US2874282A

US2874282A - Device comprising an electric discharge tube having a pentode characteristic

Info

Publication number: US2874282A
Application number: US473362A
Authority: US
Inventors: Evert Jan Van Barneveld; Janssen Peter Johanne Hubertus
Original assignee: US Philips Corp
Current assignee: US Philips Corp; North American Philips Co Inc
Priority date: 1953-12-10
Filing date: 1954-12-06
Publication date: 1959-02-17
Anticipated expiration: 1976-02-17
Also published as: NL85200C; NL183506B; FR1118463A

Description

Feb. 17, 1959 E. J. VAN BARNEVELD ET AL 2,874,282

DEVICE COMPRISING AN ELECTRIC DISCHARGE TUBE HAVING A PENTODE CHARACTERISTIC Filed Dec. 6, 1954 INVENTOFG EVERT JAN VAN BARNEVELD PETER JOHANNES HUBERTUS JANSSEh U te S ates. P te 0.

DEVICE COMPRISING AN ELECTRIC DISCHARGE TUBE HAVING A r -Nronn cnsnnornmsrrc Application December 6, 1954, Serial 'No. 473,362 Claims priority, application Netherlands December 10, 1953 2 Claims. (Cl. 250-27) The invention relates to arrangements comprising an electric discharge tube having a pentode characteristic and more particularly to arrangements to which a signal s supplied and which comprise a control device which is rendered operative by means of an auxiliary signal at instants at which the signal reaches a reference value, the control device with the aid of an integrating network producing a control voltage controlling the transmission of the signal.

Such devices may be used for various purposes such as the introduction of the direct current component into television, radar and facsimile signals or automatic gain control such as, for example, is used in television receivers.

According to the invention an input signal, such as a composite television signal including synchronizing pulses is supplied to a control electrode of a discharge tube having a pentode characteristic and comprising at least a cathode, a control electrode, a screen electrode, a suppressor electrode, and an anode; and an auxiliary signal, such as a synchronizing signal alone, is supplied to an auxiliary electrode which is arranged between the suppressor grid and the anode and is located substantially outside the primary electron current. This auxiliary electrode exhibits a penetration coefficient such that the variation of the anode current is substantially entirely counteracted. That is to say, the auxiliary electrode does not simply intercept a certain percentage of the electrons which should go to the anode, thus decreasing the total anode current by the amount of the intercepted electrons; instead, the auxiliary electrode attracts more electrons from the cathode region of the tube so that the anode current remains substantially unchanged. Preferably this auxiliary electrode consists of two supporting rods which are located entirely outside the primary electron current and are interconnected by a narrow metal strip adjacent one of the ends of the electrode system. The width of this strip preferably is approximately 10 to 15% of the axial length of the anode, while the penetration coefficient preferably exceeds .05% but is less than .2%

The invention will now be described with reference to the accompanying drawing, in which Fig. 1 is a diagram of an arrangement according to the invention and Figs. 2 and 3 show details of the tube for use in this arrangement.

In Figs. 1 and 2, the discharge tube of the invention comprises a cathode 1, a control grid 2, a screen grid 3, a suppressor grid 4, and an output anode 5, which are arranged in the customary cylindrical electrode type of structure and are enclosed in a bulb 7. An auxiliary electrode 6 is arranged between the suppressor grid 4 and the anode 5 in accordance with the invention. Electrode 6 consists of a metallic strip secured to two supporting rods which, as is shown in Fig. 3, are secured to a pair of insulating discs 9 and 10 located at opposite ends of the cylindrical electrode structure. Preferably, the strip 2,874,282 Patented Feb. 17, 1955 ICE 6 is arranged at the very end of the structure, the ar' rangement being such that the penetration coeflicient of the auxiliary electrode is at least .05 but does not exceed .2%. The term penetration coeflicient" is defined as the .reciprocal of the amplification factor, or 11., and is' therefore a measure of the influence of electrode 6 on the control electrode 3.

In the operation of thecircuit of Fig. 1 a received signal, for example a detected television signal 13 consisting of a video portion and repetitive synchronizing pulses,is supplied to the input terminal 11 and through a capacitor 12 tothe control grid 2. As is well-known, this signal comprises reference values, for example during the line synchronizing pulses, while a further reference value is available during the remainder of the re trace intervals, the latter value corresponding to the black level.

During the occurrence of the reference value at the control electrode a highly positive voltage pulse or key pulse signal 14 having a repetition rate equal to that of the synchronizing pulses in signal 13 is supplied to the auxiliary electrode 6. Consequently, at this instant an electron current flows to this electrode 6 which may be approximately 1 to 2% of the anode curent at this instant. Due to the negative reference voltage at the control grid during the retrace interval the anode current is comparatively small. The current of electrode 6 is subtracted from the anode current so that the electrode 6 tends to reduce slightly the anode current. However, since the electrode 6 exhibits a certain penetration coefficient, the anode current will not be subjected to a permanent decrease during the entire key pulse 14 but will be subjected to a transient variation of lower amplitude, which is more desirable than a comparatively prolonged stronger decrease of the anode current.

Because the auxiliary electrode 6 is arranged behind the suppressor grid 4, its current is substantially independent of the voltage of key pulse 14. This current is integrated with the aid of an integrating network consistmg of condenser 15 and resistor 16 and the voltage set up across this integrating network is supplied to the control grid 2 through resistor 17.

If the reference value of the alternating voltage signal at the control grid 2 shifts to a higher level, a larger current will flow to the electrode 6 during each of the pulses 14 with the result that a higher negative voltage will be set up across the integrating network and will be fed back to reduce the control grid voltage. Consequently, the variation of the reference value at the control grid is counteracted so that the level of the reference value at the control grid is rendered substantially constant, that is to say a direct current component is introduced. In a television signal the black level can thus be maintained constant.

Although only a single embodiment of a tube according to the invention has been described, it will be understood -that alternative constructions in accordance with the invention are possible.

What is claimed is:

1. A black level control circuit comprising an electron discharge tube having a cathode, a control grid, a screen grid, a suppressor grid, an anode, and an auxiliary elecconnected to apply a pulse voltage to said auxiliaryelec; trode to make said auxiliaryplectrode positiveduring the occurrence of each of said reference portions of said first signal voltage whereby the instantaneous current flowing to said auxiliary electrode during each of said reference portions is determined by the reference level of the voltage between said. control grid and said cathode; and a connection between said auxiliary electrode and said control grid, said connection comprising an integrating circuit to return said voltage between said cathode and said control grid to substantially the same value during each of said reference portions.

2. A black level control circuit as claimed in claim 7 in which the auxiliary electrode of said electron discharge tube comprises a strip of conductive material and support rods for said strip, so located within said tube that the support means lie outside of the primary path of electron flow between said cathode and said anode and said strip lies partially within said path, the width of said strip being in the range of 10 to 15% of the axial length of said anode.

References Cited in the file of this patent V UNITED STATES PATENTS 2,143,916 Jonker et a1 Jan. 17, 1939 2,239,677 Iobst Apr. 29, 1941 2,244,672 Brett June 10, 1941 2,454,377 Curtis Nov. 23, 1948 2,491,932 Reitz et a1. Dec. 20, 1949 2,551,057 Schweizer May 1, 1951 2,601,491 Baker June 24, 1952 2,656,414 Roschke et al Oct. 20, 1953