MXPA01007885A - Control of scanning velocity modulation at multiple scanning frequencies - Google Patents

Abstract

A method for controlling scan velocity modulation in a video display apparatus operable at a plurality of horizontal scanning frequencies. The method comprises the steps of, generating respective scanning velocity modulation signals from signals having a plurality of horizontal scanning frequencies and coupled for display by said apparatus, and, selectively controlling an amplitude of each respective scanning velocity modulation signal to a predetermined range of amplitudes.

Description

SPEED MODULATION CONTROL PE EXPLORATION MULTIPLE EXPLORATION FREQUENCIES FIELD OF THE INVENTION This invention relates to scanning speed modulation (SVM) systems, and more particularly to the automatic control of scanning speed modulation signal amplitude at multiple scanning frequencies.

BACKGROUND OF THE INVENTION It is well known that in a representation of cathode ray tubes, an improvement in the apparent sharpness of the image can be obtained by modulating the scanning speed of a beam of electrons according to the derivative of the luminance portion of the presentation signal. . This derivative signal, or scanning speed signal, may be derived from the luminance portion of the video signal and identify when variations of the scanning light beam rate should be employed. The reduction of the scanning speed of the electron beam causes a greater number of electrons to reach a particular point in the screen presentation, resulting in the brilliance of the presentation of the video monitor in that particular place on the screen or presentation. Conversely, by accelerating the scanning speed in a particular portion of the screen, a darkening of the presentation occurs. In this way, the horizons of the horizontal regime can be visually improved through variations in the intensity of the presentation in edge transitions caused by the variation of the speed of the electronic beam. This method to improve the image sharpness has advantages over a pi aspect with the improvement of image sharpness, such as avoiding fluorination d elements of high peak luminance image (white) and avoiding the improvement of video noise that occurs within of the bandwidth in peak signals. In Japanese patent 61-099467 and PAJ vol. 010, No. 279 s describes a multi-scan television receiver, the cu employing an exploded beam speed modulation modulating the voltage applied to a fourth grid of the CRT. The reference also teaches that the velocity modulation voltage applied to the CRT grid is also applied to a peak-to-peak detector (83). The output of the detector (83) is coupled to an AGC circuit (82), which controls the amplitude of the velocity modulation voltage applied to the CRT. In this manner, a closed circuit is formed which maintains the peak-to-peak value of the speed modulation voltage at a prescribed amount. The separate horizontal synchronizations are fed discriminator (84) which produces an output signal that is applied to control a time constant of the AG circuit A TV receiver, which employs scanning beam speed modulation through a deflection coil magnetic is described in the US patent No. 5,982,449 and EPO 784 4 A2. A signal for the derivation of the signal SVM is coupled through a digital filtering means (12), which is programmed through the CPU (3) based on the information derived from the content format of the input signal selected for the presentation. In this way, the sharpness of the presented image is adapted to the selected input signal. This reference also describes the use of an SVM driving current feedback circuit where the driving current is converted to a digital signal coupled to the CPU (3) to change the characteristic of the programmable filtering means (12). SVM systems such as those described above are all known for use in television systems, eg they are typically not used in computer monitors. The SVM systems are generally not very suitable for using monitors that present video signals of several different formats such as VGA to SVGA, which can use alternative scanning frequencies. The horizont scanning speeds of these video formats can be at any time 2 2.4 times as large as a NTSC horizont scan frequency. With the convergence of television and computer monitor, SVM is starting to be used under much more demanding conditions. For example, multimedia monitors are being made available that are also capable of handling computer formats. This presents important problems regarding the use of SVM. Not only are the horizontal scanning speeds of computer monitors larger than conventional NTS scanning speeds, but new high definition television scanning speeds defined by the Advanced Television System Committee (ATSC) standards can also be as low as 2.14. times larger than NTSC scanning speeds. Thus, for example, if NTSC television systems are referred to as having a 1H scanning frequency, then it is said that the VGA, HDTV and SVGA systems have scanning frequencies of 2H, 2.14H and 2.4H, respectively.

A problem with the use of SVM technology in relation to presentations that are going to be used for video signals at a variety of different scanning speeds, is that there is usually a doubling in the amplitude of the SV signal for each eighth increment in the frequency of he explored horizontally. For example, the SVM signal generated from the derivative of a luminance component of a signal of a scanning frequency 2H will generally be 6 dB greater than the SV signal that is generated by an NTSC signal (1H). This magnitude scale can result in an SVM signal that is less than optimal. In particular, when using SVM systems and presentations of fixed scanning speed, the application of speed modulation of scanning to any video signal is optimized, having a previously determined scale of amplitudes for signal processing at scanning speed. particular to which the presentation is used. However, when a presentation can operate multiple scanning speeds, it is very difficult to optimize the processing of the SVM signal, since the SVM amplitude scale can at least be duplicated for the various video signal formats. For example, if the speed of scanning modulation in a multiple speed scan monitor, optimized for 1H video signals, then the amplitude of excess SVM signals may result in fluorescence or other undesirable artifacts when it is required to work with a 2H video signal. Similarly, when the scanning speed modulation, in a multi-speed scan monitor, is optimized for 2H video signals, the amplitude d of the SVM signal will be too small to provide sufficient image enhancement for 1H signal inputs. In this way, it is desirable to determine a way in which it is ensured that a previously determined scale of SVM signal amplitudes is used, without considering the scanning frequency rate d a particular video presentation format.

COMPENDIUM OF THE INVENTION In a method of the invention, the signal amplitude of the scanning speed modulation is controlled at a plurality of horizontal scanning frequencies. The method comprises the steps of generating respective scanning velocity modulation signals from signals having a plurality of horizontal scanning frequencies coupled for presentation by said apparatus, and selectively controlling an amplitude of each respective scanning signal modulation signal. at a predetermined scale of amplitudes.

According to one aspect of the invention, the gain amount applied to the reduced scanning modulation signal as the frequency of the horizontal scanning frequency is increased. For example, the gain can be reduced by 6dB for each eighth increment in the horizontal scan frequency in order to compensate for the differences introduced by the associated horizontal scan frequency c in the various video formats. According to another aspect of the invention, the horizontal scanning frequency is determined by a scanning frequency detector circuit. In this case, the control signal is a DC voltage generated by said scan frequency detector which varies proportionally as a function of the horizontal scan frequency. This DC voltage can then be used to directly control an amplification gain. Alternatively, the control signal can be a digital command signal generated by a microprocessor responsive to horizontal scanning frequency selection dat. In that case, digital command signal is preferably used to selectively vary an SVM gain register to control amplitude of the SVM signal. In an alternative embodiment, the amplifier control signal SVM may be a digital command signal generated by microprocessor sensitive to presentation source selection data. In that case, the command signal digit is preferably used to selectively vary an SVM gain register to control the SVM signal amplitude.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph of an SV signal amplitude versus scan frequency. Figure 2 is a block diagram of an automatic control gain system SVM of the invention, for controlling an amplitude of signal SVM, Figure 3 is a detailed circuit diagram showing the modality of an SVM circuit with a control system of automatic gain according to Figure 2. Figure 4 is a block diagram of an alternative embodiment of invention using an automatic gain control system SVM according to Figure 2. Figure 5a shows an SVM signal output of differentiator for a 1H video signal. Figure 5b shows the signal of Figure 5a after amplitude control. Figure 5c shows an SVM signal output from a differentiator for a 2H video signal. Figure 5d shows the signal of Figure 5c after amplitude control.

DETAILED DESCRIPTION Figure 1 is a graph showing the amplitude of signal SV against the scanning frequency in a presentation that can operate at multiple scanning frequencies. The y-axis represents amplitude of the SVM signal, for example, in decibles, when it is generated through a conventional SVM differentiator circuit. The axis represents the horizontal scan frequency of an input video signal. The standard NTS horizontal scanning frequency is denoted by 1H, thus, 2H denotes a scanning frequency that is one-eighth higher, for example as used for a 640 x 480 video format. The Figure illustrates that the signal amplitude SVM is increased approximately 6dB for video signals having horizontal scanning frequencies in the 2H or higher frequency band. In this way, an SVM circuit designed for specific operating parameters, such as clamping from peak to peak noise nucleation with a predetermined scale of SMV signal amplitudes with 1H signals, can be directed when processing SVM signals derived from video signals in the 2H frequency band. Overriding an SVM system for example, may present an output signal hold or activation SVM output, the output impeller amplifier operating in a power limiting condition, with the addition of continuous peak-to-peak clamping activation and loss of improvement of sharpness in image. Alternatively, if the SVM circuit is designed for optimal operation with a scale of SV signal amplitudes derived from 2H video signals, but receives a 1H signal, SVM signal amplitude will be too small, possibly falling to exceed the signal scale for nucleation of noise and certainly resulting in an improvement of insufficient image. Figure 2 illustrates a block diagram of an open circuit SVM automatic gain control system, for adjusting the SVM signal amplitude to be on a predetermined amplitude scale when operating with vid formats having a different spatial resolution and different scanning frequency. In Figure 2, a video signal, which includes horizontal frequency information is applied to the drift circuit 1. In the branch circuit 1, the luminance component of the video signal is differentiated to produce an SVM signal. The branch circuit output 1 is coupled to the variable gain amplifier 2. There, the SVM signal is amplified and is used to generate a deflection current in the SVM coil to modulate the beam scanning speed. According to a preferred embodiment of the invention, scanning frequency detector 3 makes use of a portion of the horizontal scanning frequency information containing input signal to provide an indicator of a probable spatial frequency content of the input signal. In simple terms, Figure 1 shows the increase in amplitude of the SVM signal that occurs with a doubling of the input frequency. that an illustrative ATSC image is capable of at least duplicizing the horizontal resolution of an NTSC signal, an open circuit feeding the amplitude control signal SVM, based on horizontal synchronization frequency determination provides a reliable indication of the presented image spectral content. To control the gain or amplitude of the SVM signal generated by the amplifier 2, the horizontal scan frequency verified and when it is increased above 1H, the control signal d feed advance of the scanning detector d frequency 3 causes the signal SVM of the amplifier 2 is reduced in amplitude. In addition, the gain of the open circuit SVM signal and / or the amplitude control can generally be applied in accordance with a complementary or inverse transfer function to that illustrated in the Figure. 1. In this manner, or the amplitude SVM, preferably divided into signal having double frequency scanning regimes, in reverse, the amplitude SVM or gain can similarly be increased for a corresponding reduction in the horizontal scanning frequency. Figure 3 is a detailed circuit diagram showing the modality of the automatic gain control system SVM of Figure 2. As shown in Figure 3, a luminance signal with negative forward horizontal synchronization is applied to the circuit input. This signal can be provided by horizontal synchronization, luminance (Y), with synchronization. The input video signal passes through the coupling capacitor AC C1, the cu is coupled to the base of the transistor Q2, an emitter follower. The resistors R10, R11 and R12 form a potential divider and set the base voltages of transistors Q2 and Q4. The collector electrode d transistor Q2 is coupled to a potential power source + VA, typically 24 volts, and its emitter is coupled through the resistor R13 to the emitting electrode of the base amplifier connected to ground. The base electrode of transistor Q4 is deviated from the junction of resistors R11 and R12 and the decoupling of the tier through capacitor C2. The input video signal is differentiated in the control circuit of the transistor Q4 by the parallel configured network comprising, the capacitor C5, inductor L2 and damper resistor R12, thus producing an SDM signal. The differentiating circuit output is coupled through a series d capacitor C3 and resistor R20, connected, to the base of transistor Q. A resistor R21 is coupled to the junction of capacitor C3 and resistor R20 to bypass the base of transistor Q6 at the same time. potential like that of transistor Q8. The transistors Q6 and form a differential amplifier, wherein the gain is set by resistors R26 and R28, R36 and the actual current of the current source transistor Q7. The resistors R25, R33 and R34 form a potential divis which provides deviated voltages for the transistors Q6, Q7 and Q8, where the transistor Q6 is diverted through the resistors R20 and R21 and the transistor Q8 is diverted through the resistor R30. The junction of resistors R21, R30, R33 R34 is uncoupled to ground by capacitor C14. Similarly, capacitor C11 decouples the junction of resistors R25 and R33 ground. The collecting electrode of Q6 is coupled to supply voltage + VA, and the collector electrode of transistor Q8 is coupled to the supply voltage + VA through the collector load resistor R36. In addition, the output of the SVM signal of the differential amplifier is taken from the collector electrode of the transistor Q8. By moving the scanning frequency detector portion of the circuit, the video signal with negative forward horizontal frequency information is applied through the capacitor C6 to the base electrode of the PNP transistor, Q3, which is deflected by the resistor R that It is connected to earth. The transistor Q3 is configured with a negative pulse detector, which outputs in its collector, or positive forward horizontal velocity pulse signal derived from the horizontal synchronization frequency of the video input signal. The emitter of transistor Q3 is coupled to the potential operation + VA. The resistors connected in series R16 and R17 form a collector load for transistor Q3. Positive pulses d collector are coupled through resistor R17, which determined a load current for capacitor C8. During the intervention pulse periods, capacitor C8 is discharged to ground through resistor R16, thus forming a signal of serrated teeth of horizontal regime. The waveform of serrated teeth is then applied to the base electrode of transistor Q5, a follower of emitter that dampens the sawtooth signal. The electrode of transistor Q5 is coupled to supply voltage + VA, and emitter electrode is coupled through resistor R15 to ground. transmitter of transistor Q5 is also coupled to resistor R18 and capacitor C7, which forms a low pass filter that converts sawtooth signal to a DC voltage having a proportion value to the horizontal synchronization frequency of the input video signal , that is, the higher the horizontal frequency the higher the resulting DC voltage. This frequency-dependent voltage D is coupled to the base of the emitter follower of the transistor Q10, which supplies a current I through the resistor R19 to the junction of the resistor R27 and the emitter d of the current source of the differential amplification source , Q7. The collector electrode of transistor Q7 is coupled to the junction of resistors R26 and R28, and the emitter electrode is coupled to ground through resistor R27. As the DC volta, from the scanning frequency detector, increases, the voltage at the emitter of the transistor Q7 increases causing the potential base emitter to be reduced, which at its v reduces the collector current. In this way, the current supply to the differential amplifier is reduced causing the SVM output signal in the collector of the transistor Q8 to be reduced in amplitude. The reduction in the source current of the differential amplification causes a reduction in the gain of the signal SV In this manner, the differential amplifier comprised of the transistors Q6, Q7 and Q8 is configured as a variable gain amplifier, wherein the signal amplitude output is automatically reduced when the horizontal scanning frequency of the presentation signal is increased. It can be readily appreciated that the embodiment of the invention in Figure 2 is not limited to the precise arrangement shown that there are other alternatives for implementing the contr system according to the present invention. In fact, the present invention can be implemented using any circuit that detects a horizontal scanning frequency of a video signal and that modifies the SVM signal amplitude to maintain optimal operation of SVM at different frequencies • scanning. Figure 4 shows one such alternative modality. In Figure 4, there is shown input stage 10 with a plurality of selectable video input sources per user, including several 1H video sources such as mixed vid NTSC, (VID 1, 2, 3, 4) video S ( SVID 1, 2, 3) and component video (Y Pr Pb). In addition, the input stage 10 typically has one or more input connections providing user selectable and higher scanning frequency video sources, including VGA 1, VGA 2, and HDTV. It should be noted that the invention is not limited in this respect. Other video sources can also be provided and not all identified video sources need to be supplied. In a further embodiment shown in Figure 4, when user selects an input is at an NTSC input or ot input 1H, the horizontal synchronization pulses (H) and the vertical synchronization pulses (V) are extracted by video processor, illustrated by the integrated circuit 11 illustrativ from the composite video or luminance signal components of the selected 1H source. The video processor 11 then output to the synchronization pulses H and V separated from the 1H source to the H &amp selector switch; V 12 for selection and coupling to the microprocessor 13. The processing aspects of the video processor 11 can be provided by an integrated circuit, for example, of type TA1276N, which is commercially available from Toshiba. However, the invention is limited in this respect, and those skilled in the art will recognize that a discrete component circuit or any other commercially available integrated circuit having similar capacity can also be used for this purpose. An upconverter 16 can be provided between the stage 10 and the video processor 11. The upstream processor 16 used to convert NTSC video signals or other 1H video signals to 2H video signals and, for example, can be implemented by doubling the line. As shown in the Figure, the upconverter 16 is controlled by the microprocessor 13 through a data bus, for example, it uses an I2C protocol, based on a determination of the horizontal input frequency selected by the microprocessor 13. Referring again to block 10 of Figure 4, input signals 2H or higher can provide separate horizontal and vertical synchronization pulses, which when selected, are directly coupled to the selector switch H via the data bus and B 12, finally to the microprocessor 13 for further processing. In the case of these 2.4H video sources, the video processor 1 will preferably receive the video signals of the component (R, B) as shown, with the selection within the processor 1 controlled by the microprocessor 13 through the busbar lzC. As described, the microprocessor 13 in various form is coupled to provide control through the busbar l2C. The microprocessor 13, for example, can be an ST 9296 IC which is commercially available Microelectronics. However, the invention is not limited to this respect and any other similar capacid processor can be used for this purpose. As illustrated in Figure 4, the microprocessor 13 synchronization receivers H and V selected from selector switch H and V 12 to determine the horizontal frequency of video source selected for SVM display and enhancement. The microprocessor 13 can determine the horizontal frequency of the presentation signal selected through the number of methods. For example, as described with reference to Figure 2, a frequency-dependent voltage can be generated, with the resulting DC value measured by the microprocess 13 and compared to stored values to determine the horizontal frequency of the selected source. In a second method, the microprocessor 13 can measure a duration or width of a selected horizontal synchronization pulse element to determine the horizontal scanning frequency f. In an additional method, since the microprocessor 13 is sensitive to selection by the user of the presentation signal input, the logic indicating the horizontal frequency can, for example, be implemented by hard wiring or a consult table to associate the signal of input selected by the user with specific input signal format and scanning frequency In addition, since several presentation signals are connected presentation device through different mechanical connectors, the determination of the horizontal frequency can be derived from the selected input receptacle . For example, the NTSC signals, the S video signals and the SVGA ca one signals are introduced to the presentation through different non-interchangeable connectors. In this way, based on one a combination of the various horizontal frequency determination methods, the microprocessor 13 is preferably programmed to send a specific horizontal frequency gain or amplitude control command through the data bus to the processor. video 11. Video processor 11 preferably contains an SVM generator with a gain signal amplitude or SVM output controlled response control of command data received from microprocessor 13 through bus l2C. For example in the case of CI of type TA 1276N previously observed, the signal SVM is controlled by a 2-bit register that can attenuate SVM signal by OdB, -6dB, -9dB, in addition to, the ability to inhibit the SVM signal output. The microprocessor 13 is preferably programmed such that the SVM signal is not attenuated, that is, gain is set to OdB when the vide sources 1H are determined, and for sources 2H the microprocessor 13 generates control data that provides a 6dB reduction in the SV signal gain Video sources with scanning rates that are preferably attenuated according to the transfer function illustrated in Figure 1. In general 1, for the eighth increment in scanning frequency, signal S is attenuated by 6dB to determine the SVM signal within a predetermined scale of amplitudes. As shown in FIG. 4, the SVM signal of controlled amplitude is coupled to the impeller S 14 and finally to the SVM coil 15 to produce a substantially similar image enhancement, independent of the scanning frequency for presentation. As previously described, the NTSC video signals other 1H video signals can be converted to vine signals 2H by the up-converter 16. In this way, the signals with inherently smaller image detail, or spatial resolution are converted and receive detectable attributes indicative of 2H video signals. However, although said up-converted signals can be detected with video signals 2H, the image detail is not comparable to that of a signal that originated as a 2H signal. In simple terms the upconversion process can not add missing image detail of the original 1H image. In this way it can be appreciated that although these signals can be detected as 2H video signals, the presented image can benefit from a higher level of SVM improvement than that provided for original 2H signals. In this way, when the upconverting 16 is enabled, the microprocessor 13 can determine, from an illustrative look-up table or similar amplitude control value suitable for the improvement of SVM, said images converted in ascending form. For example, an image converted with the up-converter can receive amplitude value SVM between those provided for 1 H and 2 H frequency sources. Figures 5 (a), 5 (b), 5 (c) and 5 (d) illustrate the problem identified by the applicants and the control solution advantage described herein. Figure 5 (a) shows an example of an SVM signal at an output of a differentiator or signal generator SVM. SVM signal was formed by the differentiation of a 1H luminance sig component, comprising a 100 IRÉ pulse with nanoseconds of increment and decay times. Figure 5 (shows an SVM signal formed by the differentiation of a 2H video signal comprising a 100 IRÉ pulse with an increase of 30 nanoseconds and decay times The illustrative waveforms of Figures 5 (a) and 5 (c) are selected to be visual, when displayed, both signals are illustrated c reference to the output of the derivative circuit 1 of Figure 2. As described above, the SVM signal resulting from the source 2 is illustrated with approximately double the amplitude of the SVM signal from source 1H.

Referring now to Figures 5 (b) and 5 (d), the effects of the advantageous automatic control system are shown according to a preferred embodiment of the invention. Figure 5 (b) illustrates amplitude of the output signal SVM 1H as measured from the output of a variable gain amplifier 2 in Figure 2. Figure 5 (d) shows the amplitude of the output signal SVM 2 similarly measured at the output of the variable gain amplifier 2 in Figure 2. As can be seen from the waveforms illustrated in Figures 5 (b) and 5 (d), the amplitude of output signals SVM 1H and 2H are approximately the same. this way, the automatic gain control system SV maintains an optimal amplitude scale for the scanning speed modulation signal at multiple scanning frequencies

Claims (14)

1. A video display apparatus, operating at a plurality of scanning frequencies and including scanning beam speed modulation, comprising: a controllable scanning speed modulation signal amplifier for generating a deflection signal; scanning sensitive to a signal scanning speed modulation; and means for generating a control signal coupled to an amplifier to open the circuit control of said scanning velocity modulation signal at amplitude sensitive to selected frequencies of said plurality of scanning frequencies.

2. The video display apparatus according to claim 1, wherein the control signal reduces the scanning speed modulation deflection signal amplitude in accordance with an increase in the scanning speed of said plurality of scanning frequencies. The method according to claim 1, comprising the additional step of: selecting a frequency different from the plurality of horizontal scanning frequencies and reducing the amplitude of the scanning speed modulation deflection signal according to a different frequency having a frequency of horizontal scanning greater than a horizontal scanning frequency a previous selection. 4. A method for controlling the scanning speed modulation in a video display apparatus that can operate at a plurality of horizontal scanning frequencies, comprising the steps of: generating, from a signal coupled for presentation through said apparatus , a deflection signal of scanning velocity modulation with an amplitude scale representative of a horizontal scan signal frequency coupled for presentation; determine the horizontal scanning frequencies of the signal coupled for presentation; generating a control signal according to the determined scanning frequency to maintain the scanning speed modulation signal within the amplitude scale substantially independent of the horizontal scanning frequency of the coupled signal for presentation. The method according to claim 4, wherein step of generating control signal comprises the steps of: representing the horizontal scanning frequency determined with a DC voltage that proportionally varies as a function the determined horizontal scanning frequency. 6. The method according to claim 5, comprising the step of: controlling the amplitude of the scanning velocity modulation signal responsive to the DC voltage. The method according to claim 4, wherein step of generating control signal comprises the step of: representing the horizontal scanning frequency determined with a digital signal generated by a microprocessor. The method according to claim 7, comprising the step of: controlling the amplitude of the scanning speed modulation signal sensitive to the digital signal. 9. A video display apparatus with scanning speed modulation and operating at a plurality of scanning frequencies, comprising: means for generating a scanning speed modulation signal from a presentation signal coupled apparatus, the signal from scanning speed modulation having an amplitude scale; means for determining the horizontal scanning frequency of the presentation signal; means for generating a control signal responsive to a determined horizontal scan frequency; and a differential amplifier responsive to the control signal for selectively controlling the scanning rate modulation signal to maintain the scanning velocity modulation signal within the amplitude scale substantially independent of the determined horizontal scan frequency. 10. The video presentation apparatus according to claim 9, wherein the means for selectively controlling reduce the amplitude of the scanning velocity modulation signal according to a determined horizontal scanning frequency frequency increase. 11. The video display apparatus according to claim 9, wherein the means for selectively controlling the amplitude of the scanning velocity modulation signal for each eighth increment in the determined horizontal scan frequency. The video display apparatus according to claim 9, wherein the control signal representing determined horizontal scanning frequency is a voltage D that varies proportionally as a determined horizontal scanning frequency function. The video display apparatus according to claim 9, wherein the control signal representing determined horizontal scanning frequency is a digit signal generated by a microprocessor. 14. The video display apparatus according to claim 13, wherein the digital establishes a gain register to control the amplitude of the scanning speed modulation signal.