US2582014A - Scanning device for television transmitters - Google Patents

Description

1952 1-1.0. 01-: FRANCE ETAL 2,582,014

' SCANNING DEVICE'FOR TELEVISION TRANSMITTERS Filed May 4, 1949 2 SHEETS-SHEET 1 Mil/1?! TOR S HENRY GEORGES 05 Pm NCE llE/PBERT ERNYE'I ATTORNEYS Jan. 8, 1952 H. G. DE FRANCE ET AL 2,582,014 SCANNING DEVICE FOR TELEVISION TRANSMITTERS Filed May 4, 1949 2 SHEETS-SHEET 2 F RA ME 5CA N N G MEANS #EA/Ry G-EQRGES o; FRANCE HERBERT ERA/ye! fiaug fwyud Patented Jan. 8, 1952 UNITED ST:

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SCANNING DEVICE FOR'TELEVISION TRANSMITTERS France Application -May-4, 1949, Serial-=No. 91,242 In France Mayi8, 1948 (01. sis-c4) 6 Claims. 1

Our invention relates to. electron scanning devices for television transmitters.

.Its..chief..object. is to providea deviceof this kind which is .betteradapted to .meet the requirements of practice than those usedv up to this time for. the same purpose.

-It consists chiefly in providing devices of the -kind.in questionwith. correcting means capable of modifyingthe direction of the scanning beam .in.order-to correct defects of the image to be analyzed.

Preferred embodiments of our invention will -.be...hereinafter described, with referenceto. the accompanying. drawings, given merely by way of .example, and in which:

..Fig.l1-shows, in diagrammatic section, a television. analyzer tubev to which the invention may .beapplied;

.Fig- 2 shows, at aand. 1), vertical and horizontal stripsbelonging to the picture to be repro- ..duced;

Fig. 3 shows, at-a. and b,..the same strips subjected.tothedeformation effect which the invention is to eliminate.

Figs. 4. and 5 show .embodimentsof meansfor correcting scanning ina tube of this .kind shown by Fig. l.

.The .analyzer tube shown by Fig. 1 is of conventional construction. Animage of the object 'tocbe televised is projected through an optical system 2 ontoa photocathode 3 included in tube 4. Thisphotocathode releases. electronsproportionally to illumination, and the resulting emission-is focused by electron means 5 upon'a target 6 where the coil image thus formed produces acharge image with respect to a metal plate 1 through a process of secondary emission.

.This'target subjected-to the action of a scanning beam produced by a hot cathode '8, con centrated through other coil means '9 and deflected :by twodefiecting coils Hi,- i i in the horizontal and vertical directions respectively. This beamgives back to each element the number of electrons lost through secondary emission and thus produces a. corresponding current through resistance 12' across the terminals of which the useful image voltage V1 is collected.

Now, it has been found that thepath of travel of the electrons issued from photocathode 3 is not truly parallel to" axis XX, but is helicoidal, so that the whole of the image on target 5 is rotated through about 45 with reference to that 1 produced by photocathodeS. The angle of rotation'depends upon the field-of focusing coil 5. Besides-this angle is-not the same for all the tpoints,.and variesaccordingas the point that is -being considered is more or less remote from the center ofimage, ie.. from axis'XX'. Thus two vertical (Fig. 2, a) or horizontal (Fig. 2,"b)"strlps are ,.deformed,into sinuous shapes such as disclosed by Fig. 3, at a and b. Inthe remainder of the description and'in the claims, this will be called. S distortion.

In order to remedy this drawback, according to our invention, scanningof the electron image" is performed in accordance with the deformation thereof, so as to permit of. creating, at the output of the tube, the same voltages as ifthisdeformation did not exist.

"For this purpose, we may proceed, among other advantageous ways, as follows.

Concerning first the deformations of the vertical strips or lines (Fig. 3, a), that. is to say deformations taking place in the horizontal direction, ordirection of thescanning lines, the desired correction can be obtained by superimposing on the line scanning deflecting voltages or currents an approximately sinusoidal voltage or current of a frequency equal to the frame scanning frequency, say periods per second.

Concerning the deformations of the horizontal strips (Fig. 3, b), i. e. deformations taking place in the vertical direction, in order to obtain the desired correction, that is tosay to obtain a .line. scanning not along straight lines but along sinuous lines, substantially sinusoidal voltages or currents of a frequency equal to line scanning frequency should be superimposed on the frame scanning deflecting voltages or currents.

Besides, it should be well understood that these correcting voltages or currents may be applied either to the existing deflecting coils II), II or to coils, or other deflecting means, distinct from coils I0, I i.

The means for obtaining the correcting voltages or currents may be devised in many ways, advantageously by making use of the scanning saw teeth which are modified in suitable circuits so as to transform them into sinusoidal voltages, in'particular as follows.

'In order tocorrect' the defect of Fig. 3,0, we start. from the framescanning sawtooth, which is deformed and brought out of phase so as to 0btain therefrom a more or less distortedsinusoid according .to thecut-ofi frequency of a low-pass filter or. the like.

Thus, according to the embodimentfofFig. 4, the frame scanningsaw-tooth signal i3 is supplied through a. coupling capacitor Manda high resistor. iii to thelgrid of a tube ifi'which is'biased for-instance by acathode resistor i! and a grid rleak resistor i8. Resistor i5 rounds off the shape --of: the.sauctoothpwherebya somewhat sinusoidal signal is obtained across a load resistor-such as v: I 9.-1This "signal: iseappliedto-tubeiiithrou'gh a phase changing system 2|, 22, 23, advantageously adjustable at 231.

The plate of this tube 20 is connected with the high voltage whereas there is inserted on the cathode a low-pass filter 24 which determines the necessary rate of harmonics. The circuit of this tube is closed on cathode resistor 25, and a potentiometer 26 of high resistance permits of coupling the value of the voltage thus obtained.

This correction voltage is then injected for instance in series with a leak resistor 21 belonging to the line scanning 28 (not shown).

According to the embodiment of Fig. 4, in order to correct the defect of Fig. 3b, we make use, for instance, of line scanning synchronizing pulses 29, which are applied to a tube 35 through a derivation cell 30, 3|, 32, advantageously adjustable at 321.

The plate of this cell is connected with a circuit 35 tuned to the line frequency.

There is thus obtained across the terminals of this circuit a sinusoidal voltage at line scanning frequency and out of phase, the phase position of which with respect to the line pulses is variable according to the degree of derivation in cell 30, 3|, 32. This derivation permits of obtaining a fine phase adjustment.

The sinusoidal voltage thus obtained is amplifled in a tube 36 and a potentiometer 3! permits of adjusting its value. A condenser 38 acts as connection and a resistor 39 supplies bias.

At the output of tube 36, the useful plate voltage is obtained across a low load resistor 4| which is advantageously constituted by the cathode resistor of the amplifier tube 44 of the frame saw tooth l 3.

The frame scanning tube is then subjected to the action of the cathode of said tube 44,,through a capacitor 42. It should be noted that capacitor 40 acts as a connection whereas resistor 43 serves to the supply of the plate of tube 36.

Our device has the advantage of making it possible to avoid S distortion.

In a general manner, while we have, in the above description, disclosed what we deem to be practical and efficient embodiments of the present invention, it should be well understood that we do not wish to be limited thereto as there might be changes made in the arrangements, disposition and form of the parts without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.

What we claim is:

1. In combination with a television camera tube including a, photocathode, a target, electron optics means for directing the electrons released by said photocathode onto said target to form an electron image thereon, and an electron beam scanning device including means for defiecting the electron beam in the horizontal direction, means for deflecting the electron beam in the vertical direction and means for supplying each of said deflecting means with respective periodically varying voltages, means for superimposing on the voltage supplied to the means for deflecting the beam in one of said directions in at least substantially sinusoidal correcting voltage of a frequency equal to that of the voltage supplied to the means for deflecting the beam in the other direction and of a phase adjusted to tube including a photocathode, a target, electron optics means for directing the electrons released by said photocathode onto said target to form an electron image thereon and an electron beam scanning device including line scanning means, frame scanning means and means for producing saw-tooth voltage variations to operate each of said scanning means respectively, means responsive to one of said saw-tooth voltage variations for producing a substantially sinusoidal voltage variation and superimposing it on the other sawtooth voltage variation in correct phase relation to compensate for S distortion of said electron image.

3. In combination with a television camera tube including a photocathode, a target, electron optics means for directing the electrons released by said photocathode onto said target to form an electron image thereon and an electron beam scanning device including line scanning means, frame scanning means and means for producing saw-tooth voltage variations to operate each of obtain at least partial compensation of the S dissaid scanning means respectively, means responsive to frame scanning saw-tooth voltage variations for producing a substantially sinusoidal voltage variation and superimposin it on the line scanning saw-tooth voltage variation in correct phase relation to compensate for S distortion of said electron image.

4. A combination according to claim 3 in which the last mentioned means include a capacitor and resistor device for flattening the saw-tooth signal wave-form, a tube connected with the output of said device so as to receive on its grid said flattened signal and means connected with said tube for changing the phase of the substantially sinusoidal signal supplied by said tube.

5. In combination with a television camera tube including a photocathode, a target, electron optics means for directing the electrons released by said photocathode onto said target to form an electron image thereon and an electron beam scanning device including line scanning means, frame scanning means, means for producing voltage pulses to control said line scanning means, and means for producing said tooth voltage variations to operate said frame scanning means, means responsive to said pulses for producing a substantially sinusoidal voltage variation and superimposing it on said saw tooth voltage variation in correct phase relation to compensate for S distortion of said electron image.

6. A combination according to claim 5 in which the last mentioned means include derivation means for deforming said line pulse signals, a tube connected with the output of said derivation means to amplify said deformed signals and a potentiometer for adjusting the voltage obtained.

HENRI GEORGES DE FRANCE. HERBERT ERNYEI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,773,980 Farnsworth Aug. 26, 1930 2,047,533 Von Ardenne July 14, 1936 2,100,702 Schlesinger Nov. 30, 1937 2,248,556 Schlesinger July 8, 1941 2,310,197 Hansell Feb. 2, 1943 2,425,491 Schlesinger Aug. 12, 1947 2,477,557 Torsch July 26, 1949

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