JPH04147405A - Image recorder and reproducer - Google Patents

Abstract

PURPOSE:To execute recording reproduction with little deteriotation in image quality to improve the S/N of a system by providing a recording system in which a rectangular wave is used as an FM signal waveform which should be recorded and a reproducing system with a reproducing equalizer which has the reverse characteristic of the frequency characteristic of the recording system. CONSTITUTION:An input signal becomes the FM signal of the rectangular wave by a limmiter 2 and is written on a magnetic tape 6 after being FM modulated by an FM modulator. At the time of reproduction, the input signal is read out by a magnetic head for reproduction 7, is amplified by a reproducing amplifier 9, and the frequency characteristic of the reproducing system is corrected by an FQ compensator 10. The compensator 10 generates the reverse characteristic of the resonance characteristic of a reproducing circuit by the magnetic head 7, a rotary transformer 8 and the reproducing amplifier 9, etc. The output signal of the FQ compensator 10 becomes a signal which only causes a loss to the magnetic recording system compared to the output of the limitter 2. Thus, the recording reproduction with little deterioration of image quality due to a loss in the magnetic recording system is executed even in VTR in which a low carrier wave FM recording with wide deviation is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image recording and reproducing apparatus such as a VTR using a low carrier FM recording method.

[Conventional technology]

Conventionally, V using a low-carrier FM (frequency modulation) recording method
In a TR (video tape recorder), a sine wave is used as a recording waveform, and a cosine equalizer is used as an equalizer. The characteristics of this cosine equalizer are determined by measuring the sideband change rate. The sideband change rate is a parameter that expresses how the sideband changes due to recording and reproduction (Tsumiyama: Basic research on the design of magnetic recording devices, NHK
Technical Research, Vol. 21. No. 4 (1961) p.
8), the coefficients of the cosine equalizer are determined by actually repeating recording and reproduction, measuring the sideband change rate under various conditions, and compensating for them. Since magnetic recording systems are inherently nonlinear systems, all conditions (carrier frequency.

There is no cosine equalizer coefficient that can compensate for the loss of the magnetic recording system (modulation frequency, deviation, etc.), so the image quality must be determined comprehensively while looking at the sideband change rate under various conditions. Cosine equalizer coefficients are selected to minimize deterioration.

[Problem to be solved by the invention] However, in VTRs that require high image quality, such as professional VTRs, the deviation is set widely in order to obtain a predetermined S/N (signal-to-noise ratio). Nonlinearity of the recording system becomes noticeable. Specifically, nonlinearity appears significantly when the modulation index exceeds 0.8. In that case, the cosine equalizer cannot fully compensate for the nonlinear loss in the magnetic recording system, causing
Image quality deterioration phenomena such as deterioration of zero frequency characteristics and deterioration of waveform response occurred.

In view of the above-mentioned points, an object of the present invention is to enable recording and reproduction with less deterioration of image quality due to loss in the magnetic recording system, even in an apparatus that performs low carrier wave FM recording with a wide deviation.
An object of the present invention is to provide an image recording/reproducing device that can improve the S/N ratio of the system.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an image recording and reproducing apparatus that uses low carrier wave FM recording.
The present invention is characterized by comprising a recording system using a rectangular wave as a signal waveform, and a reproduction system having a reproduction equalizer having frequency characteristics opposite to those of the recording system.

Further, in one form of the present invention, the regenerative equalizer includes:
The present invention is characterized in that the inverse characteristic of the frequency characteristic of the recording system is linearly sloped so as to suppress or emphasize high frequencies around the carrier wave frequency.

[For production]

In the present invention, a rectangular wave is used as the FM signal waveform to be recorded, and a reproduction equalizer with a frequency characteristic opposite to that of the magnetic recording system is used. , recording and reproducing can be performed with less deterioration of image quality due to loss in the magnetic recording system.

In addition, in the present invention, the magnetic recording system is made to It is possible to compensate for this loss, and the S/N ratio of the system can be improved by suppressing the high frequency range.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a schematic circuit configuration of a VTR according to an embodiment of the present invention.

During recording, the input signal (modulated signal) input to the input terminal is FM modulated by the FM modulator 1, then converted into a rectangular FM signal by the limiter 2, and then sent to the recording amplifier 3.
After the signal is amplified by the recording magnetic head 5, it is written onto the magnetic tape 6. As the recording amplifier 3, one having flat frequency characteristics is used.

On the other hand, during playback, the signal recorded on the magnetic tape 6 is read out by the playback magnetic head 7 and amplified by the playback amplifier 9, and the FQ compensator (resonance characteristic compensation circuit) 10 corrects the frequency characteristics of the playback system. be done. This F
In the Q convencator IO, a magnetic head 7, a rotary transformer 8. The regenerative amplifier 9 and the like create a characteristic opposite to the resonant characteristic of the reproducing circuit, and the reproducing circuit has a flat frequency characteristic when the reproducing signal passes through the FQ convencator IO. Therefore, FQ compensator 10
Compared to the output of the limiter 2, the output signal is a signal that has suffered only losses in the magnetic recording system.

Figure 2 shows the frequency characteristics of the magnetic recording system that were actually measured. Second
The figure shows the frequency characteristics of the playback output in rectangular wave recording. A single-frequency rectangular wave is recorded on a magnetic tape, and the fundamental wave component of the playback output waveform is plotted.
This can be interpreted as an impulse response when the magnetic recording system is regarded as a type of transmission path. Therefore, when an FM-modulated rectangular wave train is input as an input signal to a magnetic recording system, which is a transmission path, the equalization characteristic of the reproduced waveform, which is the output signal, is the inverse characteristic of the frequency characteristic of the magnetic recording system. It turns out to be appropriate.

Further, the equalizer 11 in FIG. 1 is replaced by a series LC (inductance-capacitance) equalizer 13 as shown in FIG.
and a cosine equalizer 14. This LC equalizer 13
The characteristics are shown in Figure 4. The solid line in Figure 4 is the LC equalizer 13.
The broken line is the inverse characteristic of the frequency characteristic of the magnetic recording system shown in FIG. In this example, the carrier frequency is 16M.
Since we are considering an FM signal with a frequency of Hz to 22 MHz, a modulation signal band of 12 MHz, and a maximum deviation of 20 MHz pp, the required band is approximately 7 MHz to 31 Mt (z. As can be seen from Fig. 4, the characteristics of the LC equalizer 13 matches only the necessary band to the reverse characteristics of the magnetic recording system,
It has a characteristic that attenuates high frequencies outside the required band. Here, consideration has been given to the simplicity of the displacement circuit that has flat characteristics without attenuating the low frequency range below 7 MHz.

Next, the characteristics of the cosine equalizer 14 are shown in FIG. The cosine equalizer 14 has a characteristic of linearly inclining the carrier wave frequency, and is intended for FM signal gradient transmission.

As described above, the reproduced signal whose loss in the magnetic recording system has been compensated for by the equalizer 11 consisting of the LC equalizer 13 and the cosine equalizer 14 is demodulated by the FM demodulator 12.

Next, the characteristics and effects of the FM signal in each component in this embodiment will be specifically explained.

Now, carrier frequency is 19M1lz, modulation signal frequency is 12M
Hz, deviation 5 MHzpp FM signal
Considering the case where the modulator 1 is outputting, its frequency spectrum becomes as shown in FIG. Here, the carrier wave (
Figure 7 shows the results of measuring the relative values with respect to the carrier wave level by focusing on the three spectra of the first lower sideband wave (Jo), the first lower sideband wave (J-11), and the first upper sideband wave (J-11). The horizontal axis of the figure is the deviation, and here recording and reproduction is performed with a maximum deviation of about 20 MHz.In this case, the modulation index exceeds 0.8, which can be said to be a setting with a fairly wide deviation.

FIG. 8 shows the results of recording and reproducing the FM signal having the characteristics shown in FIG. 7 through the limiter 2 and observing it at the output of the FQ convencator IO in the reproducing system. As shown in Figure 8, by passing through the magnetic recording system, the first lower sideband wave (J-11) is emphasized and the first upper sideband wave (J, , ) is suppressed, but due to changes in deviation. It can be seen that relatively linearity is maintained.

In contrast, FIG. 9 shows reproduction output characteristics when conventional sine wave recording is performed. In FIG. 9, compared to FIG. 8, in addition to suppressing/emphasizing sideband waves, the carrier wave itself is also suppressed. Particularly in a region where the deviation is wide (a region where the modulation index is 0.5 or more), the carrier wave itself is suppressed significantly and exhibits clearly nonlinear behavior with respect to changes in the deviation.

Now, from what I have said above, I think you understand that the degree of linearity of the recording and reproduction characteristics is better when using a rectangular wave as the FM signal waveform to record than when using a sine wave. When rectangular wave recording is performed, it is possible to equalize the reproduced FM signal with characteristics that are inverse to the frequency characteristics of the magnetic recording system.

The result of observing the reproduced signal having the characteristic shown in FIG. 8 using the equalizer output of the equalizer 11 shown in FIG. 1 is shown in FIG. 1θ.

Here, the characteristics of the cosine equalizer 14 are flat with respect to frequency, and the equalizer 11 as a whole has characteristics inverse to those of the magnetic recording system. It can be seen from FIG. 10 that an FM signal without inversion is obtained up to a deviation of around 20 MHz. Furthermore, by making the cosine equalizer 14 variable, it is possible to suppress/emphasize upper and lower sidebands centering on the carrier frequency, making it possible to realize so-called slope transmission, thereby improving S/N and suppressing inversion. Can be adjusted.

[Effects of the Invention] As explained above, according to the present invention, in an image recording and reproducing apparatus using a low carrier wave FM recording method, "square wave recording" in which the degree of nonlinearity due to recording and reproduction is small is performed, and magnetic recording is performed. Since a reproduction equalizer having characteristics opposite to the frequency characteristics of the system is used, FM recording with a wide deviation is possible.

Further, according to the present invention, the target characteristics of the equalizer can be determined with a relatively simple configuration, so that the equalizer can be configured with a simple LC circuit network, for example.

Furthermore, in the present invention, it is also possible to compensate for losses in a magnetic recording system by using, as the equalizer characteristic, a characteristic in which the above-mentioned inverse characteristic is linearly sloped around the carrier frequency.
In this case, by suppressing the high frequency range, the system's S/N
An effect that can improve the results can be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the circuit configuration of an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the frequency characteristics of the magnetic recording system in the embodiment of the invention, and Fig. 3 is the equalizer of Fig. 1. FIG. 4 is a characteristic diagram showing the frequency characteristics of the LC equalizer in the embodiment of the present invention. FIG. 5 is a characteristic diagram showing the frequency characteristics of the cosine equalizer in the embodiment of the present invention. , Fig. 6 is a characteristic diagram showing the spectral ram of the FM signal in the embodiment of the present invention, Fig. 7 is a characteristic diagram showing the deviation characteristic (modulator output) of the FM signal in the embodiment of the present invention, and Fig. 8 is a characteristic diagram showing the deviation characteristic (modulator output) of the FM signal in the embodiment of the present invention. Figure 9 is a characteristic diagram showing the deviation characteristic (reproduction output) in the embodiment of the present invention. Figure 9 is a characteristic diagram showing the deviation characteristic (reproduction output of sine wave recording) in the conventional example. FIG. 3 is a characteristic diagram showing deviation characteristics (equalizer output). 1...FM modulator, 2...Limiter, 3.9...Amplifier, ■4.8...Rotary transformer, 5.7...Magnetic head, 6...Magnetic tape, lO・...FQ convencator, 11... Equalizer, 12... FM demodulator, 13... LC equalizer, 14... Cosine equalizer. Deviation (MHz) Fig. 7 Fig. 8 Deviation (Ml-1z) Deviation (MHz)

Claims (1)

[Claims] 1) In an image recording/reproducing apparatus using low carrier wave FM recording, a recording system using a rectangular wave as the recorded FM signal waveform, and a reproduction equalizer having frequency characteristics opposite to those of the recording system. An image recording and reproducing device characterized by comprising a reproducing system having the following. 2) The reproduction equalizer is characterized in that the reproduction equalizer has a characteristic that is inverse to the frequency characteristic of the recording system and is linearly sloped so as to suppress or emphasize high frequencies centered on the carrier frequency. Item 1. Image recording and reproducing device according to item 1.