Computer graphics processing and selective visual display system – Display peripheral interface input device – Light pen for fluid matrix display panel
Reexamination Certificate
1997-06-03
2001-06-12
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Light pen for fluid matrix display panel
C345S182000
Reexamination Certificate
active
06246389
ABSTRACT:
FIELD OF INVENTION
This invention relates generally to digital graphics displays and more specifically to display of digitized waveforms in instruments such as digital oscilloscopes, heart monitors and spectrum analyzers.
BACKGROUND OF THE INVENTION
Oscilloscopes, spectrum analyzers, heart monitors and other electronic instruments often use an analog vector cathode-ray tube (CRT) to display waveform information. In the typical analog vector CRT, an electron beam sweeps at a fixed speed in one direction while being deflected by an analog signal at a variable speed in a perpendicular direction. Analog CRTs have an inherent intensity variation as a function of the velocity of the electron beam across the face of the display (slew rate) and the intensity build-up and decay times (persistence) of the phosphors used in the display. A waveform being displayed on an analog CRT has a high intensity where the slew rate of the electron beam is relatively slow and may have a lower intensity where the slew rate is relatively high. In general, this intensity variation provides useful information to a human observer. In particular, intensity provides a visual clue as to rate of change. High intensity indicates slow change and low intensity indicates rapid change. For example, if a square wave is displayed on an analog display oscilloscope, the vertical rate of change of the waveform is much higher than the horizontal sweep rate so that the high levels and the low levels of the square wave are typically at a high intensity and the rising and falling edges of the square wave are at a lower intensity.
Instruments may also use digital graphics displays similar to the displays used for most computer monitors. A digital graphics display is divided into rows and columns of addressable areas called pixels. The intensity of each pixel in a digital graphics display is typically controlled by a digital value stored in a memory associated with the display. In an instrument using a digital graphics display, a waveform is sampled, the samples are converted into digital values and the digital values are stored into an acquisition memory. The waveform samples determine which pixels are illuminated but the samples do not inherently control intensity. Any intensity variation must be accomplished as a digital computation on digital waveform data, typically by post processing the waveform image. In many systems, display update speed is a critical requirement and software post processing typically requires a relatively complex and time consuming computational burden. Alternatively, specialized hardware for high speed vector drawing may include intensity variation. A system is needed that provides intensity variation for slew rate with high speed, simplicity and low cost.
SUMMARY OF THE INVENTION
Slew rate based intensity variations mimicking analog vector CRT behavior are used when rendering waveforms on digital graphics displays. Slew rate based intensity variations may be computed algorithmically. Alternatively, for speed, the slew rate may be estimated and look-up tables may be used to determine the intensity. The slew rate of a signal, about a point, is estimated based on measuring the magnitude of the vertical change of the waveform between consecutive samples. A smaller vertical waveform change means a lower slew rate about the point and intensity is set to a higher value. A larger vertical waveform change means a higher slew rate about the point and intensity is set to a lower value. A look-up table is used for intensity of a point or line segment as a function of vertical waveform change about the point. Therefore, computation is reduced to a single subtraction and a table look-up.
In an alternative embodiment, the table of intensity as a function of slew rate is reversed so that a point or line segment having a higher slew rate has higher intensity and a point or line segment having lower slew rate has lower intensity. The alternative embodiment is particularly useful, for example, for viewing digital waveforms where timing of rising and falling edges is of particular interest.
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Agilent Technologie,s Inc.
Frenel Vanel
Shalwala Bipin
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