DE1023077B - Circuit for cathode ray display tubes - Google Patents

Description

The invention relates to circuits with cathode ray display tubes.

In some cathode ray display tube circuits, an important requirement is a high degree of linearity between the input signal and the brightness of the light spot on your Fluorescent screen of the tube. Such a requirement occurs in particular with display tubes, which are used in standards converting devices, the image to be converted through a cathode ray playback tube is stored in the target electrode of a television pickup tube and then read with the new scanning standards through the electron beam of the pickup tube will. The invention is particularly directed to an arrangement for converting image sequence color television signals in simultaneous color signals in which different arrangements for standard implementation, as above specified, must work together and have the same characteristics, if not color distortion should be introduced. Another application is in color television monitors where Multiple cathode ray tubes are used to create different components of the final color image to reproduce.

The non-linearity of cathode ray tubes has various causes. The electron gun itself has a non-linear characteristic which is further complicated by beam restriction orifices, poor alignment of the electrode system, or uneven effectiveness of the cathode surface. In addition, the shape of the characteristic is not exactly reproducible from one tube to another and is not completely stable in a single tube, but shows changes with aging and heating. In particular, the change in the cut-off voltage with heating is disruptive. Difficulties have also arisen as a result of phosphor saturation at high current and, in particular, as a result of uneven effectiveness of the phosphor screen. Non-linear fluctuations in converting devices as a result of these and other causes are commonly referred to as transmission fluctuations. It would appear possible to correct for cathode ray tube non-linearity by using a cathode feedback circuit. However, it has been found that this type of correction is not effective over the entire frequency band in question, since there is inevitably a coupling capacitance between the cathode and the modulator electrode of the cathode ray tube as a result of the interelectrode capacitance, and this fact makes the negative feedback when switching
for cathode ray display tube !!

Applicant:

Electric & Musical Industries Limited,
Hayes, Middlesex (Great Britain)

Representative: Dipl.-Ing. W. Bisdioff, patent attorney,
Hanover, Hainhoelzer Str. 4

Claimed priority:
Great Britain April 27, 1955 and April 19, 1956

Eric Wilfred Taylor, Gerrards Cross,

Buckinghamshire (UK),

has been named as the inventor

higher frequencies void. Cathode circuit feedback also compensates for the Cathode ray tube does not have transmission fluctuations due to unevenness of the phosphor or of the optical system or as a result of interception of Beam electrons through electrodes beyond the modulator electrode.

The purpose of the present invention is to reduce the effect of errors as mentioned above are to be reduced and to provide an improved arrangement for a cathode ray display tube, those with a high degree of linearity between the image signal and the brightness of the on the Fluorescent screen generated light spot can work.

According to the invention is a circuit arrangement for cathode ray display tubes with a the cathode ray tube upstream amplifier proposed that the image signals of a beam modulating Electrode of the cathode ray tube feeds and in which the light trail generated on the screen acts on a photosensitive organ, which is characterized in that the in the photosensitive Organ depending on the current screen reverberation generated signal to the amplifier is supplied as a negative feedback signal.

In the further pursuit of the inventive idea it is proposed that the one described in the previous paragraph Arrangement in a standard converter

709 350/156

turn to where that's on the screen of the cathode ray tube television picture recorded with a first scanning standard through a on the screen picture directional pickup tube is scanned with a second scanning standard.

Further advantages and details of the invention are given with reference to the drawings in FIG the following description. The description serves for a clearer understanding and for easier implementation of the invention and shows exemplary embodiments.

. Fig. 1 represents schematically and partly in block form Figure 3 illustrates an embodiment of standards converting devices in accordance with the present invention; FIG. 2 shows a modification of FIG. 1.

The apparatus shown in Fig. 1 forms part of an arrangement for image sequence color television signals in to convert simultaneous color television signals. The image sequence signals are through a. Follow-up camera 1 generated, in front of which a rotatable color filter disc 2 is arranged in a known manner. The camera can be of the usual design and is only shown in block form. It is believed to be with 150 images works per second, with the lines jumping between lines with alternating images to have. The boundary line 3 represents a generator for image tilting impulses with 150 'images per second. The pulses from FIG. 3 are applied to the camera 1 in order to cover its field scanning passes in a known manner synchronize. Likewise, the boundary line 4 represents a generator for line toggle pulses that are sent to the Camera 1 are placed so that their line scan passes are synchronized, the generators 3 and 4 are both synchronized by a control transmitter 5 in a known manner. The staining filter disc 2 is also synchronized with the image tilt pulses in such a way that with successive Groups of three pictures color components "in the sequence red, green and blue arise.

The conversion arrangement converts image film color signals from the camera 1 into three simultaneous signals with one Rapid repetition of 50 frames per second order, with one of the signals from the images of red Signals from the camera 1 is obtained, a second from the images of the green signals and a third set is obtained from the images of the blue signals. One of the simultaneous Signal sets obtained from a combination of red, green and blue signals from the camera 1 so that a brightness signal or a so-called Y signal is formed. A separate transfer device is used for each of the Simultaneous signals are required and since the converter is generally the same for each set of signals, it is only a conversion device shown in the drawing, the red signals from the camera to this device be created.

These red signals are received from a lock 6, which the image sequence signals on different Channels are divided according to the color, the lock being synchronized by the image tilting impulses from the source 3 is. The output channel from the lock 6, in which the red signals appear, is denoted by the reference number 7 and this channel results in a non-phase inverting amplifier 8 with high Reinforcement. The output channels from the lock 6, in which the green signals and the blue signals appear are denoted by the reference numerals 9 and 10, and it can be seen that these become a Transfer device, as it is to be described, lead.

The output signals from the amplifier 8 are sent to the modulator electrode 11 of a cathode ray display tube 12 out with a fluorescent screen 13. The cathode 14 of the display tube is like shown grounded, and the acceleration and terminal anode electrodes 15 and 16 are with a source appropriate positive potential connected as indicated in the drawing. The electrodes 15 and 16 can draw current from the beam if, for example, they contain an opening around the diameter of the beam to limit. The beam is incident on the fluorescent screen 13 in any desired manner Focused and deflected over it by means of the image and line scan circuits provided by the Blocks 17 and 18 are shown and which are synchronized by toggle pulses from sources 3 and 4, respectively will. The scanning coils are not shown in the drawing, but are shown schematically by the arrows 19 and 20 specified.

It should be noted that with these arrangements the red signals from the image follower camera 1 after amplification in the amplifier 8 the beam in the Modulate tube 12 and generate a light trail on screen 13, the brightness of which depends on the red signals changes, thereby creating an optical image on the screen 13, which the red component of the scene to be watched. A television pickup tube21 is for the purpose the exposure through the optical image on the fluorescent screen 13. This tube is only shown schematically as it can be of any suitable design. It is preferred, however a low speed type tube such as that described in the Journal of the Institution of Electrical Engineers, Volume 97 part. Ill, No. 50, Line 383 ff., Is described. The tube has a target electrode 22 on which the light image from the screen 13 is focused by a lens system shown schematically at 23. A load resistance 24 is connected to the signal electrode, which forms part of the target electrode. When the target electrode is scanned by the electron beam of the tube, signals are sent to the resistor 24, which represent the image focused on the target electrode, generated and picked up by means of a conductor 25. The electron beam generator of the tube 21 is shown with the reference number 26. the however, other electrodes of the tube are not shown since they are designed in the usual manner could be. Since the signals extracted from the tube 21 are one of three simultaneous color signals are, the tube 21 works with the scanning standard deviating from the tube 12, in particular it will with an image repetition of 50 images per second operated so that the duration of each frame is three times the duration of each frame in the frame follower camera 1 is. The squares 27 and 28 represent the Represent image and line scan circuits for tube 21 and, as indicated, are not associated with the generators 3 and 4 coupled.

In the described arrangements, undesired transmission fluctuations of the converter between the image follower camera 1 and the pickup tube 21 a color distortion in the from the simultaneous color television signals bring in reproduced image. To reduce such distortion, becomes part of the light emitted from the fluorescent screen 13 by a partial Silver-plated mirror 29 is reflected and through a lens system 30 onto the photocathode 31 of a photo

Claims (6)

electric cell 32 focused. The lens system 30 is preferably the same as the lens system 23 so that when transmission fluctuations are introduced through the lens 23, corresponding fluctuations in the light input voltage to the photoelectric cell 32 are produced by the lens 30. The photoelectric cell 32 is shown as a multiplier type, and the collector electrode 33 is connected to ground or another fixed potential via a load resistor 34, at which a signal proportional to the instantaneous brightness of the track on the fluorescent screen 13 is generated. This signal passes through a frequency-dependent compensation circuit 35 in order to compensate for the effect of the inertia in the phosphor of the screen 13. The circuit 35 contains a capacitance 35 a and resistors 35 b and 35 c, of which the first is variable. The signal output voltage of the photoelectric cell 32, after each correction by the circuit 35, represents the brightness of the point on the phosphor at which the electron beam is incident in the tube 12 at the specific moment, and it is applied to the input circuit of the amplifier S, which is off the signal taken from the circuit 35 is in phase opposition to that taken from the lock 6 and consequently generates a negative feedback. The gain in the negative feedback path thus produced and containing the display tube 12 and the photocell 33 is selected to be so high that any non-linearity in the conversion device is substantially reduced in a known manner. If the pickup tube 21 of the converter is a pre-imaging tube, it may in some cases be possible to omit the photoelectric cell 33 and to take the required negative feedback signal from the pickup tube itself. This is reproduced in the modification shown in FIG. 2, in which the receiving tube 21 is shown as of the so-called image orthicon type. It has a photoelectric cathode 36 on which the optical image from the fluorescent screen 13 is focused, and the electrode image cleared by the cathode 36 is projected in a known manner onto the target electrode 37 of the pick-up tube, where it releases secondary electrons, which are released by a mesh electrode 38 to be collected. Since the construction of an Image Orthicon tube is well known, further details of this tube will not be described. Meanwhile, according to the invention, a load resistor 39 is connected to the photoelectric cathode 36, and it will be seen that the current flowing in this resistor is the same in shape as that produced by the photocell 33 of FIG. After modification in the compensation circuit 35, this signal is consequently used as the negative feedback signal of the amplifier 8. The image signal output voltage of the image orthicon tube 21 in accordance with the scanning standards of the simultaneous color signals is of course obtained from the returning beam reflected at the target electrode 37 in a known manner. The invention is described in its application to standards conversion devices in order to convert image sequence color signals into simultaneous color signals. However, it can also be applied to other conversion devices in which, for example, it is only desired to change the image or line repetition frequency. The invention is also applicable to other cathode ray display tube circuits even if not implemented, for example it can be applied to color television monitors and cinema television sets where a high degree of linearity is required between the applied image signals and the optical images produced therefrom. Godparents ta ν s ρ r j c ii e: 1. Circuit arrangement for cathode ray display tubes with an amplifier connected upstream of the cathode ray tube, which generates the image signals a beam-modulating electrode of the cathode ray tube and in which the on The light trail generated by the screen acts on a light-sensitive organ, characterized in that that that in the light-sensitive organ as a function of the current screen brightness The generated signal is fed to the amplifier as a negative feedback signal. 2. Arrangement according to claim 1, characterized by its application in a standard converter, in which the recorded on the screen of the cathode ray tube with a first scanning standard Television picture through a pick-up tube directed at the screen picture with a second scanning standard is scanned. 3. Arrangement according to claim 2, characterized by its application in a device for converting image sequence color television signals into simultaneous color television signals ¹ , this device having a color television camera, which generates the primary color signals in sequence and each primary color signal consists of a cathode ray display tube and a pickup tube Converter passes. 4. Arrangement according to claim 1 to 3, characterized in that the photoelectric organ a photocell is used, which is arranged separately from the playback and recording tubes. 5. Arrangement according to claim 1 to 3, characterized in that the photoelectric organ homogeneous photoelectrically sensitive electrode of a pickup tube with electron-optical Pre-illustration is used. 6. Arrangement according to claim 1 to 5, characterized by a control element which controls the amplitude allow the low-frequency components to be reduced relative to the high-frequency components of the negative feedback signal. References considered: British Patent Nos. 602 053, 648 2S7; U.S. Patent Nos. 2,188,679, 2,415,059; Journal of the British Institution of Radio Engineers, June 1952, pp. 325, 326. 1 sheet of drawings © 709 850/156 1.58