JPS58199413A - Reader of digital modulated signal - Google Patents

Abstract

PURPOSE:To obtain a tracking error signal accurately by providing the 1st comparing means which compares a reproduced signal with a specific level to obtain a waveform-shaped output and the 2nd comparing means which compares a high frequency component with a specific reference level, and obtaining a switching output according to the operation modes of said comparing means. CONSTITUTION:The cascade circuit of a high-pass filter 16 and a level comparator 17 is provided separately in parallel to an ATC circuit 10, and the output of the ATC circuit 10 and that of the level comparator 17 are inputted to a switch circuit 8. This switching circuit 8 is controlled by a device operation mode specifying signal to send the output of the ATC circuit 10 in normal reproduction mode and the output of the level comparator 17 in fast-forward mode selectively to differentiating circuits 9 and 11.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital modulation signal reading device, and
The present invention relates to an apparatus for reading recorded information using a modulation method in which the time ratios occupied by high level and low level per unit time are approximately equal when recording a (pulse code modulation) signal on a recording medium.

When recording a digital information signal such as a PCM signal on a recording medium, a predetermined modulation process is performed, and in this case, a modulation method is used in which the time ratios occupied by high level and low level per unit time are almost equal. There is.

This has the advantage that no DC component is included in the reproduced output. When reproducing such digitally modulated signals, due to the finite frequency characteristics of the recording medium, the reproduction RF
The (high frequency) signal does not become a rectangular wave but a sinusoidal distorted waveform. Therefore, in order to shape the sinusoidal distorted wave into the original rectangular wave, a level comparator is provided to compare the reproduced RF signal from the pickup with, for example, a zero level.

For example, in a recording/reproducing system such as a laser disc, where the state with pits corresponds to the low level of the digital modulation signal, and the state without pits corresponds to the no level, and these are detected optically. Since the presence or absence of pits is detected during reproduction using the amount of reflected light of the irradiated light to detect the binary level, the peak values of the high level and low level of the reproduced signal are not symmetrical. Even if the levels of this reproduced output are compared using a level comparator, it is not possible to obtain accurate original digital information.

Therefore, as shown in Fig. 1, the DC component contained in the output of the level comparator 1 for waveform shaping is detected by the integrator 2, and the output corresponding to this DC component is input to the differential amplifier 3. , this output is used as the comparison level of the level comparator 1. That is, if the DC component included in the output of level comparator 1 increases in the positive direction, the high level time rate 3- of the reproduction input increases, and therefore the comparison level of comparator 1 is changed accordingly. If it is increased, the time ratio of high level and low level becomes approximately equal. Conversely, if the DC component included in the output of comparator 1 increases in the negative direction, the high level time rate of the reproduction input becomes smaller, so the comparison level of comparator 1 decreases accordingly. and
It is designated as ATC (Automatic Threshold Control) circuit. Call AT
For details of the C circuit, please refer to the patent application filed by the applicant in 1982.
-215207 specification.

FIG. 2 is a block diagram of a circuit that uses the output of the above-mentioned ATC circuit 10 to generate a so-called tracking error signal that indicates the perpendicularity of the pickup information detection point and the recording track (disc radius) and the separation state in the direction. It is a diagram. Reference numeral 4 denotes a so-called four-division type light receiving element, and the reflected light of the pickup information detection spot light from the recording disk is irradiated onto this four-division light receiving surface. 5 and 6 are
This is an adder that receives the sum of the outputs of the light receiving elements arranged diagonally with each other, and the outputs of these adders 5 and 6 are further subjected to addition processing in the adder 7. The output of the adder 7, that is, the total power sum (4) of the light receiving element 4, is input to the ATC circuit 10, where it is waveform-shaped and becomes a reproduced output.
and input to 11.

Both differential outputs sample and hold the sampling pulses (C) and (D) of the sample held circuits 12 and 13, and the output (B) of the differential amplifier 14, respectively.

- The differential amplifier 14 subtracts the respective outputs of the adders 5 and 6, and this difference output (B) is input to the sample and hold circuit 12.13. The hold outputs (E) and (F) of both sample and hold circuits 12 and 13 are input to the differential amplifier 15, and the difference output (G) serves as a tracking error signal.

Figure 3 is an operational waveform diagram of the block in Figure 2.
) to (G) are the respective signals (A) to (G) of the block in Figure 2.
) It corresponds to each race. In the normal reproduction mode, the reproduced RF signal (A) obtained by 1b4÷41→kibit pickup (4) is shown in a case where the level fluctuates as shown in FIG. 3(A) 4- due to tracking deviation.

The output (B) of the differential amplifier 14 has a phase difference of 90' from the signal (A) as shown in FIG.

The zero cross point of the output of the ATC circuit 10 is the differential circuit 9.1
1, as shown in Figures (C) and (D). Since waveform (B) is sampled and held by these pulses (C) and (D), both pulses (C) and (D)
The field output will be as shown in Figures (E) and (F). Therefore, the difference signal from the differential amplifier 15 for both hold outputs is as shown in Figure (G), and when the reproduction RF level (A) is at its maximum.
-, the output (, G) is minimum (zero), and as the reproduction RF level becomes smaller, the absolute value level increases correspondingly. That is, the tracking state of the pickup can be detected by the signal (G).

In such a circuit configuration, it is necessary to generate a tracking error signal even when controlling the rapid forward movement of the information detection point in the disk radial direction, but the time constant of the ATC circuit 10 is generally an extremely large value of several tens of m5. The response is poor due to the fact that the tracking servo loop The reproduced RF signal waveform when open and fast forward movement control is performed.
Its envelope is about 10 to 20 KHz, so the ATC circuit 10
cannot respond. For this purpose, ATC circuit 1
The comparator level of 0 is a substantially constant value as shown by the dashed line in the figure, and hardly fluctuates. Therefore, since the comparator 1 of the ATC circuit 10 does not operate during the period in which the RF multiplied signal level between recording tracks is reduced, a waveform-shaped output cannot be obtained during that period, and an accurate tracking error signal cannot be obtained.

An object of the present invention is to provide a digital modulation signal reading device that can accurately obtain a tracking error signal not only during normal playback but also during fast forward operation.

A digital modulation signal reading device according to the present invention compares a reproduced signal obtained by picking up digital information recorded using a modulation method such that the occupied time rate per unit time of the bi-level and the low-level are approximately equal, with a predetermined comparison level. a first comparison means for shaping a waveform and outputting the resultant waveform, a means for detecting a DC component of the waveform shaping output and controlling the predetermined comparison level according to the DC component, and a high-frequency component of the reproduced signal. and a switch means for selectively outputting one of the outputs of the first and second comparing means depending on the device operating mode. There is.

The present invention will be explained below using the drawings.

FIG. 5 is a circuit diagram of an embodiment of the present invention, in which parts equivalent to those in FIG. 2 are designated by the same reference numerals.

In this example, a cascade circuit including an HPF (no pass filter) 16 and a level comparator 17 is separately provided in parallel with the ATC circuit 10, and the output of the ATC circuit 10 and the output of the level comparator 17 are connected to the switch circuit 8. I am trying to input it. This switch circuit 8 is controlled by a device operation mode command signal, and the output of the ATC circuit 10 is selected in the normal playback mode, and the output of the level comparator 17 is selected in the fast forward mode, and the differential circuit is operated. 9 and 11.

The other configurations are the same as those shown in FIG. 2, and their explanation will be omitted.

If the lower limit frequency of the HPF 16 is set to, for example, 20 KHz, the frequency of the envelope of the RF signal is 10~'201tG(
The reduced components below z are removed and input to the level comparator 17. FIG. 6 shows the output (
A) shows the signal waveform that has passed through the HPF 16. Therefore, the comparison level of the level comparator 17 at the next stage is set to RF in FIG.
If set at the center of the signal amplitude, a waveform-shaped signal will be obtained at the output of the level comparator 17, and this will be sent to the switch 8.
Since the differential circuits 9 and 11 select the exact rising and falling edges (zero cross point) of the RF multiplied signal
is detected. Therefore, an accurate tracking error signal can be obtained.

FIG. 7 is a diagram showing a specific example of a part of the circuit shown in FIG. 5, and portions equivalent to those in FIG. 5 are designated by the same reference numerals. The switch circuit 8 for signal selection includes transistors Q,...
This is a current switching type differential switch circuit having a transistor Q and a current source 11, and an operation mode command signal is applied to the base of a transistor Q2 via a resistor R1. A bias is applied to the base of transistor Q1, and this bias also serves as a base bias for transistor Q2 via the base-emitter junction of transistor QB.

A pair of collector outputs of the differential switch circuit 8 are connected to respective inputs of the current mirror circuits 18 and 19, and both current mirror circuits 18 and 19 attract currents corresponding to these input currents.

Differential circuits 1a and 17a are provided, each using the output suction currents of both current mirror circuits 18 and 19 as current sources. Reproduction R and F signals are applied. The differential circuit 17a has transistors Q6' and Q*, and the transistor Q6
A reproduced RF signal passed through the HPF 16 is applied to the base of the RF signal. Transistor Q4゜Q6. A bias is applied to each base of Q through resistors R4, Rr, and Re, respectively. And both differential circuits 1a, 17a
The outputs of each pair of are made common through the respective resistors R12 and R8, and these common outputs become regenerative shaping outputs through the amplifier 20 and are not switch outputs. , 11.

Further, the output of the amplifier 20 is applied to the level comparator 3 via the integrator 2, and the comparison output thereof serves as the base input of the transistor Q5.

In such a configuration, if the device is in normal playback mode,
The operation mode command signal is at the N/E level, the transistor Ql of the differential switch circuit 8 is turned on and the transistor Q2 is turned off. Therefore, the current mirror circuit 18
A current flows into the differential circuit 1a, activating the differential circuit 1a. The other differential circuit 17a is in an inactive state. Therefore, the reproduced RF signal from the pickup is transmitted through the differential circuit 1a and the amplifier 2.
0. Integrator 2. It will be input to an ATC circuit consisting of a level comparator 3. That is, the differential circuit 1a and the amplifier 20 operate as a level comparator at the input stage of the ATC circuit.

When the device is in the fast-forward operation mode, the operation monitor command signal is at a low level, the transistor Q2 is turned off, and current flows only into the current mirror circuit 19. As a result, only the differential circuit 17a is activated, and the reproduced RF signal is waveform-shaped through the HPF 16, the differential circuit 17a, and the amplifier 20, and then output as a switch output.

That is, the differential circuit 17a and the amplifier 20 operate as the level comparator 17 shown in FIG.

FIG. 8 is a diagram showing another specific example of a part of the circuit shown in FIG. 5, and the same parts as those in FIG. 5.7 are designated by the same reference numerals, and the explanation thereof will be omitted. The level comparator 3 of the ATC circuit 10 has a differential transistor Qs +Q9, and its current source is the output suction current of the current mirror circuit 18 which receives the collector current of the transistor Ql of the differential switch circuit 8 as input.

An eleventh current mirror circuit 21 which receives the collector current of the transistor Q9 as an input is provided, and the mirror output flows into the current mirror circuit 18. Also, a resistor R? is connected between the output terminal of the mirror circuit 21 and a predetermined bias. is provided, and the voltage generated by this resistor R7 is applied to the differential circuit 1a.
, 17a each transistor Qs +Q? This is the base input for . The output of the integrator 2 is applied to the base of the transistor Q9, and a bias is supplied to the base of the transistor Q8 via a resistor R8.

In such a configuration, in the normal reproduction mode, the transistor Q of the differential switch circuit 8 is turned on, and the current mirror circuits 18 and 21 are activated, respectively, so that the differential circuits 1a and 3 are activated. .

Therefore, the differential circuit 1a, the amplifier 20. The integrator 2 and the differential circuit 3 constitute an ATC circuit 10.

On the other hand, in the fast forward operation mode, the differential transistor Q is turned on and only the current mirror circuit 19 is activated, so that only the differential circuit 17a is in the operating state. At this time, the base reference voltage of transistor Q7 is determined by the bias provided by resistor R7.

12- Therefore, the reproduced RF signal is transmitted through HPF16. Differential circuit 17a
, the waveform is shaped through the amplifier 20 and becomes a switch output.

As described above, according to the present invention, it is possible to accurately obtain the tracking error signal required even during fast forward operation, and with the configuration shown in FIGS. 7 and 8, the level comparator 1 of the ATC circuit 10 Since the level comparator 17 and the level comparator 17 can have the same differential switch configuration, it is easy to integrate the circuit and the device can be miniaturized.

[Brief explanation of the drawing]

Figure 1 shows the ATC at the input stage of a digital modulation signal reading device.
Figure 2 is an input circuit diagram of a digital modulation signal reading device for obtaining a tracking error signal using a pickup reproduction RF signal, Figure 3 is a waveform diagram of each part of the circuit in Figure 2, and Figure 4 is a diagram showing the circuit. The figure is a waveform diagram of reproduced R and F signals during fast forward operation, Figure 5 is a circuit diagram of an embodiment of the present invention, and Figure 6 is a diagram of reproduced R and F signal waveforms during fast forward operation.
The output waveform diagram of HPF16 in the figure, Figures 7 and 8 are
FIG. 2 is a diagram showing a specific example of a part of the circuit shown in the figure. Explanation of symbols of main parts 1.3.17 ... Level comparator 2 ...
... Integrator 8 ... Switch circuit 18.19.21 ... Current mirror circuit Applicant Pioneer Corporation Agent Patent attorney Motohiko Fujimura

Claims (2)

[Claims] (1) Waveform shaping is performed by comparing the reproduced signal obtained by picking up digital information recorded using a modulation method such that the high level and low level occupy approximately the same time rate per unit time with a predetermined comparison level. The first output
a comparison means for detecting a DC component of the waveform shaping output and controlling the predetermined comparison level according to the DC component; and a second comparison for comparing the high frequency component of the reproduced signal with a predetermined reference level. and switch means for selecting and outputting either the first or second comparing means according to the operating mode of the apparatus. (2) The switch means is a differential switch circuit controlled in accordance with a command signal of the operation mode, and the first and second comparison means are configured to be connected to a pair of outputs of the differential switch circuit. 2. The device according to claim 1, comprising first and second differential circuits whose activation and deactivation are respectively controlled.