JPS6356007A - Envelope detection circuit - Google Patents

Abstract

PURPOSE:To change the response against the envelope change depending on the reproducing state by providing a variable gain circuit so as to change at least one level of an envelope signal and an amplitude level signal. CONSTITUTION:A reproducing signal S is inputted to an input terminal 1 and signals M, N and R are obtained respectively by a maximum level detector 2, a minimum level detector 3 and an envelope detection circuit 4. The signals M and N are added by an adder 8 whose output level is variable, the output level is controlled by a signal V inputted from a control signal input terminal 9 to form a signal Q. Signals Q and R are compared by a comparator 6 to obtain an output signal C. A proper gain is given to a variable gain circuit for the normal reproduction and in other cases in this way to obtain an envelope detection signal whose response with respect to the envelope change depending on the reproducing state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an envelope detection circuit for recording information signals, etc.

[Conventional technology]

FIG. 5 is a block diagram showing a conventional envelope detection circuit disclosed in, for example, Japanese Patent Application Laid-Open No. 58-143472. In the figure, 1 is an input terminal, 2 is a maximum level detector, and 3 is a maximum level detector. 4 is an envelope detection circuit that takes the envelope of the input signal; 5 is the maximum level detector 2 mentioned above;
and an adder that outputs the average value of the two input signals from the minimum level detector 3, 6 a comparator, and 7 an output terminal.

Further, FIG. 6 is a diagram for explaining the signal flow of the circuit of FIG. 5.

Next, the operation will be explained. At the input terminal 1, the signals shown in FIG. 6, M, N, and R are detected through the path 4, respectively. The signals M and N are compared by an adder 5 with the output R of the oil passage 4 by a comparator 6, and a signal C shown in FIG. 6('b) is output.

[Problem that the invention seeks to solve]

Since the conventional envelope detection circuit is configured as described above, there is a problem in that the slice level of the comparator cannot be changed, and the response to envelope changes cannot be changed depending on the reproduction state.

This invention was made to solve the above-mentioned problems, and provides an envelope detection circuit that can change the slice level of the comparator and change the response to envelope changes depending on the playback state. The purpose is to

[Means for solving problems]

The envelope detection circuit according to the present invention is provided with a variable gain circuit to change the level of at least one of the envelope signal and the amplitude level signal.

[Effect]

In this invention, since the slice level of the comparator can be changed by the variable gain circuit, the response to envelope changes can be changed depending on the reproduction state.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure shows an envelope detection circuit according to an embodiment of the present invention, in which 1 is an input terminal, 2 is a maximum level detector, 3 is a minimum level detector, and 4 is an envelope detection circuit that takes the envelope of the input signal S. 8 is a variable output level adder that sums the output of the maximum level detector 2 and the output of the minimum level detector 3 and outputs the average value of the re-output; A control signal input terminal is used to input a control signal, 6 is a comparator, and 7 is an output terminal.

Next, the operation will be explained. Input terminal 1 is connected as shown in Figure 2 (
A reproduced signal S' shown in a) is input, and signals M, N, and R are obtained by the maximum level detector 2, the minimum level detector 3, and the envelope 'gA detection circuit 4, respectively. Signal M
and the signal N are added by the adder 8, and the signal V shown in FIG.
The output level is controlled by Q, resulting in the signal shown in Q.

Signal Q and signal R are compared by comparator 6 and shown in FIG.
The output signal C is shown in C).

In the above embodiment, the amplitude level is obtained directly from the reproduced signal, but the amplitude level may be obtained from the envelope signal of the reproduced signal.

Further, in the above embodiment, only the output level of the adder was changed, but it is also possible to change only the output level of the envelope detection circuit, or both the output level of the adder and the output level of the envelope detection circuit. The same effect as in the above embodiment can be obtained.

The usefulness of the present invention will become more apparent when applied to a recording information signal reproducing device.

Next, a case where the above embodiment is used in a tracking servo of an optical disc reproducing device will be described as an example.

BACKGROUND ART Conventionally, in an optical disk reproducing apparatus, a pickup reproducing element is tracking-controlled using a tracking error signal so that the pickup reproducing element accurately follows a recording track.

The method of adjusting the loop gain in such a tracking servo circuit is to close the servo loop during normal playback, and in the case of signal loss due to scratches, etc., if the servo gain is high, the spot may move to an adjacent track. Therefore, the servo loop is opened for a very short period of time. The opening and closing of this loop is controlled by the signal C shown in Figure 6(b), but in the conventional method, the slice level P shown in Figure 6(ta+) cannot be varied, so the signal level may change due to fingerprints attached to the disc. If the servo loop decreases, the servo loop will also open and tracking will become unstable.

On the other hand, in the device using the present invention, since the slice level can be varied, tracking can be easily stabilized even if the signal level decreases.

FIG. 3 shows a conventional example of a tracking servo circuit as described above. In the figure, 10 is a photodetector that outputs a current according to the amount of incident light, 11, 13, and 14 are preamplifiers for converting the output current of the photodetector 10 into voltage, and 12 is a conventional An envelope detection circuit, 15 a differential amplifier, 16 a servo loop 0N10FF switch, 17 a phase compensation circuit, 18 a phase compensation changeover switch, 19 an amplifier, and 20 an actuator.

Next, the operation will be briefly explained.

The information on the disc is read by the photodetector 10, and currents corresponding to the intensity of the light incident on portions B and C are input to preamplifiers 13 and 14, respectively, where the valley current is converted to voltage. And these amplifiers 1
The output of 3.14 is calculated by the differential amplifier 15 and becomes a tracking error signal. The tracking error signal is turned into an optimal signal by the phase compensation circuit 16 and amplifier 19, and is applied to the actuator 20. On the other hand, a current whose magnitude corresponds to the intensity of the light incident on the part a at the back of the photodetector 10 is converted into a voltage by the preamplifier 11, and an envelope detection circuit 12 outputs a pulse when a signal is missing. In response to this pulse, the phase compensation changeover switch 18
．． Switch the servo loop 0N10FF switch 16.

FIGS. 4(a) and 4(c)) show the reproduction signal and tracking error signal of the optical disc reproduction device when the disc has scratches. If the signal is lost as shown in this figure, the tracking error signal will be disturbed, and if the servo gain is normal, the beam spot may move to the adjacent track. Therefore, the envelope detection circuit is used to prevent the beam spot from moving. It is necessary to turn off the servo loop for a short period of time.

FIGS. 4(C) and 4(d) show reproduction signals and tracking error signals when there are fingerprints on the disc. As shown in this figure, even when the level of the reproduced signal decreases, if the servo loop is turned off, the period during which the level of the reproduced signal decreases is long, making reproduction very unstable.

Furthermore, the servo loop must be kept closed because the tracking error signal remains undisturbed and there is no risk of the beam spot moving to an adjacent track even if the gain remains increased.

Moreover, FIGS. 4(e) and 4(f) show the reproduction signal and tracking error signal at the time of jumping.

In this case, it is necessary to turn the servo loop ON10FF by the envelope detection circuit according to the movement of the beam spot.

Therefore, in the circuit shown in FIG.
If 2 is a conventional circuit configuration, set the servo loop to 0.
Since the slice level for N10FF is constant, for example, if a proper slice level is given at the time of a jump, the servo loop will open even if there is a fingerprint.
The tracking servo is unstable. On the other hand, with the circuit configuration of the present invention, the slice level can be changed between jump and normal playback, and the servo loop will not open if the signal level only decreases like a fingerprint. , it is possible to obtain an extremely stable tracking servo circuit in which the servo loop opens only in the case of a complete signal loss such as a scratch.

〔Effect of the invention〕

As described above, according to the envelope detection circuit according to the present invention, by giving appropriate gains to the variable gain circuit both during normal playback and in other cases, the response to envelope changes can be changed depending on the playback state. This has the effect of providing a detection signal.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram showing an envelope negative extraction circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing signals of the circuit of FIG. 1, and FIG. A block configuration diagram showing an example of use in an optical disc playback device, FIG. 4 is a diagram showing playback signal waveforms and tracking error signal waveforms in the optical disc device, and FIG. 5 is a block configuration diagram showing a conventional envelope detection circuit. 6 is a waveform diagram showing signals of the circuit of FIG. 5. In the figure, 2 is a maximum level detector (first peak level detector), 3 is a minimum level detector (second peak level detector), 4 is an envelope detection circuit (envelope detection means),
6 is a comparator (comparison means), and 8 is an adder (variable gain circuit) with variable output level. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (3)

[Claims] (1) An envelope detection circuit that obtains an envelope detection signal having a different level depending on whether a reproduction signal reproduced from a recording medium is above or below a slice level obtained from the reproduction signal, the envelope detection circuit of the reproduction signal envelope detection means for obtaining a line signal; amplitude detection means for detecting the amplitude level of the reproduced signal; and changing the amplitude of at least one of the two detection output signals from the envelope signal and the amplitude detection means. 1. An envelope detection circuit comprising: a variable gain circuit; and comparison means for discriminating an envelope detection signal from the amplitude of one output signal and the amplitude of the other output signal from the variable gain circuit. (2) The amplitude detection means includes a first peak level detector that detects the maximum level of the reproduced signal, and a second peak level detector that detects the minimum level of the reproduced signal. An envelope detection circuit according to claim 1, characterized in that: (3) The envelope according to claim 1 or 2, wherein the variable gain circuit is controlled so that its gain is different during normal playback of the recording medium and in other cases. Line detection circuit.