DE1512417C - Rainbow generator for testing a PAL color television receiver - Google Patents

Description

The present invention relates to a rainbow generator for testing a PAL color television receiver with two oscillator circuits for generating of two oscillations that contain signals or consist of signals whose frequencies are the same the color subcarrier frequency plus or minus the line frequency or a whole multiple of the Line frequency are, and with a switch that the outputs of the oscillator circuits in the rhythm of the Line frequency alternately connects to an output terminal.

A rainbow generator of the type known above is already described in German patents 1,258,449 and 1,263,818 have been proposed. In the proposed rainbow generator, the two work Oscillator circuits independent of each other and supply oscillations of the color subcarrier frequency plus or minus the line frequency to the switch. Also, the vibrations! a phase dependent Rectifier, which supplies a signal of twice the line frequency, for coupling with the clock generator frequency fed. You can choose between the phase-dependent rectifier and the clock generator a phase shifter can be provided to relate the blanking interval for the color synchronous oscillation train to move to the color wheel.

The present invention is based on the object of a rainbow generator for testing a Specify PAL color television receiver, in which a perfect phase lock between the successive Lines and the correct PAL switching polarity z. B. despite tolerances and signs of aging are guaranteed.

According to the invention, this object is achieved in a rainbow generator of the type specified at the beginning solved in that the first oscillator circuit, which supplies one of the two oscillations, over a sensing stage, which is opened by pulses of single or double line frequency, via a phase synchronization device is coupled to the second oscillator circuit.

Further developments and refinements of the invention are characterized in the subclaims.

An embodiment of the invention is shown in the following an.Hand shown in the drawing Block diagram explained ..

In the following explanation, the following abbreviations are used used:

fsc - ■ color subcarrier frequency; fh --- line frequency;

F, --- a frequency that is Fn or a multiple of Fn below the color carrier frequency /.

located: · , . .

F ₁₁ - · a frequency which is Fh or a multiple of Fu above the color subcarrier frequency F ₁ - ; ·

Fxc - ■ Signal component with color subcarrier frequency, which is the sideband of F ₁ or F ₂ after sampling by a gate circuit.

If in a PAL receiver the reference voltage of the frequency / »« is _{phase-locked with an input signal voltage F 1} - ■ - (fnc-Fn) during the line blanking interval, the phase difference between Fi and / _sc in the course of each line is a rotating vector, which runs through an angle of 360 ° during each line period.

In the receiver (s) with a precise phase relationship to F ₁ , the input signal voltage F ₁ is fed to a color sync pulse gate circuit, as is normally found in a color television receiver, which composes a subcarrier-frequency signal component F _{S (} - in the form of a sideband with other frequencies above and below F ₁ , which are suppressed by the reference generator control circuit, the bandwidth of which is normally smaller than Fn , generated at intervals of Fh. This circuit synchronizes the phase of the reference oscillator voltage f _{sc of} the receiver with the component F _sc of F ₁ .

If now voltages with the frequencies f _sc and F _{1 are} fed to the color demodulators of the receiver at the same time, the voltage of the frequency F ₁ is treated as a color signal, and color signals are _{generated according to the instantaneous phase difference between F 1} and fsc and as colors along the relevant Line reproduced.

In the next line, the phase of the reference voltage f _se is reversed by the PAL switch, and the same colors are only generated at the same positions in the successive lines if the phase of the signal corresponds to that of the signal presented in the previous line. les F _{1 is} conjugated.

Such a signal can be generated in the manner already proposed by means of a voltage of frequency F ₂ = (fsc. + Fh) , which is processed by the receiver, as described above in connection with F ₁ . The vector of the instantaneous. The phase difference 'between F ₂ and f _{sc again} runs through an angle of 360 ° during each line, but in this case in the opposite direction to the vector generated _{by the voltage with frequency F 1.} If now during the retrace interval F ₁ and F _{2 are} phase-locked with each other and used alternately during successive lines, their phases are conjugated at corresponding points on successive lines, and if the PAL receiver is properly synchronized at the corresponding points, the reproduced in the same colors.

The complete signal must of course also have components for synchronizing the horizontal and vertical deflection, the color subcarrier oscillator and the PAL switch.

According to the invention is a rainbow generator for testing a PAL color television receiver with two oscillator circuits for generating two oscillations that contain signals or consist of signals whose frequencies are equal to the color subcarrier frequency plus or minus the line frequency or an integral multiple of the line frequency, and with a switch which connects the outputs of the oscillator circuits in the rhythm of the line frequency alternately with an output terminal, characterized in that the first oscillator circuit, which supplies the one of the two oscillations, ■ via a feeler stage, which by pulses of simple. or double line frequency is opened, and via a phase synchronization device with the second. Oscillator circuit is coupled. ;

The other of the two oscillations can be supplied directly from the output of the Taststufe also ■ .. switch. '.

Such a rainbow generator, which contains a phase shifter which ^{ensures a phase difference of 90 c} between the two oscillations at the beginning of each scan, is preferably characterized in that a phase shifter circuit is arranged in the path of at least one of the two oscillations. The phase shifter circuit can be connected between the two oscillators or between one or both oscillators on the one hand and the switch on the other. .

The phase shifter circuit is preferably between the key stage and the switch arranged.

In the following an embodiment of a rainbow generator according to the invention is given of the block diagram shown in the drawing.

The illustrated rainbow generator contains a first oscillator circuit 1, which can contain a crystal oscillator and _{supplies an output voltage with the frequency F 1} to a gate circuit 3, which is normally blocked and is gated by pulses of the frequency Fh or 2 Fh at the beginning of each line. The gating pulses are supplied by a pulse generator circuit, not shown, which can be implemented in a known manner.

The output signal of the gate circuit 3. consists of a color sync pulse (burst) that occurs during the opening interval and contains. not only components of the frequency F _1,. but also sidebands including F ₁ + 2 Fh, ie F ₂ .

The output signal of the gate circuit 3 is fed to a frequency and phase control circuit 4 which controls an oscillator circuit 2 which oscillates _{at the frequency F 2 and contains a crystal oscillator.}

The following relationships now apply:

F, -

fs, - = F ₁ + F /,

Fsc = F ₂ - Fh

Fh-F ₁ + Fh

F ₂ = F ₁ +

40

The bandwidth of the frequency and phase control circuit which controls the oscillator circuit 2 with a center frequency which is approximately equal to F ₂ is so narrow that only the desired sideband F ₁ + 2 H is passed, and the oscillator circuit 2 is accordingly through this sideband , which has the same initial phase as F ₁ during the opening interval.

The output signal of the oscillator circuit 2, which has the frequency F _{2 , is therefore initially phase-synchronized with the output signal of the frequency F 1 of} the oscillator circuit 1 during the opening interval of the gate circuit 3. ^!

The output signals of the two oscillator circuits 1 and 2 are fed to an electronic switch 5, which switches over with the frequency F //, ie operates with a period corresponding to (Fn) β. The output signal of the switch 5 appearing on an output line 6 has the frequency F ₁ if the line 6 is connected to the oscillator circuit 1 during one half cycle and the frequency F ₂ if the output line 6 is connected to the oscillator circuit 2 during the other half cycle is. These intervals follow one another with the frequency (F //) / 2, so that the output signal on line 6 has frequency F _{1 during one line and frequency F 2} during the next line. ,,. ■■■! .- ■■■.: ■

With the output signal, pulses of frequency Fh and the other necessary synchronization pulses are combined so that a composite signal is obtained, as required by the color television receiver.

In the receiver, the color synchronization takes place through the "color signal" with the frequencies F ₁ and F ₂ in successive lines by the fact that this signal passes through the normally blocked and opened during the line return with the line frequency Fh color sync separator, whereby during one line under other sidebands of the frequency F ₁ + F h = F "and during the next row, among other sidebands of the frequency F ₂ - Fh = Fsc are generated and the reference voltage /« · of the receiver by the signal component at the frequency F _sc phase synchronized wirdv

F ₁ and F ₂ can be swapped so that F ₁ is synchronized by F _2.

The frequency of the final output of the Rainbow generator can be used in high frequency, intermediate frequency, Video frequency or color signal frequency range.

In another embodiment of the invention, the sideband with the frequency F _{2 is} selected and fed to the switch 5, so that the oscillator circuit 2 can be omitted. .. ·., ·

The PAL standard of the color signal dictates that the phase of the Farbsynchronisierimpulses in consecutive lines with respect to the negative (B- K) direction by 45 ^r upstream and .nacheilt to not only the time of switching, but also the phase of the PAL switch to be able to synchronize. . ■.

The vector for. the voltage with the frequency F ₁ rotates during a line period by 360 ° with respect to the reference voltage f _{ec of} the receiver, and in the color demodulators the voltage with the frequency F ₁ is processed as a color signal and a voltage is generated that corresponds to the instantaneous phase and amplitude difference between F ₁ and / _sc along the relevant line.

The corresponding processes take place in the following line when the PAL switch of the receiver works synchronously with F ₂ . The vector of the voltage with the frequency F ₂ now rotates with respect to / «in the opposite direction as with F ₁ . However, since the polarity of the reference voltage is reversed, the relative phase differences between F ₂ and fsc are the same as in the previous line, and the demodulation supplies the same voltages as before. In the receiver, the same colors are therefore reproduced at corresponding points along all lines.

If a phase difference of 90 ° is set between the voltages of frequencies F ₁ and F ₂ , the phase difference between the two signals at the beginning of the line is 90 ° plus or minus the control deviation of the frequency and phase control circuit 4. At the beginning of a line then deviates thus / _t by 45 ° in one direction and in the next line F ₂ deviates by 45 ° in the opposite direction from the middle phase of F ₁ and F ₂ .
The sideband F _sc , which is generated by the color synchronizing pulse separation stage of the receiver in one line from F ₁ and in the next line from F ₂ , has the same initial phase position as F ₁

or F ₂ . If, for example, at the beginning of the opening interval of the color synchronizing pulse separation stage F ₁ and F _{2 have} a phase difference of 90 °, the sideband F _x , - has the same phase difference. The phase demodulator of the receiver is thus supplied with a voltage with F _xc -j- 45 ° during one line and a voltage with F _{S (} · - 45 ° in the next line, and it accordingly supplies an output voltage with the phase of the reference voltage remaining the same changes in the positive or negative sense synchronously with the line-by-line phase changes of Fse , which are superimposed on a DC voltage value that results from a possible difference between the phase of the reference voltage and the mean of the positive and negative phase changes of Fsr . A signal with a corresponding profile is obtained from the phase demodulator when the test signal generated with the present rainbow generator is fed to it, which corresponds to a conventional PAL signal and controls the -PAL switch of the receiver in a corresponding manner ° introduced between F ₁ and F ₂ in order to emulate deir color synchronization pulse of a standardized PAL signal, so that it is not necessary. to generate a separate color synchronization pulse or to take other measures for the synchronization of the PAL switch. In the in the. The rainbow generator shown in the drawing can be used for this purpose suitable phase shifter circuits between the oscillator circuit 1 and the gate circuit 3 or between the gate circuit 3 and the frequency and phase control circuit 4 or between one of the two oscillator circuits 1 or 2 and the switch 5, or several of these measures can be combined. For example, you can. generate ^{a phase shift of 45 C} between each oscillator circuit and the switch 5. Another possibility is to control the oscillator 2 in such a way that the desired phase shift of 90 ° results.

The rainbow generator described provides a color signal in the form of a voltage, the vector of which is added Beginning of successive lines forms an angle of} 45 or -45 ° with respect to / „·, as required is. in order to produce on average the same colors in the same relative position.

A high level of accuracy is not required in practice, because the recipient always adjusts to the means, even if the color is the same at the beginning the scan is generated changes slightly the same color is generated again at the beginning of the next scan. In the present circuit it has this is merely a change in the amplitude of the signal supplied by the phase demodulator of the receiver result that the recipient can easily process.

If vertical color bars are to be generated, the signals supplied by the oscillator circuits 1 and 2 with the frequencies F ₁ and F _{2 can be} interrupted or blanked at suitable intervals in the course of the line deflection. This interruption can take place, for example, at the output of switch 5 or between oscillator circuits 1 and 2 and switch 5. .

Claims (5)

Patent claims: • ■ 1. Rainbow generator for testing a PAL color television receiver with two oscillator circuits for generating two oscillations that contain signals or consist of signals whose frequencies are equal to the color subcarrier frequency plus or minus the line frequency or a whole multiple of the line frequency, and * - connecting with a switch which gates the outputs of the oscil- vl in the rhythm of the line frequency \ alternately to an output terminal, characterized gekennzeichne I t that the first! Oscillator circuit (1), which _{supplies one (F 1} ) of the j two oscillations (F ₁ , ■ F ₂ ) via a | Tas.tstufe (3), which is opened by pulses of single or double line frequency, and is coupled to the second oscillator circuit (2) via a phase synchronization device (4). 2. Rainbow generator according to claim 1, characterized in that the other (F ₂ ) of the two oscillations (F ₁ , F ₂ ) is fed to the switch (5) directly from the output of the sensing stage (3). 3. Rainbow generator according to claim 1 or 2 with a phase shifter which ensures a phase difference of 90 ° between the two oscillations at the beginning of each sampling. (F ₁ , F ₂ ), characterized in that at least one of the two oscillations (F ₁ , F ₂ ) a phase shift circuit is arranged. 4. rainbow generator according to claim 3, characterized in that the phase shifter circuit between the two oscillators (1, 2) or between one or both oscillators (1, 2) on the one hand and the switch (5) on the other hand is switched on. ■ 5. rainbow generator according to claim 3, characterized in that the phase shifter circuit between the probe stage (3) and the Switch (5) is arranged. 1 sheet of drawings