US2265290A - System of synchronizing television transmissions - Google Patents

Description

Dec. 9, 1941. u. KNICK f S 2,265,290

SYSTEM OF SYNCHRONIZING TELEVISION TRANSMISSIONS Filed April 15,. 1940 INVENTOR Patented Dec. 9, 1941 SYSTEM OF SYNCHRONIZING TELEVISION TRANSDHSSIONS Ulrich Knick, Berlin-Steglitz, Germany, assignor to Fernseh G. 111. b. H., Berlin-Zehlendorf, Ger,-

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Application April 13, 1940, Serial No. 329,568 In Germany December 30, 1937 3 Claims.

This invention relates to the synchronization of television transmissions, particularly to the synchronization of saw-tooth wave generators for deflection of electron beams, and is a refiling of application Serial No. 248,483 filed December 30, 1938.

Especially in so-called interlaced scanning the required accuracy of the deflecting waves is very great. If the transmitted synchronizing impulses are not accurately timed, which can happen under the influence of pick-up of interfering impulses, or if the frequency or phase of the synchronizing impulses varies because of powerline fluctuations, these defects, which may be small for the individual impulse, may become additive. If this happens to the line-synchronizing impulses, ragged pictureedges mayresult. In the case of framing impulses, such variation may cause jumping of the entire picture in the vertical direction, which in turn results in pairing oil of lines for interlaced scanning or complete loss of interlace.

It is the object of this invention to eliminate the above described defects. A further object of this invention is to hold the voltage or current amplitude reached at the end of each saw-tooth cycle constant.

Broadly considered, this invention provides the use of non-self-oscillatory circuits in which two conditions may prevail, according to the rising or declining portion of the saw-tooth wave to be produced; the first condition representing the charging period of a condenser, the second the discharging period of the same condenser. A switching impulse is used to introduce the second condition, while a derivative thereof is used to terminate the second condition and to re-introduce the first condition.

More specifically, an electron discharge tube may be used as a discharge path for the abovementioned condenser, whereby this discharge tube is rendered conductive by an impulse and rendered non-conductive by a derivative thereof.

Still more specifically, the electron discharge tube can be rendered conductive by an impulse so as to discharge the aforementioned condenser, and, after the voltage across the condenser has reached a certain value, an impulse is released rendering the discharge tube non-conductive again.

Other objects, features and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawing, showing embodiments of the invention, in Which:

Fig. 1 shows a circuit for voltage waves; v

Fig. 2 shows a circuit for producing saw-tooth producing saw-tooth current waves and Fig. 3 is a curve showing the potential of grid 34 of tube 35 in Fig. 2, as a function of time.

Referring to Fig. 1 of the drawing, there is illustrated an impulse generator I, which is not self-oscillatory. 'Tubes '2 and 3 are connected through condensers 4 and 5 and resistors 6, I and 8 in a circuit of the multivibrator type. Generator I is preferably synchronized by applying impulses of positive polarity to the control grid of tube 2. This circuit is externally excited inasmuch as, upon arrival of an impulse from an impulse generator (not shown) of any known type capable of producing a periodical train of rectangular impulses, it initiates an impulse which is terminated by an impulse derived from theremaining part of the circuit, as will be seen later. The impulses produced by the generator I are supplied through conductor I1 and condenser I8 to control grid I ea of discharge tube I 9.

This tube when conductive forms a discharge path for charging condenser 20. Condenser 20 is charged through'resistor 25. -As condenser 20 becomespositively charged, the control grid 26a of tube 26 becomes more positive and the plate current in'tube 2'6 rises, causing an increasing voltage'drop across resistor'I5' in the plate circuit of tube 26. At the proper time during the charging'period of condenser 20, when the voltage drop across resistor I5 has reached the desired value, an impulse is initiated by generator I which renders discharge tube I9 conductive, whereupon condenser 20 starts to discharge through resistor 22 and tube I9. During this discharge, the point I6 becomes more positive and finally reaches a value at which diode 28, biased by means of voltage source 21, becomes conductive. This causes an impulse to be applied to the control grid of tube 3, causing this tube to become conductive and thus terminating the impulse applied to tube I9, which thereupon becomes non-conductive. Condenser 29 then starts to charge again,-and the cycle repeats itself. A saw-tooth voltage can be taken from the terminals 24 and 25. Thus it may be seen that if generator I is held at a constant frequency, for m stance by means of injected synchronizing impulses supplied by any source (not shown) of square-topped impulses, the saw-tooth voltage amplitudes will remain constant because the duration of the condenser charging time is fixed by the interval between synchronizing impulses and the duration of the discharge time is fixed by a predetermined potential level reached by condenser 20 at the desired terminating point of the discharge period.

Referring to Fig. 2 of the drawing, a charging condenser 53 ischarged through resistors46, 41, 54 and 55 and periodically discharged through resistor 4| and electron discharge tube 35, when the latter is rendered conductive. The potential acquired by condenser 53 is applied to the control grid 42 of tube 43, causing a saw-tooth curtube 43. The combination, consisting ofre'sistors 45, 46, 41 and choke coil 48, serves to cause an on suppressor grid 34 of tube 35 as a function of time, the dotted line representing the value which the voltage on suppressor grid 34 must exceed before current may flow to the plate of tube-35. During the non-conductive state of tube 35, condenser 36, which was previously negatively charged as will be explained below, discharges through resistors 46, 41 and 58 and variable resistor 33 by means of which the discharge time can be varied. Suppressor grid 34 becomes more positive and would finally render the tube conductive. These synchronizing impulsesrnay be generated by any suitable generator (not shown) of periodical square-topped waves, as is well known in the art. Before this happens, however, a synchronizing impulse of positive polarity is applied at terminal 30, and reaches suppressor grid 34 through condenser 32, rendering tube 35 conductive. Thereupon, condenser 53 starts to discharge through resistor 4 I and tube 3 5. I The plate current in tube 43 decreases, and [the cathode of tube 43 becomes less positive, as the voltage drop across cathode resistor v56 decreases. This in turn applies an increasingly negative potential to the cathode of diode 59, which is directly connected to the cathode of tube 43, so that diode 59 becomes conductive when the plate current in tube 43 has decreased to a certain value. Whentube 59 is rendered conductive, a negativeimpulse is applied to screen grid 31 of tube 35, blocking this tube immediately. A negative charge is thereby also conveyed to condenser 36 which is also connected to lead 60 between screen grid 31 and the anode of diode 59 Tube 35 is rendered non-conductive, condenser 53 begins to charge again, plate current through tube 43 starts to rise and condenser 36 begins to charge, and the cycle repeats itself.

The plate of tube 35 is coupled with control grid 38 throughcondenser 40, a grid resistor 39 being connectedbetween control grid 38 and the cathode as shown. Resistors 5B, 54 and 55 constitute a voltage divider. By-,-pass condenser 51 is pro- It may be seen that the potential of a coridenser allowed to charge and periodically dis- 'rent wave to flow through scanning coil 44 connected between plate 43a. and screen grid 5| of 70 vided for, the current impulse through diode 59.

charge is used to control the current in an electron discharge tube and its load circuit, in such a manner that the condenser is discharged to a certain predetermined value.

It will be understood that other methods of operating the discharge path of the charging condenser can be used within the scope of this invention.

What I claim is:

, l. A saw-tooth wave generator comprising in combination a first electron discharge tube having a cathode, a control grid and an anode, a condenser coupled to said cathode and said control grid for controlling the flow of current in said tube in accordance with voltages developed across said condenser, a resistance element coupled to said anode and said cathode for developing a voltage drop" thereacross in accordance with the flow of current in said tube, means for charging said condenser, means for discharging said condenser including a second electron discharge tube, means for rendering said-discharge means operative, and a biased rectifier responsive to a predetermined value of the voltage drop across said resistance element and eflectively coupled to said discharging means for rendering said last-named means inoperative.

2. A saw-tooth wave generator comprising in combination a first electron discharge tube having a cathode, a control grid and an anode, a condenser coupled to said cathode and said control grid for controlling the flow of current in said tube in accordance with voltages developed across said condenser, a resistance element coupled to said anodev and said cathode fordeveloping a voltage drop thereacross in accordance with the flow of current in said tube, means for charging said condenser, means for discharging said condenser including a second electron discharge tube, a non-self-oscillating pulse generator adapted to initiate r'pulses, means for applying said pulses to said discharging means to render said last-named means operative, and a biased rectifier responsive to a predetermined value of the voltage drop across said resistance element and coupled to said generator for applying pulses thereto for terminating said pulses initiated by said-generator and rendering said discharging means inoperative.

3. A saw-tooth wave generator comprising in combination a first electron discharge tube having a cathode, a control grid and an anode, a condenser coupled to said cathode and said control grid for controlling the flow of current in said tube in accordance-with voltages developed ULRICH KNICK.

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