JPS6150239A - Information signal reproducer - Google Patents

Abstract

PURPOSE:To obtain an information signal reproducer assuring accurate tracking without being affected with a noise generated from a motor turning control circuit by setting a frequency of a control signal of a switching element to a specific frequency inserted to the frequency of plural kinds of pilot signals. CONSTITUTION:An analog control signal is compared with a sawtooth wave signal generated from a pulse width modulation (PWM) basic frequency oscillator 1 at a comparator 2 so as to apply PWM. A transistor (TR) 3 is switched synchronously with the basic frequency of a PWM signal and a desired smoothed control voltage is generated at a point P. The control voltage is used as a drive voltage of a motor 8 to control the number of revolutions of the motor 8. A comparatively low frequency is desired as the switching frequency of the switching element 3, any of 2fH, 4.5fH, 12.5fH is set to a VTR using a 4f pilot signal to apply tracking control so as to exclude the effect of noise.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an information signal reproducing device, and particularly relates to setting of a rotation control voltage of a motor.

[Prior art]

As for the above-mentioned information No. 48 reproducing device, the video signal (
The description will be given by taking as an example a magnetic recording/reproducing apparatus i (hereinafter referred to as a VTR) that records and reproduces video signals.

In recent years, with the advancement of technology for high-density recording on magnetic tapes, V'1' devices have been developed that have narrowed trunk pitches and are capable of recording/reproducing over long periods of time. In this way, when reproducing recorded signals from a magnetic tape recorded at high density with a narrow track pitch using a rotating magnetic head for reproduction, the most important thing is to direct the reproduction head to the recording track on the magnetic tape. The problem is how to trace accurately (hereinafter simply referred to as tracking), and several tracking methods have been proposed/implemented so far. In this type of general method, a control signal (hereinafter referred to as CTL signal) synchronized with the vertical synchronization signal of the video signal to be recorded is recorded in advance on a dedicated control trunk separate from the recording track of the video signal. A method is known in which tracking is performed by detecting seven OTL signals during playback. However, such a system requires a dedicated fixed head and a dedicated control track for obtaining OTL signals.

Therefore, recently, unlike the above-mentioned method, pilot signals (hereinafter referred to as 4f
A pilot signal) is superimposed and recorded on a video signal for one field, and during playback, the pilot signals from the recording tracks on both sides adjacent to the recording track to be reproduced are reproduced, and the difference in the reproduction level is recorded. is detected to obtain a trunking control signal (hereinafter referred to as ATF signal),
A method for performing accurate tracking by equalizing the reproduction levels has been proposed and is attracting attention.

In such a system, there is no need for a dedicated fixed head for recording and reproducing the above-mentioned detailed CTL signals, and there is no need for a dedicated control trunk. Furthermore, the obtained ATF signal has good frequency characteristics, and has many advantages, such as being able to read even ATF signals with relatively high frequency components and perform accurate tracking control.

However, adjacent 4 on magnetic tape as above
In the method of recording a 4f pilot signal on one recording track, the level of the 4f pilot signal to be recorded needs to be lower than the luminance signal level (-25 to 30 dB) in order to reduce the influence on the video signal. Ash,
Therefore, the crosstalk component of the pilot signal reproduced from the adjacent recording track generally has an extremely low output level, and there is a problem that an ATF signal with a good S/N ratio cannot be obtained. Obtaining a good reproduced ATF signal has become an extremely important factor in obtaining good tracking characteristics.

〔the purpose〕

The present invention has been made in view of the above-mentioned situation, and an object of the present invention is to provide an information signal reproducing device that can perform accurate tracking without being affected by noise generated from a motor rotation control circuit.

An embodiment in which the present invention is applied to a VTR will be described below with reference to the drawings. FIG. 1 is a block circuit diagram showing the configuration of a motor drive circuit used in a VTR according to the present invention, and FIG. 2 is a 4f pilot signal in this VTR and a signal obtained by frequency converting these signals. FIG.

In FIG. 1, l is a fundamental frequency oscillator (080
), 2 is a comparator for PWM signal generation, 3 is a transistor as a switching element switched by the PWM output signal of comparator 2, 4 is a load resistance ()L) of comparator 2, and 5 is a diode (D
), 6゜7 is an inductance (L) and a capacitor (0) that constitute a low-pass filter (LPF), 8 is a three-phase frictionless motor as a controlled object, and 9 is a three-phase winding corresponding to the rotation of the motor 8. A motor coil drive circuit switches the currents of lines U, V, and W, and 10 is a power supply voltage (Vcc) supply section.

In the above motor control circuit, the control signal of the analog signal is transmitted to the PWM fundamental frequency oscillator 1 by the comparator 2.
The signal is compared with a sawtooth wave signal generated from the signal and PWM modulated. Since this PWM signal is applied to the base of the transistor 30, the transistor 3 performs a switching operation in synchronization with the fundamental frequency of the PWM signal, and supplies current to the capacitor 7 from the power source 1O via the inductance 6. In this way, a desired smooth control voltage is generated at point P. Therefore, by using this control voltage as the drive voltage of the motor, it is possible to control the rotation of the motor. According to this method, the power supply 10
This circuit has been widely used in recent years because the power consumption loss when obtaining the voltage drop from to point P is extremely low.

In the motor control circuit configured as above,
By using the frequency described below as the switching frequency of the switching element 3, it is particularly useful for a VTR that performs tracking control of the 4f method using the 4f pilot signal described above, as described below.

That is, in a VTR that performs 4f tracking control, signals with four different frequencies f, , f2, fl, and f4 are used as the 4f pilot signal, and each of the frequencies is f, = 6.5fH. , f2
='y,sfH,f,=9.5f' r f4 =1
Assume that it is set to 0.5 f H1
Ru. Here, fH is the frequency (15,
75kHz). This is 1r2-fll-f
By using the relationship zl=3f)r, the pilot signals that are reproduced from both adjacent tracks during playback are once
This is because the ATF signal is obtained by converting and comparing the frequency signals of 1 (and 3fo).
In the tracking control circuit of this method, the reproduced 4f)(
Because the level of the pilot signal is extremely low, it is generally susceptible to noise, especially at 500V near the pilot frequency.
It is weak against noise having a frequency of 2 to 230 kHz, and is likely to cause deterioration of the ATF signal O8N.

In particular, noise from the motor control circuit using the switching element 3 has a great influence in terms of its level and frequency.

In this case, this embodiment is provided with means for adjusting the frequency of the switching signal that controls the switching element 3 of the motor control circuit, and in view of the characteristics of the 4f method described above, switching is performed at a frequency that is relatively resistant to noise. This allows the frequency of the signal to be softened and finely adjusted, for example, before assembling the device. That is, this can be achieved by adjusting the firing frequency of the oscillator 10 of the motor control circuit to a desired frequency.

If the frequency of the above switching signal is below 20kHz, it will mix into the audio reproduction circuit and be heard as noise.
In addition, the efficiency decreases when the frequency exceeds 200kHz, so
It is desirable to adjust the frequency to a range of kHz to about 200 kHz.

Moreover, FIG. 2 shows a 4f pilot signal having frequencies of fI +'2, rl, r4 and f n , 3fH obtained by frequency converting this 4f pilot signal.
This is a diagram showing a signal with a frequency of f1=6.5fH, f
2=7.5fH, f,=9.5fH.

This figure shows the case where f4 is set to 10.5 fH. From this figure, when setting the frequency of the switching signal, 6.5fH, 7,5fH, 9,5fH1]
0.5fH (of course, it matches the frequency of the 4f pilot signal, and the sensitivity of the circuit is extremely high, so it must be avoided. Also, 3.5fH).

For 13.5 f H, 1r1-3.
5 r should be avoided as well. In this way, 4f
Frequencies having a frequency difference of fH and 3fH from the pilot signal frequency fI+'2+f3+f4 are undesirable as switching signal frequencies and need to be avoided, and at the same time, it is also desirable to avoid frequencies fH and 3fH.

As mentioned above, the frequency of the switching signal is preferably a frequency with relatively low sensitivity, and f, , f4
4, 5 fH and 12.5 f over a distance of 2 f o from
11 frequencies are preferred. Also, 2fH is also f u and 3
(It is at the midpoint between 11 and 11, which is the valley of each bandpass filter (BPF), so the sensitivity is similarly low,
Can be used. Therefore, the PWM shown in FIG.
The frequency of the switching signal output from the oscillator 1 to the switching element circuit 3 via the converter 2 is 2f.
By setting it to either H, 4, or 5f Hs 12.5 f o, the effect of noise from the motor 11] control circuit with built-in switching elements is eliminated, and the SN of ATFi is prevented from changing. This makes it possible to perform accurate tracking control.

[Other Examples]

Moreover, as shown by the broken line in FIG. 2, N×fH(
It can be seen that even at a frequency of Ni (an integer greater than or equal to 4), the sensitivity is relatively low because there is an interleaving relationship with the 4f pilot signal. Therefore, similar effects can be obtained even if the switching frequency is set to the above frequency.

〔effect〕

As explained above, according to the present invention, by setting the fundamental frequency of the control signal No. 7 to a specific frequency, the adverse effect of noise generated from the switching element in the motor rotation control circuit on the tracking signal is reduced. The effect is that accurate tracking control can be performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a VTR motor drive circuit as an embodiment of the present invention, and FIG. 2 is a block diagram of a VTR motor drive circuit shown in FIG.
It is a figure which shows the frequency of the 4f pilot signal of R, and its frequency conversion signal. 1...Pulse width modulation fundamental frequency oscillator 2
......Comparator 3...Switching element (transistor) 8...Motor

Claims (3)

[Claims] (1) It has a motor control circuit that obtains a control voltage by controlling a switching element with a control signal having a variable pulse width at a predetermined frequency, and has a motor control circuit that obtains a control voltage by controlling a switching element with a control signal having a variable pulse width at a predetermined frequency. An information signal reproducing device that obtains a tracking control signal by detecting a part of pilot signals among a plurality of different types of pilot signals, the information signal reproducing device detecting a part of pilot signals among a plurality of different types of pilot signals, the frequency of the control signal of the switching element being set relative to the frequency of the plurality of types of pilot signals. An information signal reproducing device characterized in that the information signal is set to a specific frequency that is interpolated. (2) The information signal is a video signal, and the fundamental frequency is 4.5f_H or 12.5f_H (only f_H
2. The information signal reproducing apparatus according to claim 1, wherein is one of the horizontal synchronization frequencies of the video signal. (3) The information signal is a video signal, and the fundamental frequency is N×f_H (where N is a positive integer and f_H is the horizontal synchronization frequency of the video signal). The information signal reproducing device according to item 1.