US2175335A - Television synchronizing circuits - Google Patents

Description

Oct. 10, 1939. R ANDRlEU 2,175,335

TELEVISION SYNCHRONIZING CIRCUITS Filed May 6, 1957 '13 mow/7g g \27 INVENTOR ROBERT AfVDR/EU BY MQW- ATTORNEY Patented Oct. 10, 1939 UNITED S ATES 2,175,335 TELEVISION SYNCHRONIZING cmonrr Robert Andrieu, Berlin, Germany, assignor .to

Telefunken Gesellschaft fiir Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Application May 6, 1937, Serial No. 141,082 In Germany May 6, 1936 6 Claims.

In the transmission of television images 'in' which the synchronizing impulses and the image always been connected to the detector circuit supplying the modulation potential, i. e. the socalled low-frequency potential, and with the said tube the line impulses have been filtered out of the image content. This tube and its associated circuits have been termed the amplitude selection stage. In connection with this amplitude selection stage, a separate so-called automatic relaxation device was used which is either a tube connected in a blocking oscillator or a grid controlled discharge vessel with gas or vapor filling and are discharge, serving to amplify the line im pulses and to convert them into impulses having the same energy content.

In accordance with the invention the separa tion of the line impulses from the image content;

as well as the amplification and conversion into impulses having the same energy content will be obtained by means of a single tube. This can be achieved with a combination of a tube in block-- ing oscillator circuit and suitable connection of the detector circuit as will be seen from the examples of construction described in the following, wherein Fig. 1 is an embodiment of my invention,

Figs. 2, 3 and 4 are explanatory curves, and

Fig. 5 is a modification of a portion of Fig. 1.

In the mode of construction represented in Fig. 1, the secondary winding it of a high-frequency transformer has connected thereto a detector II and a resistance t2, the latter having the condenser l3 placed in parallel thereto. The lower end of the resistor I2 is joined to the negative pole of a direct potential source it whose positive pole is grounded. The blocking oscillator consists of a tube 55 whose plate circuit contains the primary winding l5 of a transformer which winding may be joined with a condenser connected in parallel thereto, while the secondary winding l! of the said transformer is very closely coupled to the said primary winding. Furthermore, the

plate circuit of the tub-e !5 also contains a resistor l8. nected by means of line l9 with the upperend of the resistor 12, while the other end of the secondary winding is connected to the grid of the tube across a resistor 29 having the condenser 2| placed in parallel thereto. The condenser 2| must be large compared with the ground capacity of the control grid, and it is furthermore tube One end of the secondary winding H is conby S in Fig. 2, and controlled by the synchronizing impulses below said value. It is possible to assign the value S of the carrier amplitude to the black image parts, and a higher value for the carrier amplitude to the white image parts, or viceversa, to transmit at the value S the white image-parts and at a higher value, the black parts. Furthermore, in each of the two cases, the synchronizing impulses can be transmitted by reducing the amplitude of the carrier wave to the zero value ort'o a value lower than the value S, yet still 'a-finite value.

During the duration of the line there occurs a varying potentialdrop across the resistor l2 corresponding to the distribution of the brightness along the line, and having the direction indicated by the plus and minus signs. The voltage l4 must be lower than the negative grid bias potential V appertaining to the lower bend of the plate current grid voltage characteristic of tube l5 '(see Fig. 3) such that the voltage drop through the resistor l2 is'so high during the line duration and'together with the potential 14 that no plate current can flo'w in the tube i5. The'voltage at the condenser Z! placed at the grid circuit of tube [5 should for the first be assumed equal'to zero,

so that at the grid circuit only the voltage M and the voltage drop through the resistor l 2 are effective. If in the moment in in Fig. 2 the value S of the carrier amplitude has not been reached, then the potential of the control grid moves relatively to the cathode in the positive direction, and at the value A the voltage drop through the resistor I2 together with the voltage l4 may be assumed to have a smaller value than the value V in Fig. 3. Now, a plate current begins to flow in the tube, whereby a voltage appears at the secondary winding I! which is positive'as regards the control grid. The plate current once present will therefore be amplified until the control grid assumes cathode potential. At a slight increase beyond this value a grid current begins to flow producing a potential drop through the resistor 20, so that the grid potential remains constant for some time. As soon as the potential at the secondary winding ll has exceeded its maximum value, the control grid potential'will again be displaced in the negative direction so that the plate current begins to' decrease again. This decrease entails a reversing of the voltage at the secondary winding tent is independent of the interval between lines,

and independent of the value to which the amplitude of the carrier wave has been reduced during the line interval. Consequently, also at the left end of the resistor IS, a voltage impulse appears having always the samepattern and always the same value and which can be utilized for synchronizing the saw-tooth line generator. The anode current impulse may however also be used to discharge a condenser inserted between the left end of the resistor l8 and ground. The resistor l8 operates then as charging resistor. The sawtooth may, for instance, also be produced directly by means of the plate current impulse. for instance in that a condenser is placed parallel to the resistor l8, and which will be charged bythe plate current impulse; and will again be; discharged, during the duration ofthe line and across the resistor.

In the circuit arrangement describedthus, the line impulses are separated from the image content, since during the duration of the line a voltage drop exists at the resistor l2 whose value is so high that the tube l5 cannot respond; Furthermore, in tube IS the line impulse will. be amplified very efiectively, and converted at the same time into an impulse. having constant energy content, since in fact the pattern of the plate current of tube [5 develops entirelyindependently of the pattern of the further line impulse as soonas the carrier amplitude has gone below the value A in Fig. 2. More especiallythe plate current does not depend on whether the line impulse lasts for a. longer or shorter time, and is independent of the amplitude of said line impulse. A particular advantage of the described circuit arrangement is seen in that di rectly after the plate current impulse of the tube I5, the condenser 2| is being charged to acomparatively high potential representing a negative grid voltage forthe tube t5, andthat this voltage again disappears in a relatively slow manner across the resistor 2-0; The tube l5 thereforecannot be brought to response by disturbing impulses during the-line deviation even where these impulses have a considerable amplitude, Not before the end of the line duration. has the charge at the condenser 21 been able to become balanced to a fair degree across the resistor 20', so that then the reduction of the carrier wave amplitude below the value 8- and A (see Fig. 2') can again produce a flow of current in tube l5. Another embodiment of the idea ofthe in.- vention relating to transmission methods according to Fig. 4 is shown in Fig. 5- of the drawing. In Fig. 4-, theamplitude of the carrier wave W is controlled downwards bythe image content, and upwards by the synchronizing impulses. During the duration of the line therefore, the carrier wave has for-instancethe-amplitude value Z which is lower than the value W, and during the line interval the value W will be exceeded.

-In Fig. 5, the reference characters 10 to M-refer to the same means as in Fig. 1. However, during the duration of the line a voltage drop occurs through the resistor I2 which contrary to the circuit of Fig. 1: has thedirection opposite to that of the potential source M. The value ofthe potential. source l4= is so dimensioned. that theupper end of the, resistor-t2 also still retains at the value W of. the amplitude of the carrier wave a negative potential relative to ground, andwhich is higher than the value V in Fig. 3. Only.

when the carrier wave amplitude exceeds the value W in Fig. 4 does the upper end of the resistor I2 assume a negative potential relative ground whose value is lower than the value V, so that across the line IS the blocking oscillator circuit l5 to II, 20, 2| can be' operated in the same manner as was explained on hand of the Figs. 1 and 3.

It should also be remarked that in arrangements'according to the invention also the vertical impulses can be separated from the image content, and can cause the response of the line generator: This condition need not be explained in, detail herein, since the synchronizing of the generator for the vertical deviation can be carried out in various ways when utilizing the invention.

What I claim is:

1. Apparatus for separating sets of electrical signals having differing amplitudes comprising means for rectifying said impulses, a normally conductive path joined to said rectifying means, means for normally maintaining said conductive path at a point on its conductivity characteristic close to its cut-off point, and means; for superimposing the rectified signals onto said latter means for controlling the conductivity of the conductive path.

2. Apparatus for separating sets of electrical signals having differing: amplitudes comprising means for rectifying said impulses, a time constant circuit connected to. said rectifying means, a normally conductive path joined to said rectifying means, means for normally maintaining said conductive path at a point on its conductivity characteristic close to its cut-oif point, and means for superimposing the rectified signals onto said latter means for controlling the conductivityof the 1 conductive path.

3. Apparatus for separating sets of electrical signals having differing amplitudes comprising a rectifier, a time constant circuit connected to said rectifier, a thermionic vacuum tube having anode, cathode andat least one control electrode, means for electrically connecting a control grid of the thermionic tube to the time constant circuit whereby increasing amplitudes of signals impressed on the rectifier'bias the grid of the thermionic tube-increasingly negative, and means for normally maintaining the thermionic tube at a point on its conducting characteristic close to its cut-off point.

4. Apparatus for separating sets of electricalsignals having differing amplitudes comprising a rectifier, a time constant circuit connected to 0 said rectifier, a thermionic vacuum tube having anode, cathode and at least one control electrode, means for electrically connecting a control grid of the thermionic tube-to thetime constant circuit whereby increasing amplitudes ofsignalsimpressed on the rectifier bias the grid of the thermionic tube increasingly positive, and means for normally maintaining the thermionic tube at a point on its conducting characteristic closeto its cut-off point.

5. Apparatus in accordance with claim 3 wherein there is provided in addition a second time constant circuit connected serially with a control gridof the thermionic vacuum tube.

6. Apparatus. in accordance with claim 4 wherein there is provided in addition a second.

time constant circuit connected serially with a control grid of the thermionic vacuum tube.

ROBERT ANDRIEU.

Images