GB2273230A - Cancelling radiated electric fields in crt displays - Google Patents
Cancelling radiated electric fields in crt displays Download PDFInfo
- Publication number
- GB2273230A GB2273230A GB9225237A GB9225237A GB2273230A GB 2273230 A GB2273230 A GB 2273230A GB 9225237 A GB9225237 A GB 9225237A GB 9225237 A GB9225237 A GB 9225237A GB 2273230 A GB2273230 A GB 2273230A
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- United Kingdom
- Prior art keywords
- signal
- display
- cancellation
- circuit
- component
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
- H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
- H04N3/16—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by deflecting electron beam in cathode-ray tube, e.g. scanning corrections
- H04N3/18—Generation of supply voltages, in combination with electron beam deflecting
- H04N3/185—Maintaining dc voltage constant
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G1/00—Control arrangements or circuits, of interest only in connection with cathode-ray tube indicators; General aspects or details, e.g. selection emphasis on particular characters, dashed line or dotted line generation; Preprocessing of data
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2229/00—Details of cathode ray tubes or electron beam tubes
- H01J2229/0007—Elimination of unwanted or stray electromagnetic effects
- H01J2229/0015—Preventing or cancelling fields leaving the enclosure
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- Engineering & Computer Science (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- General Physics & Mathematics (AREA)
- Theoretical Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Details Of Television Scanning (AREA)
Abstract
A cathode ray tube display comprises a cathode ray tube display screen 100. A drive circuit 20, 30, 40, 50 generates drive signals for producing a raster-scanned picture on the screen as a function of one or more input signals. One or more of the drive signals also generate a stray electric field that radiates from the display. The display further comprises a cancellation circuit 60, 70, 80, 90 connected to an emitter 120. In operation, the cancellation circuit 60, 70, 80, 90 generates a cancellation signal as a function of said one or more of the drive signals. The emitter 120 radiates a cancellation electric field in response to the cancellation signal to cancel or at least reduce the stray electric field. <IMAGE>
Description
CATHODE RAY TUBE DISPLAY WITH REDUCED ELECTRIC FIELD RADIATION
The present invention relates to a cathode ray tube (CRT) display in which electric field emissions are reduced by signal.
cancellation.
A conventional raster scanned CRT display such as a television receiver or a computer visual display unit comprises drive circuitry that can generate electric fields of sufficient strength to radiate beyond the display. Conventionally, electric field emissions are split into two bands nown as Band I and Band II. Band I extends from 5Hz to 2kHz and Band II extends from 2kHz to 400kHz.
A colour CRT display typically comprises horizontal and vertical electromagnfetic deflection coils arranged on a yoke mounted around the neck of the CRT. In operation, sawtooth currents flow through the deflection coils to scan three electron beams (corresponding to red, green and blue video content) across the CRT screen in a raster pattern. The voltages across the deflection coils reach a peak during the retrace or flyback period of the sawtooth currents. In the vertical deflection coil, the peak voltage is typically several tens of volts. In the horizontal deflection coil, the peak voltage may be as much as lkV. The peak voltage signals are rich in high order harmonics oj ihe corresponding deflection frequencies.The peak voltage signal in the horizontal reflection coil generates an electric field component in Band II and the Fcak voltage signal in the vertical deflection coil generates an electric field component in Band I. The electron beams are accelerated from the neck of the CRT to the screen by a "final anode" or Extra High Tension (EHT) voltage of typically 25kV. The EHT voltage is typically generated by an EHT generator having a step up transformer from a voltage pulse signal synchronised to the line scan signal. In some displays, the voltage pulse signal is derived from the peak voltage across the horizontal deflection coil.
However, in other displays, the voltage pulse signal is generated separately from the line scan signal. The voltage pulse signal generates Band II electric field components radiating from the screen and step transformer respectively In addition, the output impedance of the EHT generator may be sufficiently high that changes in beam current loading through screen content cause modulation of the EHT.
The modulated EHT voltage signal is ri.ch in harmonics of both deflection frequencies and therefore generates electric field components radiating from the CRT screen in both Bands I and II.
Conventionally, a CRT display receives power from the mains via a power cable containing Live and Neutral conductors and, in some cases, an Earth conductor. The conductors carry unbalanced voltage signals.
Therefore, in operation, the cable contributes to the electric field emissions in Band I by radiating an electric field at the mains frequency.
Some efforts have been made in the past to reduce the electric field emissions from CRT displays by enclosing the radiating conductors with grounded metal screens. However, such screens can be expensive to manufacture and also complicate assembly of the displays.
Furthermore, such screens may not provide acceptable electric field reductions in the upper regions of Band II.
In accordance with the present invention, there is now provided a cathode ray tube display comprising: a cathode ray tube display screen; and a drive circuit for generating a drive signals for producing a raster-scanned picture on the screen as a function of one or more input signals, one or more of the drive signals also generating an electric field radiating from the display; characterised in that the display further comprises: a cancellation circuit for generating a cancellation signal as a function of said one or more of the drive signals; and an emitter for radiating a cancellation electric field in response to the cancellation signal to at least reduce the electric field radiating from the display.
The present invention is based on the realisation that a stray electric field radiating from a CRT display can be cancelled or at least reduced by generating, within the display, a cancellation voltage signal of similar shape to but inverted with respect to that which causes the stray electric field. The cancellation voltage signal is connected to an appropriately shaped and positioned emitter formed from electrically conductive material which then radiates an inverse electric field thereby cancelling the unwanted field or at least reducing it to a negligible level.
The surface area of the emitter is preferably maximised within the confines of the display to minimi.se the amplitude of cancellation signal needed to produce an acceptable reduction in the electric field radiated by the display.
The cancellation circuit may comprise a plurality of signal generators each for generating a separate component of the cancellation signal in response to a different one of the drive signals; and a summing amplifier for generating the cancellation signal by adding the components together. The summing amplifier enables components of the cancellation signal to be obtained from each of the various sources contributing to the electric field radiating from the display and thus permits the cancellation field to be conveniently optimised.
In a preferred embodiment of the present invention, the cancellation circuit comprises a first signal generator for generating a first component of the cancellation signal as a function of a drive signal generated by a horizontal deflection circuit of the drive circuit. The first signal generator may comprise a simple transformer for generating the first component of the cancellaton signal as a function of a pulse voltage signal across a horizontal deflection coil of the horizontal scan circuit.Alternatively, the first signal generator may comprise: a peak detector for detecting each peak of the pulse voltage signal; a delay for extending the decay of each peak detected by the peak detector to generate a decaying peak signal; an invertor for inverting the decaying peak signal; and means for adding .he inverted decaying peak signal to the pulse voltage signals to generate the first component of the cancellation signal.
This permits components of the electric field radiating from the display at higher order harmonics of the horizontal deflection frequency to be reduced to acceptable levels through the addition of only a few low cost components.
The cancellation circuit may further comprise a second signal generator for generating a second component of the cancellation signal as a functinn of a drive signal generated by an Extra High Tension voltage generator of the drive circuit. This permits electric field components generated through modulation of the EHT voltage by screen content or screen refreshing to be reduced to acceptable levels. The second signal generator may simply comprise a potential divider connected to a bleed resistor chain of the voltage generator for detecting the second component of the cancellation signal.
Furthermore, the second signal generator may simply comprise a capacitive coupling to a capacitor chain of the voltage generator for detecting the second component of the cancellation signal. This permits any higher frequency electric field components produced through modulation of the EHT to be reduced to an acceptable level.
Preferably, the cancellation circuit also comprises a third signal generator for generating a third component of the cancellation signal as a function of the difference between a pair of voltage signals in a power supply cable of the display. This permits any electric field component generated by unbalanced voltage signals in the mains power supply cable to be reduced to an acceptable level. The third signal generator may simply comprise a sense conductor adjacent the power supply cable for detecting the third component of the cancellation signal by capacitive coupling. For further convenience, the sense conductor may comprise a copper pad on printed circuit board material.
In a particularly preferred embodiment of the present invention, the emitter surrounds the screen. The emitter may be in the form of a electrically conductive frame that can be conveniently housed in the bezel surrounding the screen.
The electric fields radiating from the display can be further reduced by positioning passive screening over the terminals of the horizontal deflection coil on the yoke. The screening is preferably positioned as closely as possible to the terminals. Further improvements in the electric field reduction can be realised by extending the screening from the terminals over one or both sides of the yoke.
Preferred embodiments of the present invention will now be described with reference to the accompanying drawings in which:
Figure 1 is a block diagram of a CRT display of the present invention;
Figure 2 is a waveform diagram of a typical Band II electric field component generated at the horizontal deflection coil before and after cance'lation; Figure 3 is a waveform diagram of a typical Band II electric field component generated by modulati.on of the EHT by a screen of white "H"s against a dark background;
Figure 4 is a waveform diagram of a typical Band II electric field component generated by modulation of the EHT by a blank screen;
Figure 5 is a waveform diagram of a typical Band I electric field component generated by modulation of the EHT by frame refresh;;
Figure 6 is a circuit diagram of a circuit for generating a signal for cancelling the electric field component generated by the horizontal deflection signal at the screen and the deflection coil;
Figure 7 is a circuit diagram of a circuit for generating a signal for cancelling the electric field component generated at the display power supply;
Figure 8 is a circuit diagram of a circuit for generating a signal for cancelling the Band II electric field component generated by modulation of the EHT in the display by screen content;
Figure 9 is a waveform diagram showing the cancellation signal at the output of summing amplifier;
Figure 10 is a waveform diagram showing the Band I electric field radiated from the display with no cancellation; and
Figure 11 is waveform diagram showing the Band I electric field radiated from the display with cancellation.
Referring first to Figure 1, a colour CRT display of the present invention comprises a CRT 100 framed in, and supported by a bezel 130.
Horizontal and vertical deflection coils are disposed around the neck of the CRT in a yoke 110. In use, the CRT is controlled by a drive circuit. The drive circuit comprises horizontal and vertical scan circuits 40 and 30 connected to the horizontal and vertical deflection coils respectively, a video amplifier connected to the electron gun of the CRT 100, and a power supply 20 for supplying power from the mains at 10 to scan circuits 40 and 30 and video amplifier 50 via supply rails Vs and OV. Horizontal deflection circuit 40 comprises an integral EHT generator connected to the final anode of CRT 100.
In operation, power supply 90 receives power from the mains at 10 via a power cable 140 comprising Live and Neutral conductors, L and
N. Line and frame scan circuits 40 and 30 generate line and frame sawtooth currents in the horizontal and vertical deflection coils scan three electron beams across the CRT screen 100 in a raster pattern.
Video amplifier 50 modulates the electron beam intensities with picture information in response to externally supplied red, green and blue video signals. The sawtooth scan currents are synchronised to the input picture information by externally supplied horizontal and vertical synchronisation signals. The voltages generated across the deflection coils reach a peak during the retrace or flyback period of the respective scan currents. In the vertical deflection coil, the peak voltage is typically several tens of volts. In the horizontal deflection coil, the peak voltage may be as much as lkV. The peak voltage signals across the horizontal and vertical deflection coils contribute o the total electric field radiating from the display.
Referring to Figure 2, trace 1 shows the Band II electric field component generated by the lkV peak voltage signal across the horizontal deflection coil and radiating from the coil and screen.
The EHT generator comprises a step up transformer with a secondary winding connected, via a rectifier and smoothing capacitor to the final anode of CRT 100. In operation, the transformer steps up the peak voltage associated with the line sawtooth current to an EHT voltage of around 25kV. The EHT voltage directs the electron beams from the electron gun towards the CRT screen. The output impedance of the EHT generator is in general sufficiently high that changes beam current loading through screen content cause modulation of the EHT at harmonics of the line and frame deflection frequencies. The modulation contributes to the electric field radiating from the display. For example, Figure 3 shows the waveform of the Band II electric field component generated by modulation of the EHT voltage by a screen of white "H"s against a dark background. Figure 4 shows the waveform of the Band II electric field component in generated by modulation of the
EHT voltage by a blank screen. Referring to Figure 5, trace 3 shows the waveform of the Band I electric field component generated by modulation of the EHT by the action of refreshing the screen content at the vertical deflection frequency.
The Live and Neutral conductors L and N of power cable 140 carry unbalanced voltage signals. Therefore, in operation, a Band I electric field component at the mains frequency radiates from the cable 140.
The strength of this component can be reduced by screening cable 140 with a grounded sleeve.
In accordance with the present invention, the screen of CRT 100 is surrounded along its periphery by a electrically conductive emitter 120 in the form of a metal insert located within the bezel. In other embodiments of the present invention, emitter 120 may be constituted by a conductive coating applied to the internal surfaces of bezel 130.
Emitter 120 is connected to the output of a summing and inverting amplifier 80. One input to amplifier 80 is coupled to the output of horizontal scan circuit 40 by circuit block 70. Another input to amplifier 80 is coupled to the output of the EHT generator within the horizontal scan circuit 60 by circuit block 70. A third input to amplifier 80 is coupled to power cable 140 by circuit block 90.
In operation, circuit block 70 generates a cancellation signal of similar shape to the peak voltage signal across the horizontal deflection co-.l.. The cancellation signal generated by circuit block 70 is inverted and amplified by amplifier 80 and applied as a voltage signal to emitter 120. In response to the cancellation signal generated by circuit block 70, the emitter radiates a cancellation electric field comprising a component for cancelling or at least reducing the Band II electric field component produced by the peak voltage signal across the horizontal deflection coils. Referring back to Figure 2. trace 2 shows the Band II electric field component generated by the peak voltage signal across the horizontal deflection coil when the cancellation voltage signal generated by circuit block 70 is applied to emitter 120.
For simplicity, circuit block 70 may be formed by transformercoupling the input of amplifier 80 to the horizontal deflection coil in such a manner that the cancellation signal is generated by transformer action. However, experiment has shown that such transformer action may not produce a cancellation voltage signal of sufficient magnitude or optimum shape at higher horizontal deflection frequencies (greater than 32kHz). Therefore, in preferred embodiments of the present invention, circuit block 70 comprises an active circuit for generating a cancellation signal of optimum shape over a wider range of frequencies. Referring now to Figure 6, a preferred example of such an active circuit comprises a peak detector 200 receiving a scaled down version of the peak voltage signal across the horizontal deflection coil.It will be appreciated that the node at which such a signal can be obtained depends on the topology of horizontal scan circuit 40. However, in a preferred embodiment of the present invention, the scaled down version is readily obtained from a CRT cathode heater circuit (not shown). The output response of peak detector 200 to an input pulse 201 is shown at 202. The output of peak detector 200 is connected to inverting amplifier 210. The output response of inverting amplifier 210 is shown at 203. The output of inverting amplifier 210 is added to the input pulse at node A at the input of summing amplifier 80. Summing amplifier 80 comprises an inverting amplifier 220 which is buffered at its output from emitter 120 by an emitter follower 230. The output of summing amplifier 80 in response to the input pulse is shown at 204.The parameters of the electrical components of peak detector 200 and 210 are selected in such a manner that the waveform shown at 204 is substantially mirrors that shown in trace 1 of Figure 2.
Returning to Figure 1, in operation, circuit block 90 generates a substantially sinusoidal cancellation signal of similar shape to the difference between the voltage signals carried by the Live and Neutral conductors L and N. The cancellation signal generated by circuit block 90 is also amplified and inverted by amplifier 80 and applied as a voltage signal to emitter 120. In response to the cancellation signal generated by circuit block 90, the emitter radiates a cancellation electric field comprising a component for cancelling or at least reducing the Rand I electric field component produced by the unbalanced voltage signals in power cable 140.
Referring now to Figure 7, in a preferred example of the present invention, circuit block 90 comprises a sensor 300 for generating an output signal as a function of the difference between the voltage signals in the Live and Neutral conductors of cable 149. In some embodiments of the present invention, sensor 300 may comprise a sense wire secured at least along side power cable 140 for generating the output signal by capacitive coupling. However, in preferred embodiments of the present invention, sensor 300 comprises a copper pad over which power cable 140 passes for generating the output signal again by capacitive coupling. The copper pad may, for simplicity, be advantageously formed into printed circuit board material carrying circuit block 90. The output signal from sensor 300 is amplified by non-inverting amplifier 310.The output of amplifier 310 is connected to an inverting low pass filter 320 to remove any unwanted high frequency noise from the amplified output signal. The output of low pass filter 320 is inverted by an inverting amplifier 330. The output of inverting amplifier 330 is coupled to node A in Figure 2 at the input of summing amplifier 80. Amplifiers 310, 320, and 330 are formed from operational amplifiers to provide high impedance buffering between each stage of circuit block 90 and thus to provide a relatively noise free sinusoidal output signal at the input to summing amplifier 80. The values of the passive components connected to the operational amplifiers are selected to shape and amplify the sensor output sufficiently to provide cancellation or at least sufficient reduction of the Band I electric field component radiated from the power cable.It will be appreciated that discrete transistor amplifier circuits may be used instead of one or more of the operational amplifier circuits.
In operation, circuit block 60 generates a cancellation signal of similar shape to the modulation of the EHT voltage by both the screen content and the action of refreshing the screen content at the vertical deflection frequency. The cancellation signal generated by circuit block 60 is amplified by amplifier 80 and applied as a voltage signal to emitter 120. In response to the cancellation signal generated by circuit block 60, the emitter 120 radiates a cancellation electric field comprising a component for cancelling or at least reducing the electric field components in both Band I and
Band II produced by the modulation of the EHT voltage.
Referring now to Figure 8, in a preferred embodiment of the present invention, circuit block 60 comprises a voltage sense circuit 400 comprising a sense resistor R1 connected between the bleed resistor chain on the secondary side of EHT generator and ground. In operation, as is well-known, the bleed resistor chain acts as a potential divider from which fractions of the EHT voltage are tapped for biasing focus and Grid electrodes of the electron gun in CRT 100.
The voltage across R1 varies with variations in the EHT voltage and serves as the input to emitter follower 400. The output of emitter follower 400 is connected to the input of non inverting buffer 410.
The output of buffer 420 is connected to a three pole low pass filter 420. The output of filter 420 is connected to a high gain inverting amplifier 430. The output of amplifier 430 is inverted by an invertor 440 and connected to node B of circuit block 90 shown in Figure 7. In operation, emitter follower 400 and buffer 410 scale down the voltage signal sensed across R1 before it reaches the input to filter 420 and also buffer the bleed resistor chain from filter 420. Filter 420 removes high requency noise from the scaled down signal. The filtered signal is then amplified by amplifier 430, inverted by invertor 440, and combined with the output signal from low pass filter 320 in circuit block 90 (see Figure 7) at the input, Node B, of invertor 330.
The inverted sum of the output signal from filter 320 and invertor 440 at the output of invertor 330 is combined with the output signal from circuit block 70 at the input of summing amplifier 80 (see Node A in
Figure 6). Referring back to Figure 5, trace 4 shows the input signal to summing amplifier 80 from circuit block 60 alone. Figure 9 shows the cancellation signal at the output of summing amplifier 80 when receiving inputs from circuit blocks 60, 70, and 90.
Referring again to Figure 8, in some CRT displays, there may be so much high frequency noise in the signal sensed across R1 that the
Band I frequency component of the EHT modulation signal can only be recovered at the expense of the Band II frequency component of the EHT modulation signal being removed altogether by filter 420. Therefore, in a particularly preferred embodiment of the present invention, the
Band II frequency component of the EHT modulation signal is detected by capacitive coupling at the bleed resistor chain. The detected Band
II component is then added to Band I component at the input to invertor 440.
Figure 10 shows the Band I electric field component radiated from the display with no cancellation. Figure 11 shows the Band I electric field component radiated from the display when the signal shown in Figure 9 is applied to emitter 120.
In the preferred embodiments of the present invention hereinbefore described, emitter 120 is located within the bezel 130 of the display. However, it will be appreciated that in other embodiments of the present invention, emitter 130 may be located at or near the top, bottom, back or sde of the display. It will also be appreciated that, in other embodiments of the present invention, there may be a plurality of emitters each arranged to cancel a different component of the electric field radiating from the display in response to a different cancellation signal. In the preferred embodiments of the present invention hereinbefore described, no cancellation field component is generated to cancel the Band I electric field component produced by the peak voltage across the vertical deflection coil.
However, it will be appreciated that other embodiments of the present invention may include a circuit block connected to vertical scan circuit 30 for producing a such a cancellation field component should the Band I electric field component radiating from the vertical deflection coil make a significant contribution to the total electric field radiated from the display. In the preferred embodiments of the present invention hereinbefore described, the EHT generator was integral to the horizontal scan circuit. However, in other embodiments of the present invention, the EHT generator may be separated from the horiòntal deflection circuit in the interests of providing, for example, closed loop EHT regulation. Preferred embodiments of the present invention have been hereinbefore described with reference to a colour CRT display. However, it will now be appreciated that the present invention is equally applicable to monochrome CRT displays.
Claims (13)
1. A cathode ray tube display comprising: a cathode ray tube display screen (100); and a drive circuit (20,30,40,50) for generating drive signals for producing a raster-scanned picture on the screen (100) as a function of one or more input signals, one or more of the drive signals also generating an electric field radiating from the display; characterised in that the display further comprises: a cancellation circuit (60,70,80,90i for generating a cancellation signal as a function of said one or more of the drive signals; and an emitter (120) for radiating a cancellation electric field in response te the cancellation signal to at least reduce the electric field radiating from the display.
2. A display as claimed in claim 1, wherein the cancellation circuit (60,70,80,90) comprises a plurality of signal generators (60,70,90) each for generating a separate component of the cancellation signal in response to a different one of the drive signals; and a summing amplifier (80) for generating the cancellation signal by adding the components together.
3. A display as claimed in claim 2, wherein the cancellation circuit comprises a first signal generator for generating a first component of the cancellation signal as a function of a drive signal generated by a horizontal deflection circuit (40) of the drive circuit (20,30,40,50,).
4. A display as claimed in claim 3, wherein the first signal generator (70) comprises a transformer for generating the first component of the cancellation signal as a function of a pulse voltage signal across a horizontal deflection coil of the horizontal scan circuit (40).
5. A display as claimed in claim 4, wherein the first signal generator comprises: a peak detector (200) for detecting each peak of the pulse voltage signal; a delay (200) for extending the decay of each peak detected by the peak detector to generate a decaying peak signal; an invertor for inverting the decaying peak signal (210); and means for adding the inverted decaying peak signal to the pulse voltage signals to generate the first component of the cancellation signal.
6. A display as claimed in any of claims 2 to 5, wherein the cancellation circuit (60,70,80,90) comprises a second signal generator (60) for generating a second component of the cancellation signal as a function of a drive signal generated by an Extra High Tension voltage generator (40j of the drive circuit (20,30,40,50).
7. A display as claimed in claim 6, wherein the second signal generator (60) comprises a potential divider connected to a bleed resistor chain of the voltage generator (40) for detecting the second component of the cancellation signal.
8. A display as claimed in claim 6, wherein the second signal generator (60) comprises a capacitive coupling to a bleed resistor chain of the voltage generator (40) for detecting the second component of the cancellation signal.
9. A display as claimed in any of claims 2 to 9 wherein the cancellation circuit (60,70,80,90) comprises a third signal generator (90) for generating a third component of the cancellation signal as a function of the difference between a pair of voltage signals in a power supply cable (140) of the display.
10. A display as claimed in claim 9, wherein the third signal generator (90) comprises a sense conductor adjacent the power supply cable for detecting the third component of the cancellation signal by capacitive coupling.
11. A display as claimed in claim 10, wherein the sense conductor comprises a copper pad on printed circuit board material.
12. A display as claimed in any preceding claim, wherein the emitter surrounds the screen (120).
13. A display as claimed in claim 12, wherein the emitter is in the form of a electrically conductive frame attached to a bezel housing the screen.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9225237A GB2273230A (en) | 1992-12-02 | 1992-12-02 | Cancelling radiated electric fields in crt displays |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9225237A GB2273230A (en) | 1992-12-02 | 1992-12-02 | Cancelling radiated electric fields in crt displays |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9225237D0 GB9225237D0 (en) | 1993-01-20 |
| GB2273230A true GB2273230A (en) | 1994-06-08 |
Family
ID=10726028
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9225237A Withdrawn GB2273230A (en) | 1992-12-02 | 1992-12-02 | Cancelling radiated electric fields in crt displays |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2273230A (en) |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2293299A (en) * | 1994-09-15 | 1996-03-20 | Ibm | Electric field emission reduction system |
| GB2306872A (en) * | 1995-10-27 | 1997-05-07 | Samsung Electronics Co Ltd | An electromagnetic field shielding circuit for a display |
| GB2309366A (en) * | 1996-01-16 | 1997-07-23 | Samsung Electronics Co Ltd | Device for cancelling stray electric fields of CRT displays |
| EP0774743A3 (en) * | 1995-11-15 | 1998-04-29 | Nanao Corporation | Apparatus for suppressing field radiation from a cathode ray tube |
| GB2322270A (en) * | 1997-02-15 | 1998-08-19 | Lg Electronics Inc | Circuit for eliminating radiated electric field noise in a video display |
| GB2332842A (en) * | 1997-12-23 | 1999-06-30 | Daewoo Electronics Co Ltd | Apparatus for reducing alternating electric field emission in video display device |
| EP1026881A1 (en) * | 1999-02-05 | 2000-08-09 | Nokia Display Products Oy | A method and a device for reducing an electric field produced by a cathode ray tube in its surroundings |
| EP1172951A2 (en) * | 2000-07-12 | 2002-01-16 | Hirschmann Electronics GmbH & Co. KG | Radio frequency apparatus with interference compensation |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5151635A (en) * | 1991-06-20 | 1992-09-29 | Apple Computer, Inc. | Apparatus and method for reducing the magnitude of time varying electric fields in CRT displays |
-
1992
- 1992-12-02 GB GB9225237A patent/GB2273230A/en not_active Withdrawn
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5151635A (en) * | 1991-06-20 | 1992-09-29 | Apple Computer, Inc. | Apparatus and method for reducing the magnitude of time varying electric fields in CRT displays |
Cited By (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2293299A (en) * | 1994-09-15 | 1996-03-20 | Ibm | Electric field emission reduction system |
| US5534756A (en) * | 1994-09-15 | 1996-07-09 | International Business Machines Corporation | Electric field emission reduction system |
| GB2306872A (en) * | 1995-10-27 | 1997-05-07 | Samsung Electronics Co Ltd | An electromagnetic field shielding circuit for a display |
| GB2306872B (en) * | 1995-10-27 | 2000-03-29 | Samsung Electronics Co Ltd | An electromagnetic field shielding circuit for a display |
| US5965987A (en) * | 1995-11-15 | 1999-10-12 | Nanao Corporation | Apparatus for suppressing electric field radiation from a cathode ray tube |
| EP0774743A3 (en) * | 1995-11-15 | 1998-04-29 | Nanao Corporation | Apparatus for suppressing field radiation from a cathode ray tube |
| US6049173A (en) * | 1995-11-15 | 2000-04-11 | Nanao Corporation | Apparatus for suppressing electric field radiation from a cathode ray tube |
| GB2309366B (en) * | 1996-01-16 | 1999-12-29 | Samsung Electronics Co Ltd | Device for cancelling electric field of display |
| GB2309366A (en) * | 1996-01-16 | 1997-07-23 | Samsung Electronics Co Ltd | Device for cancelling stray electric fields of CRT displays |
| GB2322270A (en) * | 1997-02-15 | 1998-08-19 | Lg Electronics Inc | Circuit for eliminating radiated electric field noise in a video display |
| GB2322270B (en) * | 1997-02-15 | 1999-06-09 | Lg Electronics Inc | Circuit for eliminating radiated electric field noise in a video appliance |
| US5986406A (en) * | 1997-02-15 | 1999-11-16 | Lg Electronics Inc. | Electric field noise eliminating circuit in a video display appliance |
| GB2332842A (en) * | 1997-12-23 | 1999-06-30 | Daewoo Electronics Co Ltd | Apparatus for reducing alternating electric field emission in video display device |
| EP1026881A1 (en) * | 1999-02-05 | 2000-08-09 | Nokia Display Products Oy | A method and a device for reducing an electric field produced by a cathode ray tube in its surroundings |
| US6351084B1 (en) | 1999-02-05 | 2002-02-26 | Nokia Display Products Oy | Method and a device for reducing an electric field produced by a cathode ray tube in its surroundings |
| EP1172951A2 (en) * | 2000-07-12 | 2002-01-16 | Hirschmann Electronics GmbH & Co. KG | Radio frequency apparatus with interference compensation |
| EP1172951A3 (en) * | 2000-07-12 | 2003-07-09 | Hirschmann Electronics GmbH & Co. KG | Radio frequency apparatus with interference compensation |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9225237D0 (en) | 1993-01-20 |
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