JPS62164397A - Tracking control circuit - Google Patents

Abstract

PURPOSE:To stabilize a tracking operation by providing a gain control circuit which controls the amplitude of a reference four frequency pilot signal in a four frequency pilot signal reproduction detecting system. CONSTITUTION:A video and a four frequency pilot signal recorded on a magnetic tape 107 are detected with heads A and B, and it is amplified so that the amplitude of a burst signal in chrominance signal is regulated at an ACC circuit 113, and is inputted to a balanced mixer 116 as a reproducing pilot signal 508. An oscillation frequency fosc in a crystal oscillator 102 is divided at a variable divider 101, and is inputted to the balanced mixer 116 through an output voltage variable buffer (gain control circuit) as a reference four frequency pilot signal rcf.PLT. The difference frequency between a reproducing pilot and a reference pilot is generated, and the difference of the difference frequency is taken at a differential amplifier 123, then becoming position error signals for a head and a track. An output voltage is inputted to a differential amplifier 139, and the power source voltage VD of a voltage variable buffer is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tracking control circuit for a video magnetic recording apparatus such as an 8mm IJ VTR.

[Summary of the invention]

The present invention uses a reference 4-frequency signal in a reproduction detection system of a 4-frequency pilot signal in an apparatus that performs tracking between a track recorded on a magnetic tape and a magnetic head using a 4-frequency pilot signal such as an 8 mm VTR. The tracking operation is stabilized by providing a gain control circuit that controls the amplitude of the signal in the pilot signal generation section.

[Conventional technology]

For a conventional trunking control circuit for an 8 mm VTR using four-frequency pilot signals, see Japanese Patent Application No. 10245/1983. The gist of this tracking control circuit is to perform gain control (AGO) amplification on the 4-frequency pilot signal reproduced and detected by the magnetic head together with the video signal so as to keep the amplitude of the color burst signal in the video signal constant. This stabilizes the 4-frequency pilot toy signal from decreasing in amplitude due to the slight rise above the tape.

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional technology, there is a need for improvement due to fluctuation factors generated by the tracking control circuit itself, such as temperature characteristics of the active and passive elements of the circuit, and amplitude variations due to individual differences between devices.

The present invention is intended to solve these problems, and its purpose is to ensure stable reproduced image quality even when it is carried and operated like an 8 mm video camera.

[Means for solving problems]

The tracking control circuit of the present invention has the following features: (1) In a video magnetic recording device that winds a video magnetic recording tape around a cylinder and performs recording and reproduction by operating a rotating magnetic head diagonally with respect to the longitudinal direction of the tape, two magnetic heads that alternately detect the video recorded on the video and a four-frequency pilot signal, a video intensifier that amplifies the signals detected by the magnetic heads, and a switch that alternately switches all the outputs of the amplifiers. After the 4-frequency pilot signal passes through the reproduced color signal, an ACJC circuit undergoes AGC amplification to keep the amplitude of the color burst signal completely constant, and the 4-frequency pilot signal is output from the output signal of the ACC circuit. a low-pass filter that separates the signal, a balanced mixer that amplifies the separated signal and generates a frequency difference signal between the appropriately selected reference pilot signal, and a balanced mixer that generates fH and Proportional to the amplitude of the 3fH frequency signal (two systems of bandpass filters and amplifiers that obtain the signal, an envelope detector, a differential amplifier that amplifies the difference between the amplitudes of the fH and 3fH, and the output of the differential amplifier) The first (A) and second (B) sample and hold circuits perform zero-order hold using the sampling pulse generated by the sampling pulse generation circuit, and the output of the inner result of the two sample and hold circuits (A) is amplified. After that, the position error e between the magnetic head and the track on the tape is input to the capstan motor control drive system, and the rotational speed of the capstan motor is fully controlled to perform tracking 772. A differential 59 amplifier which receives the output signal of the sample bold circuit as a gain control signal at its negative terminal, and an amplitude control circuit which uses the output voltage of the differential amplifier as a source pressure for controlling the amplitude ib of the reference pilot signal. The gain control was performed and stabilized by controlling the amplitude of the reference pilot signal.

(2) ial It is detected that the waveform of the position error signal obtained by amplifying the output of the sample and hold circuit in (A) is unstable and vibratory, and the tracking is off or the position error is detected. A lock detector that outputs a logic state of a lower or high level voltage depending on whether the signal maintains a stable value and tracking is achieved, respectively, and a lock detector that outputs a logic state of a lower or high level voltage, and a binary voltage output edge of the detector in the opposite direction. After passing through a connected diode that performs a switch function, the signal is added to the output signal of the second (B) sample-and-hold circuit, and a differential amplifier supplies the source pressure of the amplitude control circuit of the reference pilot signal. It is assumed that the output voltage of the differential amplifier is fixed to the maximum voltage in the recording state of the video magnetic recording device or in the playback state with no trunking. The tracking control circuit according to the first item in the range.

<34 In the sampling pulse generation circuit, uFsw (head switching) (g
From the drum frequency signal (DFG) phase-synchronized with the RFSW signal, which is provided to detect the rotational speed of the drum motor that rotates the magnetic head and the rotational speed of the drum motor that rotates the magnetic head, it is possible to determine the phase negation relationship between the first and second sample hold circuits. 2. A tracking control circuit according to claim 1, wherein the tracking control circuit generates a sampling pulse signal.

(4) The method for generating the reference pilot signal consisting of the four frequencies includes an oscillator, a variable frequency divider that divides the periodic output signal after shaping the full waveform of the oscillator, and 2 bits input to the variable frequency divider. A special iFF claim in which the data signal for setting the frequency division ratio of is generated by logical operation between the 2-bit data signal output from the system processing circuit and the sampling pulse signal output from the sampling pulse generation circuit. The tracking control circuit according to item 1.

It is characterized by

[For production]

According to the above configuration of the present invention, since the AOC amplifier of the color signal system removes the variation of the position error signal due to the head floating above the tape and the variation caused by the video amplification system, the remaining 4-frequency pilot is used to remove the variation of the position error signal. (a) Differences in reference pilot signal imaging width due to frequency; (1) Temperature changes in circuit parameters such as balanced mixers and amplifiers;
C) Due to individual differences between devices, etc., the amplitude of the pilot signal is varied by varying the amplitude of the reference pilot signal using a control signal obtained by intermittently detecting the amplitude of the pilot signal recorded on the tape. By keeping the size constant, extremely stable trunking is possible.

〔Example〕

FIG. 1 is a tracking control circuit diagram in an embodiment of the present invention. First, list the names of each part in nest 1 diagram.
100 is a system processing circuit, 101 is a variable frequency divider, 10
2 is a crystal oscillator, 105° and 104 are PNP and N, respectively.
PN) transistor, 105, 104, 141, 142
, 158, 138° 156 is a resistor, 114, 106 is a low pass filter (LPF), 107 is a magnetic tape, +
os, +o9 are heads A and B, 110, 111 respectively
112 is a video amplifier, 112 is a head selection switch, 115 is an ACC circuit in the video processing system, 115, 119° 120
．． 128 is an amplifier, 159, 125.126 is a differential amplifier, 127 is a bumper amplifier, 116 is a balanced mixer, 117. IIEI is 3fH each.

fH band pass filter (BPF), 121 and 122 are envelope detectors, 124 and 125 are sample and hold circuits, 129 and 150 are capacitors, 131 is a lock detector, 154 diodes, and 152 is a capstan motor control drive system. , 133 is a sampling pulse generation circuit, 12
is an inverter, 145°148 is an exclusive OR circuit, 14
9 is an AND circuit, 144 is an RFSW/1st signal input terminal, 145 is a DFG signal input terminal, and 147 is an RKC! /P
This is a B signal input terminal. Next, the operational functions of the circuit of FIG. 1 will be explained below. First, the magnetic tape is wound diagonally around a cylinder that rotates at 1800 revolutions per minute, and runs in the longitudinal direction of the tape, and two heads 'iA and B alternately trace the tracks recorded on the tape. ing.

The video recorded on the track on the magnetic tape and the 4-frequency pilot signal are detected alternately by heads A and B, and then the ACC circuit 115 amplifies the amplification factor to keep the width of the burst signal in the color signal constant. is controlled and amplified. After being amplified by the ACC circuit, only the 4-frequency pilot signal is separated by T and PF 114, amplified by an amplifier 115, and then input to the balanced mixer 116 as a reproduced pilot signal 508. On the other hand, the reference 4-frequency pilot signal rcf, PL which is one input of the balanced mixer
T [oscillation frequency of crystal oscillator 102 fosc f 10
A variable frequency divider of 1 is used to input a rectangular wave with a frequency division redundancy of 50 degrees to a variable output voltage bumper (gain control circuit) via a resistor 140. take. The rectangular waveform of the bumper is passed through a resistor 105 by a high-order LPEF to remove high frequency components and is input to the balanced mixer as a sine wave. The function of the 116 balanced mixer is to generate a difference frequency between the regenerated pilot and the reference pilot.
In the case of 8mm video, approximately f as a 4-frequency pilot
1 = 102.5KE(z, fH-11a9'KHz
, f3 xl 65.2111z, f4-14a7
There are four types of frequency signals of KHz, and the regenerated pilot and reference pilot take one of the above four frequencies. As a precaution, the difference frequencies generated by the balanced mixer are +6KHz and 46KHz.

29K[(Z, 62KH2, of which 16KHz(
fH).

46xHz' (+fl is extracted by 118 and 117 BPFs, respectively amplified, envelope detected, and differential amplifier 12
In step 3, the difference between the two is taken to obtain a head and track position error signal. Furthermore, the output voltage of the difference #IJ amplifier 125 is passed through the sample hold circuit 125, the bumper, and the equalizer to the position error signal θ of the capstan motor control drive system.
becomes. For details of the aforementioned burst signal trunking method using the ACC circuit, please refer to Japanese Patent Application No. 10245/1983.

Next, the newly added portions of the present invention will be explained. After inputting the output of the differential amplifier 123 to another sample-and-hold circuit, the output is current-amplified by a bumper with an extremely high amplification factor of 1 that has an extremely high input impedance and which directly feeds back the output of the differential amplifier to the negative terminal. After (cV
), is input to the negative polarity terminal of the differential amplifier 159 via a resistor.

The other input signal LV to the negative polarity terminal is output as a binary logic level voltage to a lock detector which determines whether trunking is at or not from the voltage waveform of the position error signal e. The LV voltage is at a high level (power supply voltage) when trunking is established, and at a low level (ground voltage) when trunking is not established. The diode +54- plays the role of a switch, and is turned off when LV is at a high level, and the ground voltage is input when it is at a low level. The capacitor 146 forms an LPF with the resistor 136, and serves to smooth the voltage cV.

The differential amplifier 159 is for inverting and amplifying the voltage QV, and the negative polarity terminal of the bias voltage VB is
and outputs the power supply voltage VD of the voltage variable buffer. In the sampling pulse generation circuit of 135, R'F synchronized with the drum (cylinder) motor.
8W signal and a sample hold circuit +24. from the frequency signal DFG for detecting the rotational speed of the drum motor.
A sampling pulse s/Hp at t25 is created. s/
One side of aP is negated by the inverter 12 and then becomes a sampling pulse of the sample and hold circuit 124. The sampling pulse is also input to one input terminal of the exclusive OR circuit 143 and the A'AND circuit 149. The sampling pulse 8/'HP is the RWC (
*) Occasionally it does not occur.

Next, the method of generating the reference four-frequency pilot signal will be explained. During recording, flsf2ef3*f, ,
The frequency is changed and outputted to R in the order of fl... each time the SW multiplier signal is switched. On the other hand, during reproduction, the following table shows the output for the number of reproduction pilot cycles eL.

Table 1: Frequency selection logic in variable frequency divider (Table 2)

Table 2 In FIG. 1, particularly the sampling pulse generation circuit diagram, sample hold circuit diagram, and block diagram of the ACO circuit are shown in FIGS. 2, 5, and 4. First, to add an explanation to Figure 2, 201 is the RFSW signal input terminal, 20
2 is a DFG signal input terminal, 205 and 204 are D-type flip 70 tubes, 205 and 206 are AND gates, 207 is an OR gate, 208i sampling pulse output terminal, 2
09 is an input terminal for the REO/PB signal. The RFSW signal is delayed by one clock of the DFG signal by the circuit, and then differential pulses are formed at the rising and falling edges and added at ○R of 207 to output SβP. During RWC, 204 and 205 are reset and 8/HP is not output.

Figure 5 shows an example of a sample and hold circuit, in which 500 is an input terminal, 501 is a transmission gate, 502 is a high input impedance bumper circuit composed of a differential amplifier, 505 is an output terminal, 504 is a capacitor, and 505 is a sampling pulse input terminal. When the s/uP signal is at the low level, the input signal is charged in the capacitor 504 and appears at the output terminal of 505.

Furthermore, when B/Hp becomes high level, the switch between the input terminal 500 and the capacitor terminal is turned off, so the read voltage is maintained as it is. Considering the pilot frequency, etc., the sampling pulse width is considered to be about 1 m56 (approx. The color burst signal in the video signal is extracted by a burst gate 402, and then amplitude detected and the gain of the variable gain amplifier is controlled to stabilize the output amplitude.

Next, FIG. 5 shows a time chart of operating waveforms and signals of the main parts of the circuit shown in FIG. Select signal 502.50 of C1 + 02 that selects the reference 4-frequency pilot signal frequency in phase synchronization with the RIFSW signal of 501! There is an S. The DFG signal 504 is generated from the drum motor in phase synchronization with the R1 day W of 501, and serves as a clock for creating differential pulses at the rising and falling edges of the RFSW signal.

505 is the created sampling pulse.

512 is the result of the exclusive OR of C1 and the sampling pulse output from the □p 1rq system processing circuit of 506 and 507, and the series of reference pilot signals selected by the select signal of CF2, which is obtained by logic operation in the same way as CPl.
It was shown to. On the other hand, the frequency order of the regenerated Bairrad signal is 508 out of 9, and at the timing that is not in the normal response state shown in Table 1, the difference frequency between the regenerated and reference pilots is 46 K[(z Center voltage of the resulting position error signal, for example 2.57 (median value of power supply voltage 5V)
A voltage of 5 to 55 V, which is increased by about 1 to 2 V to the positive side, is obtained as a result of being extracted by the sampling pulse.

510 indicates a cicada. 509 is a position error signal e which maintains the previous voltage value while the sampling pulse is at a high level. Furthermore, 511 is a voltage VD obtained by smoothing and non-inverting amplification of 510. As can be seen from FIG. 5, it can be seen that the amplitude level of the reproduced pilot increases while the amplitude level of the reference pilot decreases. FIG. 7 shows the output voltage of the sample and hold circuit with respect to the reference pilot amplitude, which has a linear relationship with a coefficient of 1. That is, the output voltage e or CV=K), (ref, pLT)-A(PBPT, T
) (1) However; the constant and A represent the amplitude value.

Here, in order to keep the voltage CV or the position error output voltage e proportional to CV constant, the amplifier composed of the differential amplifier 159 is All that is required is to set the amplification factor A. Especially A(ref
, PLT) - A (PBPLT), where A:1 is sufficient. This condition is achievable.

In the example of FIG. 1, although the reproduced biloft signal amplitude ΔA (FBFT, T ) obtained by the sample-and-hold circuit B has positive polarity, the 159 differential amplifier is used as an inverting amplifier. Therefore, in order to make ΔA(PBPLT) negative, it can be easily estimated that if a combination of 16 KHz regenerated Birorad and reference pilot frequency is used, the 159 differential amplifier described above can be configured as a non-inverting amplifier. can. Finally, the time chart shown in FIG. 6 will be explained. In the figure, 514uRRKc/'PB signal, 515 is the output voltage of the detector 1fi in FIG. When R80 is set, VD is clamped to the maximum output value, such as the power supply voltage level, and there is no fluctuation.

Further, during PB (reproduction), the tracking position error signal θ is stabilized and tracking is achieved, and the lock detection signal LV of 515 becomes high level. This causes the switch by diode 154 to operate (7
Automatic operation is possible in which the differential amplifier enters the linear operating region and the AGC (gain control) operation of the trunking control circuit starts.

〔Effect of the invention〕

As described above, according to the present invention, by adding the AGO to the tracking control circuit, fluctuations in the temperature environment,
Since it is possible to provide a circuit that performs stable tracking control against individual differences between devices, it is expected that the image quality of 8mm video cameras and the like will be significantly improved.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the trunking control circuit of the present invention, Fig. 2 is a sampling pulse generation circuit, Fig. 5 is a sample hold circuit diagram, Fig. 4 is a block diagram of an ACC circuit, and Fig. 4 is a block diagram of an ACC circuit. 5 and 6 are time charts of the circuit of FIG. 1, and FIG. 7 is a characteristic diagram of the present invention. 115...ACC circuit 116...Balanced mixer 124.125
...Sample and hold circuit diagram 152...
・Capstan motor control drive system Applicant: Seiko Epson Corporation figure

Claims (4)

[Claims] (1) In a video magnetic recording device in which a video magnetic recording tape is wound around a cylinder and recording and reproduction is performed by operating a rotating magnetic head diagonally with respect to the longitudinal direction of the tape, the video recorded on the tape and the After passing through two magnetic heads that alternately detect frequency pilot signals, a video amplifier that amplifies the signals detected by the magnetic heads, and a switch that alternately switches the output of the amplifier, the four-frequency pilot signal is reproduced. An ACC circuit that receives AGC amplification to keep the amplitude of the color burst signal included in the color signal constant, a low-pass filter that separates a 4-frequency pilot signal from the output signal of the ACC circuit, and amplifies the separated signal. A balanced mixer that generates a frequency difference signal between a properly selected reference pilot signal and two bands that obtain signals proportional to the amplitudes of fH and 3fH frequency signals from the output of the balanced mixer. pass filter and amplifier,
an envelope detector, a differential amplifier that amplifies the difference between the amplitudes of fH and 3fH, and a first (A) and a first (A) differential amplifier that amplifies the difference between the amplitudes of the fH and 3fH, and a first (A) and a first (A) that hold the output of the differential amplifier by a sampling pulse generated by a sampling pulse generation circuit. 2(B) sample hold circuit, and the first sample hold circuit (A) of the two sample hold circuits.
) is amplified and then input to the capstan motor control drive system as a position error signal between the magnetic head and the track on the tape, and tracking is performed by controlling the rotational speed of the capstan motor. On the other hand, a differential amplifier receives the output signal of the second (B) sample and hold circuit as a gain control signal at its negative terminal; A tracking control circuit characterized in that a control circuit is provided to control the amplitude of a reference pilot signal to perform gain control and stabilize the signal. (2) It is detected that the waveform of the position error signal obtained by amplifying the output of the first (A) sample and hold circuit is unstable and vibratory, and the tracking is off, or the position error signal A lock detector that outputs a logic state of a low or high level voltage depending on whether tracking is achieved while maintaining a stable value, and the binary voltage output of the detector are connected in opposite directions. After passing through a diode that performs a switch function, the signal is added to the output signal of the second (B) sample-and-hold circuit and inputted to the negative terminal of a differential amplifier that supplies the power supply voltage of the reference pilot signal amplitude control circuit. The tracking control circuit according to claim 1, wherein the output voltage of the differential amplifier is fixed to a maximum voltage in a recording state of the video magnetic recording device or in a reproducing state in which tracking is off. . (3) In the sampling pulse generation circuit, the phase is synchronized with the RFSW (head switching) signal used for switching the magnetic head and the RFSW signal provided for detecting the rotation speed of the drum motor that rotates the magnetic head. 2. The tracking control circuit according to claim 1, wherein the tracking control circuit generates a sampling pulse signal having a negative phase relationship between the first and second sample and hold circuits from a drum frequency signal (DFG). (4) The method for generating the reference pilot signal consisting of the four frequencies includes an oscillator, a variable frequency divider that divides the periodic output signal of the oscillator after waveform shaping, and 2 bits input to the variable frequency divider. Claims characterized in that the data signal for setting the frequency division ratio is generated by logical operation between the subbit data signal output from the system processing circuit and the sampling pulse signal output from the sampling pulse generation circuit. The tracking control circuit according to item 1.