DE2538355A1 - DEVICE FOR ADJUSTING THE INACTIVE FREQUENCY OF A COLOR TELEVISION SUPPORT - Google Patents

Description

75008 PARIS / France

Our sign; T 1836

Device for readjusting the resting frequency of a color remote

visual aid wearer

The invention relates to a further development of devices for readjusting the rest frequency of a frequency-modulated color television auxiliary carrier.

The "rest frequency" of the subcarrier is understood to mean the Frequency corresponding to a chrominance signal zero, in contrast to the rest frequency of the modulated oscillator supplying the subcarrier, which is the frequency which it delivers for an input signal zero.

This distinction must be made in the SECAM system,

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as is currently in use, in which two different idle frequencies F_ and F _{n are used} for the alternate transmission of the colors blue and red. In the encoders, a single modulated oscillator is generally used, the rest frequency of which is equal to F_,

rS

where a square pulse corresponding to the difference F_, - F_ added to the modulation signal in the course of the line periods which require the transmission of the red color type.

The readjustment of the rest frequency then proceeds as follows itself: During the horizontal blanking intervals, the frequency supplied by the modulated oscillator alternates between the Reference frequencies F "and F readjusted, which of

.--. j-- rs K

Harmonic filters are supplied, which are excited by impulses »,

Such a device has certain disadvantages, namely:

a) - the complexity of the system for fast phase adjustment during the blanking that lasts for a few microseconds

of the SECAM auxiliary carrier.
■ ■■. '■ - .. ■'. ■ · *

b) - the use of quartz filters, which are activated by impulses

are excited, which are facilities that are more expensive than crystal oscillators.

The invention allows these disadvantages to be eliminated the use of reference frequencies generated by crystal oscillators and through the use of control loops, which the error signal in the course of active Generate line times. This error signal is used for a single resting rate or for each resting rate a discriminator obtained, which the output signal of the Modulator during the line blanking intervals as well as the Reference frequency or one of the reference frequencies during the receives active time times. The output signal of the

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The discriminator is activated at a specific point in time of the line blanking interval clamped to ground (this operation is referred to as "clamping" in English-language texts) and in the The course of the active line time is queried, this query delivering the error signal.

Further features and advantages of the invention emerge from the following description of exemplary embodiments of the invention. In the drawings show:

Fig. 1 is the block diagram of an embodiment

form of the invention when applied to the current SECAM system, and

Fig. 2 shows a modification of the device ναι

Fig. 1.

1 shows a frequency readjustment device in the context of a coder of the current SECAM system.

There are three inputs shown, which the clamping pulses C or the square wave signal S with half the horizontal frequency, which determines the change in the transmission of the color types blue and red, or the horizontal sync pulses H of the coder. These three inputs are labeled with the same symbols as the signals they deliver. To the To make the drawing easier, their connections to the inputs that receive these signals are not all shown been. However, these inputs are also labeled with the symbols C, S or H according to the signal that they receive.

An input 1 supplies the signal ready for application to the control input of a modulated oscillator 7, with the exception of two operations. The first operation is

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about adding certain signals to the input signal in an adder 2. The second operation is is a limitation in a limiter 3, which is connected to the output of the adder 2, this limitation the over-modulation of the oscillator at the pre-distortion points which avoids chrominance signals.

When added in the adder 2 to the input signal Signals are as follows:

1) A blocking signal, which causes the oscillator

7 for approximately 1 με at the beginning of the horizontal blanking intervals blocked. It is a well known arrangement with respect to the initial phase conditions. This The signal is delivered to the adder 2 by a generator 28 which is triggered by the leading edges of the clamping pulses C will.

2) A square wave that is added over the course of the lines

which contain the transmission of the chrominance red ^ where

R "~ B the amplitude of this square-wave signal is equal to V = - is,

where K is the conversion factor of the modulator in kHz / volt, with P ₀ '=' 4 406.25 kHz and with F_ = 4 250 kHz.

For this purpose, a third input of the adder 2 is connected to the switch 4 controlled by the signal S Output of an adder 29 connected, the first input of which receives the voltage V of a voltage source.

3) A rain signal.

The foregoing is part of the prior art, apart from the adder 29, which is an additional one Circuit used in the first embodiment of the invention. The invention is concerned with the type of generation of the control signal, which is applied to a fourth input of the adder 2, and with the generation

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a second control signal which is applied to the second input of the adder 29. These signals are as follows won:

In addition to the other conventional circuits of the encoder, the output of the oscillator 7 feeds the first input a changeover switch 5, the second input of which is connected to the output of another changeover switch 8. The switch 8 has two inputs which are connected to the outputs of two crystal oscillators 9 or IO of frequencies F_ and F_.

K B

The switch 8 is controlled at its control input by the signal S with half the horizontal frequency, so that it is dependent alternating the frequencies F_ of the chrominance transmitted in the course of the relevant line. and F_ returns.

K JB

The switch 5 receives the pulses at its control input C (12 ps), during which it has the output signal at its output of the oscillator 7 transmits, namely alternately the frequencies f _, and f, which after the unlocking of the oscillator

13 R

are actually supplied by the oscillator during the blanking intervals. During the active line times, the changeover switch 5 supplies the output signal of the changeover switch 8, namely alternately the frequencies F _D and F.

The output signal of the switch 5 is sent to the input a frequency discriminator 11 is applied, the output signal of which feeds two independent loops, which alternately operate to form error signals which are maintained for two lines at a time.

Each of these loops allows alternating clamping in the course of the horizontal blanking intervals, for example between times 5 and 6, the time origin being the

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ORIGINAL INSPECTED

Beginning of the horizontal blanking interval and the unit used is the microsecond, and one sample in the course of the active line times, preferably in their initial part, for example between the points in time 16 and 17.

The required clamping pulses C are generated with the aid of two monostable multivibrators 13 connected in series and 15 obtained, the first of which is triggered by the leading edge of the horizontal sync pulses H, with you quasi-stable state the beginning of the clamping pulse C while the duration of the quasi-stable state of the second flip-flop determines the duration of the pulses.

The sampling pulses E are also generated with the aid of two monostable multivibrators 12 and 14 connected in series won, the first of which by the trailing edge of the Clamping pulse C is triggered.

Two changeover switches 17 and 16, which are operated in synchronism by the signal S, conduct the pulses C ¹ or the pulses E to their first or to their second output, depending on whether the current image line is the transmission of the color type blue or the Color type red required. Each of these changeover switches is advantageously constructed from two gate circuits which are controlled in opposite directions by the signal S.

During a line assigned to the transmission of the color type blue, a clamping circuit 18 whose input is connected to the Output of the discriminator 11 is connected to its terminal input the pulses of the first output of the switch 17, while their reference input is connected to ground. The output signal the clamping circuit is sampled in a key memory 19, which receives its sampling pulses from the first output

/ 07 12

25 ^ 8355

of the switch 16 receives. The term "sampling memory" is to be understood as meaning a sampler that stores the sampled value between stores two consecutive samples.

The clamping thus takes place when the discriminator receives the frequency f 1 and the sampling when it receives _{the frequency F n.}

The discriminator 11 can advantageously have the frequency F as the center frequency, but it can easily be demonstrated that the deviations from its zero point will not affect the output signal of the tactile memory 19, which supplies a signal which is equal to zero _{for f = F D and the} if this is not the case, add one to the difference F_, - f_

D ti

provides a proportional signal.

This signal is provided with the correct polarity via a gain adjustment device 20, which is an RC integrator 40 is connected downstream, applied to the fourth input of the adder 2, the device 2O the conversion coefficient the modulated oscillator 7 and the discriminator 11 take into account not igt.

This control device thus keeps the rest frequency of the modulated Oscillator 7 to the value F ".

In the course of the next line, the same loop acts, the 'a clamping circuit 21 with a downstream Tactile memory 22 contains, in the same way, the output signal of the discriminator 11 due to the Kiemmund Sampling pulses which it receives from the second outputs of the switch 17 and 16, respectively.

The key memory 22 consequently supplies a to the

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ORIGINAL INSPECTED

- σ -

Error in the value of the square-wave pulse, a proportional error signal which allows the rest frequency of the subcarrier to be increased from the value F to the value F _R in the course of the lines with the transmission of the red chrominance. This error signal is applied with the appropriate polarity to the second input of the adder 29 via a gain setting device 23 and an RC integrator 41.

Fig. 2 shows a preferred modified embodiment the invention.

In this second embodiment of the invention, the same type of readjustment is used in which the quiescent frequency of the modulated oscillator of the frequency F _R is readjusted.

The readjustment of the frequency of the modulated oscillator to the fourth F _R , which corresponds to a chrominance signal red of zero, is achieved in the following way, which simultaneously allows the entire frequency deviation to be controlled.

In FIG. 2, only those parts are shown which have been changed compared to FIG. 1. These changes are: the adder 29 is omitted and the voltage V is applied directly to the input of the switch 4.

In this second embodiment, to achieve the rest frequency F _n for a chrominance signal red, the square pulse is no longer additively corrected by the algebraic addition of a correction voltage, but multiplicatively simultaneously with the rest of the modulation signal, so that the deviations in the slope of the modulator are corrected. If one assumes that the slope remains linear, correct it

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one consequently the modulator for the entire frequency deviation.

Between the adder 2 and the limiter 3 there is thus now a device 30 with a variable around the value 1 Gain arranged, the control input of which the output signal of the key memory 22 with the appropriate polarity via a Gain adjuster 24 and an RC integrator 43 receives.

This second embodiment thus yields better results than the first, but it is in terms of their Application conditions more demanding:

The voltage V must be carefully set to the value corresponding to a chrominance signal blue, which would cause _{a frequency deviation F n} - F _n.

The alternating modulation signal must be generated in such a way that that the errors, deviations and distortions of low frequency in the color types red and blue are the same or through Devices are created that are corrected for these errors.

Of course, in the case where the idle frequency of the subcarrier is the only frequency, the second control loop unnecessary, since the first control loop then generates an error signal in the course of each active line time supplies.

Finally, if one were to use two modulated oscillators, each of them would work in the same way as readjusted in the case of a single resting frequency.

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ORIGINAL INSPECTED

Claims (4)

Patent claims: .j device for readjusting the quiescent frequency of a frequency-modulated color television subcarrier to a given reference frequency F ₁ during at least certain predetermined line periods by means of a correction signal which is applied to a modulated oscillator supplying the subcarrier, characterized in that the reference frequency is supplied by a quartz oscillator, that the circuit , which supplies the error signal from which the correction signal is generated, a frequency discriminator that a switching device supplies the discriminator with the subcarrier during the horizontal blanking intervals and the reference frequency during the active line times of the line periods during which the subcarrier should have a rest frequency, which is equal to the reference frequency F, and that the discriminator is followed by a series circuit which has a clamping circuit, which its output signal at a certain point in time of the horizontal blanking intervals d he clamps line periods to ground, and contains a key memory which samples the output signal of the clamp circuit at a certain point in time of the active line times. 2. Device according to claim 1 for the alternating readjustment of the rest frequency of the subcarrier to two reference frequencies F, and F "in the course of successive line periods, wherein the modulation signal which is applied to the single modulated oscillator which is used for all line periods, in the course of the line periods , which require readjustment to the frequency F ~, is added with a square pulse which nominally corresponds to the frequency deviation F ₉ - F ₁ , characterized in that the second reference _{frequency F 2 is} also from a ORIGINAL INSPECTED 253R355 - left - Quartz oscillator is supplied so that the switching device alternately supplies the reference frequency F and the reference frequency F ~ to the discriminator during the active line times, depending on the readjustment to be carried out, so that the discriminator feeds a second series circuit with a key memory and a clamping circuit, which is the same as the first series circuit and works during the line periods which require readjustment of the rest frequency to the frequency F ₂ , the key memory supplying a second error signal which leads to a second correction signal which is applied to the modulated oscillator in order to determine the frequency deviation between the two rest frequencies to maintain the target difference F ₂ - Fj. 3. Device according to claim 2, characterized in that the second correction signal is an additive correction signal, which changes the value of the square pulse. 4. Device according to claim 2, characterized in that a device with variable gain in the Modulation path of the modulated oscillator is inserted, so that this is already through the first correction signal receives corrected modulation signal, and that the second correction signal is a multiplicative correction signal, which acts on the gain of the variable gain device. 6098 1 1/0712 Blank page