DE1182689B - Method and arrangement for operating image pick-up tubes of the superorthicon type - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school KL: H 04 n;

HOIj

German class: 21 al -32/35

Number: 1182 689

File number: F 37918 VIII a / 21 al

Filing date: September 29, 1962

Opening day: December 3, 1964

The invention relates to a method and an arrangement for operating image pickup tubes of the superorthicon type and relates to obtaining an interference-free reference value, preferably for picture black, in the television signal supplied by a picture pick-up tube.

To obtain a reference value for image black in that produced by a superorthicon Up to now, it has been customary to signal the potential of the storage electrode during the return times of the scanning beam so much more negative that no electrons of the scanning beam on the storage disk can land and all beam electrodes to the first electrode of the built into the image pickup tube Return to the secondary electron multiplier. In the output circuit of the secondary electron multiplier A current corresponding to the image black then flows during the flyback times. The one from the pickup tube The signal delivered therefore has the black level in the blanking intervals to which the im In the course of amplification, clamping circuits provided for the signal to reintroduce the direct current component speak to.

This has the disadvantage that as a result of the statistical fluctuations of the superimposed on the signal Output current (noise) at the end of the sampling time of the clamping circuits on from line to line fluctuating potential is present and that, therefore, the brightness value in the line periods as well fluctuates irregularly. This phenomenon known as "line noise" appears in the television picture noticeable through irregularly occurring lighter and darker stripes, which create a restless image impression cause and with the same amplitude of the noise are much more disturbing than the dem Image signal superimposed noise component.

To avoid this phenomenon, it is already known to interrupt the beam current of the image pickup tube during the retrace times. There is then no signal and therefore no noise during the flyback times. The reference values produced in this way are therefore free of interference, and after reintroduction of the direct current component by means of clamping circuits, fluctuations in the brightness values in the line periods can no longer occur. In this case, however, the reference potential corresponds to a signal value “whiter than white”, which is undesirable in itself, since this value and not the black value is brought to a constant potential by means of the clamping circuits.
In the method according to the invention for loading method and arrangement for operation
of image pick-up tubes of the
Super orthicons

Applicant:
TV G. mb H.,
Darmstadt, Am Alten Bahnhof 6

Named as inventor:

Dr.-Ing. Wolfgang Dillenburger,

Nieder-Ramstadt near Darmstadt

Driven by image pickup tubes of the superorthicon type, the beam current is increased during the retrace times by applying a positive pulse voltage to the Wehnelt electrode to a multiple of its strength during the scanning times. This creates a signal value "blacker than black" during the flyback times, and this is cut off, preferably at the black level of the image signal. In this way, an interference-free reference value is obtained in a particularly simple manner, which corresponds approximately to the black value.
To solve other problems, it is already known to temporarily increase the beam current strength of a storage tube compared to its value in the scanning lines.

In an arrangement in which a single optical image briefly on the photocathode of an image storage tube imaged and then scanned in a long time compared to the exposure time after scanning is complete, the storage disk is subsequently erased by means of a sawtooth voltage with higher than line frequency with increased beam current strength.

It is also known in a super orthicontype image pickup tube to measure the electron velocity to increase in the scanning space to regenerate the storage electrode.

The invention will now be explained on the basis of the figures representing the exemplary embodiments will.

F i g. 1 is a block diagram of a television camera train with a superorthicon as an image recording tube, However, this only contains the facilities necessary to understand the invention;

409 730/122

parallel capacities did not yet form a shunt for the signal current; This is practically the case at frequencies below 100 kHz. When upsampling the beam current to z. B. 5 times Value thus arises at the resistor 41 a ten times larger voltage pulse of z. B. 3 V, whose Edges are correspondingly integrated by the influence of the parallel capacitance to the resistor 41. To cut off of the pulse is a diode 42 in front of

Clamping circuit 22 supplied to reintroduce the direct current component, then in the Blanking stage 23 blanked and amplified in the output amplifier 24 to the output level.

Line-frequency pulses are transmitted to the camera train by a pulse generator (not shown) the line 32 supplied, which are transmitted via the line 5 to the camera 1 and in this to

F i g. 2 shows schematically the time course of the occurring in the method according to the invention Waveform, and

F i g. 3 is an embodiment of a clipping circuit to obtain the interference-free reference values.

The television camera train according to FIG. 1 consists of the television camera 1 and the camera amplifier 2. The television camera 1 includes, among other things

Superorthicon 11. Immediately after the image is taken, which is monitored by means of a voltage divider 11 in front of the preamplifier 13 is a standing one from the resistors 43 (e.g. 50 kOhm) Cut-off circuit 12 is provided. and 44 is biased in such a way that the cut-off,

The signal amplified in the preamplifier 13 as in FIG. 2 b indicated, a little below the reaches the black level in the image signal via line 4 in the camera cable. About a Camera amplifier 2. After another amplifier 15 coupling capacitor 45 (e.g. 0.1 μΡ) the In the repeater 21, the signal becomes a signal with the interference-free produced in this way Reference values to a tube 46 with the grid bleeder resistor 47 (e.g. 1 MOhm). At the output resistance 48 the amplified 20 signal can now be picked up.

The described arrangement for carrying out the method according to the invention is distinguished characterized by particular simplicity. So that the reference potential has the desired value compared to

Synchronization of the deflection device 14 to the beam 25 image signal somewhat below the black level of the deflection to be used. Maintained by the same in the same, care must be taken that the pulse sequence is the potential of the Wehnelt electrode 15 output current of the image pickup tube for images Superorthikons 11 during the return times black when operating the tube is not changed of the scanning beam increased in the positive direction. From will. This requires an approximately correct setting Via the line 32 supplied pulse sequence 30 development of the beam current as well as a constant amplification on the other hand in the device 13 kung of the secondary electron multiplier what Clamping pulses of suitable amplitude and polarity also to the setting of a constant current for blanking the clamping step 22 produced. for this one amounts to.

Fig. 2 shows the in this mode of operation of the In some cases it is desirable to

Superorthicons occurring signal form at the output 35 reinforcement of the secondary electron multiplier to the tube, α shows the pulse sequence that is applied to the other, for example when changing the tube, around the output Wehnelt electrode 15. The pulse signal, even in the case of differences in the sensitivity amplitude, is selected to be so large that a multiple of the beam current can be brought to the same size during the time of different image pick-up tubes. According to a further development, the sampling times occurs; z. B. the beam current 40 of the invention will, when regulating the secondary in the flyback times, have 5 times the value of its electron multiplier at the same time as the cutoff size in the sampling times. This is shown in FIG. 2 B.
Because the beam is between image white and image black
only 50% due to the charges on the storage disk
is modulated, the 45
occurring impulses at 5 times the beam current compared to the normal value is 10 times the amplitude of the
Image signal for a black and white jump. That through
The pulse-shaped signal generated in the return times has a superimposed disturbance 5 °
(Noise) that is | / 5 times larger than the
Noise component of the beam current in the sampling times.
To obtain an interference-free reference value
the signal delivered by the tube is now included
a potential slightly below the black value 55
truncated as indicated by the dashed line in

potential for the diode 42 changed, so that the limitation of the pulse amplitude in each case something takes place below the black level of the image signal.

Fig. 2b is indicated. After the clipping stage, the television signal thus contains a reference value close to the black level without superimposed interference.

F i g. 3 shows a circuit arrangement 12 for clipping the television signal and the first stage of the preamplifier 13. The current from the last stage of the secondary electron multiplier flows through it the terminating resistor 41 of z. B. 30 kOhm. Da, s image signal during the sampling periods of z. B. 10 μΑ causes a signal voltage of 0.3 V on this resistor, provided that the cons

Claims (5)

Patent claims: 1. A method of operating an image pickup tube of the superorthicon type, thereby characterized in that the beam current is a multiple during the retrace times its size is increased in the sampling times and that that arises in the return times Pulse for producing a noise-free reference value in a clipping circuit, preferably slightly below the black level, is cut off in the image signal. 2. The method according to claim 1, characterized in that in the return times in the Signal a counter pulse is inserted, the size of which is dimensioned so that during the flyback times exactly the corresponding potential is present. 3. Arrangement for performing the method according to claim 1 in a television camera train with superorthicon, characterized in that by means of the transmitted to the camera horizontal frequency pulses to synchronize the deflection device the potential of the Wehnelt electrode is increased so far that the beam current is several times, preferably that 5 times its value reached in the sampling times, and that from the same pulse train the Clamping pulses generated for the clamping circuit to reintroduce the direct current component will. 4. Arrangement for performing the method according to claim 1, characterized in that that the terminating resistor (42) in the anode circuit of the secondary electron multiplier Image pickup tube is chosen so large that the smallest signal current to be expected is at least causes a voltage drop of 0.5 V. 5. Arrangement for performing the method according to claim 1, characterized in that that the cut-off potential to limit the pulse in the return times as a function from the output current of the secondary electron multiplier through a running voltage divider is changed in such a way that the potential difference between black value and blanking value as a percentage of the black and white jump remains approximately constant. Considered publications:
German Auslegeschrift No. 1 000 436;
German patent specification No. 892 768. For this purpose, 1 sheet of drawings 409 730/122 11.64 © Bundesdruckerei Berlin