DE2424402C3 - Method and arrangement for controlling the strength of the electron beam in a vidicon-type image pick-up tube - Google Patents

Description

The invention relates to a method of control the strength of the electron beam in a vidicon-type image pick-up tube according to the generic term des Claim I and an arrangement for performing this method according to the preamble of Claim 2.

In a vidicon-type image pickup tube, the strength of a memory or Target electrode directed thereon electron beam is limited essentially to an amount that is less is as a certain limit to ensure high resolution. In other words, the one on the Storage electrode (photoelectric transducer surface) incident electron beam for scanning the storage electrode tends with increasing strength of the electric tend to be less focused. So that the signal flow from the image pickup tube is satisfactory can be generated, the strength of the electron beam must be limited to the minimum value of the current required for generating the signal current. In this case, the strength of the electron beam is generally at a suitable value set the taking into account a safety factor is fixed, and it is a more precise setting

ίο required if a higher resolution is required for that Image pickup tube is required. Despite the setting described above, a very good result healing part, such as a light reflecting glass or metal, to the difficulty that the part of the Storage electrode that does not correspond to the bright part of the object by scanning with the Electron beam can be neutralized so that the beam becomes too weak. Continue to join weak jet disadvantageously with the movement a "comet's tail" on the image pickup tube.

An arrangement as shown in FIG. 1 has already been shown to avoid the above Disadvantages developed in FIG. 1, a is generated from a storage electrode 2 of an image pickup tube 1 ter signal stream amplified by an amplifier 3 and then fed into a clamping member 4 which then limits the direct current level of the signal current the bright part (shown in FIG. 2B) of that in FIG. 2A through a non-linear Element 5 picked out, and then after the passage of this video signal part through a Vibration suppressing low-pass filter 6 the signal part to a beam current control electrode 7 in the form fed back, in which he overloaded a DC voltage gert is the continuous at the beam current control electrode 7 is located

Such a feedback circuit tends to generate vibrations. The reason for that could not yet be determined and it have been including numerous attempts so far undertaken to insert the low-pass filter described above in order to reduce the undesired oscillations suppress. However, since the oscillation frequency, which depends on the structure of such a feedback circuit is fixed cannot be predetermined, and since the inserted in the feedback circuit low-pass filter due to z. B. the phase response of the Filters represents a further source of vibration is that shown in FIG. 1 arrangement shown highly unstable and for unsuitable for practical use.

There is also a method of the type mentioned has become known (see. US-PS 37 15 490), in which a portion of a video signal is fed back from the storage electrode to the cathode of the image pickup tube while at the same time applying some of the rest of the video signal to the control grid in order to this way to reduce the residual image. More specifically, the output of the storage electrode is converted into a Video preamplifier whose output

to gnal on the one hand to a video signal output and on the other hand, arrives at a circuit which reverses the polarity of the signal. The reversed signal then becomes one DC recovery circuit supplied to the output signal on a predetermined DC

■ '' 5 voltage level, and then over a variable resistor for adjusting the amplitude of the output signal passed to the cathode. That Output signal of the direct current recovery

circuit (which is in phase with the polarized signal to the cathode) is also on the control grid over a Resistance applied to fluctuations in the operating point the electrode bias of the image pickup tube and thus a change in the strength of the the beam emitted from the cathode when the potential of the cathode changes

On the other hand, it is an object of the invention to improve strength in a vidicon type image pickup tube to control the electron beam so that the image recording ι ο meröhre produces a high quality, high resolution image

This task is solved by one Method of the type mentioned according to the invention by the characterizing part of the patent claim 1.

Accordingly, an arrangement for performing the method according to the invention with one on the Boosting feedback circuit coupled to the storage electrode formed according to the invention according to the characterizing part of claim 2

While in the previously known method (vgL US-PS 33 92 236) the polarity of the output signalanieii fed into both the cathode and the control grid to modulate the beam voltage, According to the invention, the cathode potential remains fixed in a current obtained from the storage electrode is fed back only to the beam current control electrode, with a gain factor smaller than the reciprocal of the maximum degree of implementation. This way you will get the high quality picture you want high resolution achieved

There is still an arrangement for controlling the strength of the electron beam in an image pickup tube became known with the »return beam read-out«, which is also a Has a feedback circuit which, however, consists of two loops The input signal of these feedback loops, i.e. the signal current is equal to the difference between the beam current and the storage electrode current, which is why the control signal is equal to the difference between the beam current and the storage electrode current is

In contrast to this, according to the invention, the Signal current equal to the storage electrode current itself during the control current from the signal current is derived, d. H. the memory; Electrode current. As a result, the invention advantageously comes with a single feedback loop.

In addition, the degree of conversion in the sense of the invention and the transition function are in the The latter known arrangement is completely different from a physical point of view:

In the transition function of the known arrangement, which represents a fraction, the current goes as a counter on when the reverse flow image pickup tube is operating normally d. H. the current proportional to the amount of light of an object, while according to the invention the current occurs as a counter of the degree of conversion when the beam in the vidicon type image pickup tube becomes weak, d. H. from normal operating condition deviates. That is, the degree of implementation according to the invention is equal to the quotient of the signal current, if the beam is too weak, and the beam current. In addition, it is essential to the invention that the gain factor of the feedback circuit is smaller than the reciprocal of the maximum degree of implementation is at least then. if the jet current is too weak In this way it is ensured that the beam Strom always exactly corresponding to changes in the amount of incident light, namely without unstable Oscillations of the feedback circuit, can be fed. Thus, stable operation of the control arrangement according to the invention achieved in particular an undesirable reduction in Image quality, i.e. the image resolution, due to poor quality Electron beam avoided because the beam strength always changes with the brightness of the object is secured

Advantageous embodiments of the invention are given by claims 3 and 4.

The invention is explained in more detail below with reference to the drawing

F i g. 1 is a block diagram of an arrangement that has already been developed, dealing with a too weak beam employed,

F i g. 2A shows a waveform of a video signal;

F i g. Fig. 2B is a waveform of a bright part obtained by Cutting off the waveform shown in FIG. 2A is obtained

F i g. 3 shows a diagram to explain the basic principle of the method according to the invention,

FIG. 4 is a graph for explaining the relationship between the scanning beam current / * and the signal current / ₅ bt: i the in FIG. 3 arrangement shown,

F i g. 5 shows another exemplary embodiment of the FIG. 3 shown circuit and

F i g. 6 shows a block diagram of an exemplary embodiment the arrangement according to the invention.

In FIG. 3. which explain the basic principle of the method according to the invention are provided a Image pickup tube 8, a storage electrode 9, an adder 10, a reference current source 11, an amplifier 12, a resistor 13, a beam current control electrode 14, a cathode 15 and an accelerating electrode 16.

In the case of the FIG. 3, a signal current / i is generated from the storage electrode 9 of the image pickup tube 8 and added by the adder 10 to a reference current k which is fed in from the reference current source 11. The output of the adder 10 is amplified by the amplifier 12 and then fed to the beam current control electrode 14 after being converted into a voltage signal by the resistor J3. The gain of this feedback circuit is determined by factors which include the steepness of the image pickup tube 8, the gain of the amplifier 12, the ratio between the cathode current and the beam current and the impedance of the resistor 13 which converts the current signal into the voltage signal.

In the case of the FIG. 3 apply the following equations (1) to (3):

AU _n +!.) = - ^ L. (1)

A = gain factor of amplifier 12.
Ib = beam current.

/ = Cathode current.

R = resistance value de «. Resistance U.

l ·.,. = Voltage on the S-Mahlsirom control electrode 14.

g- = steepness of the image pickup tube 8 and t = constant of proportionality.

From the equations (1) to (3), the following can be made Relationships are maintained:

/, I

with

Experiments by the inventors have shown that the beam current / - and the signal current Λ are in a relationship that is shown in four F ι g. 4 is shown. when the amount of incident light is constant. In the figure. 4 aiii uCr OrUiPi (IiC c | ._i .Jifnaiiuuin '. ■■' fir-i uiiu on the uti abscissa the beam current U is shown in uA . From FIG. 4 it can be seen that the signal current /, regardless of the value of the beam current / - is saturated at a certain point If, therefore, it is assumed that the signal current /. is saturated at a point /, ■ and the corresponding value of h is /, - <, then the relation /. = / applies. in the range in which />-> Ir . In this way there is no functional relationship between /, and /. and the circuit shown in FIG. 3 oscillates "it does not oscillate because it is an open circuit. Therefore, the circuit operates normally in the upper range, and a stable state is maintained while the image pickup tube is scanning the object.

W hen ledoch a / \ i schw acher beam due to a light Teiies of the article "which occurs a change in the object or a movement of the image pickup tube, heat a Linschw ingvorgang before. Kind in which a the Schal'unu ausschlieft weak beam. With In other words, there can be a positive pickup and a vibration or oscillation is favored. More precisely, the S'r.'hls-rum / - is in the state in which the / u s. is awake Beam occurs, in the wrong area / wipe

(X

and the- relationship between the signal current / <and de "i beam current /.- is expressed by ^ h the following equation (ϊ) :

/. = F ■ / ,. I5i

nut f- = I nset / unpsgrad.

In this case; n corresponds to F: g. 3, a circuit shown in FIG. 5 is shown. and the following equation (6) results from equations (4) and (5):

h =

Kl _n

1 -KF

From equation (6) it can be seen that no vibrations occur if KF < 1 applies. It is obvious that the feedback loop gain with such a positive feedback is obtained by the product of the degree of conversion F of the beam current into the signal current and the gain K of the feedback circuit. Since the degree of implementation is a constant inherent to the image pickup tube, it has already been suggested that the circuit shown in FIG. 3 can work stably without any oscillation if the gain factor K of the circuit is chosen to be smaller than the reciprocal of the degree of conversion F. As can be seen from FIG. 4, the degree of conversion F is not always constant in the range between

", O </" </ ",.

The desired relationship K ■ I - '<1 can, however, be obtained in the range of all values of lh if the maximum value F _n of F is chosen such that the relationship K ■ F _n , < I holds

^M Fig. H shows! a block diagram of an embodiment of the arrangement according to the invention wherein corresponding parts are provided with the same reference numerals as in FIG. 3. In the g i F. 6, an image pickup tube 8 has a storage electrode

• speak 9. a Sirshlsirorr; Control electrode M ür; dc; nc cathode 15. Also provided are a load resistor 19. An amplifier 20, a clamping member 21. A reference voltage source 22 and a comparison amplifier 23. A horizontal synchronization signal is converted into the

: s Clamping member 21 fed in via a connection 24.

In an arrangement having the structure described above, one of the storage electrode 9 is the Image pick-up tube 8 converted signal stream into a voltage / .-. Jssignal by a preamplifier

<and reinforced, the one from the load resistance 19 and the Amplifier 20 consists. This voltage signal is subjected to a pcgel hold by the clamping member 21, on which the Horizontal-Syixrhronisiersignal practices the connection 24 is located. The comparative amplifier 23

·. * Compares the output signal il of the clamping member 21 with a reference voltage applied from the reference voltage source 22 and amplifies the result Comparison. The output signal of the comparison amplifier 23 is fed into the beam current control electrode 14 of the

4> - image pickup tube 8 fed. The> reinforcement factor A. the feedback circuit is determined by the resistance of the load resistor 19, the ampl The gain factor of the amplifier 20. The gain factor of the comparison amplifier 23. The steepness of the image

4 <receiving tube 8 and the proportionality constant ι determined during the conversion of the cathode current into the scanning stream. Among these factors, t and g _{m change} depending on the image pickup tubes. With one of the inventors in an experiment

^; - The image pickup tubes used had λ and g - the values 0.6 ^{× 10 J and} 40- ΙΟ " ⁶ Ω"'. The maximum value F _n , the further factor F among the factors determining the oscillation conditions of this feedback circuit is approximately "1", and this value does not change substantially depending on the image pickup tube. In this way, A is smaller than "1", no oscillation occurs. The inventors designed the circuit by determining a value K = 03, taking into account the safety factor , and determined the product of the gain factor A of the amplifier and the resistance value R of the load resistance by using the values of α and g _m already discussed the product used RA thus obtained was 13.5 x 10 "ft experimental results prove that the beam current can be controlled stably an established on the basis of these values circuit.

For this purpose 3 blue drawings

Claims (4)

Patent claims: 1. Method stubborn control of the strength of the electron beam in an image pickup tube from Vidicon-type in which the strength is increased by a beam current control electrode of the image pickup tube of the electron beam is controlled, which scans a storage electrode and thereby into a Signal current is converted, which amplifies as a signal voltage to the beam current control electrode is fed back, characterized in that the electron beam in the signal stream is implemented with a predetermined degree of conversion, and that the feedback with a Gain factor takes place which is smaller than the reciprocal value of the maximum degree of conversion at least when the beam current is too weak 2. Order to carry out the procedure according to claim 1, with an amplifying feedback circuit coupled to the storage electrode, characterized in that the feedback circuit at the other end is only connected to the Beam current control electrode (14) is connected 3. Arrangement for performing the method according to claim 1, wherein the feedback circuit comprises a first device for implementing the Signal current into a voltage signal and its amplification as well as one with the output of the first Device connected to the second device for direct current level maintenance of the output signal of the first device, characterized in that the feedback circuit further comprises one of the second device (21> downstream comparator (23), desstn the other input with a predetermined voltage !, vert applied and whose output is only connected to the beam current control electrode (14) 4. The arrangement of claim 3, wherein the first device has an amplifier connected to the storage electrode. at its exit Clamping or level holding element of the second device is connected, characterized in that the first device further comprises a resistor (19) connected between the storage electrode (9) and a first reference voltage source, and that the comparator (23) has its other input connected to a second reference voltage source (22) connected.