JPS6355155B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking control system for a grooveless capacitive disc player.

Reproduction methods for recording information signals such as video signals and audio signals on a disk-shaped recording medium (hereinafter referred to as a disk) and reproducing them using a disk player include a capacitance method and an optical method. The capacitance type includes a type with grooves for mechanically tracking the pickup, and a type without grooves in which tracking is electronically controlled. Here, we will use VHD, which is a type of capacitance method.
Let us explain the case without grooves.

In the case of VHD video discs, the recording signal band is much wider than that of audio signals.
Since the recording wavelength of the disk is also on the order of microns, the resolution for signal reproduction also requires a detection section with extremely high precision. Therefore, when playing a disc and performing tracking control, in order to increase the dynamic range of tracking control, AGC is applied to the tracking control signal to eliminate level fluctuations. That is,
It is well known that by applying AGC, the dynamic range of tracking control is increased by increasing the output difference between the inside and outside of the disk and the level fluctuation of the input control signal when changing the disk or pick-up needle.

However, if the pick-up needle for disk reproduction is damaged or if there is a large dropout in the control signal on the disk, it is impossible to perform accurate tracking control.
When such an abnormal situation occurs, it is necessary to quickly return the pick-up arm to the reject position. The control signal for returning the pick-up arm to the reject position is called an automatic reject signal, and conventionally, it is generated from a reproduction video signal generating circuit. A conventional example of this automatic reject signal generation method will be explained with reference to FIG. In Figure 1, 1 is the terminal to which the RF output signal is applied, 2
3 is an AGC amplifier, 3 is a detection rectifier circuit, and 4 is a DC voltage amplifier. The AGC amplifier 2, the detection rectifier circuit 3, and the DC voltage amplifier 4 constitute an AGC circuit A. 5 is a delay circuit to which the output of the DC voltage amplifier 4 is input. 6 is a waveform shaping circuit, and delay circuit 5
It converts the signal output from the terminal into a pulse waveform and outputs an automatic reject signal to the terminal 7. Generally, a circuit made up of the above circuit elements is called a reproduced video signal generation circuit. Next, 8 is a low pass filter that in this case passes only the tracking control signal.
9 is an AGC amplifier, 10 is a detection rectifier circuit, and 11 is a DC voltage amplifier.
Configure circuit B. Reference numeral 12 denotes a tracking control circuit which is operated by a tracking control signal sent from the AGC. Now, suppose that an RF output signal picked up from the disk is continuously applied to terminal 1. This RF output signal is subjected to AGC in AGC circuit A and then input to low-pass filter 8. The low-pass filter 8 passes only the tracking control signal, which is further subjected to AGC in the AGC circuit B, and then passes through the tracking control circuit 12.
is input. Therefore, as the RF output signal increases or decreases, the output of the DC voltage amplifier 4 also fluctuates, but as mentioned above, if the pick-up needle for disc playback is damaged or there is a large dropout in the control signal on the disc (dropout). If the RF output signal cannot be picked up, as in the case of
The output of the DC voltage amplifier 4 varies extremely. The output of the DC voltage amplifier 4 at this time is delayed by a delay circuit 5 and converted into a pulse waveform by a waveform shaping circuit 6 to obtain an automatic reject signal.

However, when tracking control is performed by obtaining an automatic reject signal from the playback video signal generation circuit as described above, AGC circuit A for applying AGC to the RF signal, AGC circuit B for applying AGC to the tracking control signal, and AGC circuit B for applying AGC to the tracking control signal. This has the disadvantage that two stages of circuitry are required and the number of circuit elements increases.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and the automatic reject signal is directly obtained from the DC voltage that controls the gain of the AGC amplifier that applies AGC to the tracking control signal. Make the circuit one stage,
The aim is to significantly reduce the number of circuit elements.

An embodiment of the present invention will be described below with reference to FIG. In FIG. 2, 13 is a terminal to which an RF output signal is applied, and 14 is a low-pass filter that in this case passes only the tracking control signal. 15 is
The AGC amplifier 16 is a detection rectifier circuit, and 17 is a DC voltage amplifier. The AGC amplifier 15, the wave rectifier circuit 16, and the DC voltage amplifier 17 constitute an AGC circuit C. 18 is a delay circuit into which the output of the DC voltage amplifier 17 is input. A waveform shaping circuit 19 converts the signal output from the delay circuit 18 into a pulse waveform and outputs an automatic reject signal to a terminal 20. 21 is a tracking control circuit;
The AGC circuit C is operated by the tracking control signal applied by the AGC.

Now, suppose that the picked-up RF output signal from the disk is continuously applied to terminal 13.
In the low-pass filter 14, only the tracking control signal among the RF output signals is passed and inputted to the AGC circuit C. This tracking signal is subjected to AGC in an AGC circuit C and is input to a tracking control circuit. Here, if the RF output signal cannot be picked up, such as when the pick-up needle for disk playback is damaged or there is a large dropout in the control signal on the disk, the gain control of the AGC amplifier 15 is performed. , the output of the DC voltage amplifier 17 changes drastically. The output of the DC voltage amplifier 17 at this time is delayed by a delay circuit 18,
The waveform shaping circuit 19 converts it into a pulse waveform to obtain an automatic reject signal.

In the above embodiment, a type of capacitance method is used.
I explained about VHD format video discs,
A similar effect can be achieved for tracking control of AHD audio discs.

As described above, in a grooveless capacitive disc player, if an abnormal situation occurs during playback, such as breakage of the pick-up needle or large signal loss on the disc, the pick-up arm is returned to the reject position. Tracking control signal input to the tracking control circuit
Since it is supplied from AGC circuit C, the number of circuit elements can be significantly reduced compared to the conventional system.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional automatic reject signal generation system, and FIG. 2 is a block diagram showing an embodiment of the present invention. 15...AGC amplifier, 16...detection rectifier circuit,
17...DC voltage amplifier.

Claims (1)

[Claims] 1. In a grooveless capacitive disc player, if an abnormal situation occurs during playback, such as breakage of the pick-up needle or large signal loss on the disc, the control circuit tracks the control signal to return the pick-up arm to the reject position. A system for generating an automatic reject signal in a disc player, characterized in that a tracking control signal input to the AGC circuit is supplied from an AGC circuit.