US2170847A - Electron beam deflection circuits - Google Patents

Description

Aug. 29, 1939. G. B. BANKS 2,370,847

I ELECTRON BEAM DEFLECTION cmcurrs Filed June 3, 1936 ATTORNEY Patented Aug. 29, 1939 UE'E'ED STAT.

George Baldwin Banks,

Chelmsford, England, as-

signor to Radio Corporation of America, a corporation of Delaware Application June 3, 1936, Serial No. 83,196 In Great Britain June 8, 1935 4 Claims.

This invention relates to cathode ray tube apparatus and more particularly to such cathode ray tube oscillograph arrangements of the kind wherein a cathode ray beam is deflected in at least one direction by electromagnetic deflection means. Though not limited to its application thereto the invention is particularly Well adapted to cathode ray tube oscillograph apparatus for use for television and like transmission or reception.

It is common in cathode ray tube television apparatus to cause an area to be explored or scanned by a cathode ray beam which sweeps across said area in a succession of lines and it is also common to produce the necessary deflection for scanning action by means of electromagnetic deflecting coils acting on the cathode ray beam. Sometimes both co-ordinates of scanning movement are obtained by deflecting coils and sometimes one only of the co-ordinate components is so obtained, but in any case the usual requirements for each component of scanning deflection is that said component shall follow a substantially rectilinear saw-tooth wave form; that is to say each component of scanning shall be such that the cathode ray beam is deflected in the appropriate direction at a constant speed and is then deflected back at a much higher constant speed. Now the obtaining of such a component of scanning by means of electromagnetic deflecting means is a matter of considerable difliculty in practice principally by reason of the necessarily relatively high inductance of the deflecting coils. The requirement is that the current wave form through the deflecting coils shall be of substantially rectilinear saw-tooth wave shape but, owing to the inductance of the said inflecting coils, the production of such a current wave devolves the application to the coils of a voltage wave form which rises from an initial value rectilinearly to a maximum value and then comes down very sharply to a value well below said initial value thereafter rising very sharply back to said initial value. The downward peak in this wave form is necessitated by the inductance of the deflecting coils.

The object of the present invention is to meet the difficulty above referred toand enable the deleterious efiect of the self-inductance of de- 'flecting coils in a cathode ray tube to be substantially eliminated, or at any rate, very greatly reduced.

For the purpose of convenience in description that portion of the deflecting wave form during which the deflection increases at a substantially constant speed in one direction will be. herein referred to as the deflecting period and the successive portion during which rapid return of the ray is effected will be herein referred to as the return period.

According to this invention in a cathode ray tube apparatus wherein electromagneticdeflection in at least one direction is resorted to, means are provided for short circuiting or substantially short circuit during return periods the deflecting coils employed for such deflection.

Preferably the short circuiting action is obtained by means of electronic or ionic discharge means connected across the deflecting coils to be short circuited.

The invention is illustrated in the accompanying drawing in which Figs. 1 and 2 show diagrammatically two embodiments thereof.

Referring to Figure 1 a neon or other gas-filled discharge device I is connected across the deflecting coils 2 of a cathode ray tube apparatus (not shown), the said deflecting coils being energized in any convenient known manner with a suitable voltage wave form. In the arrangement of Figure l the voltage wave form is applied from a saw-tooth wave generator (not shown) between control grid 3 and cathode 4 of a valve 5 Whose anode circuit contains a choke 6. The voltages set up across the choke B are applied through condenser l to the deflecting coils 2. The neon or other discharge device I is chosen. to have a break down voltage which is higher than the voltage which is set up across the coils 2 during the deflecting period, but is less than the voltage which would (but for the provision of the discharge device) be set up across the said coils during the return period. It will be appreciated that owing to the fact that the return period is much shorter than the deflecting period, the voltage set up across the coils 2 due to their self-inductance (i. e. the back E. M. F.) will be considerably higher than the voltage set up across the said coils during the deflecting periods and accordingly the gas discharge device I will flash only during return periods (thereby effectively short circuiting the coils) but not during deflecting periods.

In the embodiment shown in Figure 2 the coils 2 are shunted by the anode-cathode space 89 of a gasfilled triode or gas relay II] the grid H of which is connected to the cathode 9 through a suitable resistance I2 in series with a negative bias source l3. By adjusting the bias on the grid II the break-down voltage of the gas relay I!) may be adjusted. One advantage of this em- 55 flection in mutually perpendicular directions is resorted to short circuiting means may be associated with each of the two mutually perpendicu lar deflecting means. It will, however, be appreciated that the advantages of the invention are most marked in respect of the high speed component of scanning deflection. v In carrying out the invention as applied to the normal television case using electromagnetic deflection in both directions, it is accordingly necessary merely to arrange for periodic short circuiting of the deflecting coils which efiect scanning deflection in the line direction for it is, of course, as regards the high speed component of scanning deflection that the question of self-inductance of deflecting coils is most material. If desired, however, means may be provided for periodically short circuiting the coils for framing deflection also.

What I claim is:

1. In apparatus for controlling the deflection of an electronic beam, a thermionic amplifying tube having anode, cathode and at least one control electrode, means for impressing on a control electrode of said tube an electrical impulse of predetermined wave form, inductive deflecting means connected in the anode-cathode circuit of said tube, a thermionic tube having anode, cathode, and at least one control electrode, means for connecting the said deflecting means in the anode-cathode circuit of said latter tube, and means for impressing on 'a control grid of said latter tube an electrical impulse of predetermined wave form.

2-. An'apparatus for deflecting an electronic beam comprising a first thermionic tube having anode, cathode and at least one control electrode, means for impressing on a control electrode of said tube an electrical impulse of predetermined wave form, inductive deflecting means connected in the anode-cathode circuit of said tube, a second thermionic tube having anode, cathode and at least one control electrode, means for connecting said inductive deflecting means in the anodecathode circuit of said second tube, means for adjustably biasing the grid of said latter tube with respect to the cathode thereof, and means for impressing on a control grid of said latter tube an electrical impulse of predetermined wave form.

.3. Apparatus in accordance with claim 2 wherein the electrical impulses of predetermined wave form, impressed on the control grid of the first and second tubes comprise waves of the same wave form.

4. Apparatus in accordance with claim 2 wherein the electrical impulses of predetermined wave form'impressed on a control grid of the first and second tube comprise at least a portion of the same wave. 7

' GEORGE BALDWIN BANKS.

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