JPS58155508A - Magnetic video recorder - Google Patents

Abstract

PURPOSE:To improve the transmission efficiency of an FM signal and the S/N of a reproducing luminance signal, by emphasizing the lower frequency band of the reocording equalizing characteristics in response to an average picture level of a luminance signal sufficiently and preventing the upper side band almost from being suppressed. CONSTITUTION:The luminance signal being an output of an LPF1 is branched to a video emphasis circuit 2 and an LPF13 to obtain an average picture level (APL) at recording. The output of an FM modulation circuit 3 is inputted from a terminal 15, amplified at transistors (TRs) Q1, Q2 and the FM signal in which frequencies of 4-5MHz are made flat is obtained at an output terminal 16 of a TRQ3. The APL signal shown in Figure is applied to a cathode of a varactor diode D1 as a control signal, the flat portion near 4-5MHz is changed according to the APL, and when the APL is near the white level, for example, the flat portion is moved to high freqencies, that is, 0 dB reference is moved to the high frequencies, allowing to obtain the optimum recording equalizing characteristics at all times.

Description

DETAILED DESCRIPTION OF THE INVENTION U) Field of Application of the Invention The present invention relates to a magnetic recording/reproducing device, and particularly to improving the signal-to-noise ratio of a luminance signal.

B) Prior Art FIG. 1 is a signal processing system diagram of a luminance signal in a conventional magnetic recording/reproducing apparatus.

3MH with low pass filter 1 during recording! After the high-frequency components of the brightness signal, which has been band-limited to a certain degree, are emphasized by a video emphasis circuit 2, the synchronization signal of the brightness signal is clamped to a predetermined potential by a clamp circuit (not shown) and sent to an FM modulation circuit 3, which transmits the signal at a predetermined frequency. where it is converted to a low carrier FM signal. After that, the recording equalization circuit 4 provides appropriate recording equalization characteristics to improve the transmission efficiency of the FM signal in the magnetic tape head system, and then the recording amplifier 5
The data is recorded from the magnetic head 6 onto the magnetic tape 7 via the magnetic head 6.

On the other hand, during playback, the playback equalization circuit 9 uses the playback FM signal obtained from the magnetic tape head system via the playback amplifier 8 to emphasize the recording equalization characteristics performed on the recording side and the lower sideband waves of the magnetic tape head system. However, the transmission characteristics that suppress the upper sideband are compensated. Furthermore, after removing amplitude fluctuation components caused by variations in the contact state between the magnetic tape and the head in the limiter circuit 10, FM demodulation is performed in the FM demodulation circuit 11. The circuit 12 obtains the original luminance signal.

FIG. 2 shows an example of a conventional recording equalization characteristic, which has a frequency characteristic that emphasizes the lower sideband of an FM signal and suppresses the upper sideband.

The carrier wave frequency of the FM signal corresponds to the level of the luminance signal, and in the case of a VB2-VTR, for example, it is set to &4 MHz at the synchronization tip and 4.4 MHz at the white peak, as shown in FIG.

With conventional recording equalization characteristics, as shown in FIG.
e Level is abbreviated as APL. ) is assumed to be the gray level, and the gray level 4, IMHg
is taken as OdB. As the first l11 signal, the fourth
As shown in Figures (a) and (b), there are many types of AFL, such as AFL (a) which is close to the black level, and (b) which is close to the white level. Therefore, with the following recording equalization characteristics shown in Figure 2, the problem arises that the lower sideband is not emphasized enough or is overemphasized. There is a drawback that it cannot be roomed.

(3) Purpose of the Invention The object of the present invention is to improve the transmission efficiency of FM signals in a magnetic tape head system by providing recording equalization characteristics that can address these drawbacks, and to improve the signal-to-noise ratio of reproduced luminance signals. .

(4) General explanation of the invention In order to achieve the above object, the present invention provides an AP for luminance signals.
According to L, the recording equalization characteristics are changed so that the lower sideband is sufficiently emphasized and the upper sideband is hardly suppressed.

(5) Examples Hereinafter, the present invention will be explained in detail with reference to examples. 6th
The figure is a signal processing system diagram of a luminance signal showing one embodiment of the present invention. In the figure, the same components as in FIG. 1 are denoted by the same reference numerals, and their explanations will be omitted.

During recording, the luminance signal output from the low-pass filter 1 is branched to a video emphasis circuit 2 and a low-pass filter 13 for determining the APLt of the luminance signal. The APL signal thus obtained serves as a control signal for changing the recording equalization characteristics of the recording equalization circuit 4'.

FIG. 7 shows part 1 of the recording equalization circuit 4' which is a component of the present invention.
An example is shown.

The FM signal, which is the output of the FM modulation circuit 3, is transmitted from the terminal 15 to the DC blocking capacitor C8, the power supply Vcc, and the resistors R, , R.
, and a transistor Q, which is connected to the emitter end of the resistor R and t, and to the collector end of the resistor Rat, to form an amplifier.

is amplified. As shown in FIG. 2, the capacitor C is for bypassing high frequency components to emphasize the lower sideband. Thereafter, it is applied to the base of a transistor Q having a resistor R and a collector terminal connected to a resistor R6 and an emitter terminal, and is amplified. Further, at the emitter end of the transistor Q, there is an inductance L1 that resonates at the FM carrier frequency fc via a DC blocking capacitor Ca, a variable capacitance diode D, and a resistor R? that adjusts the Q of this resonant circuit. is connected. Therefore, the resistor R1 and the output terminal 16 of the transistor Qs constituting the emitter 7 lower are connected to the 4
~ SMH2 is flattened and an FM signal subjected to recording equalization is obtained. Cando side terminal 1 of variable capacitance diode D1
7KtX The APL signal shown in FIG. 7 is added as a control signal for changing the recording equalization characteristic tube. Since the capacitance of the variable capacitance diode D1 changes due to this APL signal, the second
The flat part near 4 to 5 MHz shown in the figure changes depending on APLt. For example, when APL is close to the white level, the flat part moves to a high frequency. In other words, the OdB standard moves to a high frequency, so it is always optimal. Recording equalization characteristics can be given to the tube.

The new station wave number f of this low-pass 4 filter 13.

and the order n are selected so that the delay time r is one horizontal scanning period. For example, the delay time rH of a non-polar Wagner type low-pass filter can be determined by the following equation as long as the order n is small.

Therefore, if a fifth-order Wagner type low-pass filter is used, HE can be determined from equation (1).

Here, the reason why the delay time of the low-pass filter 13 is set to one horizontal scanning period is to match the phase of the APL signal and the FM signal which is the output of the FM modulation circuit 3. Otherwise, it is not possible to appropriately change the recording equalization characteristics according to the APL of the luminance signal.

Luminance signals generally have strong correlation in the vertical direction. That is, there is almost no difference between the signal level one horizontal scanning period ago and the current signal level. Therefore, there is no practical problem even if the recording equalization characteristics are controlled to be changed by the 7'j APL signal delayed by one horizontal scanning period as described in 9 above.

As mentioned above, since control is always performed to provide the optimum recording equalization characteristics according to the APL of the llf signal, the recording efficiency of the magnetic tape-head system can always be utilized to the maximum, so that playback is possible. The signal-to-noise ratio of the luminance signal is improved by several dB compared to the conventional method.

In FIG. 7, the reproduction systems 8 to 12 may be provided as separate devices, and the present invention can be completed with only the recording systems 1 to 3°4', 5 to 6, and 13 at the bare minimum.

[Brief explanation of the drawing]

Fig. 1 is a signal processing system diagram of luminance signals in a conventional magnetic brass picture reproduction device, Fig. 2 is an example of conventional recording equalization characteristics, and Fig. 3 is a diagram showing frequency allocation of luminance signals in a VH8-VTR. , FIG. 4 shows examples of brightness signals with APL close to black level and white level, FIG. 5 shows conventional reproduction equalization characteristics, and FIG. 6 is a block diagram showing one embodiment of the present invention. FIG. 7 shows 11th embodiment of the recording equalization circuit of the present invention. DESCRIPTION OF SYMBOLS 1... Low pass filter, 2... Emphasis circuit, 3... FM modulation circuit, 4.4'... Recording equivalent circuit, 5... Recording amplifier, 6... Magnetic head, magnetic tape, 8... Reproduction amplifier, 9... Reproduction equalization circuit, 10
...Limiter circuit, 11...FM demodulation circuit, 12.
... Dayenfu VJ, I Z Atsushi Z Figure 1 Z31L56"# lfl number [Mfh] No. 3 Figure 34 Hz Il: J4 Figure No. 5 Figure mantissa (MHz)

Claims (1)

[Claims] 1. In a magnetic recording device that performs magnetic recording by performing t-FM modulation on a luminance signal during recording, an equalization circuit that changes the frequency characteristic according to the average level of the luminance signal is provided. A magnetic recording device characterized in that it is configured to perform magnetic recording via a signal t-mosquito equalization circuit. 2. A magnetic recording apparatus according to claim 1, comprising a reproducing circuit for FM demodulating the recorded high-luminance signal via another equalizing circuit.