DE1122097B - Color television receiver - Google Patents

Description

The invention relates to color television receivers and relates to a type of receiver in which the Three-color information or that from three at different phase angles on a color subcarrier color signal formed by modulated colors is converted to an index frequency carrier, the frequency of which and phase is regulated by index means responsive to the transverse scanning of color strips on the screen a cathode ray tube respond by a scanning beam of the tube.

The use of an index frequency carrier is necessary when the electron beam is over quickly moves the colored stripes so that the electron beam is properly modulated in intensity at all times can to achieve correct color rendering, despite the fact that there are always certain irregularities can occur in the scanning speed of the beam and in the spacing of the stripes.

It has already been proposed to convert the color information from one carrier to the other using a number of mixers. Mixers are usually non-linear devices and generate additional signals on harmonics of the two signals to be mixed and also on frequencies, the combinations of harmonic frequencies represent. Several of these unwanted signals occur at frequencies ranging from are distant from the desired signals and can therefore be suppressed with the help of traps, however, these have the disadvantage that they increase the overall group delay time of the circuit. Other unwanted signals are very close in frequency to the useful signals and can therefore can only be suppressed by special mixer circuits.

The object of the invention is to simplify the color television receiver of the specified type and to improve.

According to the invention, the color television receiver includes three circles of the type indicated, each of which is a demodulation tube or a Has demodulation transistor, the anode or its collector with the cathode or the emitter a modulation tube or a modulation transistor is connected via a low-pass filter, wherein Means are provided to supply three different phase reference signals of the color subcarrier frequency to the demodulation tubes or the demodulation transistors, and means for supplying the color signal to the circuits and means for supplying three carrier signals of index frequency to the modulating color television receivers

Applicant:

Sylvania -Thorn Color Television
Laboratories Limited, London

Representative: Dr.-Ing. E. Liebau, patent attorney,
Augsburg-Göggingen, Von-Eichendorfr-Str. 10

Claimed priority:
Great Britain June 15, 1959 (No. 20,500)

John Kenneth Oxenham and Reginald Graham,

London,
have been named as inventors

tube or to the modulation transistors and a tuned circuit through which the output values of the three modulation tubes or transistors are combined, the arrangement being made in this way is that in operation the color signal is demodulated at the three phase angles η of the three reference signals that the three demodulated signals through the low-pass filter, which make the color subcarrier frequency strong attenuate, pass through and be modulated onto the carrier of the index frequency, and that three um Phase angle of 120 ° against each other shifted signals of index frequency generated and tuned in the Circle can be combined.

The three index frequency signals shifted by a phase angle of 120 ° can thereby be generated be that by 120 ° phase-shifted carrier signals applied to the modulation tubes or transistors. Another possibility is that the three carrier signals have the same phase position and the 120 ° phase shift, z. B. with the help of a Delay line, effected in the tuned combining circuit.

A particular advantage of the invention is that only one tuned circuit to the index frequency is required, which does not need to have a narrow bandwidth, so that the group delay is short. The circle can not only deliver an equiangular color signal as a function of the scanning of the color stripes, but also produces an M-F signal which, combined with the brightness signal Y , is a

109 760/176

3 4

Signal M for controlling the overall brightness, which consequently only changes by a few volts, like the

Cathode ray picture tube results. Current in Vl (a) fluctuates. Thus, the circuit

The invention and its broader features are considered to be the top of Al

Advantages are kept at 125 volts in two exemplary embodiments.

is explained in more detail by drawings, namely 5 The triode Vl (ä) works as a grid-controlled

Fig. 1 is a circuit diagram of an embodiment of the rectifiers, and in the absence of one

Invention, color input voltage lower the high peak

2 shows a representation of various curve values for the anode current and the mean anode shapes to explain the operation of the voltage to a low value in the size-Fig. 1 and io order of 20 volts. Assuming that

Fig. 3 is a circuit diagram in which different levels due to the clamping effect of the triode, the eye

Conversions are shown, soft according to a visual anode voltage in the conductive state

second embodiment is kept constant in the circuit of FIG. 1, the demodulated appears

can be made. Output voltage VR over Al and has a maximum

The circuit shown in Fig. 1 is for processing 15 amplitude equal to the peak-to-peak distance

of the NTSC color signal, which is suitable for demo of the color input signal. Fig. 2 shows the operating

dulation at phase angles of 121 °, 219 ° and 353 ° conditions for a color signal of constant

Signals 0.90 (RM), 0.83 (GM) and 0.67 (BM) amplitude (α) in phase, (b) under 90 ° phase shift

yields, where M = V ₃ (R - {- G + B). It can be seen, shift and (c) out of phase with the reference

that these signals are converted and added 20 signal (d).

can, so that a signal 0.30 (RM) + 0.59. When the voltage across Rl changes, so changes

(GM) + 0.11 (BM) = YM results. The for this purpose the through this and through the triode Vl (b)

required resources are known per se and are flowing electricity. The triode Vl (b) acts as a modul

therefore not explained in detail. lator to which a carrier signal of index frequency ω

The circuit shown contains three double triodes 35 which are fed at 0 °, which are connected to terminal / 1 (b)

Vl, Vl and V3, both halves of which are created with Vl (a) . The index carrier is made by scanning

Vl (b) etc. are designated. The three triodes Vl (a), created by special index strips in the tube.

Vl (ä) and V3 (a) form the lower tubes of three The triode Vl (b) thus generates a signal of

Cascode circuits and the triodes Vl (b), Vl (b) index frequency in their anode circuit, and the signal

and V3 (b) the top tubes of the three cascode 30 becomes proportional with a peak-to-peak amplitude

circuits. The three circuits are the same, and the current flowing through Vl (b) (and Al) is ampli-

therefore only the first is described in detail. tude modulated. The triode Vl (b) can be in C mode

The cathode of the triode Vl (ä) is operated with earth, whereby the index signal has a large bound, and its anode is connected to the cathode of amplitude and the tube for the largest Vl (b) via a transformer winding Ll, a 35 Part of the working period locks. The anode current resistor Al and a low-pass filter Fl in Ver then consists of narrow current pulses with a bond. A trap circle Tl of 3.6 MHz is occurring with the index frequency, and the fundamental lower end of Al connected to the signal component has a peak-to-peak amplitude very color subcarrier frequency of about 3.58 MHz to approximately four times the mean current by suppressing. An input terminal / 1 (a) is the tube at 40. This mode of operation leads to a signal form very suitable for the grid of Vl (a) via a capacitor Cl (a) for the cathode connected, and between the grid of Vl (a) and the radiation tube. The signals of the index frequency ω that the earth is connected to a grid resistor Λ1 (α). Triodes Vl (b) and V3 (b) have The input terminal / 1 (b) has a phase angle of 120 or 240 ° via a condenser.
sator Cl (b) connected to the grid of Vl (b) , 45 The overall mode of operation, in which the circuit and a grid resistor Al (b) is processed between the color signal, shall now be considered more closely grid of Vl (b) and a voltage source of be. The phase angle at which the demo switched + 125 volts. The anode of Vl (b) is effected with dulation, result in an (R- M) signal from an output terminal 100 and via a parallel via the resistor Al and (GM) - or (BM) - resonance circuit FF with a voltage source of 50 signals connected via the corresponding resistors of the + 250VoIt. Terminal 100 and the other two cascode circuits. If all demo circles FF are common to all three cascode circles. dulators have the same gain, the

The winding Ll and the windings Ll and L3 signals according to the previous findings with regard to

the other cascode circles are with a color signal borrowed the NTSC color signal in the ratio 0.90: 0.83

input winding LL coupled. 55: 0.67. The signals are, however, in the same

The triode Vl (a) is required as a demodulator in C operation ratio, and the demodulators must be operated and on the grid with a large signal, therefore have amplifications that are controlled in the ratio of the color subcarrier frequency, which at / 1 (a) I: 1, 09: 1.34 stand. This is expediently applied by. This signal is supplied by a coherent oscillator using different color transformers, which achieves 60 tongues on the various tubes in a known manner, with the tubes Vl (a), Vl (a) and V3 (a) being regulated by the bursts of color in the video sync signal It is used and arranged so that its phase angle has 121 ° strengthening. Another possibility is. Correspondingly, Vl (a) and V3 (a) are operated in that the signal ratio at the resistors is phase angles of 219 and 353 °. Rl etc. is chosen differently, with a com-

Since the function of Vl (a) as a demodulator to 65 pensation is effected by the fact that the amplification is considered, the presence of Vl (b) kungen the modulators can be made different, since their grids on 125VoIt which ratio the signals is held above the negative and their cathode potential would also have, it is clear that they are like the

NTSC techniques for deriving a ( Y- M) signal can be used, as previously stated, for the subsequent derivation of an M signal. (Usually the M brightness signal is applied to the cathode of the cathode ray tube and the processed color signal of frequency co is applied to the grid of the tube.)

The use of index carriers at phase angles of 0, 120 and 240 ° results in an equiangular color signal and, based on a suitable setting of the overall gains of the cascode circles, as explained above, the condition that for R = G = B and in particular for /? = G = β = 0, the voltage applied to the cathode ray tube color signal is equal to zero, is achieved as A · coscui + A ■ cos (cot + 120 °) + A ■ cos (o) i + 240 °) = 0 for all t.

It should be mentioned here that the process of demodulation and modulation only has to be carried out at two phase angles in order to obtain all of the information in the color signal, and that a (Y- M) signal can be derived in this process. However, if only two phases, e.g. B. under 90 °, are used, the output values of the modulators must be zero when the color signal is zero. Otherwise, in contrast to the case of the circuit described with reference to FIG. 1, a resulting color signal would be applied to the cathode ray tube. The most common way of eliminating standing waves is to use balanced modulators, but then in reality four phases are used, as opposed to the three according to the invention.

In the second embodiment of the invention , the demodulators are designed differently. Fig. 3 shows the other circuit arrangement for the triode Vl (a). The anode is connected directly to the resistor Rl , and the color signal is fed to the grid via a transformer Zl. The cathode line contains a resistor Rl bridged by a capacitor Cl and a winding of a transformer Zl, with the aid of which the subcarrier reference signal is fed to the triode. This is a common type of demodulator per se. The demodulator shown in Fig. 1 has the advantage of greater direct current stability and therefore zero stability for the processed color signal.

The only circuit tuned to the index frequency is circuit FF in both embodiments. The 3.6 MHz traps and the low-pass filter ensure that only the demodulated color information reaches the modulators. The only signals separate from the useful signal that can occur at the output of the circuit are harmonics of the index carrier and harmonics of the demodulated color signal. The latter can be generated in the modulators, but they occur at a relatively low level and at a frequency that is far removed from the useful signal. As a result, the circuit FF can be made broadband so that it has a small group delay.

Various modifications can be made in the circuit arrangement shown. One The possibility is that the demodulation angle on more common phases, e.g. B. 0, 120 and 240 °, is effected and that the output values are processed in order to produce the necessary signals for supply to the modulators and derive an equiangular color signal.

It should be noted that the circuit shown can be easily modified by replacing the tubes Vl (a), Vl (b) , etc. with transistors. It is not necessary to design and illustrate the various circuit possibilities with transistors in detail, since the person skilled in the art knows the equivalent transistor circuits for the corresponding tube circuits.

Claims (10)

PATENT CLAIMS: 1. Color television receiver, in which the three-color information or the color signal formed from three colors modulated on a color subcarrier at different phase angles is converted to an index frequency carrier, the frequency and phase of which is regulated by index means which are based on the transverse scanning of color strips on the screen of a cathode ray tube address a scanning beam of the tube, characterized in that three circles are provided, each of which has a demodulation tube [Vl (a), Vl (α), V7> (d) \ or a demodulation transistor, whose anode or collector with the cathode or the emitter of a modulation tube or a modulation transistor [Vl (b), Vl (b), V3 (b)] is connected via a low-pass filter (Fl), means [/ 1 (a) ...] being provided to to supply three different-phase reference signals of the color subcarrier frequency to the demodulation tubes or transistors, and means (LL, Ll, Ll, L3 or Zl ...) for supplying the color signal s to the circuits, and means [/ 1 (b) ...] for supplying three carrier signals of index frequency to the modulation tubes or transistors, and a tuned circuit (FF) through which the output values of the three modulation tubes or transistors are combined, the arrangement being such that in operation the color signal is demodulated at the three phase angles of the three reference signals, that the three demodulated signals pass through the low-pass filters, which strongly attenuate the color subcarrier frequency, and are modulated onto the carriers of the index frequency and that three signals of index frequency shifted from one another by phase angles of 120 ° are generated and combined in the tuned circuit. 2. Color television receiver according to claim 1, characterized in that the means for feeding of the carrier signals in operation are suitable, three carrier signals of index frequency with phase shift of 120 ° to the three modulation tubes or transistors. 3. Color television receiver according to claim 1, characterized in that the means for supplying the carrier signals in operation are suitable for supplying three in-phase carrier signals of index frequency to the three modulation tubes or transistors, the tuned combination circuit having delay means through the relative phase shifts with respect to the index frequency of 0.120 and 240 ° can be impressed on the signals to be combined. 4. Color television receiver according to claim 1, 2 or 3, for use in connection with a color signal which is modulated with color information at phase angles ix, β and y with respect to three primary colors, characterized in that the Means for supplying the reference signals in operation are suitable for supplying three reference signals of color subcarrier frequency at phase angles of α, β and γ to the demodulation tubes or transistors. 5. Color television receiver according to one of the preceding claims, characterized in that for feeding the color signal to the circles three transformer windings (Ll, Ll, L3) in the respective connections from the anode or the collector of the demodulation tube or the transistor to the cathode or are provided for the emitter of the modulation tube or transistor and one or more further transformer windings (LL) are coupled to the three windings to which the color signal is applied during operation. 6. Color television receiver according to claim 5, characterized in that the gain of the Demodulation tubes or transistors and the * ° modulation tubes or transistors essentially are the same, while the mutual turns ratios of the transformer windings are chosen so that the signal generated in the tuned loop goes to zero when equality is present between the three color signals. 7. Color television circuit according to claim 5 or 6, characterized in that in each demodulation tube [Vl (ä) ...] or in each transistor, the cathode or emitter with a point of fixed potential and the anode or the collector with the associated winding of the three transformer windings is connected and that the current sources [71 (α) ...], which supply the reference signals of color subcarrier frequency for the demodulation tubes, are connected to the control grid of these tubes or to the base electrodes of the transistors. 8. Color television circuit according to claim 1, 2, 3 or 4, characterized in that each demodulation tube or each demodulation transistor is a tube [Vl (a) in Fig. 3] or a transistor, the cathode or emitter of which is connected to a transformer winding ( Zl) is connected, which is coupled to a further transformer winding, via which the respective reference signal of the tube or the transistor is fed, and that three transformer windings (Zl) are provided for feeding the color signal to the circles, which are connected to the control grids of the three Demodulation tubes or the base electrodes of the transistors are connected, one or more further windings being coupled to the three windings to which the color signal is applied during operation. 9. Color television receiver according to one of the preceding claims, characterized in that a series resistor (Rl ...) is switched on in the connection from the anode or the collector of the demodulation tubes or transistors to the cathode or the emitter of the modulation tubes or transistors is. 10. Color television receiver according to one of the preceding claims, characterized in that a trap circle (Ti ...) is switched on in the connection from the anode or the collector of the demodulation tubes or transistors to the cathode or the emitter of the modulation tubes or transistors which is matched to the color subcarrier frequency. 1 sheet of drawings θ 109 760/176 1.62