US2244794A - Television system - Google Patents

Description

June 10, 1941.

P. NEIDH ARDT TELEVISION SYSTEII Filed larch 14, 1939 2 sneags sne t 1' F19. ad

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. zz/mama by v 1 Patented June 16, 1941 UNITED STATE-S PATENT OFFICE rnmvr s r s rsram y 1 Peter Neidhardt, Berlin-Schoneberg, Germany,

asslgnor to C. Lorena -lin-Tempelhof, Germany, a company Application March 14, In Germany llachait, Ber- 1939, Serial No. 261,716 August 5, 1937 4 Claims. (01. 178-69.5)

The present invention relates particularly to television-systems in which the synchronising impulses are given by modulating the carrier wave on one side of a certain amplitude level, and the picture impulses by modulation'from same level on the other side. Processes of this given a bias in such a way that the black nonoperating level of the picture modulation just does not permit any anode current to flow in the separator tube whilst the synchronisation impulse itself causes the fiow of the anode current. This process operates satisfactorily per se. A further consideration of the associations between conditions in the picture channel and the synchronisation channel, however, shows that in the case of the circuits hitherto used there is an excessive outlay which is not essential. When modulating a Br'aun valve in a television receiver, as generally known, a peak voltage 'of about 15' volts is required. The synchronisation voltage which is to control the time base apparatus amounts to about 8 volts. It is, therefore, not necessary that amplification of the synchronization impulse should take place as has been done with the separator valves used hitherto. It would rather s'ufilce for the separator equipment to operate completely without any amplification. and only switching elements to be used which require no outside voltage such as for example diode valves. I

Inordertoaccomplishthispurposeitispropiled in accordance with the present invention that themodulationconsisting'of picture and synchronisation signals should be conveyed through a device which only permits free transmissiontoalternatingcumnt,toarectifierthat receives a bias which is dependent upon the meanpicture intensity. F lly invention will be more clearly understood by reference to the accompanying drawings Fig. 1 illustrates a portion of a band filter and an anode rectifier tube stage;

Figs. 1a and 1b are graphs of signal voltages used to describe the operation of the circuit of s- 1;-

Figs. 2 and 3 illustrate modifications ofthe' four-pole network shown in F18. 1;

Figs. 2a and 3a are graphs of signal voltages used to explainv the operation of the circuits shown in Figs. 2 and 3, respectively;

Fig. 4 illustrates a circuit for producing a bias which fluctuates with mean picture intensity;

Fig. 5 illustrates a modification of the circuit.

shown in Fig. 2; i

Fig. 6 illustrates a modification of the circuit shown in Fig. 5;

Fig. 7 illustrates a circuit for producing a bias which fluctuates with mean picture intensity;

Fig.8 illustrates a modification of thecircult shown in Fig, 4;

Fig. 9 illustrates a modification of the circuit shown inFlg. 'l.

The invention will now be described with reference to the accompanying drawings; In Fig. 1,

' II is the coilof a band filter, in one of the last stages of the intermediate-frequency picture receiver, and which feeds the input circuit ii of the valve l2. This valve may. for example,

- operate as an anode rectifier so that in the anode resistance of this valve the transmitter modulation is present, as shown in Fig. 1a, Here the signals below the non-operating level line a, are, as is generally known, the synchronisation impulses, and the signals above represent the picture variations or intensity values. A four-pole member is connected to the anode resistance of this valve through a condenser 5 over the input terminals i and 2, and the output terminals 2 and I areconne'cted to the time base apparatus or so-called relaxation device. Let this mem- "ber in the first instance only consist of a resistance 8. The voltage arising at terminals 3 and I will then have the form shown in Fig. 1b, as the condenser I only permits alternating current to pass through. The synchronisation impulses are then accordingly below the zero line and the picture impulses for the most part above this zero line. It now, as shown in 118.2. a

rectifier 22 is, for example, connected in series with the resistance 0, then it is possible-to cut off the tips which come above the zero line in H8.l.sothatasinl"ig.2aonlythesynchronisation impulses remain which are, however, loaded with the residues of the picture impulses. This disadvantage can in the first instance be lessened by giving the rectifier a constant bias as in Fig. 3, for example, with the assistance of battery 25. If the polarity of the bias is correct synchronisation impulses. are obtained The rectifier 22 and the resistance 6 of this circuit arrangement coincides with the elements similarly indicated in Fig. 3. To terminals I and 2 there is conveyed the demodulated voltage in the secondary winding of a transformer which is fed by the primary winding 26. The winding also feeds a second secondary winding which is wound in such a way that the polarities of the terminals 28 and l, or 21 and 2 coincide. This second secondary winding feeds a rectifier 29 which is so arranged that it permits the upper parts of the mixture shown in Fig. 1b to pass through and cuts oil those signals lying below the zero line. A drop in voltage accordingly occurs at the condenser resistance combination 30 which is dependent upon the mean picture intensity. The time constant of the resistance capacity member lies in the order of magnitude of the duration of a line. This voltage now takes the place of the constant bias of the battery 25 in Fig. 3. At terminals 4 and the cleanly cut oil synchronisation impulses now appear.

A modified circuit arrangement for the recti- I fler is shown as a schematic diagram in Fig. 5. This is fundamentally different from Fig. 2 in that the rectifier is connected in the reverse manner, that is to say, it acts in this circuit arrangement for the halt-wave which the synchronisation impulse contains as a choke, and tor the other half-wave as a short circuit. A winding 3| is inductively fed from a winding 26 which has flowing through it the demodulated minals of this winding 9. rectifier 32 is connected and at the same time at terminals 1 and 8 of this winding the synchronisation signals which, of course, have the picture content signals adhering to them are drawn ofi. These terminals, therefore, correspond to terminals 3 and 4 of Fig.2.

Fig. 6 shows the circuit arrangement with a bias battery 33 which lies in series with winding 3| and rectifier 32.

This bias is now as shown in Fig. 7 replaced by a bias which fluctuates with the mean picture intensity. This bias is produced by a second secondary winding 34 which is connected in series with a rectifier 35 and a resistance capacity combination 36. This member takes the place of the battery 33 in Fig, 6.

Figs. 4 and 7 are, accordingly, two final circuit arrangements which give the desired results. In both circuit arrangements two rectifiers are required. This does not, however, prevent the variable bias for the main rectifier from being obtained in some other way.

It has been found advisable when using valve rectiflers to combine the two rectifiers shown in Fig. 4 or Fig. 7 in a common vacuum container 31. The circuit arrangement as in Fig. 4 can, for example, be embodied with such a 'valve as shown in Fig. 8 which otherwise completely coincides with Fig. 4. Equally the circuit arrangement according to Fig. 7 may be arranged according to mixture as shown in Figs. 1a or 1b. To the teroutput of said transmission means and poled to permit the transmission to the timing apparatus of pulses of synchronization polarity, a second rectifier connected to the output of said transmission means and poled to cause rectiflcation of pulses of opposite polarity, voltage smoothing means having a time constant of the order of magnitude of the duration of a scanning line connected to smooth the output of said secondrectifier, and means for applying to said flrstrectifier in a transmission-reducing sense the rectified and smoothed output of said second rectifier.

2. In a gap-synchronized television system a circuit accordingto claim 1 wherein said first rectifier is serially connected between said transmission means and said timing apparatus with such polarity as to pass pulses of synchronization polarity and block pulses of opposite polarity.

3. In a gap-synchronized television system a circuit according to claim 1 wherein said first rectifier is shunt connected between said transmission means and said timing apparatus with such polarity as to permit the passage of pulses of synchronization polarity while bypassing pulses of opposite polarity.

4. In a gap-synchronized television system a circuit according to claim 1 wherein said first and said second rectifiers are electronic diodes contained ina common evacuated vessel.

' PETER NEIDHARDT.

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