency signal component Lf is provided on the output side of the low-frequency component detection circuit 66. It was installed.

The LPF 80 is configured by, for example, a circuit including a resistor and a capacitor, or a programmable low-pass filter that can be adjusted to an appropriate time constant.

In this case, the RF signal obtained through the preamplifier 38, a DC fluctuation of the reference level V _M and the envelope of the reference level setting circuit 42 from the (DC) at 400Hz frequency band occurs, the track information in a frequency band of 20kHz from 400Hz Is stored, and only pit information is contained in a frequency band exceeding 190 kHz. From the relationship between such a frequency band and necessary components, for example, the LPF 80 has a low frequency signal (20 kHz) representing the mirror surface 36. And no significant phase delay occurs. Set 160kHz (4 times 20kHz) or higher as the prohibited area.

Then, the reference level setting circuit 42, a peak level detecting circuit 44 is an npn transistor 48, with a constant current source 50 and capacitor 52, the constant tau _P when long set corresponding to the peak level V _P at the capacitor 52, detecting a peak level V _P is the upper limit level of the RF signal and the bottom level detection circuit 46, pnp-type transistor 54, a constant current source 56
And with a capacitor 58, the constant tau _B short time set corresponding to the bottom level V _B a capacitor 58, to detect the bottom level V _B is the lower limit level. After extracting the upper and lower levels of the envelope of the RF signal in this manner, the output levels V _P and V _B of the peak level detection circuit 44 and the bottom level detection circuit 46 are changed to both ends of the series circuit of the resistors 60 and 62. in addition the reference level V _M is set from the midpoint by the ratio of resistors 60 and 62.

Thus the reference level V _M obtained, and a low-frequency signal component Lf ₀ removing the unwanted signal components in LPF80 comparator 74
Can be compared with each other to obtain a mirror surface detection signal V _mr .

Therefore, an LPF 80 is provided at the output side of the low-frequency component detection circuit 66 for removing unnecessary signal components for the detection of the mirror surface 36 from the signal representing the mirror surface information, and as shown in FIG. As a result, erroneous detection of the mirror surface 36 can be prevented, and a phase delay can be prevented.
In particular, the effect of the longest pit generated in the conventional circuit can be avoided, and the phase lag during high-speed access and the mirror surface detection signal V _mr
Can be prevented, and chattering can be prevented even in low-speed access.

〔The invention's effect〕

According to the present invention, a low-pass filter that cuts off unnecessary high-frequency components on mirror surface detection included in a signal representing mirror surface information output by the low-frequency component detection unit is provided on the output side of the low-frequency component detection unit. Since the detector is installed, it is possible to prevent a detection error and a phase delay due to unnecessary high frequency components, and to realize a highly reliable mirror surface detection from high-speed access to low-speed access.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a mirror surface detection circuit according to the present invention, FIG. 2 is a diagram showing phase compensation of a low frequency component detection circuit in the mirror surface detection circuit shown in FIG. 1, and FIG. FIG. 4 is a circuit diagram showing a track skipping control unit in a conventional optical disc reproducing apparatus, FIG.
FIG. 7 to FIG. 7 are diagrams showing the operation of the mirror surface detection circuit in the track jump control unit shown in FIG. 2 Optical disk 14 Laser light (light) 36 Mirror surface 40 Mirror surface detection circuit 42 Reference level setting circuit (reference level setting means) 66 Low frequency component detection circuit (Low frequency component detection) Means) 74 Comparator (Comparison means) 80 Low-pass filter

Claims (1)

(57) [Claims] 1. A reference level setting means for detecting an upper limit level and a lower limit level of a high-frequency signal detected using light from an optical disc as a medium, and setting an intermediate level between the upper and lower levels as a reference level; The mirror surface includes low-frequency component detection means for obtaining a low-frequency signal component with a specific time constant as a starting point, and comparison means for comparing the low-frequency signal component passed through the low-frequency component detection means with a reference level. In a mirror surface detection circuit that obtains a mirror surface detection signal, a low-pass filter that removes high-frequency components from a signal representing mirror surface information is provided on the output side of the low-frequency component detection means,
A mirror surface detection circuit for adding the low-frequency signal component passed through the low-pass filter to the comparison means;