JPS61122959A - Tracking control circuit - Google Patents

Abstract

PURPOSE:To eliminate a change of a phase error signal characteristic due to not only an unevenness of a regenerating level of a pilot signal but also a head width and a change of a ratio of a track pitch by detecting a peak of a specific pilot signal taken out by a filter and the like. CONSTITUTION:Plural pilot signals having different frequencies between neighboring tracks and regenerated by a regenerating head 1 are processed by an LPF 3 and an amplifier 4 and a BPF 5 and a main track pilot signal is taken out. A peak of this signal is detected by a peak detector 6, fed back and a gain of the amplifier 4 is controlled. Accordingly, a processing corresponding to a level change of the pilot signal of the main track on which a characteristic of a phase error signal for controlling a tracing is carried out, and a tracing control circuit having no change in the phase error signal characteristic due to not only an unevenness in a regenerating level of the pilot signal but also a head width and a change of a ratio of a track pitch is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a tracking control circuit for a video tape recorder (hereinafter referred to as 'VTR') or the like.

(b) Conventional technology An example of a tracking control circuit that performs control using a pilot signal of a different frequency between adjacent tracks recorded on a track along with a recording signal is the Japanese Patent Publication Publication No. 59-3, for example.
There is one shown in Publication No. 1795. These tracking control circuits control the relative positions of the head and the main track so that the reproduction levels of pilot signals from both adjacent tracks of the main track being traced by the head are equal. That is, the head reproduces pilot signals having different frequencies from the main track and both adjacent tracks, and the tracking control circuit outputs the difference in each reproduction level from both adjacent tracks as a phase error signal. However, due to uneven characteristics of the recording medium, changes in the distance between the head and the recording medium, changes in the ratio of head width to track pitch (switching between standard mode and long-time mode in a VTR), etc., the overall level of the pilot signal reproduced by the head may vary. If this happens, the characteristics of the phase error signal output from the tracking control circuit which receives the output of the head as input will change, and of course the characteristics of the phase servo (pulling range, pulling time, etc.) will change, causing a problem.

Therefore, a method can be considered in which the level change of the entire reproduced pilot signal is removed using an AGC circuit to make the characteristics of the phase error signal constant. However, although it is effective against simple level changes, it is necessary to keep the characteristics of phase error No. 2 constant against changes in the frequency spectrum of the entire pilot signal due to changes in the head width to track pitch ratio, etc. The problem is that it is not possible. The above problem will be explained in detail below with reference to FIG.

The level of the phase error signal when the head position shifts to the center of the adjacent track (T2) with respect to the main track (T1) to be traced by the head, that is, the maximum level in this characteristic, is for a track that is two or more tracks away. (T4)
Assuming that the crosstalk level generated in the head by the pilot signal (T4) that has been completely recorded is almost zero, it is determined by the level of the pilot signal (T2) that can be reproduced from the adjacent track (T2). Also, from a different perspective, the level of the pilot signal (T2) reproduced from the adjacent track (T2) is determined by the level of the pilot signal (T2) reproduced from the main track (T1) when the head is accurately tracing the main track (T). In other words, the characteristics of the phase error signal depend on the level of the pilot signal regenerated from the main track.However, in the method using the AGC circuit, the level of the entire regenerated pilot signal Therefore, if the frequency spectrum of the entire pilot signal changes, even if the overall level is constant, the level of the pilot signal reproduced from the main track will change, so the phase that depends on it will change. The characteristics of the error signal will change.

(c) Problems to be Solved by the Invention The present invention solves the problem that the characteristics of the phase error signal change due to changes in the frequency spectrum of the entire regenerated pilot signal.

(D) Means for Solving the Problems The present invention includes a filter that extracts a specific pilot signal from a plurality of regenerated pilot signals, a detector that peak-detects the signal from the filter, and a detector that detects the peak of the signal from the filter. It is characterized by being provided with a pilot signal amplifier for use as a control signal.

(E) The present invention can be configured as described above, and the gain of the pilot signal amplifier is controlled by the peak level of a specific pilot signal.

(f) Embodiment Figure 1 shows an 8mm video tape recorder (hereinafter referred to as '8mmV').
FIG. 2 is a circuit configuration diagram showing an embodiment in which the present invention is applied to a tracking control circuit of a device (referred to as "TR"). (1> is the playback head, and the frequency multiplexer 1! is on the magnetic tape (not shown).
Regenerates broken video signals, FM audio signals, and pilot signals. In addition, in the 8m1IIVTR, the video signal for one field is recorded on one track, and four pilot signals are recorded on one track.
one low frequency signal, i.e. f' t -102,544
KHz, f 2 = 118°951KHz, f
' 3-165.210KH2, r 4 =148.
689 KHz is recorded in a circular order for each track. Therefore, the side wave number difference between the pilot signals of all two adjacent continuous tracks is about 16 KHz and about 46 KHz.
There are only types. The signal reproduced by the reproduction head (1) passes through a rotary transformer (2) and a low-pass filter (3), and only a pilot signal, which is a low frequency signal, is input to a pilot signal amplifier (4). Its output is fed back to the pilot signal amplifier (4) by a bandpass filter (5) that passes only the f't pilot signal and a peak detector (6). Details will be explained later. (7) is a mixer, in which the regenerated pilot signal is mixed with the output of the oscillator (8>).
It can be controlled by switching pulses, and the oscillation frequency is switched for each track so that it has the same frequency as the pilot signal recorded on the main track that the head is trying to trace. Then, in the mixer (7), a beat is generated between the pyroft signals of the adjacent continuous tracks, and signals of 16 KHz and 46 KHz are output. Note that the frequency of the pilot signal that can be reproduced from the main track is the same as the output wave number of the oscillator (8), so the beat frequency is zero. In addition, FIG. 3 shows the frequency of the pilot signal completely recorded on each track, the output frequency of the oscillator (8), and the mixer (7) using the pilot signal reproduced from the adjacent tracks (previous track, next track) to the main track. ), the frequency of the beat signal generated at the 0th order is 16 KHz from the output of the mixer.

Each 46KHz beat signal is passed through a 16KHz bandpass filter (10) and a 46KHz bandpass filter (
11) and detect the output of each bandpass filter! ! <12) <13) and converts it into a DC voltage according to the amplitude of each beat signal. Since the output level of the oscillator (8) is constant, these DC voltages are approximately proportional to the level of the pilot signal reproduced from the adjacent tracker, and the level changes depending on the tracking deviation of the head. Therefore, the two detectors (1
2) Input the output of (13) to the differential amplifier (14), and
The polarity switch (15) controlled by the F switching pulse is used to finally output as a phase error signal.The polarity switch (15), as shown in No. 311, outputs the 16KHz, 4'8KHz beat signal. but,
Since the output from the previous track or the next track is switched for each main track, the polarity of the output of the differential amplifier (14) is switched in synchronization with the RF switching pulse. .

A feature of the present invention is that the bandpass filter (5) and the peak detector (6) are provided. That is, the gain of the pilot signal amplifier (4) is controlled by the peak level of fl, which is a specific pilot signal.
In the case of normal regeneration, the pilot signal of 1 becomes the pilot signal acknowledged from the main track once every 4 feeds, but it is sufficient to use a peak detection circuit with a large time constant, and special regeneration can be used. In this case, the fl pilot signal is reproduced from the main track at a period corresponding to the reproduction speed. In addition, when a tracking deviation occurs during normal playback, the level of the pilot signal that can be reproduced becomes smaller than the main track, but the tracking deviation is transient, and the phase error signal eliminates the tracking deviation and lowers the level. There is no problem because it works in the direction of increasing the size.

The signal passed by the bandpass filter (5) was a pilot signal of rl in the embodiment, but it was a pilot signal of f2°f3. r4
It goes without saying that either of these may be used.

FIG. 2, like FIG. 1, is a circuit configuration diagram showing another embodiment in which the present invention is applied to a tracking control circuit of an 8 mm VTR. Compared to the first @, the gain control of the differential amplifier (14') is performed using the bandpass filter (5') and the peak detector (6'), and the pilot signal amplifier (4') has a fixed gain. are different. Since the other components are the same, the same components as in FIG. 1 are designated by the same reference numerals and detailed explanations are omitted.

(G) Effects of the Invention With the present invention, by simply adding n simple circuits, the characteristics of the phase error signal do not change not only due to variations in the reproduction level of the pilot signal but also due to changes in the ratio of the head width to the track pitch. A tracking control circuit can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a tracking control circuit embodying the present invention, and FIG. 2 is a circuit block diagram of another embodiment of the present invention. FIG. 3 is an explanatory diagram of the operation of FIGS. 1 and 2. FIG. 4 is a diagram for explaining the conventional problems. (4)...Pilot signal amplifier, (5)...Band pass filter, (6>...Peak detector.

Claims (1)

[Claims] (1) In a tracking control circuit that performs control using pilot signals of different frequencies between adjacent tracks recorded on a track together with a recording signal, a filter that extracts a specific pilot signal from a plurality of reproduced pilot signals; A tracking control circuit comprising: a detector that peak-detects a signal from a filter; and a pilot signal amplifier that uses the output of the detector as a control signal.