DE3503120A1 - CIRCUIT FOR THE AUTOMATIC DYNAMIC FOCUSING OF THE ELECTRON BEAM IN CATHODE BEAM TUBES - Google Patents

Description

DORNER & HUFNAGEL 3 0 U 0 I L · U PATENT LAWYERS LANDVWEHRSTR. »T SOOO MUNICH 2 Tel. O es / ca er s4

Munich, January 29, 1985 / A Lawyer files .: 27 - Pat. 364

RAYTHEON COMPANY, 141 Spring Street, Lexington, Mass. 02173, United States of America

Circuit for automatic dynamic focusing of the electron beam in cathode ray tubes

The invention relates generally to imaging systems or display systems with cathode ray tubes and in particular the automatic dynamic focusing of the electron beam in Cathode ray tubes of such systems.

It is known that display systems with cathode ray tubes ■ used in a wide variety of applications. For cathode ray tube Imaging systems without an automatic dynamic focusing circuit will generate an electron beam in a certain starting position on the screen, for example focused on the center of the screen. Unfortunately the electron beam suffers a defocusing when deflected from the starting position on the screen. These Defocusing is particularly pronounced in systems which have an essentially flat screen, since it is relatively here there are large differences in the distances over which the electron beam travels from the electron gun needs to spread to the various points on the screen. With cathode ray tube display systems with a circuit for dynamic focusing are devices

provided, which seek to keep the electron beam focused in every beam position on the screen.

For raster scan imaging systems, there are several Dynamic focusing circuits have been described which keep the electron beam in focus when the beam repeats the screen at a predetermined speed scans. One such system, described in U.S. Patent 3,412,281, uses the periodic Beam control signal or deflection signal for generating the focusing signal. The periodic, the position of the electron beam determining signal is pre-amplified and with a predetermined DC voltage level corresponding to a DC recovery signal biased. The DC voltage level is chosen so that the beam is properly focused in the center of the screen and the periodic changes from the DC voltage level cause proper beam focusing when the beam is in its position continuously and periodically from the center of the screen removed. In order to obtain sufficient gain for the operation of the focusing electrodes, the amplified and supplied with the DC voltage level biased signal to a relatively complex output stage which gates and associated transformer circuits contain.

While such a circuit is used for dynamic focusing in raster scanning cathode ray tube imaging systems works satisfactorily and also with certain imaging systems with a non-raster-bound, free scanning can be used, results in other imaging systems with such a circuit for automatic Focusing does not provide a satisfactory focusing effect, which is due, among other things, to the fact that the electron beam

τ- ■:. ■ '■■.: ■■' ■.} .ι.-ο ::: =

in typical non-grid-bound imaging systems with free beam deflection, the image spreads very irregularly across the screen emotional. In detail, the beam control signal or beam deflection signal is free in the case of a non-grid-bound one Sampling is not a regular periodic signal with a single dominant frequency component, as is the case with raster scanning, but contains a spectrum of relatively high frequency components corresponding to the relatively rapid changes in the beam position and, on the one hand, a spectrum of components that is relatively lower Frequency corresponding to relatively slow changes the beam position and, on the other hand, a DC voltage component corresponding to the steady-state focusing signal, when the electron beam has a fixed beam position. The aforementioned known circuit for automatic dynamic focusing for imaging systems with raster scanning is therefore in many cases not suitable for a free, non-raster-bound screen scanning, because the inductance their transformer tends to combine the high frequency components of the focusing signal which occurs with rapid changes in the jet position, reducing the reaction speed of the automatic focusing and keeping pace between the beam focusing and the respective Beam position is deteriorated when the beam position changes rapidly. It can also happen that with The system cannot achieve precise beam focusing if the beam is at a fixed point out of the center of the screen offset position remains, since the signal determining the beam position (namely a steady state signal for a fixed beam position) is AC-wise, i.e. capacitive, coupled to the focusing circuit and since the DC voltage recovery stage changes the level of the steady state signal to a predetermined level,

! namely that which is necessary for focusing the beam j in the center of the screen.

An automatic dynamic focusing circuit which ■ for systems with raster scanning as well as for systems! is suitable with free, non-grid-bound scanning, ; can be found in U.S. Patent 4,258,298. The circuit described there enables focusing even with a relatively rapid change in the position of the electron beam and the beam focussing also maintains then upright when the jet position changes at a relatively low speed. With this system is a first circuit for generating a focusing signal for slow changes in beam position and a second Circuitry provided for generating a focusing signal for rapid changes in the beam position. The outputs of the both circuits become a composite focus signal in a frequency crossover circuit and the composite focus signal becomes a high voltage DC voltage signal for biasing and the entire signal is fed to a focusing electrode for focusing the electrode beam. While the circuit of US Pat. No. 4,258,298 works satisfactorily in many cases, it does entire system quite complicated and requires keying or sampling, amplification, and rectification Feedback in the first circuit or low frequency circuit as well as a transformer coupling in the second circuit or high frequency circuit. In addition, as mentioned above in connection with US Pat. No. 3,412,281, the use of a transformer in US Pat Circuit that reacts to rapid changes in an input signal must respond that the output signals keep pace with question rapid changes in input signals.

ι · ■■ · -

'The invention is intended to solve the problem, a Circuit for the automatic dynamic focusing of the electron beam in cathode ray tubes with the features of the preamble of claim 1 so that with a comparatively simple circuit structure a good focusing in the case of rapid changes in the beam position and in the same way in the case of slow changes in the beam position Way is achieved.

: This object is achieved by the features mentioned in the characterizing part of claim 1.

In detail, a circuit for automatic dynamic focusing of the electron beam in cathode ray tubes is given here, which is a reference voltage source, further a circuit which a variable input focus signal receives and at a pair of output ports a pair of amplified variable Output focus signals, further coupling means with a capacitor connected to the first output terminal of said pair of output ports are coupled to the first of the pair being amplified variable output focus signals across the capacitor, and a combination circuit to couple the predetermined reference voltage of the reference voltage source to an output terminal to further with the reference voltage at the said output terminal capacitively coupled out first amplified variable output focusing signal and also the second of said pair of amplified variable output focus signals to combine, so that finally a composite focusing signal can be picked up at the aforementioned output terminal, with a nominal focusing voltage, generated at an output terminal is weakened to a certain fraction, which is the respective other of the pair of output terminals of said amplifying circuit occurs.

According to further features of the circuit specified here, the combination device contains a plurality of cons' stand, of which a first is placed between a first output terminal and said output terminal and a second is placed between a second output terminal and said output terminal. The reference voltage source for the Generation of the predetermined reference voltage is connected to the first output terminal and the respective second of said output terminal A pair of output terminals of the amplifier circuit is connected to said second output terminal. The coupling capacitor is between the first of the pair of output terminals the amplifier circuit and the aforementioned output terminal.

Further, in such a facility, the includes the pair of Output connections having a gain effecting circuit each amplifier and circuit parts for coupling different proportions of the variable input focusing signal to the amplifiers, a first of said amplifiers being the first amplified variable Output focus signal and a second one of the amplifiers provides the second amplified variable output focus signal presents. According to a preferred embodiment of the circuit specified here, the variable focus signal has a certain bandwidth that differs from a frequency extends from 0 Hz to a predetermined frequency and the amplification gain in each of the amplifiers, the proportions of the variable input focus signal, which are coupled to the amplifiers and the resistance values of the resistors mentioned are chosen so that there is a substantially uniform transfer characteristic with respect to the variable input focus signal fed to the amplifiers and the composite Focusing signal, which at said output terminal

is presented, essentially independent of the frequency of the variable focus signal via ex * the predetermined, Bandwidth adjusts.

In an imaging system in which the circuit specified here is used for automatic dynamic focusing of the electron beam in the cathode ray tube, the The electron beam is directed to an initial position of the screen and means are provided in the usual way around the electron beam to certain points on the screen to generate an image or signal representation to steer depending on deflection signals. Devices responsive to these deflection signals produce the aforesaid variable input focusing signal, which the circuit described here for automatic dynamic focusing of the electron beam is supplied. The composite focus signal transmitted by the circuit can be removed, then focusing means, for example a focusing electrode, which the electron beam in each deflection position keep focused on the screen.

So it will be a relatively simple circuit created for automatic dynamic focusing, which reacts to rapid changes in the beam position on the screen responds and keeps the beam focused and maintains focus even when the electron beam is in a only fixed position on the screen.

Exemplary embodiments are described below with reference to the drawing. They represent:

1 shows an illustration of a partially diagrammatic and partially represented in block symbols

Imaging system with a circuit for automatically dynamic focusing of the electron beam and

FIG. 2 shows an equivalent circuit diagram of the circuit for automatic dynamic focusing according to FIG. 1.

Reference is now made to FIG. In the drawing is an imaging system including a cathode ray tube denoted at 10, the cathode ray tube having magnetic deflection and electrostatic focusing having. The imaging system 10 thus includes a cathode ray tube 12 of conventional construction with a tubular envelope and a screen 16. The tube piston 14 in turn contains an electron gun 18, which as Triode can be formed and includes a cathode, a grid and a screen electrode. These parts are not shown in detail, but the electron gun contains these components as a unit.

The electron gun emits when heated an electron beam 22 through the filament 20. The electron beam extends through a first focusing reference anode 23, a second focus reference anode 25 and a focus electrode 24 interposed therebetween, said Electrodes all have a cylindrical shape and conventional structure and with through openings of such a diameter are designed so that the electron beam can pass coaxially. After passing through the anodes and 25 and the focusing electrode 24 becomes the electron beam conventionally by means of a magnetic deflection coil assembly 26 is directed to a certain point on the screen 16. The conductive covering 27 on the side walls of the tubular piston 14 is in a known manner by an anode voltage source 28 is held at a specific DC voltage potential via a line 30 in order to act as an anode

43. ■■ '' ■■■ '■■' ■ .ι. "-.: - ..:

which accelerates the electron beam towards the screen 16. The line 29 connects the conductor surface 27 of the Tubular piston with the above-mentioned focusing reference anode 25, which is also connected to the first focusing reference anode 23 via the line piece 31 is in connection. The first and second focusing reference anodes 23 and 25 are therefore open the same direct-voltage high-voltage potential as the conductive covering 27.

The focusing electrode 24 located between the focusing reference anodes 23 and 25 is formed by a composite Focusing signal applied via line 19, wherein this signal is a dynamically changing high-voltage signal, the value of which changes relative to the fixed DC voltage potential .an the focusing reference anodes 23 and 25 changes so that you can interact with the focus reference anodes 23 and 25 receives an electron lens of a type known per se. The focal length of the electron lens is determined by the dynamically changeable high-voltage focusing signal, which is fed to the focusing electrode 24 via the line 19 and that is generated in the manner to be described below. It should only be said here that the compound Focusing signal on line 19 in circuit 86 for automatic dynamic focusing as a function is formed by a variable low voltage input focus signal, in turn on line 88 of the input focus signal generation circuit 90 is provided and which corresponds to a focusing correction required when the beam hits a point of the screen 16 is deflected, which does not coincide with the screen center, which bears the reference number 82 in FIG. The variable focus input signal applied on line 88 reaches an input terminal 92 of one Amplifier section 94 of the circuit 86 for automatic

dynamic focus. The amplifier section 94 generates a pair of amplified variable focus output signals at output terminals 93 and 95. A first amplified variable output focus signal occurs at the output terminal acted upon by the amplifier 98 and is then alternating current via a capacitor coupled to output terminal 112 of a voltage divider circuit. The output connection 112 is via the line 19 is connected to focus electrode 24 and is biased to a nominal focus voltage which is the focus voltage which is required to direct the electron beam towards the center 82 of the screen 16 focus, this focusing voltage rating by the anode voltage source 28, the resistors 120 and 122, the Potentiometer 114 and the relatively low output impedance of amplifier 100 in more detail below is set in the manner described. The capacitively coupled output signal of the amplifier 98 thus has the nominal focus voltage or center focus voltage combined at output terminal 112 to produce a focus signal, which corresponds to the signal required for correct beam focusing both when the beam is set on the Screen means as well as in the case of beam positions deviating from the central position on the screen 16 is required if the electron beam moves across the screen. However, due to the action of capacitor 108, the combined falls Focus signal at output terminal 112 to the nominal focus voltage or center focus voltage, when the variable focus signal is a steady state signal, i. H. is a signal with frequency 0 Hz, where this signal occurs when the electron beam remains stationary on a certain point on the screen 16. if so the electron beam constantly maintains a position on the screen 16 deflected from the center, then falls the focusing signal at the output terminal 112, as far as this relates to the circuit described so far, to the nominal focusing voltage or center focus voltage, whereby

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the electron beam suffers a defocusing at the certain fixed position deflected from the center. To compensate for this voltage drop, a second amplified variable output focus signal, the is presented at the second output terminal 95 from the amplifier 100, in terms of direct current via the potentiometer 114 and , the resistor 122 is coupled to the output terminal 112 in order to j here said second amplified variable output

ι Focusing signal with the first amplified variable Output focus signal and with the focus nominal; frequency to combine and a compound, eventually to provide a focus signal leading to proper focusing at the output terminal 112. How on detailed below, the composite focus signal enables accurate focus when the Electron beam remains at a single fixed, deflected from the center point of the screen 16, as well as in those cases where the electron beam moves across the screen.

This can also be expressed as follows: If the position of the electron beam is changed rapidly, the correspondingly rapidly changing one becomes variable! Focusing signal to the output terminal 112 in two ways: coupled, namely via the alternating current coupling path 97, which is capacitively coupled to the capacitive load which is formed by the electron lens from the reference anodes 23 and 25 and the focusing electrode 24, where j this alternating current coupling path 97 responds quickly to correspondingly rapid changes in the variable focusing signal and effects precise focusing of the electron \ beam, and on the other hand via the direct current coupling! treatment path 99, which responds relatively slowly to signal changes due to the capacitive load formed by the electron lens and the AC coupling path 97, but a proper focusing voltage on the

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. Output terminal 112 maintains when the electron beam; assumes a deflection position on the screen 16 and in

remains in this position.

! The reproduction of information on the screen 16 is essentially controlled by the reproduction control device 32 which, in the usual way, produces reproduction command signals from! peripheral units receives, for example from a computer ' i or an operator terminal, which are not shown.

i;

ι Actuated as a function of such playback command signals! the playback controller 32 includes a vector generator 34,:! when a line is to be drawn and also operates a character generator when a character is to be displayed. If a line is to be displayed in the system, the playback control device 32 transmits the coordinates of a to the vector generator 34 via the data lines 38. Starting point and an end point of the drawing line. The vector generator 34 converts these coordinates in a known manner 1 into time-variable X and Y position signals. The X and Y position signals are on output lines 42 and 44 ^;

j available. The output signal on line 60 receives ' ■

the information about the time at which the electron beam 22 was received; clears or highlighted, d. that is, to be switched off or switched on. The degree of brightness of the line to be drawn j

is also determined by the playback control device 32, which via the line 33 a brightness control signal directly to the video amplifier 68.

'If the submission is to be reproduced, the

: Gabe control device 32 via the data lines 40 the code of the desired character to the character generator 36. The character generator 36 sets the character information in time-shifted. converts variable X and Y position signals appearing on lines 46 and 48. The reference position on the screen 16, on which the character is to be displayed, is generated by the vector generator 34 on command from the repeater

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ι the output control device 32 determined as previously indicated was ben. The character generator 36 also supplies a signal via the I line 62, which in turn causes the elec- : electron beam 22 is deleted or brightly controlled. The Hellig

The ability to display characters is controlled by the playback control ; Direction 32 is controlled in the same way as was previously carried out with regard to a line display.

Arithmetic summers 50 and 52 and a logical summer 64 (namely, an OR switch) combine the X and

I Y position signals and the signals for deletion or light control of the electron beam from the vector generator 34 and from the character generator 36. If a line is to be displayed, so , the X and Y position signals and the erasure or Brightness control signals from vector generator 34 by far the signals which are obtained from the character generator 36. ; The outputs from the three summers on lines 56, 58; and 66 are therefore essentially based only on the operation of the j vector generator 34. If a character is to be displayed, i then puts the vector generator 34 through signals on the line I Gen 42 and 44 fix the X and Y reference positions and the character generator 36 supplies the time-variable X and Y positions signals via lines 46 and 48, which are

; metic summers 50 and 52 are superimposed on the X and Y reference position signals. The output signals of the summers 50 and 52 on the lines 56 and 58 are each composite signals which cause the display system ^{: to} display the selected character at a desired position i. The deletion or light control for the relevant; Character is controlled by the sum of the erasure or brightness control signals from the vector generator 34 and the character generator 36, which is formed in the logic summer 64.

The video amplifier 68 receives the logically summed Clearance or brightness control signals from logic summer 64 over line 66 as well as the brightness control signals

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from the playback control device 63 via the line 33. As is well known in the art, video amplifier 68 pauses in response to the aforesaid signals selectively turning off or turning on the electron beam 22 and controlling the brightness of the beam Control of the voltage on line 70 which is applied to electron gun 18, whereby the Beam current is controlled, which emanates from the electron gun 18 in the cathode ray tube 12.

An image correction circuit 54 receives the arithmetically summed X and Y position signals from the summers 50 and 52 over lines 56 and 58. The image correction circuit 54 applies a correction signal to the X and Y position signals to compensate for the fact that the surface of the screen 16 is substantially flat and not spherically curved. Without such compensation it would the image on the screen 16 have the known pincushion distortion, which are very clearly noticeable would.

The mapping correction circuit 54 outputs corrected X position signals via the line 76 to the X coordinate amplifier 72. Here the signal experiences a final amplification and is then passed on to the magnetic deflection system 26 via the line 74. The image correction circuit also provides 54 sends a corrected Y position signal over line 78 to Y coordinate amplifier 80, where the signal is amplified and is again fed to the magnetic deflection system 26 via a line 81. In the magnetic deflection system 26 are, which is not shown in detail, X and Y deflection coils. As is well known, the generated due to the supply of the X and Y position signals in the coils of the deflection system flows a resulting magnetic field, which deflects the electron beam 22 so that it hits the desired location on the screen 16.

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As previously mentioned, the screen 16 is not spherically curved, but essentially flat, so that the distance over which the electron beam 22 from the electron gun 18 must spread out before it hits the screen 16, enlarged when the electron beam is deflected away from the screen center 82 to a point near the edge of the screen 16, for example on the point 83 with a radial distance d- ^ from the center 82 or to point 85 at a radial distance d2 from the center of the screen 82. This change in the path of the electron beam results in a characteristic defocusing of the beam when it is guided across the screen. A dynamic automatic focusing of the beam compensates this characteristic defocusing by changing the focal length of the electron lens from the reference anodes 23 and 25 and the focusing electrode 24 depending on the respective beam position. As briefly stated earlier, the focal length of the electron lens is determined by a via line 19 from the circuit 86 for automatic dynamic Focusing applied high voltage composite focus signal is controlled so that the electron lens continuously responds precisely to changes in the beam position on the screen 16 and for each beam position the jweils correct beam focusing.

Deviating from the conditions in an imaging system with a scanning raster, in which the electron beam with a predetermined constant speed for scanning over the Screen is guided, in a non-raster imaging system 10, the electron beam is across the screen carried away in an irregular manner, so that the electron beam sometimes jumping rapidly from position to position and sometimes in a single place either in the middle or in the middle Lingers for a relatively long time offset from the center. In playback system 10, circuit 86 provides for dynamic focus a rapidly changing composite

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set focusing signal to the focusing electrode in response to corresponding rapid changes in the Beam position, while on the other hand the one used for focusing Signal voltage at a certain value that causes the correct focus when the beam is on a certain point of the screen 16 lingers.

The input terminal 92 of the dynamic focus circuit 86 is obtained from the focus signal generator 90 via the Line 88 has a variable input focusing signal applied to it, as has already been pointed out above. the Inputs for the focusing signal generator 90 are the arithmetically summed up X and Y position signals of the arithmetic

. metallic summers 50 and 52 on lines 56 and 58, respectively. As is well known, the focus signal generator calculates 90 for a given pair of coordinate signals accordingly the X and Y position is the radial distance from the center 82 of the screen 16 that the point in question is to which the electron beam 22 is deflected based on the X and Y position signals. The focus signal

• generator 90 generates a variable focus signal with an amplitude which is proportional to the amount of the necessary focusing correction, which in the case of the Screen for the calculated radial deflection distance. Characteristically, the focus signal the smallest amplitude when the radial deflection of the beam is zero, i.e. when the electron beam hits the center 82 of the screen 16 hits. The center point can be selected as the reference point and the focusing signal generator 90 is then set so that it provides zero output voltage when the electron beam hits the center of the screen is set. The electron beam is deflected so that it hits points at a certain distance from the center of the screen hits, the amplitude of the focus signal decreases from Zero off and in the present case becomes more positive. The maximum output of the focus generator 90

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in the present case is, for example, + 10 volts. Of course the reference point can also be at one of the center of the screen different positions of the screen can be selected. Also can the focus signal generator 90 can be set so that it when the electron beam is set to the reference point emits a voltage other than zero voltage. The focus signal, which is generated by the focus signal generator follows the beam position, i.e. i.e., the focus signal has dynamic or transient components, which correspond to the change in the beam position, as well as permanent state components (i.e., zero frequency components) corresponding to a certain fixed beam setting.

The dynamic focus circuit 86 provides on the , Output line 19 a composite focus signal; high tension, which in terms of the dynamic component ; nent and the steady-state component of the changeable

Input focus signal of the focus signal generator : tor 90 is repeated, with a gain with the correct gain by the amplifier section 94 and a

Bias is made with the correct DC voltage, j to enable the desired dynamic focus. The j circuit 86 for dynamic focus thus receives as' ■ stated above, the variable input focusing; signal at the input terminal 92 of the amplifier section 94. 'The amplifier section 94 provides at a pair of output terminals 93 and 95 a pair of amplified variable output focusing signals, which are carried by the amplifier section 94 on two parallel channels, namely the circuit branch 97 for AC coupling and the circuit branch 99 for direct current coupling. The first amplified variable output focus signal is generated by the amplifier 98 at the output terminal 93, the amplifier 98 having a low impedance and being connected directly to the input terminal 92 on the input side. The second amplified variable output focus signal is provided by amplifier 100 at the output port

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Conclusion 95 presented, wherein the amplifier 100 has a low output impedance. The input to the amplifier 100 is connected to the input connection 92 via an adjustment circuit 102. The balancing circuit 102 contains a potentiometer 106 and a fixed resistor 104 and is used to adjust the input! To be able to adjust the output level to the amplifier 100 for the purposes given below. The output of the amplifier 98 is coupled in terms of alternating current via the capacitor 108 to the output terminal 112 of the voltage divider circuit 110. In addition, the output terminal 112 is connected to the focusing electrode 24 via the line 19. The output of the amplifier 100 is connected to the end connection 116 of the voltage divider circuit 110 in terms of direct current or galvanically via the trimming potentiometer 114. The high voltage of the anode voltage source 28, for example in a magnitude of 30,000 volts, is applied to the terminal 118 of the voltage divider circuit 110. The Widex ^- stand 120 is placed between the terminals 112 and 118 of the voltage divider circuit and the resistor 122 is located between terminals 112 and 116 of the voltage divider circuit. The latter is grounded via the amplifier 100, which has a relatively low output impedance, and sets the reference potential of 30,000 volts present at the terminal 118 to a nominal focusing voltage at the output terminal 112, the level of which corresponds to the focusing voltage required for the correct focusing of the electron beam 22 when it is set to the center 82 of the screen 16 is required, in the present case, for example, about 5000 volts.

As previously described, the capacitor 108 and the series connection effect the resistor 122 and the potentiometer 114 passive coupling of the first and second amplified variable output focus signals of the amplifier 98 or the amplifier 100 to the output terminal 112, where these signals with the nominal focus voltage of for example 5000 volts can be combined to present the composite focus signal at output terminal 112

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to be able to. The capacitor 108 and the series circuit from the Resistor 122 and potentiometer 114 also prevent the nominal focus voltage of, for example, 5000 volts, which is present at output terminal 112 appears at the output of either amplifier 98 or amplifier 100. In detail note that capacitor 108 is at the nominal focus voltage completely away from the output of amplifier 98 while connecting the series out of the resistor 122 and potentiometer 114 together with the relatively low output impedance of amplifier 100 Forms a voltage divider that reduces the nominal focus voltage of, for example, 5000 volts to a very low value at the output of the amplifier 100 divided down. Composite focusing signal voltages can thus be generated at the output connection which change, for example, between 5000 volts and 5500 volts, while at the outputs of the amplifier 98 and 100 only voltages from 0 volts to 500 volts need to be provided. After the reinforcement "98 and 100 at, If the voltage is so low compared to the nominal focusing voltage, the service life is increased the amplifier and a reduction in the response time of the amplifiers and their power requirements. i

i The operation of the automatic dynamic focus circuit 86 can be best understood from Figure 2 illustrate; which shows an equivalent circuit diagram of the circuit 86. In FIG. 2, the amplifiers 98 and 100 are shown as ideal voltage sources 98 'and 100', respectively. The amplitude of the input variable focus signal applied to the input of amplifier 98 is denoted by Vn (s), where (s) is the Laplacian. The variable input focusing signal has a predetermined bandwidth, which extends from a frequency of 0 Hz (i.e. direct voltage) corresponding to the dwell time of the electron beam at a certain point on the screen to a predetermined frequency, which is the fastest change in the position of the electron beam.

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λ - - '■■' ■■ :: :: = ::: ■

Corresponds to the beam on the screen. For an analysis of the operation of the circuit 86 it is assumed that the in Fig. Amplifiers 98 and 100 shown in FIG. 1 each have a sufficient | Have bandwidth to cover the entire bandwidth of the Sig-! nals V- ^ (s) to ensure the proper functioning of the circuit. The gain of the amplifier 98 is denoted by Αι. For this reason, the ideal voltage source 98 'provides an output voltage of A ^ V ^ (s). The variable aV- ^ (s) denotes the amplitude of the signal V ^ (s) reduced by the division ratio of the balancing circuit 102, i.e. the voltage divider from the potentiometer 106 and the fixed resistor 104. This is the voltage that the input of the amplifier 100 is fed. If the gain of the amplifier 100 is denoted by λ2, the result is that the ideal voltage source 100 'of the equivalent circuit has an output voltage of; aAo Vj (s) yields. Further be with reference to the figures; 1 and 2 found that V _HV denotes the voltage that can be obtained from the anode voltage source 28 and is present at the terminal I 118 of the voltage divider circuit 110. R-, and R ^ denote the resistance values of the resistors 120 and 122, respectively. BR3 denotes the resistance value set on the trimmer potentiometer 114 and C denotes the capacitance of the capacitor 108. The composite focusing signal which is finally generated at the output terminal 112 is shown in FIG 2 denoted by V _Q (s). The capacitor C shown in dashed lines in FIG. 2 symbolizes the capacitive load which is applied to the circuit due to the presence of the electron lens from the focusing electrode 24 and the two focusing reference anodes 23 and 25. As stated above, the use of the circuit branch 97 for the AC coupling of the circuit 86 enables a precise response to rapid changes in the variable input focusing signal applied to it, corresponding to rapid changes in the beam position regardless of the presence of the capacitive load C. It should be noted that the capacitance C quite small (for example of the order of 10 pF) compared to the capacitance C of the capacitor im

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'. AC coupling branch 97 is. The capacitance C ¹ can therefore; in an analysis of the normal operation of the circuit 86 except! Remain under consideration. Taking into account the principle of superposition, the output signal of the circuit at the output terminal

i>

: Final 112 written in Laplace form as follows will:

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1
sC R; (R2 + BR3) Ä. Bl
sC ¥ c '- R] .XR ₂ + BR3)
R ₁ + R ₂ + BR3 3503120 ) 1 +
V _o (s) = "sC R2 + BR3 + Ri (R ₇ + BR ^ . A ₁ V ₁ (S) 1 (R2 + BR3) • ^V HV ⁺ R2 + BI
3A ₂ Vi 1 R ₁ + R ₂ + BR3 R ₁ + SC sC 1 + R2 + BR3
sC * 3>
(S) . 3A ₂ V ₁ (p + "sC ^R l
sC SCR ₁ (R2 + BR3) R2 + BR3 + R ₁ R-j + R ^ + BR ^ Simplified: + ^R l 5CR ₁ (R ₂ + BR3)
R ₁ + R ₂ + BR3 V ₀ (S) = V _w (Rp ⁺ BR + ] ^ + R2 + BR3 + sC (
+ ^R 1

Ri + (1 + SCR ₁ ) (R2 + BR3) 15

After converting the above equation into normal form:

^V IiV * R2 + BR 3 A ₁ V ₁ (S). SCR ^ (R2 + BR 3)

V _o (s) = R1 + R2 + BR 3 + R1 + R2 + BR 3 (1)

1 + sC (R9 + BRt) 1 +

R ₁ + R ₂ + BR ₃ R ₁ + R ₂ + BR ₃

+ R Y + R7 + BR 3

1 -

^R 1 ^{+ R} 2 ^{+ BR} 3

After the summary of the V (S) expressions and treatment of V ^ as pure direct voltage:

V ₀ (S) = Vm / ( ^R 2 + BR3) + (2)

^R 1 ^{+ R} 2 ^{+ BR} 3

1 + aA? Vi

R] _ + R-5 + BR3 (1 + s (CR i (R 7 + BR -dh, V _o (s) = V _nc term + V _AC tern

■ "- ■ ■" "■ '35 (33120

To get a relatively uniform transfer function get which over the given bandwidth essentially focusing signal that is variable regardless of the frequency Vjl (s) remains, must be in the V ^ -expression in equation (2) shorten out the right fraction expression. I. E. the resistance values and the gain values must be chosen in this way that you get the following:

ι aA ₂

'-. From equation (3) one obtains after some calculation:

If equation (4) is inserted into equation (2), one obtains:

V _o (s) = V _H vXR ₂ + BR ₃ 2 + A ₁ V ₁ (S) (5)

R ₁ + R ₂ + BR ₃

Equation (5) shows that if the resistances and the gain of the amplifiers in the circuit are chosen so that equation (4) is satisfied, the circuit 86 for dynamic focusing has a transfer function between the variable input focusing signal V - ^ ( s) and the composite output focus signal V _Q (S) which is essentially independent of the frequency of the variable input focus signal over its operating bandwidth. In other words, the transfer function of circuit 86 is substantially uniform over the predetermined bandwidth of the variable focus input signal. The composite focus signal provided by the dex "automatic dynamic focus circuit 86, therefore, provides accurate beam focusing as the beam scans across the screen

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Vl

""" 35Ö3120

is guided as well as when the beam remains on a single fixed point on the screen.

As already mentioned above, it is advisable to set the focusing signal generator 90 so that it generates a voltage of 0 volts as the focusing signal V ^ (S) when the electron beam is directed at the center 82 of the image ^- ms 16. Thus, when the electron beam is focused on center 82, the composite output focus signal V ₀ (S) applied to focus electrode 24 has an amplitude determined only by the value of the first expression of equation (5). So you can see that the first expression of equation (5) related to the present example ^! represents the 5000 volt nominal focus voltage. The focus voltage applied to focus electrode 24 is; always at least equal to this nominal value for the preferred one; Exemplary embodiment, since, as already said before, the amplitude 'of the input voltage V - ^ (S) in the present case never less than. Becomes 0 volts.

From equation (5), it can be seen that the focusing nominal voltage of, for example, 5000 volts is dependent only on the values of '· of Vtiy, Ri.Ro ^{un (^} ^^. 3 In the selected exemplary embodiment, and referring to the representation of Figure 2 it should be noted in that the resistors R ^ and R2 j a fixed value are respectively set, which is selected so that! approximately the desired focusing nominal voltage of, for example, 5,000 volts is established. After V _HV (in the present case 30,000 volts) supplied by a fixed anode voltage source 28 Is anode voltage, the nominal focusing voltage is precisely adjusted to the required value by setting the trimming potentiometer 114 and thus by setting the resistance value BR3. It can be seen that the ratio of R ^ to (R2 + BR3) is set to a fairly large value of for example about 5: 1. In the present embodiment, R ^ has the value of 250 MÄ and R _{2 has} the value of 40 MSL In addition, a circuit is expediently laid out

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Generally speaking, the full value of a component used for trimming is as small as possible. In the present embodiment, the full value of the trimming potentiometer ■ the implementation of the resistance value BR3 about half of the resistance value of R2 * is the full resistance value of the trimming potentiometer is therefore present example, 20 m5 £ L and the value of BR ₃ is at approximately 10 FTE. adjusted to maintain the focus voltage rating of 5000 volts.

As can be seen from equation (5), A ^ Vn (s) is added to the nominal focus voltage to obtain the composite focus signal V _Q (s). The composite focus signal must have a sufficient range of change to achieve proper focusing of the electron beam at any point on screen 16. A certain screen of a cathode ray tube can require several 100 volts more focusing voltage to focus the electron beam when it is deflected to the outermost edge of the screen than when the electron beam is aimed at the center of the screen. The value of A- ^, i.e. the gain of the amplifier 98, must be selected so that it converts the signal V ^ (s), which changes from 0 to 10 volts, to a signal with a voltage excursion of several 100 volts (in this case 0 to 500 volts). In the reproduction system 10, which requires, for example, a voltage range of 100 volts of the focus voltage and a nominal focus voltage of 5000 volts, the composite focus signal V _Q (s), which is applied to the focus electrode 24, has a range of change from 5000 volts to 5500 volts.

If the values of V _HV , R- ^, R2 * BR3 and A · ^ are fixed, then the gain of the amplifier 100, i.e. the value A2, only needs to be set according to equation (4) in order to give the circuit 86 the desired transfer function give, namely a uniform transfer function, which in

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essentially independent of the frequency of the signal V-, (s) is over the specified bandwidth of this signal. Equation (4) can be written as follows:

^A 2 ⁼ (Rl + R2 + ^R R 3) ^A 1
aR-j ^

Since, as already stated, the ratio of the resistance values RjL and (R2 + BR3) is selected to be quite large, for example 5: 1, the above equation can also be approximated as follows:

A2 = 1.2Ai / a (£)

The correction factor a gives the fraction of the variable Input focusing voltage V- ^ (s), which is at the input for amplification "100 is available. This amplitude fraction is determined by the adjustment circuit 102, that is, the voltage divider from the potentiometer 106 and the fixed resistor 104. It can be seen from Figure 1 that the value a can be changed between 1 and a minimum value d, which is greater than 0 is determined from the value of resistor 104 and the full resistance value of potentiometer 106. Equation (6) can be satisfied either by holding A2 at a certain value and adjusting a, or by the The value of a is fixed and the value A2 is set. Preferably, however, one chooses a certain value of d and then measures A2 according to equation (6) for a value of a in the Middle between d and 1 (i.e. a = d + (l-d) / 2). This allows the potentiometer 106 in both directions from the starting position Adjust by equal amounts so that changes in A2 are compensated for after a certain period of operation can.

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If you return to equation (1) and consider its V ^ (s) expressions, it is easy to see that for relatively high frequencies of Vi (s) correspondingly rapid changes in the beam position, the expression a A ₉ V ₁ (s) versus Zero goes and the

£ * JL

Output V _Q (s) due to the signal V- ^ (s) is derived almost exclusively from the Ai Vi (s) expression. If, on the other hand, the signal V ^ (s) is a low-frequency signal up to a DC voltage signal, which corresponds to a slow change in the beam setting up to a constant beam position, the value of V _Q (s) is based on the input signal V ^ (s ) on the a A2 V ^ (s) term, while the A "1 V ₁ (s) term tends to zero. Looking at these results, it can be seen that the automatic dynamic focus circuit 86 behaves as a frequency crossover circuit with respect to the variable input focusing signal V ₁ (s), the circuit providing an output in which, for high frequencies of the variable input focusing signal, the action of the AC voltage coupling branch 97 dominates, while for low frequencies or for DC voltage form the variable Input focusing signal the influence of the DC voltage coupling branch 99 dominates.

Let us now consider FIG. 1 again. The composite focus signal presented at output terminal 112 of circuit 86 reaches the focusing electrode 24 via the line 19, which, as already stated above, with the first focusing reference anode 23 and with the second focusing reference anode 25 to form an electron lens cooperates. As already stated, the Anodes 23 and 25 are connected to a specific DC voltage of 30,000 volts in the present case, which is supplied by the anode voltage source 28 is delivered. The application of the composite focus signal to the focus electrode 24 causes a certain electric field to develop between the focusing electrode 24 and the first focusing reference

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, anode 23 and between the focusing electrode 24 and the second focusing reference anode 25 forms. Both electrical fields see • perform appropriate changes when 'the composite focusing signal sierungselektrode to the focus-I is present 24, in response to amendments: changes gen the beam position on the screen 16th The changing electric fields have a lens effect on the electron beam 22 and cause the beam to be focused on the screen 16 at the point at which the beam is currently directed.

As mentioned above, capacitor 108 in the circuit effects; according to Figure 1 a remote position of the focusing rated voltage, 'which is present at the output terminal 112 of the amplifier 98. It is also coupled to the output terminal 112 of capacitor 108, the in-zero voltage output voltage of amplifier 98 and with the 5000 volt Nennfokussie-

, roughly combined at the output terminal 112 and finally a capacitive coupling is created by the capacitor to: the capacitive load in the form of the electron lens

^; posed. The value of the capacitor 108 is chosen so that

ι i the shape of the output waveform of amplifier 98 on |

; Output terminal 112 is accurately reproduced. To an ord- ^! To achieve proper coupling, the capacitance value j

'of the capacitor 108 is much larger (for example one hundred; times larger) than the intrinsic capacitance C of the electron lens, which consists of the focusing electrode 24 and the two Focusing reference anodes 23 and 25 is formed. If a typical value of the capacitance C is, for example, 10 pF, so one chooses the value of the capacitor 108 to be 1000 pF.

It should be noted that the value of capacitor 108 is the crossover frequency the circuit 86, i. i.e., determines the frequency of the variable input focus signal V ^ (s), in which the AC voltage coupling branch 97 and the DC voltage coupling branch 99 each have equal parts

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contribute to the output of the circuit, i.e. to the composite focus signal. The crossover frequency w _Q is given by the following equation, where C denotes the capacitance value of the capacitor 108:

Wq = 1

^R 1 ^{+ R} 2 ^{+ BR} 3
As stated earlier, R ^ are to 250 mS2. , R ₂ to 40 m5E- and

g chosen to 10 MÄ. If the capacitance value of the capacitor 108 is selected to be 1000 pF, it can be seen that the crossover _{frequency w Q in the} present case is approximately 24 radians / sec. or 4 Hz. Theoretically, the crossover frequency can be selected to be even smaller by increasing the capacitance of the capacitor 108. As is known, however, high-voltage capacitors with large capacities are expensive, difficult to obtain and physically large, as a result of which the maximum capacitance of the capacitor 108 is practically kept within certain limits.

In Figure 1, an embodiment is shown in which preferred the anode voltage source 28 both the first and the second focusing reference anode 23 and 25 as well as the! Circuit 86 for dynamic focusing feeds which in turn applies to focusing electrode 24. This is j an expedient arrangement, as it is ensured that small disturbances and deviations in the output of the anode voltage source 28 due to temperature changes, aging phenomena and the like of the focusing electrode 24 and the anodes 23 and 25 communicate in the same way. In certain applications, however, it may be that the use the anode voltage source is not appropriate for both functions, since due to this circuit configuration the A considerable current is drawn from the anode voltage source.

In another embodiment of a playback system with a circuit of the type specified here accordingly feeds the anode voltage source 28 only the conductor layer 27 and the first and second focusing reference anode 23 and 25 of the cathode

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Jet pipes 12, as in the embodiment of Figure 1, while a second DC voltage source supplies a specific reference voltage of, for example, 30,000 volts to the circuit 86 outputs via the connection 118 of the voltage divider circuit. As the second voltage source with the cathode ray tube 12 has no connection, it can be a variable voltage source. The nominal focus voltage for example 5000 volts can be adjusted by adjusting the variable second DC voltage source so that the trimming potentiometer 114 for realizing the resistance value BR3 is superfluous and either omitted can be or is set to zero. Furthermore, the potentiometer 106 can be adjusted so that the full Value of the variable input focus voltage am Input of the amplifier 100 is present, so that a simpler ratio Α ^ / Α2 of the gain is obtained, which is to be satisfied in order to obtain the uniform transfer function of the circuit independent of the frequency of the variable input focus signal over its bandwidth to obtain.

Within the scope of the invention, the person skilled in the art has a large number of options for further training and modification. For example the automatic dynamic focusing circuit can also be used in playback systems which have not magnetic but electrostatic deflection systems. In this case, the magnetic deflection yoke 26 is through to replace one pair of baffles for the X coordinate and another pair of baffles for the Y coordinate. The circuit 86 for automatic dynamic focusing can also be used in conjunction with other types of focusing electrodes can be used. Finally, the circuit can also be used in playback systems that use electron beam deflection perform according to a scanning grid.

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Claims (1)

Claims / l / {Circuit for automatic dynamic focusing of the Electron beam in cathode ray tubes, in which beam deflection signals by means of a focusing signal generator '■ tors (90) the application of Fokussiex'ungsmittel (24, 23, 25) of the cathode ray tube (12) controlling variable ι focusing signals (88) are generated, characterized by [ a voltage source (28) for providing a specific reference voltage, furthermore by an amplifier section (94), which from the variable focus signals of the ; Focusing signal generator (90) is fed and at a Pair of output terminals (93, 95) present a pair of amplified variable output focus signals, further by a circuit branch (97) connected to one (93) of the output connections (93, 95) of the amplifier section (94), ; includes a capacitor (108), for capacitive Ankopp- ^ f lung of said one output focusing signal, and V by a combination circuit (110), via which on the one hand, the reference voltage of the voltage source (28) is coupled to an output terminal (112) in order to provide there a nominal focusing voltage which, on the other hand, combines the nominally coupled out amplified variable output focusing signal and the respective other amplified variable output focusing signal with the nominal focusing voltage at said output terminal (112) in order to produce a composite output focusing signal at the output terminal ( 112) to act on the focusing means (24, 23, 25) and which ultimately reduces the nominal focusing voltage present at the output terminal (112) of the combination circuit by a certain factor compared to the second (95) of the two output terminals (93, 95) of the Ve makes stronger section (94). - 1 - 2. A circuit according to claim 1, characterized in that the \ combination circuit (110, 114) contains a number of resistors, of which a first (120) between a first end; terminal (118) and said output terminal (112) is placed, of which a second (122) is placed between a second end terminal (116) and said output terminal (112) and wherein the voltage source (28) for generating the predetermined reference voltage is connected to the first end terminal (118), the circuit branch (97) containing the capacitor (108) is connected between one (93) of the output connections (93, 95) of the amplifier section (94) and the output connection (112) of the combination circuit and wherein the second exit! output connection (95) of the amplifier section (94) is coupled to said second end terminal (116). 3. A circuit according to claim 1 or 2, characterized in that the amplifier section (94) contains amplifier (98, 100) to which by means of a balancing circuit (92, 102, 104, 106) different components of the output signal of the focusing s signal genera to rs (90) are coupled, and generates a first of which (98) the former amplified variable \ output signal, and a second focusing the second-mentioned 'amplified variable output focus signal. \ 4. Circuit according to one of claims 1 to 3, characterized in that that the variable focus signal of the focus signal generator (90) has a predetermined bandwidth and that the gain of each of the amplifiers (98, 100) of the amplifier section (94), if any the components of the output signal of the focusing signal generator (90) coupled to the amplifier and the Resistance values of the resistors of the combination circuit (110, 114) can be chosen so that there is a substantially uniform transfer function between the amplifier section (94) supplied variable focus signal and the detachable assembly at the output terminal (112) Focusing signal essentially independent of the frequency of the variable introduced into the amplifier section Focusing signal over its bandwidth results. j5. Circuit according to Claim 4, characterized in that The predetermined bandwidth of the variable focusing signal fed to the amplifier section (94) changes from 0 Hz j extends up to a certain frequency. ■ 6. Circuit according to one of Claims 1 to 5 / characterized in that the voltage source (28) can be set to generate the reference voltage. J7. Circuit according to one of Claims 2 to 6, characterized in that that the combination circuit (110, 114) contains a potentiometer (114) which is in series with the second j Resistance (122) between the second output terminal (95) j of the amplifier section (94) and the output terminal (112) j the combination circuit (110, 114) is located and the nominal focus voltage, which at the output terminal (112) the combination circuit is pending, to the second output terminal (95) of the amplifier section (94) down. 8. Circuit according to one of claims 1 to 7, characterized in that that the output terminal (112) of the combination I-circuit (110, 114) with a first (24) of a plurality of the Focusing electrodes (23, 24, '25) is connected, while at least one more of the electrodes (23, 25) is connected to a certain further reference voltage. 9. A circuit according to claim 8, characterized in that the '' further predetermined reference voltage of the first-mentioned reference J I ■ voltage of the voltage source (28) is the same and that at least another electrode (23, 25) is connected to the voltage source (28). 10. Circuit according to one of claims 1 to 9, characterized in that that the focusing means are formed by focusing electrodes (23, 24, 25) of a certain intrinsic capacitance are and that the capacitance of the capacitor (108) of said circuit branch (97) is substantially greater than the intrinsic capacitance the focusing electrodes.