US2217396A - Circuit arrangement in television receivers - Google Patents

Description

@c&. 8, 3949. ANDRiEU 2,257,396

CIRCUIT ARRANGEMENT IN TELEVISION RECEIVERS Filed Feb. 15, 1937 llllll III. a

INVENTOR ROBERT ANDRIEU BY m gww ATTORNEY Patented Oct. 8, 1940 UNITED STATES ATET FFICE CIRCUIT ARRANGEDIENT IN TELEVISION RECEIVERS tion of Germany Application February 15, 1937,-Serial No. 125,715 In Germany February 20, 1936 6 Claims.

The invention concerns a circuit arrangement for control of saw-tooth generators in television receivers. It is here assumed that the generators require a negative potential impulse at their input tube for the production of the short arm of the saw-tooth curve and further that the detector circuit is connected in series in the manner that during the synchronizing impulse a negative potential exists with respect to cathode at control grid of input tube.

In accordance with the invention the detector circuit is in this case directly connected with the control grid of input tube through a resistance.

The invention may be used in principle for all conditions sufficing above assumptions.

Two embodiments of invention will be explained in what follows with the aid of the draw- In Figure 1 is represented the course of the low frequency for the case that a carrier wave of a certain finite value S is increased by image currents and decreased by synchronizing impulses below this value S down to zero. Value S may thereby correspond to the black image points so that the image points of maximum brightness are also reproduced by a carrier wave amplitude of maximum size. But, on the other hand, to value S may also be coordinated the image points of maximum brightness, in which case the maximum carrier wave amplitudes correspond accordingly to the black image points. The range of the carrier wave amplitude below size S is in both cases reserved for signal indication alone, for instance, by the synchronizing impulses.

A circuit arrangement suitable for a transmitting method according to Fig. 1 is illustrated in Fig. 2.

an designates the secondary of a transformer whose primary is joined to the high frequency amplifier. The detector circuit consists of this secondary winding, a rectifier H, as well as a resistance 12 with condenser connected in parallel thereto and it is grounded over a potential source l3. Point P of detector circuit is connected through a resistance M with the control grid of input tube E5 of a saw-tooth generator. The cathode of tube I 5 is grounded.

The circuit arrangement according to Fig. 2 operates in the manner that there appears a potential for values of the carrier wave amplitude and therewith for values of the potential appearing at resistance l2 below value S at point P, said potential being below that of the earth potential. The size of potential source I3 is dimensioned in the manner that with that potential drop at resistance l2 which corresponds to value S, point P is just impressed with earth potential. As a result thereof the synchronizing impulses which as understood produce according to Fig. 1 the potential drop zero at resistance I2, cause the ap- 5 pearance at the control grid of tube I5 of a negative potential with respect to cathode. But carrier wave amplitudes and therewith also amounts of the potential drop at resistance 2 which exceed value S raise point P to a positive potential with 10' respect to earth, but, on the other hand, there is produced by the grid current generated by positive potentials in point P a potential drop at resistance I4 with the result that the control grid potential does not rise through the image cur- 15 rents noticeably above value corresponding to value S. The mode of operation of saw-tooth generator need not be explained again in this con nection, since it is described in application Ser. No. 61,499, filed Jan. 30, 1936. 20

Fig. 3 has reference to a transmitting method whereby a carrier wave amplitude is modulated by the image currents from zero to value G, the synchronizing signals being given by carrier wave amplitudes which are greater than that corre- 25 sponding to value G.

A receiving arrangement in accordance with invention and suitable for this method of transmission is shown in Fig. 4..

Therein the symbols It) to I2, I4, l5 and P have 30 the same meaning as in Fig. 2. But the detector circuit is grounded through a direct current potential source 56 of reversed polarity of that in Fig. 2 and the transmitting direction of detector 1 I is reversed with respect to Fig. 2. 35

The circuit scheme according to Fig. 4 operates in the manner that earth potential appears at a point P with a carrier wave amplitude of the size G, in other words, that the potential [6 is as large as value G. Hence, the synchronizing 4o signals of Fig. 3 produce at point P a negative potential with respect to cathode of tube l5. As to the rest and in particular with respect to the potential drop produced by grid current at resistance I4, the manneroi operation coincides com- 45 pletely with that according to Fig. 2.

The arrangement proposed according to the invention insures the production of negative impulses of suflicient size at'control grid of tube l5. An amplification of these impulses may, 50 however, be accomplished in the manner that a feedback coil I1 is provided in the saw-tooth generator whose one end is grounded and whose other end is connected with the'control grid of input tube through resistance I8. 55

What I claim is: r

1. A synchronizing apparatus comprising a vacuum tube, having anode, cathode and control electrodes, means for storing electrical energy connected in a current carrying electrode-cathode path of said tube, means for feeding back to the control electrode of said tube a portion of said stored energy during its discharge, a rectifier, resistive means connected to said rectifier, a source of fixed bias potential electrically connected to resistive means whereby the control electrode of said tube is maintained at a predetermined bias potential, means for impressing potentials representative of the potential fall across said resistive means onto a control electrode of the vacuum tube, means for maintaining said tube normally conducting by impulses exceeding a predeterminable amplitude, and means for blocking said tube when said impulses fall below a definite value whereby said vacuum tube stores energy in said energy storage means during periods of conduction, said energy being discharged during periods when the vacuum tube is blocked.

2. A synchronizing apparatus comprising a vacuum tube having anode, cathode and control electrodes, means for storing electrical energy connected in a current carrying electrode-cathode path of said tube, means for feeding back to the control electrode of said tube a portion of said stored energy during its discharge, a rectifier, resistive means connected to said rectifier, a source of fixed bias potential electrically connected to resistive means whereby the control electrode of said tube is maintained at a predetermined bias potential, means for impressing potentials representative of the potential fall across said resistive means onto a control electrode of the vacuum tube, means for maintaining said tube normally conducting by impulses exceeding a predeterminable amplitude, means for maintaining said tube current substantially constant during periods of conduction, and means for blocking said tube when said impulses fall below a definite value whereby said vacuum tube stores energy in said energy storage means during periods of conduction, said energy being discharged during periods when the vacuum tube is blocked.

3. A sawtooth wave generator comprising means for receiving signals from a source external to the generator, means for impressing said signals onto a first uni-directional conductor, means for developing a potential difierence in accordance with the current flow in said uni-directional conductor, a thermionic vacuum tube having anode, cathode and at least one control electrode, inductive means connected in the anode-cathode circuit of said tube and adapted to store electro-magnetic energy from at least a portion of the anode current of said tube, a unidirectional conductor connected substantially in parallel with said inductive means, means for impressing the potential developed in accordance with the current flow through said first uni-directional conductor onto the control'electrodecathode circuit of said thermionic tube, and a source of fixed bias potential connected in the control electrode-cathode circuit of said thermionic tube whereby said tube remains conducting throughout a range of received signal amplitude values and is maintained blocked by signals without the conducting amplitude range.

4. Apparatus in accordance with claim 3, wherein said uni-directional conductors each comprises a diode.

5. Apparatus in accordance with claim 3, wherein there is provided in addition resistance means connected serially with the control electrode of said thermionic tube and the means for developing a potential in accordance with the current flow through the first uni-directional conductor.

6. Apparatus in accordance with claimv 3, wherein, said means for developing a potential in accordancewith the current flow in the first uni-directional conductor comprises a resistance connected serially with said uni-directional conductor and having the current from said conductor passing therethrough.

ROBERT ANDRIEU.

Images