JPH03187056A - Auto-tracking device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to, for example, a video tape recorder (hereinafter referred to as VTR).
) and other auto-tracking devices.

BACKGROUND OF THE INVENTION FIG. 3 is a block diagram showing an example of an auto-tracking device in a conventional VTR. As shown in the figure, the magnetic tape 1 is driven in the direction of arrow A by the capstan 2. Then, the rotary head 3 comes into contact with the magnetic tape 1. The FM-modulated video signal reproduced by the rotary head 3 is guided to a reproduced signal processing circuit 5 such as an FM demodulator via an amplifier circuit 4, and also to an envelope detection circuit 6. A detection signal at a level corresponding to the envelope of the reproduced signal output from the envelope detection circuit 6 is input to a tracking control circuit 7, and a capstan motor 8 drives the capstan 2 so that the level of the detection signal is maximized. Rotating head 3
The relative position between the recording track 10 on the magnetic tape 1 and the recording track 10 on the magnetic tape 1 is changed.

Problem to be Solved by the Invention However, in the conventional configuration, the reproduction signal level input to the envelope detection circuit 6 and the output detection signal voltage have a linear relationship as shown in FIG. However, the rate of change of the output voltage relative to the rate of change of the signal level changes depending on the input signal level. Therefore, when the input signal level is low, such as when a magnetic tape with poor recording condition is reproduced, a change in level is difficult to be detected as a change in output voltage, making tracking control difficult. For example, assume that the input/output characteristic of the envelope detection circuit in the conventional configuration is a straight line A in FIG.

As human signal, 30mVp p and 300mVp
Considering p, the change in output voltage that occurs when the level changes by ±20% is the input level of 300 m.
Vpp is 1.2Vpp versus Noni, 30mVp pi?
Ha0.12Vp pL. In this way, if the input signal level is small, it is difficult for the output voltage to change.
Tracking control becomes difficult.

The present invention solves the above-mentioned conventional problems, and aims to provide an auto-tracking device that can perform accurate tracking control even if the signal level input to the envelope detection circuit is small.

Means for Solving the Problems To achieve this object, the auto-tracking device of the present invention generates a control signal whose envelope is logarithmically compressed from a reproduced signal, and converts the signal conversion element so that the control signal is maximized. The configuration is such that the relative position between the recording track and the recording track is changed.

Effect With this configuration, the output signal of the envelope detection circuit is logarithmically compressed by the logarithm compression circuit and output.
Regardless of the reproduced signal level, a changing voltage having a rate of change equal to the rate of change of the reproduced signal level can be obtained, so it is possible to widen the range of reproduced signal levels that can be tracked.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIGS. 1 and 2.

In the figure, the same components as those in the conventional example shown in FIG. 3 are given the same reference numerals, and their explanations will be omitted. The difference between this embodiment and the conventional example is that the output of the envelope detection circuit 6 is input to the tracking control circuit 7 via the logarithmic compression circuit 9.

The operation of the auto-tracking device configured as above will be described below with reference to FIG. 2.

Similar to the conventional example, the reproduced signal amplified by the amplifier circuit 4 is input to the envelope detection circuit 6. The input reproduction signal is converted into a DC signal according to the envelope of the reproduction signal by the envelope detection circuit 6 and is input to the logarithmic compression circuit 9 .

The logarithmically compressed signal is input to the tracking control circuit 7 and used as a control signal.

As shown in FIG. 2, the logarithmically compressed IIJ ga multiplied signal produces a changing voltage with a rate of change equal to the rate of change of the reproduced signal level, regardless of the reproduced signal level, so accurate tracking control can be obtained. To explain with reference to FIG. 2, it is assumed that the input/output characteristics of the logarithmic compression circuit 9 including the envelope detection circuit 6 in this embodiment are linear. Input signal level 30mVpp, same as conventional example
and 300 mVpp both change by ±20%, the output voltage changes are both 0.52 Vpp.

In this way, if the rate of change in the input signal level is equal, the amount of change in the output voltage is also equal, so tracking control can be performed over a wide range of input signal levels.

As described above, according to this embodiment, by providing the logarithmic compression circuit, tracking control can be performed over a wide range of input signal levels.

In the embodiment, the envelope detection circuit 6 converts the reproduced signal into DC, and then the logarithmic compression circuit 9 performs logarithmic compression processing, but it is also possible to replace each signal and perform logarithmic compression processing, and then convert it into DC. .

Effects of the Invention As is clear from the description of the embodiments above, the auto-tracking device of the present invention is capable of auto-tracking over a wide range of playback signal levels by providing logarithmic compression means, and is particularly useful for playing back magnetic tapes with poor recording conditions. It is effective in such cases.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an auto-tracking device according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the relationship between reproduction signals and control signals of the same device, and Fig. 3 is a block diagram of a conventional auto-tracking device. , FIG. 4 is a characteristic diagram showing the relationship between the reproduction signal and the control signal of the same device. 1... Magnetic tape, 2... Capstan, 3... Rotating head, 4... Amplifying circuit, 6... Envelope detection circuit ,7...
...Tracking control circuit, 8... Capstan motor, 9... Logarithmic compression circuit, 10...
... Recording track.

Claims (1)

[Claims] A control signal whose envelope is logarithmically compressed is created using the reproduction signal reproduced from the recording track by the signal conversion element, and the relative position between the signal conversion element and the recording track is changed so that the control signal is maximized. Auto-tracking device.