JPH0664786B2 - Information signal reproducing device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an information signal reproducing apparatus, and more particularly to an information signal reproducing apparatus including a switching element in a power supply circuit.

[Prior art]

Hereinafter, in the present specification, a magnetic recording / reproducing apparatus (hereinafter referred to as a VTR) that records and reproduces a video signal (video signal) on a magnetic tape that is a recording medium will be described as an example.

In recent years, with the progress of the technology for high-density recording on a magnetic tape, a VTR has been developed which has a narrow track pitch and enables recording and reproduction for a long time. Thus, when reproducing a recording signal from a magnetic tape recorded at high density with a narrow track pitch by a rotary magnetic head for reproduction, the most important thing is how to reproduce the recording head on the magnetic tape. Whether or not to trace accurately (hereinafter, simply referred to as tracking) means that some tracking methods have been proposed and implemented so far. As a general method of this type, a control signal (hereinafter referred to as a CTL signal) synchronized with a vertical synchronizing signal of a video signal to be recorded is recorded in advance in a dedicated control track different from the recording track of the video signal and reproduced. A method is known in which the CTL signal is sometimes detected to perform tracking. However, this system requires a dedicated fixed head and a dedicated control track for obtaining the CTL signal.

Therefore, recently, unlike the above method, a pilot signal (hereinafter referred to as a 4f pilot signal) having four different frequencies is formed on each of four adjacent video signal recording tracks on the magnetic tape as one field video signal. During superimposing and recording, when reproducing, the pilot signals from the recording tracks on both sides adjacent to the recording track to be reproduced are reproduced, and the tracking control signal (hereinafter referred to as ATF signal) is obtained by detecting the difference in the reproduction levels. A method for performing accurate tracking by making the reproduction levels equal has been proposed and has been attracting attention. With this method,
The dedicated fixed head for recording and reproducing the CTL signal as described above is unnecessary, and the dedicated control track is also unnecessary. Further, the frequency characteristics of the obtained ATF signal are good, and there are many advantages such that the ATF signal having a relatively high frequency component can be read and the tracking control can be accurately performed.

However, the adjacent four on the magnetic tape as described above
In the method of recording the 4f pilot signal in 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. In general, the crosstalk component of the pilot signal reproduced from the recording track causes an extremely low output level, and an ATF signal with a good S / N cannot be obtained. This S
Obtaining a reproduced ATF signal with a good / N has become an important factor for obtaining a good tracking characteristic.

Also, in recent VTRs, as a stabilized power supply voltage circuit necessary for operating the built-in electronic circuit,
Power supply circuit (switching element is controlled by controlling the switching element) by the switching method using switching element, which has many advantages in terms of efficiency, heat generation, size, weight, etc. compared to the conventional dropper method (series pass regulator). Power supply circuit) is widely used. A power supply circuit using such a switching element is generally 20 KHz to 300 K
It has a built-in oscillator in the frequency band of Hz. At that frequency, switching elements such as transistors (Tr), thyristors (SCR) and gate turn-off thyristors (GTO, GCS) are turned on and off to obtain the required power supply voltage. Therefore, there is a drawback that electrical noise having an oscillation frequency of the oscillator and a frequency component of an integral multiple thereof is likely to occur.

This noise is one of the major causes of deteriorating the S / N ratio of the ATF signal, and has a drawback that accurate tracking control cannot be performed.

〔Purpose〕

The present invention has been made by paying attention to the above drawbacks, and by adjusting the frequency of the signal for controlling the switching element, the influence of noise generated from the power supply circuit or the like on the tracking control signal is eliminated. However, it is an object of the present invention to provide an information signal reproducing device capable of performing accurate tracking control.

〔Example〕

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 diagram showing the configuration of the power supply circuit of the VTR according to the present invention. In the figure, 1 is an input terminal to which an AC power source is input, 2 is a transformer that steps down the input AC, 3 is a rectifier circuit that rectifies and smoothes the AC generated on the secondary side of the transformer 2, and 4 is a rectifier. This is a switching element circuit for controlling the DC voltage obtained by incorporating a switching element such as a transistor or a thyristor, and a predetermined DC voltage can be obtained by controlling this switching element. 5 is a filter, 6 is an oscillator, 7 is the width of the pulse signal from the oscillator 6, and the switching element circuit 4
A PWM module for outputting a switching signal to control the switching element, 8 is obtained by comparing a predetermined reference voltage set by a reference voltage source 9 with a voltage output from the output terminal 10 via the filter 5. An error amplifier that amplifies the error of the output voltage that is generated, and the amplified signal is input to the PWM module 7. 11 is the oscillator 6
The variable resistor (VR) for adjusting the oscillation frequency of the above constitutes an adjusting means for adjusting the frequency of the above-mentioned switching signal to an arbitrary frequency.

Here, in the circuit of FIG. 1 described above, a predetermined pilot signal in a plurality of types of pilot signals having different frequencies is detected, and a plurality of types of reference signals having frequencies corresponding to the plurality of types of pilot signals are generated. Then, the tracking control signal is obtained using the detected pilot signal and this reference signal. Further, the VR 11 makes the frequency of the control signal of the switching element a specific frequency that is interpolated with respect to the frequency of each pilot signal, and is different from the difference component of each pilot signal. The frequency can be adjusted to be different from the sum component or the difference component of. Then, the frequency of the control signal is set to a plurality of frequencies that satisfy the above condition, and is switched in synchronization with the generation of the reference signal.

In the power supply circuit configured as described above, when the commercial AC power supply is input from the input terminal 1, it is first stepped down by the transformer 2, rectified and smoothed by the rectifier circuit 3, and then input to the switching element circuit 4. It In this circuit 4, the switching element is controlled to a predetermined DC voltage, which is output from the output terminal 10 via the filter 5 to a tracking control circuit, a video signal reproducing circuit, etc. (not shown). On the other hand, the pulse signal from the oscillator 6 adjusted to a desired oscillation frequency by the volume (VR) 11 is input to the PWM module 7 and output to the switching element circuit 4 as a switching signal. At that time, the PWM module 7 inputs the amplified signal from the error amplifier 8 to form a switching signal, and a stable DC voltage is obtained from the output terminal 10.

The DC voltage thus obtained is supplied as a stabilized DC voltage to the tracking control circuit, the video signal reproducing circuit, etc. as described above. The DC voltage source obtained as described above is particularly useful for the VTR which performs the tracking control of the 4f method using the 4f pilot signal as described above, as described below.

That is, in a VTR that performs tracking control in the 4f system, signals having four different frequencies ₁ , ₂ , ₃ , ₄ are used as the 4f pilot signal.
The frequencies are ₁ = 6.5H, ₂ = 7.5H,
_{It is} assumed that ₃ = 9.5H and ₄ = 10.5H are set. Here, H is the frequency (15.75 KHz) of the vertical synchronizing signal. This is | ₂ − ₁ | = | ₄ − ₃ | = H, |
_{3 - 1 | = | 4 -} 2 | = utilizing the 3H relationship by comparing to convert the pilot signal reproduced from both adjacent tracks during reproduction into a frequency signal of Ichi担H and 3H, ATF This is because the signal is obtained. In such a 4f system tracking control circuit, since the level of the reproduced 4f pilot signal is extremely low, it is generally easily affected by noise, and particularly for noise having a frequency of 50 KHz to 230 KHz close to the pilot frequency. It is weak and easily causes S / N deterioration of the ATF signal. Above all, noise from a power supply circuit using a switching element has a great influence in terms of its level and frequency.

Therefore, in the present embodiment, means for adjusting the frequency of the switching signal for controlling the switching element of the power supply circuit is provided, and in view of the characteristics of the 4f method, the frequency of the switching signal is set to a frequency relatively strong against noise, for example, in the device. Fine adjustments can be made before assembly. That is, it is achieved by adjusting the oscillation frequency of the oscillator 6 of the power supply circuit to a desired frequency by the VR 11. This adjusting means is not limited to the VR 11 of the embodiment, and other means may be used as long as it can adjust the frequency of the switching signal.

If the frequency of the above switching signal is 20 KHz or less, it jumps into the audio reproduction circuit and sounds as noise.
If the frequency exceeds 200 KHz, the efficiency will drop, so 20 KHz
It is necessary to adjust to the range of about 200 KHz.

In addition, FIG. 2 shows that ₄ having frequencies of ₁ , ₂ , ₃ , 4
The f pilot signal and the signals having frequencies of H and 3H obtained by frequency-converting the 4f pilot signal are illustrated with respect to the frequency (KHz). In addition,
As described above, ₁ = 6.5H, ₂ = 7.5H, ₃ =
The case is shown where 9.5H and ₄ = 10.5H are set. From this figure, when setting the frequency of the switching signal, it is necessary to avoid 6.5H, 7.5H, 9.5H, and 10.5H because the frequency of the 4f pilot signal coincides with the frequency of the circuit. In addition, for 3.5H and 13.5H, respectively | _1-3 .
There is a relationship of 5H | = | ₄ −13.5H | = 3H, and it is necessary to avoid it as well. Thus, frequencies having a frequency difference of H, 3H with respect to frequencies ₁ , ₂ , ₃ , ₄ , of the 4f pilot signal should be undesirably avoided as the frequency of the switching signal.
It is also desirable to avoid the H frequency.

Pursuant to the above, as the frequency of the switching-signal, a relatively low frequency is desired sensitivity, _{1, 4} frequency of 4.5H and 12.5H at a distance of 2H is desirable. Further, 2H also corresponds to the midpoint between H and 3H, and becomes a valley of each band pass filter (BPF), so that the sensitivity is similarly low and it can be used. Therefore, by adjusting VR11 shown in FIG. 1 and setting the frequency of the switching signal output from the PWM module 7 to the switching element circuit 4 to any of 2H, 4.5H, and 12.5H, the switching element is changed. Eliminates the influence of noise from the power supply circuit with built-in
/ N deterioration can be reduced, and accurate tracking control can be performed.

In the above embodiment, the case where the frequency of the switching signal is fixed to a desired frequency, for example, 4.5H or 12.5H has been described, but it is synchronized with the switching timing of the 4f pilot signal which is mixed when the frequency is converted during reproduction. It is also possible to switch and adjust the frequency of the above switching signal, and the same result can be obtained.

〔effect〕

As described above, according to the present invention, since the adjusting means for adjusting the frequency of the switching signal for controlling the switching element is provided, it is possible to eliminate the influence of noise generated from the power supply circuit or the like on the tracking control signal. Therefore, there is an effect that the accurate tracking control can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a VTR power supply circuit to which the present invention is applied, and FIG. 2 is a diagram showing a 4f pilot signal and a signal obtained by frequency-converting the 4f pilot signal. 4 ... Switching element circuit 6 ... Oscillator 7 ... PWM module 11 ... Variable resistor (VR)

Claims (1)

[Claims] 1. A plurality of types of pilot signals having different frequencies which are recorded on a recording track of a recording medium by superimposing an information signal on the recording track of a recording medium, the power source circuit controlling a switching element to obtain a predetermined voltage. Information for obtaining a tracking control signal using the detected pilot signal and the reference signal, while detecting a predetermined pilot signal of, and generating a plurality of types of reference signals having frequencies corresponding to the plurality of types of pilot signals. In the signal reproduction device, the frequency of the control signal of the switching element is a specific frequency that is interpolated with respect to the frequency of each pilot signal, and is different from the difference component of each pilot signal, and this difference Adjusting means capable of adjusting to a frequency different from the sum component or the difference component of the component and each of the pilot signals An information signal reproducing apparatus, characterized in that the frequency of the control signal is set to a plurality of frequencies satisfying the condition by the adjusting means and is switched in synchronization with the generation of the reference signal.