JPS61172272A - Fm modulating circuit - Google Patents

Abstract

PURPOSE:To eliminating aliasing-back of side band components caused by the FM modulation processing by subjecting a carrier signal having a frequency sufficiently higher than the maximum frequency of an input signal to frequency modulation by the input signal and suppressing higher side band components with a filter and subjecting the result to frequency conversion to a required low band. CONSTITUTION:A luminance signal Y is inputted to a terminal 11, and an FM carrier signal fA is applied with frequency modulation in an frequency modulating circuit 10 by the luminance signal Y. The frequency of the signal fA is set to a value sufficiently higher than the maximum frequency of the signal Y. An FM output SY1 having a side band of an n-th order has higher side band components suppressed by a BPF13, and an FM output SY2 is supplied to a balanced modulator 14 and has the frequency converted by a carrier signal fB for frequency conversion from an oscillator 15 and has the frequency converted to a low band side by an LPF16, and an FM signal SY.FM is extracted. The frequency of the signal fB is so selected that the primary side band component is not folded into the signal SY.FM even if the carrier signal after low band conversion has a differential frequency fA-fB.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM modulation circuit suitable for application to a recording device that records a pair of component color signals and a temporal luminance signal on separate tracks. [Prior Art] In a recording device such as an integrated video camera or other recording/reproducing device (VTR), the Kalani video signal is divided into a luminance signal, a pair of ``y'' signals, and a pair of chrominance signals, and recorded on separate tracks. A recording/reproducing method has been proposed (I￥
j). In this recording/reproduction method, a pair of component color signals, for example, a pair of color difference signals R-Y, B-Yll'i: as shown in FIG. Figure 8 is an example of a recording device showing a concrete example of how to realize such a recording method. be.

1, the luminance signal Y included in the horizontal synchronization signal PH' supplied to the terminal (1) is sent to the adder (2) f, the first synchronization signal (Noris) P used for time alignment between channels, etc.
Combined with Y, it is formed. (8) is this same period Gursun 2229 Nini ~ #, 2! So11, 'go7□".-; ,
The parts K and PHh are inserted and added with opposite polarities.

The reason for inserting the positive polarity pulse PT is to facilitate the synchronization separation of this arm pulse P, and to prevent the generation of moiré by preventing scorching caused by this pulse P to the low frequency components of the luminance signal Y. It is.

WY is the pulse width of the pulse PH, and in this example, the pulse width of the synchronizing pulse P7 is selected to be TwH.

The luminance signal Y into which the synchronization pulse PY has been inserted is sent to the FM modulator (
3), the recording medium, such as tape (
4) is recorded.

On the other hand, the red and blue color difference signals R-Y and B-Y are sent to the compressor (5
), the time axis is compressed to 1, and the compressed color difference signals R-Y and B-Y are sequentially and alternately arranged to form a time-division compressed multiplex signal, that is, a time-axis compressed signal. The second synchronization signal (pulse) PC is the adder (6)
The compressed color difference signal C shown in FIG. 7B is formed.

Is (9) the second synchronization? This is a circuit for forming a pulse Pc.

The second synchronization pulse Pc is inserted at the same temporal position as the insertion of the first synchronization pulse PY in order to adjust the time between channels. Note that in this example, the second synchronization pulse P is inserted in a negative polarity state.

The compressed color difference signal I'i is FM modulated by an FM modulator (7) and then recorded on a tape (4). In this case, a recording track for the compressed color difference signal is formed adjacent to a recording track for the FMM degree signal SY-FM.

[Problem that the invention seeks to solve]

By the way, when an input signal is FM-modulated using an unstable multivibrator or the like, an n-th order side pan P occurs above and below the carrier frequency.

Therefore, when performing FM modulation on an input signal whose frequency domain extends to high frequencies, for example the luminance signal mentioned above, the sync tip level is 4.4 MHz and the white level is 6.4 MHz.
Since the relationship between the FM carrier signal and the brightness signal is determined to be approximately MHz, the FM carrier frequency is selected to be close to the highest frequency of the brightness signal, and since the modulation index is large, one of the FM signal F) Folding of the next-order, second-order, and third-order sideband components occurs.

In FIG. 9, the carrier frequency is f. , are diagrams showing the relationship between the sideband and folding when the modulation frequency is 9. Figure A shows the broken line of the third-order sideband, and Figure B shows the relationship between the folding and the folding of the third-order sideband. Shows the next sideband fold.

When the 1st to 3rd order side punt 0 components are added back to the FM luminance signal, moiré occurs on the playback screen, which significantly deteriorates the image quality.

The sideband components are folded back into the FM signal, not only when the modulating signal is a luminance signal, but also when the carrier frequency is selected to be close to the highest frequency of the input signal and the modulation index is selected to be high. This can also occur when the signal is aliased, and when this aliasing occurs, the S/N deteriorates.

Therefore, the present invention solves these conventional problems, and even when the carrier frequency is selected to be close to the highest frequency of the input signal, sideband components are not mixed into the FM signal. F that only generates a return
This paper proposes an M modulation circuit.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention, as shown in FIG.
After suppressing the high-order sideband components of the output by 2), an FM modulation circuit (G) is constructed with a frequency converter α→ which converts the frequency to a required low frequency band, and this frequency converter α→5x A signal is output.

[Effect]

If the high-order sideband components are suppressed by the filter α, the frequency spectrum becomes as shown in FIG. 2B, so that the FM signal S after one frequency conversion becomes the second diagram.

Therefore, the carrier frequency for frequency conversion is selected so that aliasing does not occur even if the frequency is converted.

〔Example〕

FIG. 1 is a system diagram showing an example in which the FM modulation circuit αQ according to the present invention is applied to the FM modulation circuit (3) of the above-mentioned video signal recording circuit.

The luminance signal Y supplied to the terminal 1η is the FM signal according to the present invention.
Modulation circuit (supplied to 11. FM modulation circuit α1 is FM
It has a modulator (2), and the FM carrier signal fA is FM-modulated with the luminance signal Y. The FM carrier signal fA is selected to have a frequency sufficiently higher than the highest frequency of the luminance signal Y, for example, 14 MHz or more (eg, a frequency of about 20 MHz).

When the FM carrier signal fA is FM-modulated with the luminance signal Y, and the modulation index is large, the frequency spectrum will have n-th sidebands centered around the FM carrier signal fA above and below it, as shown in Figure 2A. . The figure shows the frequency of the luminance signal Y! 8 is the frequency spectrum.

The FM output SY, which has an n-th order sideband, has high-order sideband components suppressed by a bandpass filter (6). (Figure 2B). In this example, as shown in FIG.
The output S1□ is supplied to the balanced modulator ◆ that constitutes the frequency converter, and after being frequency-converted by the frequency conversion carrier signal fB (C in Fig. 2) supplied from the oscillator (2), it is sent to the balanced modulator ◆ that constitutes the frequency converter. The FM signal (FM luminance signal) SY-FM whose frequency is converted to the lower frequency side is extracted (FIG. 2D).

The frequency conversion carrier signal fB is selected as follows.

That is, the difference frequency fA obtained by frequency conversion
Even when −fB is the carrier signal after low-frequency conversion,
The primary side pan r component is the FM signal SY-F after low frequency conversion.
The frequency is selected so that it cannot be returned during M. In this example, fB = 15 MHz is set. fB=
If it is 15 MHz, the carrier signal f after low frequency conversion is
. is 5 MI (*.

Therefore, the low frequency converted FM signal SY-FM is one in which secondary and higher order sideband components are suppressed, and furthermore, sideband components due to aliasing are not mixed therein. The low frequency converted FM signal 8Y-FM is supplied to the magnetic head Ha and recorded on the tape (4).

Figure 3 shows the FM luminance signal 8 after low-frequency conversion of the chroma signal.
Video supplied to the O terminal (C) shows an example of the case where the FM modulation circuit αQ according to the present invention is applied to a recording circuit configured to frequency-multiplex Y-FM and record on one magnetic track. The signal is passed through η4 separator (a)
The chroma signal C is separated into a luminance signal Y and a chroma signal C, and the subcarrier frequency of the chroma signal C is frequency-converted to a predetermined low frequency by a frequency converter, and the chroma signal ScL after the low-frequency conversion is a low-pass signal. Extracted by filter (c).

The luminance signal Y is converted to FM by the FM modulation circuit 0Q according to the present invention.
A predetermined frequency band is cut by a high-pass filter (after being modified), and the low-frequency cut FM signal 8Y-F
M is frequency-multiplexed with the low-frequency converted four-channel signal 'CL' by a synthesizer (an example of its frequency spectrum is shown in Figure 4), and the frequency-multiplexed signal S is recorded at 7'' (b).
The signal is supplied to the magnetic head UK via the magnetic head and recorded on the tape (4).

In this case as well, since the sideband components of the FM output that cause moiré during recording can be suppressed, the FM according to the present invention
By applying the M modulation circuit (g), it is possible to improve the reproduced image quality.

Reproducing the FM signal SY-FM recorded in this way,
When demodulating, a well-known FM demodulation circuit may be used for demodulation, but if an FM demodulation circuit (g) as shown in Fig. 5 is used, the FM modulation shown in Figs. 1 and 3 can be performed. It is possible to realize demodulation that takes advantage of the characteristics of the method.

FIG. 5 shows an FM demodulation circuit (1) provided in a playback system of a video tape recorder having the recording circuit shown in FIG.
As an example, the FM signal SY (FIG. 6A) reproduced from the tape is supplied to the limiter 0 through the terminal 01) and its amplitude level is limited to a constant level, and then the frequency is converted. The frequency is converted by the frequency conversion carrier signal fD (FIG. 6A) supplied from the oscillator (b).゛Through this frequency conversion, the carrier signal f0 of the low-frequency converted FM signal SY-FM is frequency-converted into the sum frequency 60f0=f and the difference frequency fD-f0 (Figure 6B), and this frequency conversion The new low-frequency converted FM signal STL and high-frequency converted FM signal SY (Fig. 6B) outputted from the device are converted to high frequency by the pan-renos filter (B). □FMFM signal 8
YM is separated (Fig. 6C).

Note that the carrier signal fD for frequency conversion is the carrier signal f in order to prevent a high-order FM signal from being superimposed on the baseband component when the FM signal SY is finally demodulated. ,! The frequency is also selected to be sufficiently high, in this example 10 MHz. Therefore, the frequency is 15M
It is Hz.

The high frequency FM signal S□ is supplied to the FM demodulator 0 after its amplitude level is limited to a constant level by the limiter 0. F
In this example, a Nollus count demodulator is used as the M demodulator 0, and therefore FM demodulation is performed using a Nollus count circuit (B) consisting of a differentiating circuit and a monostable multivibrator and a low-pass filter (2).・(371 is configured.

A pulse count output having a frequency of 2 as shown in Figure 6 is obtained from the pulse count circuit (c), and by integrating this with a low-pass filter (b), a luminance signal Y (as shown in Figure 6) is obtained. baseband component) is demodulated.

In addition, in the case of a /4 pulse count demodulator, the modulation index of the pulse count output to 2 is doubled, so the sideband components include higher-order sideband components, so the frequency band As a result, the frequency band of the low frequency converted FM signal SY-FM also becomes wider. However, frequency 2
Since f exists in a sufficiently higher band than the luminance signal Y, part of the high-order sideband components of the pulse count output does not overlap with the high-frequency component side of the luminance signal Y, and one part of the pulse count output portion remains in the luminance signal Y.

In contrast, a normal pulse count demodulator is used as the FM demodulation circuit, and no frequency conversion is required (FM
When demodulating the signal SY-FM, the carrier signal of the )4 pulse count output is 2fo, so the sideband component of this pulse count output partially overlaps the frequency band of the luminance signal Y.

Therefore, even if the baseband component is extracted by the loaf 9 filter, a portion of the sideband component of the pulse count output remains.

Therefore, moiré occurs in the reproduced screen due to this residual component, and the moiré cannot be reduced. If the FM demodulation circuit 3Q) shown in Figure 5 is used, moiré will not occur even if the pulse count demodulator Of) is used, so the characteristics of the FM modulation processing described above can be utilized as is, resulting in higher image quality than before. can be significantly improved.

Note that in all of the embodiments described above, the present invention was applied to the case where the luminance signal was subjected to FM modulation, but other input signals were applied to FM modulation.
It can also be applied to the case of M modulation.

〔Effect of the invention〕

As explained above, according to the configuration of the present invention, a carrier signal that is sufficiently higher than the highest frequency of the luminance signal is FM-modulated, and after suppressing the high-order sideband components of the output using the filter (6), the desired Since the frequency is converted to a low frequency band to form an FM signal,
There is no aliasing of sideband components based on FM modulation processing in the frequency-converted FM signal 8Y-FM.

Therefore, there is no occurrence of moiré on the reproduced screen due to folded components during FM modulation, and the reproduced image quality can be significantly improved.

This invention can also use an input signal other than a luminance signal as a modulation signal, and in that case also it is possible to improve the deterioration outside S due to foldback during FM modulation.

[Brief explanation of drawings]

1 and 3 are system diagrams showing an example of the case where the FM modulation circuit according to the present invention is applied to a video signal recording circuit,
2 and @4 are diagrams for explaining its operation, FIG. 5 is a system diagram showing an example of an FM demodulation circuit suitable for applying this invention, and FIG. 6 is a waveform diagram for explaining its operation. FIG. 7 is a diagram showing the relationship between a luminance signal and a color difference signal for explaining the present invention, FIG. 8 is a system diagram when a conventional FM modulation circuit is applied to a video signal recording circuit, and FIG. 9 is a diagram showing the relationship between a luminance signal and a color difference signal. FIG. 3 is a diagram showing a frequency spectrum due to modulation. (1) is a recording circuit, α1 is an FM modulation circuit, - is an FM demodulation circuit, (6) is an FM modulator, (to) and (c) are a bandpass filter, a4. (b) is a frequency converter, (to), (
(g) is an oscillator, and 0 is an FM demodulator. JP-A-6L-172272 (6) c>< CQ So -

Claims (1)

[Claims] A carrier signal that is sufficiently higher than the highest frequency of the input signal is FM modulated, the high-order sideband components of the output are suppressed by a filter, and then the frequency is converted to the required low frequency band to form an FM signal. FM modulation circuit.