JPH0570201B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording circuit for magnetically recording FM signals.

Conventional technology In a VTR, frequency-modulated high-frequency
The FM luminance signal and the low frequency converted chroma signal are recorded and reproduced through an electromagnetic conversion system using a magnetic head and magnetic tape. Above FM
It is known that various interesting phenomena occur when an FM signal such as a luminance signal is recorded and reproduced via an electromagnetic conversion system, among which the following phenomena are related to the present invention. It has been known.

(1) If an FM signal has an AM component, this AM component is converted to a PM component during playback and appears separately from the FM component. By combining the PM component and the FM component, the modulation index of the reproduced FM signal increases.

(2) If a part of the band in the lower sideband of the FM signal is selected and attenuated during recording, the reproduced FM component in the above band at a specific amount of attenuation, as shown by curve a shown by the solid line in Figure 1. becomes almost zero.

(3) The above phenomenon (2) appears only when the frequency-phase characteristics of the recording circuit have linearity.
If the recording circuit includes a circuit with non-linear frequency-phase characteristics, such as an equalizer circuit, the above phenomenon (2) will not occur, and in that case,
When the lower sideband of the FM signal is attenuated, the reproduced FM component decreases monotonically, as shown by the dotted curve b in FIG.

These phenomena are used in VTRs, and each has its own effects. For example, by passing the FM signal through an equalizer circuit and delaying the upper sideband, an AM component is generated, and by recording the FM signal with this AM component, the modulation index of the reproduced FM signal can be increased. I have to. Image quality can be improved by increasing the modulation index.

In addition, using the AFM (Audio FM) method
In a VTR, the low-frequency chroma signal and the high-frequency chroma signal
An FM audio signal band is provided in the middle band between the FM brightness signal and the FM brightness signal. In order to prevent the lower sideband of the FM luminance signal from overlapping the band of the FM audio signal, a half-trap circuit is provided in the recording circuit. This half-trap circuit utilizes the phenomenon (2) above (the phenomenon represented by curve a in FIG. 1). That is, there is a method in which the band in the lower sideband of the FM luminance signal that overlaps with the FM audio signal is attenuated by a specific amount so that the reproduced FM component in the band becomes almost zero.

Problems to be Solved by the Invention Due to the reason (3) above, the above-mentioned half-trap circuit cannot obtain the above-mentioned trap effect if an equalizer circuit is present in the recording circuit. For this reason, it has conventionally been impossible to have both an equalizer circuit and a half-trap circuit coexist to obtain both the effect of increasing the modulation index and the above-mentioned trap effect.

Means for Solving the Problems The present invention provides that by inputting a rectangular wave to the equalizer circuit 3 of FIG. 2 having the characteristic shown by curve d in FIG. As shown in the figure, changes are effectively utilized. When an FM signal whose carrier wave is a rectangular wave whose frequency changes within the range shown by curve e in FIG. 6 is input to the equalizer circuit 3, an AM wave is generated at its output. Further, a phase compensation circuit 2 is provided to provide linearity to the frequency-phase nonlinear characteristics of the FM signal.

Effect The AM component described above can increase the modulation index, and due to the linearity of the frequency-phase nonlinear characteristic, a predetermined band of the FM signal can be removed using the half trap circuit 4 shown in FIG. You can obtain the effect of

Example In Fig. 2, 1 is an FM modulation circuit that converts a rectangular carrier wave having a predetermined frequency into a luminance signal.
FM modulates. 2 is a phase compensation circuit, 3 is an equalizer circuit, 4 is a half trap circuit, 5 is an adder circuit, 6 is a recording amplifier, 7 is a magnetic head, and 8 is a magnetic tape.

The equalizer circuit 3 has non-linear frequency-phase characteristics, as shown by curve d in FIG. If the fundamental frequency of the carrier wave is, for example, 4MHz, this fundamental wave CA exists in the non-linear part of curve d, and with respect to this fundamental wave CA, there is an upper sideband indicated by USB and a lower sideband indicated by LSB. There is a band.
In this case, the USB which is an equal frequency away from the CA
The phase differences θ ₁ and θ ₂ between the LSB and the CA are such that θ ₁ < ₂ due to the nonlinearity of the curve d.

The phase compensation circuit 2 is for correcting the non-linearity of the curve d in the equalizer circuit 3 to provide linearity, and by configuring it as an LC resonance trap circuit as shown in FIG. As shown in A, it has a correction characteristic that advances the USB phase. By adding the characteristics shown in Figure 4A and the characteristics of curve d shown in Figure 4B,
The frequency-phase characteristic at the output of the equalizer circuit 3 is corrected to have linearity, with θ ₁ =θ ₂ as shown in FIG.

Next, an equalizer circuit 3 having the characteristics shown in FIG.
Let's look at the output waveform when a square wave is input. Assuming that the above rectangular wave mainly consists of the fundamental wave CA and the third harmonic CA ₃ as shown in FIG. 5A, by passing this rectangular wave to the equalizer circuit 3, So, CA ₃ is
Later than CA. Therefore, the output waveform of the equalizer circuit 3 becomes the waveform CA ₀ shown in FIG. This waveform CA ₀ has a fundamental frequency that does not change compared to the original rectangular wave, but a peak value that changes.

The present inventor also discovered that when a rectangular wave whose waveform changes as shown in FIG. 5 is input to the equalizer circuit 3 having the characteristics shown in FIG. 3, the peak value of the output waveform with respect to frequency is shown in FIG. I found that it changes like this. In FIG. 6, in the range of angular frequencies ω ₁ to ω ₂ indicated by curve e, the peak value decreases as the angular frequency increases. Therefore,
When an FM signal whose carrier wave is a rectangular wave whose frequency changes within the range shown by the curve e is input, an AM component whose amplitude changes according to the frequency is generated in the output separately from the FM component. Also, the above FM
If the phase of the signal is corrected by the phase compensation circuit 2 as explained in FIG. I can get a signal.

Therefore, by passing this FM signal to the next-stage half-trap circuit 4, the lower sideband band overlapping with the FM audio signal can be removed. The FM signal which has been subjected to band removal and has an AM component is sent to the adder circuit 5 to receive the FM signal.
An audio signal and a low frequency chroma signal are added. The composite signal is applied to a magnetic head 7 through a recording amplifier 6, thereby being recorded on a magnetic tape 8. Therefore, the FM luminance signal reproduced from this magnetic tape 8 includes a PM component converted from an AM component during recording, and this PM component and
The modulation index is increased by the FM component. This makes it possible to improve image quality.

FIG. 7 shows a second embodiment of the phase compensation circuit 2, which is configured as a high-pass filter using CR as shown. According to this phase compensation circuit 2, the correction characteristics shown in FIG. 8A can be obtained. By adding this correction characteristic to the characteristic shown in FIG. 4B (same as FIG. 4B), it is possible to obtain the linear phase characteristic shown in FIG. 4C.

FIG. 9 shows a third embodiment of the phase compensation circuit 2, which is configured as a high-pass filter having a double time constant as shown. This phase compensation circuit 2
According to , it is possible to obtain the correction characteristic shown in FIG. 10A, and by adding this correction characteristic and the characteristic shown in FIG. can.

The arrangement order of the phase compensation circuit 2, equalizer circuit 3, and half trap circuit 4 is not limited to the arrangement shown in FIG. 2, and may be freely rearranged.

Although the embodiment shown in FIG. 2 relates to an AFM type VTR, the present invention can be applied to a normal VTR that does not use an FM audio signal.
In that case, the FM
A portion of the lower sideband of the luminance signal can be removed so that it does not overlap with the band of the chroma signal. Furthermore, the present invention is not limited to VTRs, but
Generally, it can be applied to an FM signal recording device that uses a rectangular wave as a carrier wave.

Effects of the Invention By having a half trap circuit and an equalizer circuit coexist in the recording circuit, it is possible to obtain the effect of removing a desired band of the FM signal and the effect of increasing the modulation index. When applied to a VTR, it is possible to prevent the lower sideband of the FM luminance signal from overlapping with the band of the FM audio signal or chroma signal, and to improve image quality. Furthermore, an FM modulation circuit that uses a rectangular wave as a carrier wave, which has been conventionally provided in VTRs, can be effectively used.

[Brief explanation of the drawing]

Figure 1 shows how FM signals are recorded via an electromagnetic conversion system.
A characteristic diagram for explaining one phenomenon that occurs during reproduction, Figure 2 is a block diagram showing an embodiment of the present invention, Figure 3 is a frequency-phase characteristic diagram of an equalizer circuit, and Figure 4 is a phase compensation circuit. Figure 5 is a waveform diagram showing the change in waveform when a rectangular wave is input to the equalizer circuit, and Figure 6 is a waveform diagram showing how the rectangular wave is input to the equalizer circuit. A characteristic diagram showing changes in the peak value of the output waveform when input to the circuit, Fig. 7 is a circuit diagram showing a second embodiment of the phase compensation circuit, and Fig. 8 shows the phase compensation circuit and equalizer circuit of Fig. 7. FIG. 9 is a circuit diagram showing the third embodiment of the phase compensation circuit, and FIG. 10 is a diagram showing the phase compensation circuit and equalizer circuit of FIG. 9. FIG. 2 is a characteristic diagram illustrating correcting the frequency-phase characteristics. In addition, in the symbols used in the drawings, 1...
FM modulation circuit, 2... phase compensation circuit, 3... equalizer circuit, 4... half trap circuit.

Claims (1)

[Claims] 1. An FM modulation circuit that uses a rectangular wave as a carrier wave, and a characteristic that non-linearly delays the phase of the FM signal obtained from this FM modulation circuit as the frequency increases and lowers the peak of the output waveform. an equalizer circuit comprising: a phase compensation circuit that provides linearity to the frequency-phase nonlinear characteristic of the FM signal based on the equalizer circuit; 1. A magnetic recording circuit comprising a trap circuit that attenuates a predetermined band of sidebands by a predetermined amount.