JPH07101225B2 - Disc player code jitter inspection device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc player code jitter inspecting apparatus, and more specifically, by measuring a jitter generated in a code reproduced by a CD player using a reference disc,
The present invention relates to a CD player code jitter inspection apparatus for inspecting the performance of a CD player.

[Prior Art] In the optical compact disc (hereinafter referred to as CD) system recently developed as an audio medium,
As shown in the figure, a circular track 1 is provided on the surface of an aluminum disc, and audio information coded along this is engraved as the length of a pit 2, and the pit is read by a laser beam to produce audio. Is to be played.

The CD track pitch is 1.6 μm, and the pit width is 0.5.
The minimum length is 0.9 μm and the minimum length is 0.9 μm, which has a high density and enables long-time recording. EFM is also used for audio information codes for faithful audio reproduction.
(Eight to For Modulation: E
ight to Fourteen Modulation) A special digital modulation called the method is performed and recorded.

In the EFM, each of the 8-bit structure and the 256-gradation code string representing the audio level is converted into 256 having a specific code structure out of the 14-bit structure. As the specific code configuration, the frequency band is compressed by selecting the minimum length as long as possible and the maximum length as short as possible, and the positive and negative polarities of the code are balanced as much as possible on average. Specifically, 11 bits out of 14 bits are assigned to voice, and the minimum Tmin is 3 bits and the maximum Tmax is 11 bits as shown in FIG. 6, and the bit length is 9 kinds. The remaining 3 bits are allocated to each voice unit.

In order to faithfully reproduce the audio signal from such a pit train, the CD player uses a high-precision laser-based pickup to reduce the tracking error, and the rotation is phase-locked loop (PLL) system. Thus, the linear velocity of reading is made constant, and thus the speed control is performed so that the time width of the reproduced code becomes constant for each code length. Furthermore, the reproduced signal of the pickup is once put in the buffer memory so that the frequency of the reproduced sound is strictly faithful to the original sound, where it is read out again with an accurate clock signal and then converted into sound and output. The method is taken.

In such a playback method, the first
The important thing is that the first read EFM code is correct, and for this reason, it is necessary that the pickup and other signal processing circuits are good or bad, and that the motor and its rotation control function are good. If these are defective or irregular, the reproduced code fluctuates, that is, jitter appears. Therefore, measuring this jitter is an important inspection item.

By the way, in the case where a reproduction pit signal of a compact disc contains a plurality of types of pulse widths at random, in order to select a desired pulse from these and measure its jitter, a circuit that selects the desired pulse Is complicated and the jitter inspection circuit is expensive.

[Object of the Invention] According to the present invention, in a disc player, jitter generated in a code string read by a pickup is measured, and statistical processing is performed on the jitter to create data for testing the EFM code reproducing function of the disc player. It is an object of the present invention to provide a disc player code jitter inspection apparatus.

[Means for Solving the Problems] A feature of the disc player code jitter inspection apparatus of the present invention which achieves such an object is that an electric signal obtained by reproducing a reference pit recorded on a reference disc mounted on a player is inputted. Then, a waveform shaping circuit for shaping a rectangular signal having a time width equivalent to this signal and a predetermined period before the trailing edge timing of the rectangular signal before delay corresponding to the pulse having the code length of the measurement target A delay circuit that gives a delay to the leading edge timing of the rectangular signal to the rectangular signal, a linear wave circuit that generates a linear voltage with a constant inclination angle at the timing of the leading edge of the delayed rectangular signal, and the rectangular signal before the delay. A jitter measuring circuit having a sample hall circuit that samples and holds the voltage value of the linear wave circuit at the timing of the trailing edge, and the jitter measuring circuit. And a data processing device for sampling and outputting a plurality of data at regular intervals based on an analog voltage indicating a temporal change in jitter output from the path.

The principle of the present invention will be described by taking a CD player as an example, and a method of inspecting by mounting a reference disc in which pits of regular lengths for various codes are randomly arranged at accurate positions of tracks, A method of measuring the jitter by this is shown in FIGS. 1 and 2. First, CD player 3
The waveform (a) indicating the original code of EFM is a rectangular wave (b) having the same time width Tp as that of (a) in the waveform shaping circuit 4, and then the length of the code (the number of bits) in the delay circuit 5.
A waveform (c) delayed by Td is created according to. What is important here is how to use Td, which will be described with reference to FIG. The figure (a) is the minimum code Tmin, and the figure (b) is the maximum code Tma.
Indicates x, and each has an accurate time width. Td is determined such that the remaining Trs obtained by subtracting Td from these code lengths Tmin or Tmax are the same for all code lengths. This enables the jitter measurement by the linear wave circuit 6 described below.

In the linear wave circuit 6, the rising time td of the waveform (C)
A linear voltage (d) starting from is generated, and this linear voltage (d) and rectangular wave (b) are input to the sample hold circuit 7. Here, the voltage value Vp of the linear voltage (d) at the falling time tp of the rectangular wave (b) is sampled and held.

Now, when jitter occurs and the time width Tp changes, the motion voltage Vp changes relative to the reference point at the falling time point tp of the waveform (b). Since the linear voltage value and the time have a linear relationship, the jitter is known by measuring the amount of change.

With respect to the waveform (a) that is randomly input, the above processing is sequentially performed for the code having the selected one type of code length. As a result, the output voltage Vp of the sample and hold circuit 7 has a stepwise waveform as shown in FIG. 1 (f), but when it is observed for a slightly long time, it is a curve as shown in FIG. As a result, the data processing device 8 obtains n pieces of data by sampling at times t ₁ , t ₂ , ..., Tn at regular intervals.

Codes of various lengths are randomly recorded on the tracks of the reference disc, and n is set to, for example, n with respect to the waveform curve (g) for the selected one of the code length columns.
The number of data is 1024, and the data processing device 8 performs necessary statistical processing to output and display statistical data. For example, in the case of the area averaging method, first, the central value Vs of n sampling data is calculated, then the difference between this Vs and each data is obtained, and then the average value of the differences is calculated.

Here, since the voltage vs. time characteristic of the linear wave circuit 6 is known, the statistical data of jitter can be known by a simple conversion.

Such measurement / processing is performed for each required code length.

Needless to say, the data processing device 8 can optionally perform a statistical method other than the above-described area averaging method.

[Operation] As described above, according to the disc player code jitter inspecting apparatus of the present invention, the code jitter generated by the mechanism of each part of the disc player, the circuit deficiency, or the malfunction causes the waveform shaping circuit 4 with respect to the original waveform. The delay circuit 5 processes the waveform, and the linear wave circuit 6, which has a linear voltage-time relationship, outputs the voltage as an amount of change in the voltage, and the sample-hold circuit for each code string having an appropriately selected code length. After that, statistical processing is performed in the data processing device 8 to create statistical data that can be used for product inspection. That is, as can be understood from FIG. 3, according to the present invention, a delay circuit is provided and the delay time is selected according to the pulse width of the pulse to be measured. The pulse can be selected more accurately, and the measurement of the jitter can be obtained as the change of the voltage value, which simplifies the jitter inspection apparatus.

[Embodiment] FIG. 4 shows an embodiment of a disc player code jitter inspection apparatus according to the present invention, and a portion added to the basic circuit shown in FIG. 2 will be described in detail. First of all, the jitter is measured not only on the pits of the disc but also on the pit-to-pit spacing as a negative sign.
The polarity of the signal (a) is selected by the input terminals 9a and 9b of the polarity selection circuit 9, and the pits are measured on the positive side and the pit intervals are measured on the negative side. Next, a code selection circuit 10 is provided to measure one of the randomly arranged codes of various code lengths. In this embodiment, the measurement target is a code having three code lengths, and the input terminals 10a, 10b,
Select and set by 10c. The code selection circuit 10 creates a signal by discriminating the code length of the EFM signal (a) from the CD player 3 with respect to the trailing phase of the waveform in terms of time. This signal is given to the sample hold circuit 7, and only the selected code is sampled and held.

Next, in this case, three delay circuits for three kinds of codes
a 5-1, b 5-2, and c 5-3 are provided, and the delay times thereof are Td according to each code length, as described above.

In the above, the type of code length may be arbitrary, for example, 3,
4 and 11 bits. Further, the number of types may be arbitrarily configured.

In the data processing device 8, the analog data of the sample hold circuit 7 is digitized by the A / D converter 8-1 and the above-mentioned processing is performed by the microcomputer 8-2.

[Effects of the Invention] As is clear from the above description, according to the disc player code jitter inspection apparatus of the present invention, the reproduced EFM signal of the disc player is waveform-shaped and polarity-selected by the delay circuit 5 and the linear wave circuit 6. After that, the code of various lengths randomly recorded on the reference disk and the interval between bits (as a negative code) are selected, and the jitter is accurately measured by the sample hold circuit 7 for each type. Since it is output as statistical data by the data processing device 8, this data is very effective for inspecting the malfunction of the pickup of the disc player product, the motor mechanism, or the rotation control by the PLL system.

[Brief description of drawings]

FIG. 1 is a signal waveform diagram for explaining a jitter measuring method in a disc player code jitter inspecting device according to the present invention, and FIG. 2 is a block configuration diagram of a basic circuit of the disc player code jitter inspecting device according to the present invention. FIG. 3 is a waveform diagram for explaining how to set the delay time in the delay circuit of FIG. 2, and FIG. 4 is a block diagram of the embodiment of FIG. FIG. 5 is a diagram of pits engraved on the track on the disc surface of the CD player, and FIG. 6 is a waveform diagram for explaining the signal length of the EFM signal recorded as the pit length on the disc. 1 ... Track, 2 ... Pit, 3 ... CD player, 4
... Waveform shaping circuit, 5 ... Delay circuit, 6 ... Linear wave circuit, 7 ... Sample and hold circuit, 8 ... Data processing device, 8-1 ... A / D converter, 8-2 ... Micro Computer, 9 ... Polarity selection circuit, 10 ... Sign selection circuit.

Claims (2)

[Claims] 1. A waveform shaping circuit for inputting an electric signal which reproduces a reference pit recorded on a reference disc mounted on a player and shaping it into a rectangular signal having a time width equivalent to this signal, and a code length to be measured. A delay circuit for delaying the rectangular signal by adjusting the leading edge timing before the trailing edge timing of the rectangular signal before delay corresponding to the pulse of Jitter having a linear wave circuit that generates a linear voltage with a constant inclination angle at the edge timing and a sample hold circuit that samples and holds the voltage value of the linear wave circuit at the timing of the trailing edge of the rectangular signal before delay From the measurement circuit and the analog voltage that shows the time change of the jitter output from this jitter measurement circuit, sample a plurality of data at regular intervals. Grayed to disc player code jitter inspection apparatus characterized by being constituted by a data processing device for generating and outputting the statistical data. " 2. A selection circuit for judging whether the electric signal reproduced from the reference pit is positive or negative and selecting one of them according to designation, and a plurality of delay circuits corresponding to various lengths of the reference pit. , Identify the length of the reference pit,
The disc player code jitter inspection apparatus according to claim 1, further comprising a code selection circuit that outputs a signal for operating a sample hold circuit for each length.