JPS60211655A - Tracking device - Google Patents

Abstract

PURPOSE:To prevent the interference of the pull-in of a tracking servo and the attacking time of an AGC circuit with each other when the operation mode is shifted to the playing mode, by providing a gain controlling circuit which fixes the amplitude of reproduced pilot signals and a circuit which cuts off the control voltage of a control circuit. CONSTITUTION:Four kinds of pilot signals, whose frequencies circularly change at every tracks, are recorded on each recording track of a magnetic tape 1 together with information signals. Reproduced signals from heads A and B are supplied to an AGC circuit 4 through a switch SW1 which is switched by an RF switching pulse impressed upon a terminal 2. The output of the circuit 4 is inputted in a multiplier circuit 6 and the output of a reference signal generating circuit 7 is impressed upon another input of the circuit 6. Tracking control is performed by means of the output of an amplifier 8 and a detecting circuit 21 supplies a control voltage having a prescribed attacking time and recovery time to the circuit 4. When shifting to the playing mode, the control voltage is cut off by a switch SW2 and interference of the pull-in of a tracking servo and the attacking time of the AGC circuit with each other can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Analysis of the Invention] The present invention relates to a tracking device in a magnetic recording/reproducing device such as a video tape recorder (hereinafter referred to as VTR toy).

[Technical background of the invention]

In a VTR, during reproduction, it is important to control the relative position of the head to the recording track (tracking control) so that the head accurately runs along the recording track.

As this tracking control.

There is a method proposed in Japanese Patent Application Laid-Open No. 53-116120. That is, at the time of recording, a multi-frequency pilot signal whose frequency changes in a manner of For example, a reference signal having the same frequency as the pilot signal recorded on the playback track (therefore, the frequency of this signal changes for each playback track in the manner of fl+4)
is supplied to one input end of the multiplication circuit.

A reproduced pilot signal containing crosstalk from both adjacent trunks of the reproduced track is supplied to the other input terminal of the 1 calculation circuit. Two types of difference frequency signals corresponding to the lead and lag of the head relative to the track are obtained from the multiplication circuit. These difference frequency signals are then led to a subtraction circuit to extract the level difference between the two, and output it in accordance with the deviation of the head relative to the track.

This output is used to perform head tracking control.

[Problems with background technology]

By the way, in the above tracking device, if an AGC (automatic gain control) circuit is incorporated in order to adjust the gain of the pilot signal.

There are two loops: a control loop (servo loop) that performs the original tracking and the AGC loose loop. Therefore, the control loop as a servo loop and the AU
Since the C loop controls the same signal (pilot signal), the time constant of the servo loop and the time constant of the AGC loose cause mutual interference, and when transitioning from still image playback (still) mode to playback (play) mode, Another disadvantage is that the AGC of the pilot signal interferes with the servo pull-in when transitioning from the fast-forward signal playback (cue) or rewind playback (revue) modes to the playback mode.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned points, and is designed to apply AGC to a regenerated pilot signal, which is a control signal, and to prevent mutual interference from occurring when the signal is used to form a servo loop. The purpose is to

[Summary of the invention]

In the present invention, in the mode before shifting to the playback mode,
The control voltage of the AGC circuit of the pilot signal is temporarily cut off so that the original AGC time constant is always maintained, so that there is no influence on the servo loop (interference with servo pull-in). .

[Embodiments of the invention]

Hereinafter, one embodiment of the tracking device according to the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

The configuration and playback operation will be explained below.

A pilot signal is recorded along with an information signal on each recording track of the magnetic tape (1). This pilot signal is one in which four types of pilot signals with different frequencies are recorded in a cyclical order on a recording trunk, and the recording pattern is shown in FIG. fl to f4 indicate the frequencies of pilot signals having different frequencies recorded on the recording tracks.

Note that arrows (a) and (b) indicate the tape moving direction and head scanning direction, respectively. Also, To, T,, T,
. . is the track recorded by head B, and T, , T, , T, . . . are the tracks recorded by head A.

The magnetic tape (1) is reproduced by heads A and B, which are mounted on a rotating disk facing approximately 180 degrees and have different gap azimuth angles.

First, the information signal and pilot signal on the tape (1) reproduced by heads A and B are applied to the terminal (2) using the RF
The signals are alternately input to the regenerative preamplifier (3) through the switch SW1, which is switched by a switching pulse. The output of this amplifier (3) is adjusted by an AGC circuit (4) so that the width level of the reproduced pilot signal is constant. The control signal for this circuit (4) will be described later. Next, the output of the AGC circuit (4) is input to a low pass filter (LPF) (5), where a signal in the frequency band of the pilot signal is extracted. This extracted signal is input to one input terminal of the multiplication circuit (6). A reference signal from a reference signal generation circuit (7) is supplied to the other input terminal of the multiplication circuit (6). This circuit (7
) outputs a signal with the same frequency as the four types of pilot signals recorded on tape (1) as a reference signal in the same circulation order as the recorded pilot signal, and the switching is synchronized with the RF switching pulse. There is. Therefore,
From the multiplication circuit (6), the position deviation (advance) of head A and head B relative to the normal scanning trunk is calculated as shown in the following table.

and delay).

Margin below This will be explained in detail below.

Now, one wave number f, to f of the recorded pilot signal is set to 6.
5 f) I, ? , 5 fH, 10,5bt, 9.
5 fH and consider tracking of head B. Now, if head B is scanning a recording track of Tt, head B will send an information signal and frequency f,
The pilot signal is played back. In addition, pilot signals of frequencies f1 and so on from adjacent tracks T, , T8 are also reproduced as crosstalk components. In this case, since the frequency band of the pilot signal is within about 100 to 150 KHz, there is almost no azimuth loss effect. Therefore,
The pilot signal of the adjacent track can be reliably reproduced even from the side of the head. On the other hand, the reference signal generation circuit (
7) supplies a reference signal having the same frequency (fl) as the pilot signal recorded on track T. Therefore, the output of the #I calculating circuit (6) is 1. as a signal corresponding to the tracking state of head B. For the same track (T,), zero ('t - ft=0),
For the previous track T+ (advance component), fH (= l
An output signal (difference frequency signal) having a frequency of 3rH (=lfs-ttl) is obtained for the later track Ts (delayed component) of fl-fl + ). Truck T0. The same thing applies to the scans of T, T8+, and so on. After all, from the multiplication circuit (6), the progress of heads A and B with respect to the regular track to be scanned.

A signal having the same wave number components (fH, 3fH) corresponding to the delay is obtained. As shown in the table, the frequency corresponding to the delay is inverted for each track. In order to correct this inversion state, a polarity inversion circuit (Ill) is provided as described later.

The output of the multiplication circuit (6) is then amplified by an amplifier (8), and then a band-pass filter (BPF) that extracts the first signal of the 3fH component (91 and a band-pass filter (BPF) that extracts the fH acid component signal) This is input to Q(2). Then, this BPF (9), (1(* (7)
The output is detected by a wave detector (111, H).

The signal level difference between the two is extracted by a comparator (13).

This output corresponds to the offset position (advance or lag) of heads 8 and B with respect to the trunk to be scanned.

As mentioned above, the polarity of the output signal of the ratio 12 (+9) is input to the ua for each track for lead and lag, so that the polarity is kept constant.

If the head scan is proceeding with respect to the track to be scanned, the polarity is inverted so that a signal of positive polarity (or negative polarity) is constantly obtained. Power.

This polarity inversion circuit I includes a phase inverter Q5 and a terminal (16).
It is composed of a switch SW3 which is alternately switched by an RF switching pulse inputted from the switch SW3.

Finally, the output of the one-phase inversion circuit u4) is applied to the capstan motor register (G) via the amplifier α, the loop compensation filter 0, and the motor drive circuit 09 in this order. This controls the υ capstan motor (2).

Tracking of heads A and H will be performed.

Next, the control signal to the AOC circuit (4) will be explained.

The signal that controls the AGC circuit (4) (first gain control) is created by the detection circuit (2υ).The input of this circuit Uυ is taken from the output of the circuit (6), but this is 1
From the input terminal of the calculation circuit (6) or BPF f9+
, fIQ) may be added and extracted. In the detection circuit Q1), a control signal (control voltage) having a predetermined attack time and recovery time is generated.

By the way, let's take the output voltage of this detection circuit υ as an example.

OFF signal of capstan motor (a) (motor OFF
(high level) (m3) (see Figure (a) 9) to maintain zero potential during the still mode, when the mode transitions from the still mode to the play mode.

The AGC control voltage rises with a time constant of 1 as shown in FIG. 3(b). This eliminates interference with the servo loop time constant. Therefore, the servo loop can be pulled in smoothly when the mode changes from still to play (when the capstan motor changes from OFF to ON). Switch SW2 is for this purpose.
Its opening/closing is controlled by the carburetor engine OFF signal applied to the terminal (22).
) If the signal to 71 is level, this switch SW2
is closed, and the output of the detection circuit Cυ flows to the ground terminal via switch SW2.

The output potential becomes zero. Note that when the above operation to zero potential is not performed, the AG
The original time constant does not hold true for the C control voltage.

This will interfere with the servo loop time constant. 1 more
If this example is applied not only when transitioning from still to play, but also when transitioning from key or levy to play, the servo loop will be pulled in AGC loosely in the same way as when transitioning from still to play. It runs smoothly without any hindrance.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to prevent mutual interference between the tracking servo pull-in and the attack time of the AGC circuit when transitioning from a mode other than the play mode to the play mode, and achieve smooth tracking servo pull-in. can do.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the tracking device according to the present invention, FIG. 2 is a diagram illustrating a recording pattern of a tape used in the device shown in FIG. 1, and FIG. 3 is a diagram similar to that shown in FIG. FIG. 3 is a waveform diagram for explaining the operation of the device. 4. AGC circuit, 6... 扛) Arithmetic circuit. 7...Reference signal generation circuit. 9.10... Bandpass filter. 11.12...Detection circuit, 13...Comparator. 20...Capstan motor. 21...Detection circuit, SW2...Switch. Agent Patent Attorney Noriyuki Chika 1st Lambda

Claims (2)

[Claims] (1) When equalizing a recording medium on which an information signal and a multi-frequency pilot signal whose frequency changes cyclically for each recording track are superimposed and recorded, the tracking control of the head for the recording track is reproduced. The tracking device is configured to operate based on the pilot signal, and includes a gain control circuit that keeps the amplitude of the +8 raw pilot signal constant, and a cutoff circuit that cuts off the control voltage of the gain control circuit. iifi
A tracking device characterized by: (2) The cutoff circuit is in an operative state before shifting to the normal regeneration mode, and is in an inactive state after shifting to the normal regeneration mode. tracking device.