US2248772A - Television system - Google Patents

Description

July 8, 1941. MESSNER 2,248,772

TELEVISION SYSTEM Filed March 29, 1959 fig. 1

Fig. 2.

fm/emonflax/77717180 Mess/1e!" Attorney Patented July 8, 1941 TELEVISION SYSTEM Maximilian Messner, Berlin, Germany, assignor to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof, Germany, a company Application March 29, 1939, Serial N0. 264,726-

. In Germany April 8, 1938 (c1. its-+7.5)

'7 Claims.

The present invention relates to television systems, and more specifically to new and useful improvements with respect to the output circuit of television receivers in which the image reproduction is synchronized in accordance with the field of view at the transmitter by synchronization impulses of different characteristic transmitted at given intervals between the image signals.

It is a known expedient in such systems to cause the sending equipment to continually transmit a carrier Wave, the amplitude of which may be adjusted to a given value of approximately one-fourth of the maximum amplitude of transmission. The synchronization impulses of different characteristic are produced by periodically controlling the amplitude of the carrier wave to zero value, While the image or picture signals control the amplitude positively with respect to the aforementioned continuous or reference amplitude level. The composite frequency of image signals and synchronizing impulses is transmitted to a television receiver where it is impressed upon an intermediate frequency device.

This invention has for an object to provide improvements in the circuit arrangements of television receivers which are adapted to be connected to the output of the above mentioned intermediate frequency device in order to perform the functions of reproducing an image on'the fluorescent screen of a cathode ray tube forming part of a television receiving equipment.

The demodulated mixture of image signals and synchronizing impulses-hereinafter referred to as the mixtureis according to a featureof this invention applied to a first amplifier tube, and the anode resistance of this tube is galvanically connected to an amplitude filter valve for cutting out the synchronizing impulses. Moreover, the mixture thus applied to the final amplifier tube presents such polarity that the synchronizing impulses occur in the anode circuit of this tube in the shape of voltage peaks. The main object of the final amplifier tube is therefore to revert the mixture.

According to a further feature of my invention,also the cathode rayor Braun tube is galvanically connected to the anode resistance of the final amplifier tube, which facility provides the advantage that even the average brightness is obtained in the Braun tube.

My invention will be more readily understood from the following description taken in conjunction with the accompanying drawing, in which Fig. 1 diagrammatically shows a circuit arrangement of a television receiver-designed in accordance with the principle of this invention, Fig. 2 is' a diagram explanatory of the operation of the arrangement shown in Fig. 1, while Fig. 3 is a partial modification over the arrangement of Fig. 1.

In Fig. 1, an intermediate frequency amplifier output circuit l. inductively energizes a coil .2 forming part of the grid circuit of a final am.- plifier tube. 3. A rectifier device 8 for rectifying thev induced intermediate frequency is connected in series with the coil 2. The voltage supply from the rectifier 4 produces .a voltage drop across a load .resistor 5, and this voltage drop is applied to the grid-cathode path of the tube 3. A choke coil 1 interposed between the control grid of tube 3 and the load resistor 5, and a grounded condensers connected in series with the coil I serve to remove intermediate frequency oscillations which might still exist in the mixture- A variable. resistor 8 acting as load resistance is connected in the anode circuit of the tube 3. The voltage at this resistor is according to one feature of the invention galvanically, that is, without using any type of direct current rejecting elements, applied to the control grid of an amplitude filter or cutting out valve 9. It is a necessary requirement that the filtered out synchronizing impulses are of proper polarity for controlling the time base or relaxation circuits, that is, these impulses must occur as voltage peaks in the resistor 8. This requirement can be fulfilled byvproperly regarding the polarity of the rectifier device 4 when connecting this device in the grid circuit of tube 3.

The operation of the amplitude filter valve 9 will hereinafter be more precisely explained in conjunction with Fig. 2. The dash-line K shows the characteristic of a conventional tube as a function of the current as represented by the vertical axis and of the grid voltage as represented by the horizontal axis. It is obvious that this characteristic cannot be employed for the purpose of filtering out synchronizing impulses since there is no sharply defined bend at the upper portion thereof. However, it is possible to artificially secure the desired bend by interposing a resistor ID in the conductor leading to the grid of the valve 9. This expedient makes poscaused to break down at the resistor ID, in other words, the grid voltage cannot assume positive value on account of this grid current flow. The actual characteristic of the valve now obtained corresponds to the full line of Fig. 2. The composite image signal and synchronizing impulse mixture is plotted below the horizontal axis of this figure in the polarity as actually applied to the tube. Since the position and the amplitude of the synchronizing impulse are subjected to changes, the conditions are so chosen that not the total synchronizing pulse of the magnitude a is required for modulating the plate currentgrid voltage characteristic of the valve, but that a mere portion of this impulse will sufiice for fully performing this modulation.

Since several possibilities are available for cutting out the proper portion of the synchronizing impulse, a few thereof will be briefly discussed. The first possibility is to vary the load resistance of the valve so as to change the potential at the connection point [3 with respect to that of the cathode of valve 9. This expedient requires a possibly constant potential at the screen grid of the final amplifier tube 3, which for this purpose is directly connected to one of the electrodes of a stabilizer M. This known device is a gasfilled discharge tube having a series of electrodes E9, the two outer of which are supplied with a direct voltage from a rectifier device I5. A further way for properly determining the portion of a synchronizing impulse which is to be filtered out consists in an adjustment of the screen grid potential of the final amplifier tube 3. It is thus possible to select the adequate characteristic of this tube for regulating the potential at the connection point l3 to its correct value. Still a further possibility for this purpose is to vary the characteristic of the amplitude filter valve 9, and this variation is realized by suitably selecting the volt-age supply to the screen grid of this valve.

The arrangement for cutting out the proper portion of a synchronizing impulse by varying the screen grid voltage of the final amplifier tube 3 is illustrated in Fig. 1. This voltage is derived from a potentiometer 18 connected across two of the electrodes I9 of the stabilizer [4. Each change imparted to the voltage at the screen grid causes the displacement of the tube characteristic so that a field of characteristics in parallel relation to each other is obtained. As a result, the potential of the connection point 13, and in consequence thereof also the filtered out portion of the synchronizing impulse, becomes changed.

In the embodiment shown in Fig. 3, the screen grid potential of tube 3 is maintained constant, while the anode resistor 8 is made variable for the reason of adjusting the portion of a synchronizing pulse which is to be filtered out. This arrangement involves certain advantages over that shown in Fig. "1, according to which the screen grid is connected to a voltage divider. The last mentioned expedient is somewhat disadvantageous because of the fact that the potential of the screen grid fluctuates in rhythm with the current flowing through the tube 3 since an increase of this current proportionally causes the screen grid current to increase and this increase is followed by a considerable potential drop across the voltage divider, or in other words, the screen grid potential decreases with an increased current fiow through the tube, which consequently does not operate on its static but on a dynamic characteristic. This dynamic characteristic is substantially flatter at a constant screen grid voltage than the static characteristic. This flattening would be unobjectionable from the viewpoint of synchronization, provided that the screen grid potential would instantaneously follow the variations of the alternating current fiow through the tube. However, this requirement is not satisfied since the voltage divider together with its inherent deleterious capacity causes the grid potential to lag behind the current flowin through the tube. The connection point I3 therefore would not present the same potential for each incoming synchronizing pulse, on the contrary, this potential would depend upon the preceding image signal. This drawback is avoided by employing the arrangement shown in Fig. 3,

in which the screen grid 2| of tube 3 is directly connected to one of the electrodes 19 of the stabilizer I4, so as to maintain the potential of the screen grid at a constant value. Now the tube 3 continually operates on the same characteristic. In order to still involve the possibility of varying the potential at the connection point [3, the load resistance of the tube 3 may be rendered variable. However, this variation is only possible within narrow limits since a change of the resistance value would likewise change the gain which is undesirable as regards the Braun tube. Nevertheless, if this amplification change becomes limited to a slight amount, the Braun tube will not be appreciably influenced. Since the portion of the synchronizing impulse which is to be filtered out is defined merely by the potential difference between the connection point l3 and the cathode of the tube '9, also the potential of this cathode may be varied. Such variation may be obtained by connecting this cathode to a voltage divider instead of connecting it directly to an electrode of the stabilizer M. A similar eilect is attained by varying the screen d electrode of the valve 9.

In addition to the amplitude filter valve 9, also the control electrode 16 of the Braun tube 29 is galvanically connected to the load resistance of the final amplifier tube 3 at the connection point IS. A potentiometer l1 shimted across two electrodes I9 of stabilizer I4 is provided for the purpose of controlling the bias of the Braun tube, and this potentiometer is so adjusted that the average brightness is obtained in the Braun tube.

What is claimed is:

1. A television reception system comprising, an

" input circuit adapted to receive image signals and synchronizing impulses, a final amplifier tube having a cathode, a grid circuit, a screen grid and an anode circuit for concurrently amplifying said image and synchronizing impulses, a load resistor connected in said anode circuit, an amplitude filter comprising a thermionic valve galvanically connected to said load resistor for cutting the said synchronizing impulses, and means to so adjust the polarity of image signals and synchronizing impulses impressed upon the said grid circuit that the synchronizing impulses occur as voltage peaks in said anode circuit.

2. A television reception system comprising, an input circuit adapted to receive image signals and synchronizing impulses, a final amplifier tube having a cathode, a grid circuit, a screen grid and an anode circuit for concurrently amplifying said image signals and synchronizing impulses, a load resistor connected in said anode circuit, an amplitude filter comprising a thermionic valve galvanically connected to said load resistor for cutting the said synchronizing impulses, means to so adjust the polarity of image signals and synchronizing impulses impressed upon the said grid circuit that the synchronizing impulses occur as voltage peaks in said anode circuit, and means to vary the resistance value of said load resistor for adjusting the portion of synchronizing impulses to be cut out by said amplitude filter.

3. A television reception system comprising, an input circuit adapted to receive image signals and synchronizing impulses, a final amplifier tube having a cathode, a grid circuit, a screen grid and an anode circuit for concurrently amplifying said image signals and synchronizing impulses, a load resistor connected in said anode circuit, an amplitude filter comprising a thermionic valve galvanically connected to said load resistor for cutting the said synchronizing impulses, means to vary the potential applied to the screen grid of said final amplifier tube for adjusting the portion of synchronizing pulses to be cut out by said amplitude filter, and means to so adjust the polarity of image signals and synchronizing impulses impressed upon the said grid circuit that the synchronizing impulses occur as voltage peaks in said anode circuit.

4. A television reception system comprising, an input circuit adapted to receive image signals and synchronizing impulses, a final amplifier tube having a cathode, a grid circuit, a screen grid and an anode circuit for con-currently amplifying said image signals and synchronizing impulses, a load resistor connected in said anode circuit, an amplitude filter comprising a thermionic screen grid valve galvanically connected to said load resistor for cutting the said synchronizing impulses, means to vary the potential applied to the screen grid of said thermionic screen grid valve for adjusting the portion of synchronizing pulses to be cut out by said amplitude filter, and means to so adjust the polarity of image signals and synchronizing impulses impressed upon the said grid circuit that the synchronizing impulses occur as voltage peaks in said anode circuit.

5. A television reception system comprising, an input circuit adapted to receive image signals and synchronizing impulses, a final amplifier tube having a cathode, a grid circuit, a screen grid and an anode circuit for concurrently amplifying said image signals and synchronizing impulses, a load resistor connected in said anode circuit, an amplitude filter comprising a thermionic valve galvanically connected to said load resistor for cutting the said synchronizing impulses, a continuous current fed stabilizer having a plurality of electrodes for supplying said final amplifier tube and thermionic valve with direct currents, a direct conductive connection between said screen grid and one of said electrodes for maintaining said screen grid at a constant voltage, means to vary the resistance value of said load resistor for adjusting the portion of synchronizing impulses to be cut out by said amplitude filter, and means to so adjust the polarity of image signals and synchronizing impulses impressed upon the said grid circuit that the synchronizing impulses occur as voltage peaks in said anode circuit.

6. A television reception system comprising an input circuit adapted to receive image signals and synchronizing impulses, a final amplifier tube having a cathode, a grid circuit, a screen grid and an anode circuit for concurrently amplifying said image signals and synchronizing impulses, a load resistor connected in said anode circuit, an amplitude filter comprising a thermionic valve galvani'cally connected to said load resistor for cutting the said synchronizing impulses, a continuous current fed stabilizer having a plurality of electrodes for supplying the said final amplifier tube and thermionic valve with direct current, a potentiometer connected across two of said electrodes to vary the potential applied to the screen grid of said final ainplifier tube for adjusting the portion of synchronizing pulses to be cut out by said amplitude filter, and means to so adjust the polarity of image signals and synchronizing impulses impressed upon the said grid rcircuit that the synchronizing impulses occur as voltage peaks in said anode circuit.

7. A television reception system comprising, an input circuit adapted to receive image signals and synchronizing impulses, a final amplifier tube having a cathode, a grid circuit, a screen grid and an anode circuit for concurrently am plifying said image and synchronizing impulses, a load resistor connected in said anode circuit, an amplitude filter comprising a thermionic valve galvanically connected to said load resistor for cutting the said synchronizing impulses, a continuous current fed stabilizer having a plurality of electrodes for supplying the said final amplifier tube and thermionic valve with direct current, a potentiometer connected across two of said electrodes, a Braun tube having a control grid galvanic-ally connected to said load resistor, and a cathode connected to a variable portion of said potentiometer, and means to so adjust the polarity of image signals and synchronizing impulses impressed upon the said grid circuit that the synchronizing impulses occur as voltage peaks in said anode circuit.

MAHMILIAN MESSNER.

Images