DE1292701B - Modulation circuit for a frequency-modulated color carrier - Google Patents

Description

1 2

In a known color television system (SECAM) tion characteristic and thus amplitude and distortion if a color carrier is from line to line with two equal zero frequencies, The invention is explained below with reference to the

Frequency modulated signals. Here it is known, the drawing is explained in more detail.

which corresponds to the zero value of the modulated color signal. 1 shows a block diagram of the invention and speaking zero frequency of the color subcarrier from line F i g. 2 a frequency scheme of the individual vibrations

to toggle line between two frequencies. in Fig. 1; This switchover takes place, for example, between FIG. 3 illustrates another embodiment of FIG the frequencies represent invention.

ίο In F i g. 1, two color signals U ₈ and V _{8 are} transmitted

Z ₁ = 272 · / # and / ₂ = 282 · / #, a switch 1, which by a half-line frequency

Switching voltage 2 is actuated, the modulation where fn is the line frequency. input of a modulator 3 fed to a

The implementation of such a modulator is relatively difficult because the zero frequency of the 15 generates zero frequency / ₃ with a frequency-modulated carrier. This carrier is alternating modulator must be changed from line to line. modulated with the two color signals U ₈ and V _s. Since this zero frequency is also fed to a mixer 5, which should be in proportion to the line frequency, the frequency accuracy of the zero frequency, which is also operated by the switching voltage 2, is difficult to maintain via a line-frequency switch 6 . In addition, the modulation ao are alternating line-by-line oscillations with the frequency characteristics at the two frequencies mostly / ₄ and / ₅ , which are supplied in oscillating sections so that the color carriers are generated with the two null gates 7, 8. The mixer 5 supplies mostly different amplitudes at frequencies and, under a terminal 9, a color carrier F whose different distortions of the modulated color frequency have signals from line to line in the desired manner. 25 is switched between the values f _x and / ₂ .

These disadvantages can also be solved with two separate ones. The mode of operation of this circuit is not illustrated using modulators for the two zero frequencies. 2 explained. During line 1, it stands to avoid, because these modulators in their modulation line 4, a carrier modulated with U ₈ , cannot be made to match the characteristic curve and their distortion cannot be made to match with sufficient frequency. 30 f _ goQ _t *

The invention is based on the object of providing a

simple modulation circuit for the said where fs is the line frequency. The switch 6 be-color carrier, in which these disadvantages are found, is in the left position and supplies to be avoided. 'Mixer 5 an oscillation with the frequency

The invention is based on a modulation 35 - _ _4η8

circuit for a color carrier that is switched off line by line - ^ ⁴ ~~ '* ^H '

alternating with two different color components. In mixer 5, the difference frequency is the

color signals representing frequency modulated and from the line 4 and the switch 6 coming its the zero value of the modulated color signal oscillations, ie corresponding zero frequency from line to line 40 '/ - / - / "- 77? f

between a first frequency / _x and a second - ^ ¹ ~ * ^z Ji ~ ^ l ^ 'js

Frequency / ₂ switched is evaluated and fed to terminal 9, where a with V _s

The invention consists in that the two color-frequency-modulated color carriers with the NuUfrequency / _x signals initially equals one carrier with one. During line 2, the two switches 1, 6 remaining third frequency / _{3 are} modulated on, 45 flipped to the right. The carrier with the frequency / _3, which is above the frequencies f _x and / ₂ , and that on the line 4 now has the same zero frequency, this carrier is modulated by mixing with oscillations but with the color signal V _8. This carrier from line to line by / ₂ -Λ different frequencies is now converted to the desired color carrier in mixer 5 with an oscillation / ₄ and / _{6, ",}

will. 50 fs - *** - fs

The frequency / ₃ is approximately that mixed by the oscillator 8, for example. By evaluating 2.5 times the frequency f _x or / ₂ . The carrier with the difference frequency is now a color carrier with frequency / ₃ and / or the oscillations with the zero frequency frequencies / ₄ and / ₅ can be divided by division and / or * ₌ f -f = 282 · fn

Mixture of a vibration with a whole- 55

Numerous multiples of the line frequency fs obtained. Zero frequency as desired from line to line

The invention results in the following advantages: _{vice versa between the two frequencies Z 1} and / _a since the modulation is switched at a higher frequency.

occurs, the relative modulation bandwidth is 60 In Fig. 3 is first reduced in a quartz oscillator 10, as a result of which a reduction in the distortion generates a carrier with the frequency 272 -fs. The solid is achieved. The circuitry structure of the coupling with the line frequency fs is made simple by a modulation circuit because the control zero frequency of the modulator, controlled by line frequency pulses, does not produce a switched circuit. The vibration with which you need to be freed. Nevertheless, only a single frequency 272 -fs is required with two frequency dividers 11, 12 frequency modulator. Because the same modulator with the same frequency 68 -fs is implemented for both with the division factor 2 each on an oscillation with the frequency 68 -fs, which is effective in a mixer 13 with a constant zero frequency, modula- with the oscillation with the frequency 272 -fs ge

ok

is mixed. In the mixer 13 the sum frequency 340 -fn is evaluated, doubled in a frequency multiplier 14 and as a carrier with the frequency

680-Zh = Z ₃

fed to the FM modulator 3 for synchronization. This carrier thus determines the zero frequency of the carrier on line 4 generated in modulator 3.
The oscillation with frequency

Z ₄ = 408 -f _H

is generated by mixing the oscillation with the frequency 272 -fu and the oscillation with the frequency 136 · Zh in a mixer stage 15 evaluating the sum frequency and supplied to the switch 6 via a line 16. In the oscillator 8, the oscillation with the frequency

Z ₅ = 398 -f _H

the oscillation with the frequency is generated first

Z ₄ = 408 -f _H

by mixing with an oscillation with the frequency 8 -fn, which is obtained in a frequency divider 17 with the division ratio 34: 1 from the oscillation with the frequency 272 · / h , to an oscillation with the frequency 400 -fs. implemented. From the oscillation with the frequency 8 - / h a frequency divider 18 with the division ratio 4: 1 is converted into an oscillation with the frequency 2 · / h , which is mixed in a mixer 20 with the oscillation with the frequency 400 - / h. By evaluating the difference frequency, the oscillation with the frequency is produced on a line 21

Z ₅ = 398 -f _H ,
which is fed to the switch 6.

40

Claims (6)

Patent claims: 1. Modulation circuit for a color carrier, the line-by-line alternately frequency-modulated with two different color components representing color signals and whose zero frequency corresponding to the zero value of the modulated color signal is switched from line to line between a first frequency Zi and a second frequency f ₂ , characterized in that the two Color signals (U _s , V _s ) are first modulated onto a carrier with a constant third frequency Zs, which is above the frequencies Zi and f ₂ , and that this carrier is mixed with vibrations with frequencies that differ from line to line by f _{2 -fi} f _t and Zs is implemented on the desired color carrier. 2. A circuit according to claim 1, characterized in that the frequency f _{3 is} approximately equal to 2.5 times the frequency Zi or f ₂ . 3. A circuit according to claim 1, characterized in that the carrier with the frequency Z3 and / or the vibrations with the frequencies f _t and Zb are obtained by dividing and / or mixing a vibration with an integral multiple of the line frequency fs . 4. A circuit according to claim 3, characterized in that an oscillation with the frequency 68 · fs is obtained from an oscillation at the frequency 272-Zh by division by a factor of 4 and that one by mixing the oscillations with the frequencies 272-Zh and 68-Zh obtained oscillation with the frequency 340 -fn by doubling the frequency into an oscillation with the frequency serving as a carrier Z ₃ = 680 -f _H is implemented (Fig. 3). 5. A circuit according to claim 4, characterized in that the oscillation with frequency Z ₄ = 408 -f _H by mixing the oscillation with the frequency 272 - / h and an oscillation with the frequency 136 -fu obtained therefrom by division by a factor of 2 (FIG. 3). 6. A circuit according to claim 5, characterized in that the oscillation with frequency Zs = 398 -f _H by mixing the oscillation with the frequency once or several times Z ₄ = 408 -f _H is obtained with an oscillation with a multiple of the line frequency. 1 sheet of drawings