Computer graphics processing and selective visual display system – Display peripheral interface input device – Light pen for fluid matrix display panel
Reexamination Certificate
1998-04-03
2001-08-21
Chow, Dennis-Doon (Department: 2775)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Light pen for fluid matrix display panel
C345S182000
Reexamination Certificate
active
06278435
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the processing of acquired voltage-versus-time data representative of the activity of a signal under observation into a form that is suitable for display by a digital oscilloscope, and more particularly to the efficient high speed acquisition and rasterization of such data into a form that includes multiple-bits-per-pixel intensity information for variable intensity displays.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
[Not Applicable]
BACKGROUND OF THE INVENTION
Digital oscilloscopes generally use raster scan displays to present the activity of electrical signals to their users. Each raster scan display, such as those seen every day on computer screens, consists of a two dimensional array of pixels, with each pixel location being uniquely defined by a row number and column number. The simplest and lowest cost versions of such displays are “single bit” displays, in that the memory from which they derive the information to be displayed only has one bit of intensity information associated with each pixel. In such a display that single bit of information determines whether the pixel associated with it is either “on” or “off”, with “on” dictating that a predetermined amount of intensity is to be used to illuminate the pixel and “off” indicating that the pixel is not to be illuminated at all.
The more complex and expensive alternative to a single bit display is a multi-bit display, which can provide variable intensity (also known as “gray-scale”) or color variations as a substitute indicator of brightness. The memory locations associated with each pixel of a variable intensity display contain multiple bits of intensity information, indicating the number of varying intensity levels with which they can be illuminated. Like the pixels of single bit displays, those of multi-bit displays can exhibit an “off” or dark state, but instead of one value of illumination, they have multiple values. Typically, the number of values available is 2
N
−1, where N is the memory depth at each address of the raster memory. Thus, for example, a four bit deep raster scan memory can support fifteen levels of partial through maximum illumination, as well as the dark or “off” state. Pixel intensity can also be translated into differing colors, as well as intensity or “brightness”.
With this larger amount of data, multi-bit displays can convey more information about the behavior of electrical signal waveforms under observation, particularly if the signal is not perfectly repetitive and therefore has less activity in some portions than others. U.S. Pat. No. 4,940,931 to Katayama et al. for “Digital Waveform Measuring Apparatus Having A Shading-tone Display”, hereby incorporated by reference, describes a system for producing digital variable intensity displays.
Typically, digital oscilloscopes acquire information about the behavior of a circuit node by periodically sampling the voltage present at the node. The oscilloscope probe tip is placed in contact with the node and the probe and front end of the oscilloscope precisely replicate the signal, or some predetermined fraction or multiple of the signal, and present it to an analog-to-digital converter. The output of the analog-to-digital converter is a series of multi-bit digital words that are stored in an acquisition memory. Successively acquired samples are stored at sequentially related addresses in the acquisition memory, and are thereby related to a time scale. Those addresses will eventually be converted back to a time scale, one of which is represented as horizontal distance along the x-axis of the oscilloscope's raster scan display.
In a typical digital oscilloscope, voltage amplitude values derived from the data contents of an acquisition memory location determine the vertical location (row number) of an illuminated pixel, while time values derived from the addresses of the acquisition memory determine the horizontal location (column number). The process of expanding the contents and addresses of an acquisition memory to produce contents for a two dimensional raster memory is known as “rasterization”.
The output of a rasterization process is usually combined with some preexisting content of a raster memory, and the resulting composite raster contents may thereafter be regularly subjected to some sort of decay process. For more information about digital persistence and decay, refer to the following U. S. patents, hereby incorporated by reference: U.S. Pat. No. 5,440,676 to Alappat et al. for “Raster Scan Waveform Display Rasterizer With Pixel Intensity Gradation”; U.S. Pat. No. 5,387,896 to Alappat et al. for “Rasterscan Display With Adaptive Decay”; U.S. Pat. No. 5,254,983 to Long et al. for “Digitally Synthesized Gray Scale For Raster Scan Oscilloscope Displays”.
For any particular combination of settings of the oscilloscope display and acquired waveform data, there will be some function that maps the acquired data points into the time (x-axis) versus voltage (y-axis) display raster. That mapping function will include some ratio between the number of samples to be mapped and the number of pixel columns in the raster display. While that ratio can be 1:1, it will usually be N:1 or 1:N If there are more data points than columns of pixels into which they must be mapped, some form of data compression and/or decimation will be utilized. Decimation means discarding all but every Nth data point, thereby forgoing part of the available information. Compression, on the other hand, means mapping data from multiple time locations in the acquisition memory into one horizontal location, i.e., a single column of pixels, in the raster scan display. If there are fewer data points than columns of pixels, i.e., the 1:N case above, then some sort of interpolation or equivalent time sampling is generally used. In the case of the present inventions, equivalent time sampling, which will be discussed in much greater detail below, is used.
For many years, digital oscilloscopes were limited in the percentage of activity at the probe tip that they effectively processed and displayed for the user. Although less sophisticated users and those who were only familiar with analog oscilloscopes had the impression that they were seeing most or all of the activity at their digital oscilloscope's probe tip, in many circumstances the display was really only showing a small percentage of the actual activity occurring there. This was because these oscilloscopes spent a lot more time processing signals than they did acquiring them. If a signal is perfectly repetitive, this loss of “live time” is not a problem, since one waveform looks just like another. However, when a signal is displaying some sort of intermittent anomalous behavior, a low percentage of live time may prevent such an anomaly from being detected. Therefore, increasing the waveform throughput and the percentage of signal activity at the probe tip that can actually be observed by the user has increasingly been the goal of the more recent digital oscilloscope designs. U.S. Pat. No. 5,412,579 to Meadows, et al. for “Slow Display Method for Digital Oscilloscope With Fast Acquisition System”, hereby incorporated by reference, describes an oscilloscope system in which acquisitions are composited into alternating (also known as “ping-ponging”) display buffers, so that while the contents of one display buffer is being used as the source of data being displayed, the other one is being used to gather and composite more data. However, the slow display of the design described in this patent only provided a single bit of intensity data per pixel and therefore had no analog-like gray scaling, i.e., variable intensity, capability.
The capability of processing a large number of waveforms is a highly desirable feature in a digital oscilloscope. U.S. Pat. No. 5,530,454 to Etheridge et al. for “Digital Oscilloscope Architecture For Signal Monitoring With Enhanced Duty Cycle”, herein incorporated by reference, describes an oscilloscope that is capable
Etheridge Eric P.
Ivers Kevin T.
Chow Dennis-Doon
Griffith Boulden G.
Lenihan Thomas F.
Tektronix Inc.
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