JPH0527178B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field 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). [Technical Background of the Invention] In a VTR, it is important to track the head so that it accurately scans over the recording track during playback. As this tracking control, during recording, a multi-frequency pilot signal whose frequency changes cyclically for each track is frequency-multiplexed and recorded together with the information signal, and during playback, crosstalk components from both adjacent tracks of the playback track are recorded. There is a known method of detecting the track deviation of the reproducing head using a reproducing pilot signal containing the reproducing head, and thereby tracking the head (Japanese Patent Application Laid-Open No. 116120/1984, etc.). To explain tracking control in a little more detail, during playback, a circuit multiplies a reference signal having a frequency equal to the pilot signal recorded on the playback track by a playback pilot signal containing crosstalk from both adjacent tracks of the playback track. and obtain two types of difference frequency signals corresponding to the lead and lag of the head from the pilot signals for each crosstalk.These difference frequency signals are led to a subtraction circuit to extract the level difference between the two (head (the output is proportional to the deviation from the track), thereby performing tracking control. [Problems with Background Art] By the way, in this tracking control system, various timing signals are used to switch recording and playback modes or to switch circuit characteristics. For example, after a certain period of time has elapsed since the pilot signal began to be input (that is, after the mode transitioned from the stop state to the playback state and the playback pilot signal was obtained), the characteristics of the servo loop could be changed from transient characteristics to steady characteristics. When switching the gain, a switching circuit is usually provided, and an RF switching pulse indicating the rotational phase of the video head or a change from stop to start of the cylinder motor or capstan motor (change from high level to low level, etc.) is used. The switching signal for the switching circuit is created by delaying the signal for a certain period of time. However, if this delay time is long,
The capacitance of the monomulti capacitor that constitutes the delay circuit becomes large, and the variation in delay time becomes large. Also, a microcomputer performs a delay (output signal is output after a certain period of time)
If so, there are problems such as exclusive use of the program area. Furthermore, even if the delay time can be made constant, the switching will take place regardless of the actual servo pull-in time, making it impossible to satisfy requirements such as switching the loop gain according to the reproducing state of the pilot signal. It is not possible. [Object of the Invention] The present invention has been made in view of the above-mentioned points, and provides a gain control circuit for making a timing signal used for mode switching, circuit characteristic switching, etc. constant at a reproduction level of a four-frequency pilot signal. It is an object of the present invention to provide a tracking device that is formed using a control signal, has a simple configuration, and can change the switching time of modes and circuit characteristics depending on the reproduction state of a pilot signal. [Summary of the Invention] The present invention provides a system in which pilot signals of four different frequencies (four-frequency pilot signals) are used for each recording track.
In a tracking device configured to use the reproduced pilot signal to track a magnetic head when reproducing a recording medium in which information signals are multiplexed and recorded in a cyclic order one by one, the reproduction pilot signal is The level of the control signal applied to the gain control circuit that stabilizes the level is identified by the level identification circuit, and this output is used as a timing signal for switching operations such as switching the loop gain of the servo loop and switching the mode. This is what I did. [Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described based on the drawings. FIG. 1 is a block diagram showing an embodiment of a tracking device according to the present invention. In the case of this example,
The tape 1 also includes a configuration for recording a pilot signal. The configuration and operation will be explained below. During recording, the pilot signal P generated by the pilot signal generating circuit 2 is added to the information signal I from the terminal 4 in the mixing circuit 3, and is supplied to the magnetic heads A and B via the recording amplifier 5 and switch _SW1 . Ru. The heads A and B are arranged 180 degrees apart on the rotating disk and have different gap azimuth angles. The pilot signal generating circuit 2 generates four kinds of pilot signals having different frequencies in a circular order corresponding to (synchronized with) the scanning of the heads A and B. As a result, one type of pilot signal is recorded on each recording track on the tape 1 together with the information signal. FIG. 2 shows this situation, and is a plan view showing each recording track on the tape. Arrows a and b indicate the tape moving direction and head scanning direction, respectively. Further, ₁ to ₄ indicate the frequencies of the pilot signals recorded on the track. Furthermore, A ₀ , A ₁ , . . . indicate tracks recorded by head A, and B ₀ , B ₁ , . . . indicate tracks recorded by head B. Next, the operation during playback will be explained. At this time, the switch _SW1 is in an open state. First, the information signal and pilot signal reproduced by heads A and B are switched by a switch that is switched by an RF switching pulse applied to terminal 6.
SW ₂ alternately inputs the input to the regenerative preamplifier 7, and the output of this amplifier 7 is AGC (automatic gain control).
It is input to circuit 8. This circuit 8 is for making the amplitude level of the reproduced pilot signal constant, and the output obtained by detecting the output of a multiplication circuit 10, which will be described later, by a detection circuit 11 is used as the gain control signal. The output of the AGC circuit 8 is input to a low pass filter (LPF) 9, where signal components in the frequency band of the pilot signal are extracted.
The pilot signal frequency component extracted by the LPF 9 is then multiplied by a pilot signal generated from the pilot signal generating circuit 2 (in this case, it is used as a reference signal as described later) in a multiplication circuit 10. The four types of reference signals generated from the pilot signal generating circuit 2 during reproduction have the same frequencies as during recording, and the order of generation thereof is also the same as during recording. That is, during recording, four types of pilot signals P ₁ , P ₂ , P ₃ ,
If P ₄ (its frequencies are ₁ , ₂ , ₃ , ₄ ) are alternately supplied to heads A and B in this order, they are also supplied to the multiplication circuit 10 in this order during reproduction. In this case, the reference signal is switched in synchronization with the RF switching pulse. As the output of the multiplication circuit 10, both a signal corresponding to the amount of advance of head A or B with respect to the track to be normally scanned and a signal corresponding to the amount of delay are obtained. This will be explained in detail based on the table below and FIG.

〔Effect of the invention〕

As described above, according to the present invention, a monomulti is not required to form a timing signal, the number of circuit components can be reduced, and a timing signal can be formed according to the amount of a pilot signal. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a tracking device according to the present invention, FIG. 2 is a diagram showing recording tracks on a magnetic tape, and FIG. 3 is a waveform diagram for explaining the operation of the device shown in FIG. 4 are circuit diagrams showing one embodiment of a specific circuit of the main part of the apparatus shown in FIG. 1. 1... Tape, 8... AGC circuit, 19... Gain switching circuit, 26... Level discrimination circuit, A, B...
...Head, SW3...Switch.

Claims (1)

[Claims] 1. A tracking device configured to track a magnetic head using the reproduced pilot signals when reproducing a recording medium in which four types of pilot signals having different frequencies are recorded together with information signals in a circulating order on a recording track. The apparatus includes a gain control circuit for controlling the gain of the reproduced pilot signal, and a level identification circuit for identifying the level of the control signal applied to the gain control circuit, and for controlling the output of the level identification circuit according to a predetermined switching operation. A tracking device characterized in that it is configured to be used as a timing signal.