JP2658449B2 - Auto tracking device - Google Patents

Description

The present invention relates to a video tape recorder (hereinafter referred to as a VTR).
Etc.) etc.

2. Description of the Related Art FIG. 3 is a block diagram showing an example of a conventional auto tracking device in a VTR. As shown, the capstan 2 drives the magnetic tape 1 in the direction of arrow A. Then, the rotary head 3 comes into contact with the magnetic tape 1. The FM-modulated video signal reproduced by the rotating head 3 is guided to a reproduction signal processing circuit 5 such as an FM demodulator via an amplifier circuit 4 and to an envelope detection circuit 6. A detection signal having a level corresponding to the envelope of the reproduced signal, which is the output of the envelope detection circuit 6, is input to a tracking control circuit 7, and a capstan motor 8 for driving the capstan 2 so that the level of the detection signal is maximized. Is changed to change the relative position between the rotary head 3 and the recording track 10 on the magnetic tape 1.

However, in the conventional configuration, the reproduction signal level input to the envelope detection circuit 6 and the detection signal voltage output have a linear relationship as shown in FIG. In addition, the rate of change of the output voltage with respect 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 reproducing a magnetic tape having a poor recording state, a change in the level is unlikely to appear as a change in the output voltage, and tracking control becomes difficult. For example, it is assumed that the input / output characteristic of the envelope detection circuit in the conventional configuration is a straight line A in FIG. Considering 30mVpp and 300mVpp as input signals,
The output voltage change voltage that appears when the level changes by ± 20% is 1.2 Vpp for the input level of 300 mVpp,
At 0mVpp there is only 0.12Vpp. As described above, if the input signal level is low, the output voltage hardly changes, and tracking control becomes difficult.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide an automatic tracking device capable of performing accurate tracking control even when a signal level input to the envelope detection circuit is low.

Means for Solving the Problems In order to achieve this object, an auto-tracking device of the present invention creates a control signal in which the envelope level is continuously logarithmically compressed from a reproduction signal, and sets the control signal so that the control signal is maximized. In this configuration, the relative position between the signal conversion element and the recording track is changed.

Operation With this configuration, since the output signal of the envelope detection circuit is logarithmically compressed and output by the logarithmic compression circuit, it is equal to the rate of change of the reproduction signal level using continuous control characteristics regardless of the reproduction signal level. A change voltage of the change rate is obtained, and a sufficient dynamic range and tracking accuracy are obtained from a minute input reproduction signal level to a large signal level.

Embodiment An embodiment of the present invention will be described below with reference to FIG. 1 and FIG.

In the figure, the same components as those of the conventional example shown in FIG. The difference between the present 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 thus configured auto-tracking device will be described below with reference to FIG.

As in 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 to a signal corresponding to the envelope of the reproduction signal by the envelope detection circuit 6 and 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, a continuous control signal subjected to logarithmic compression processing has a change voltage having a change rate equal to the change rate of the reproduction signal level regardless of the reproduction signal level.
Accurate tracking control is obtained. Referring to FIG. 2, for example, it is assumed that the input / output characteristic of the logarithmic compression circuit 9 including the envelope detection circuit 6 in the present embodiment is a straight line A '. Input signal levels 30mVpp and 30
The change voltage of the output voltage that appears when both 0mVpp changes by ± 20% is 0.52Vpp. in this way,
If the rate of change of the input signal level is equal, the change of the output voltage is also equal, so that tracking control is possible for a wide range of input signal levels. In the case of continuous playback of a continuous shot tape, no gain switching occurs even at a minute playback signal level during a non-recording period, so that continuous tracking is performed over all playback signal levels without changing tracking accuracy. Control becomes possible.

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

In the embodiment, the reproduction signal is converted to DC by the envelope detection circuit 6 and then subjected to the logarithmic compression processing by the logarithmic compression circuit 9. However, the respective signals may be exchanged and the logarithmic compression processing may be performed to convert to DC. .

As is clear from the above description of the embodiment, the auto-tracking device of the present invention is capable of performing auto-tracking in a wide range of reproduction signal levels by providing logarithmic compression means, and in particular, reproducing a magnetic tape having a poor recording state. It is effective in such a case.

[Brief description of the 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 a relationship between a reproduction signal and a control signal of the device, FIG. 3 is a block diagram of a conventional auto tracking device, FIG. 4 is a characteristic diagram showing a relationship between a reproduction signal and a control signal of the device. 1 ... magnetic tape, 2 ... capstan, 3 ... rotary head, 4 ... amplification circuit, 6 ... envelope detection circuit,
7: tracking control circuit, 8: capstan motor, 9: logarithmic compression circuit, 10: recording track.

Claims (1)

(57) [Claims] 1. A control signal in which an envelope level is continuously logarithmically compressed by a reproduction signal reproduced from a recording track by a signal conversion element, and the control signal is recorded with the signal conversion element so that the control signal is maximized. An automatic tracking device characterized by changing a relative position with respect to a track.