Introducing The Digital Phosphor Oscilloscope and the DPX^TM Technology that Makes It a Reality

Welcome to a new era in oscilloscope technology with the Digital Phosphor Oscilloscope (DPO). Architected to meet the emerging challenges in electronic design, the DPO enables engineers to see, store and analyze today and tomorrow’s complex signals.

DPOs go beyond analog real-time (ART) and digital storage oscilloscopes (DSOs) by incorporating an information-rich, real-time display that surpasses any analog or digital scope's capabilities. This incredible new instrument delivers a level of insight that makes dealing with complex signals straightforward—a level of insight engineers must see to believe. Of course, all of this is combined with the full spectrum of digital acquisition, storage and analysis capabilities that engineers have come to expect in their oscilloscope solutions.

Digital Phosphor Oscilloscopes by definition display, store and analyze complex signals in real-time using three dimensions of signal information: amplitude, time and distribution of amplitude over time.

Digital Phosphor Oscilloscopes

Like the actual phosphor on an ART display, the DPO captures and remembers the frequency of events, resulting in a three-dimensional array that retains information for hundreds of millions of samples. Chemical phosphorescence creates a gray scale because of the decay in its energy over time. Digital phosphor replicates this decay in intensity by digitally controlling the replacement of data in the three-dimensional array. As a result, a DPO can display, store, and analyze three dimensions of signal information: amplitude, time, and the distribution of amplitude over time. (See Figure 1)

The DPO model takes a hardware-based approach to achieve this remarkable performance. Using advanced ASIC technology, it accumulates multiple images of signal information in a 500x200 array of integers. Each integer represents a pixel in the DPO's display and is used to control intensity. As a signal is acquired over time, this array is continuously updated with image after image of the signal. Unlike DSOs that decimate or throw away an enormous number of samples, the incoming samples are acquired at rates comparable to an analog oscilloscope and are all used to create the image. As a result, engineers are finally protected against aliasing because of the abundance of samples collected and used by a DPO.

To retain information about each snapshot, the integers in the array are adjusted. Consequently, if the signal traverses one point again and again, that integer will be repeatedly reflected to highlight that fact. The accumulated result of this updating is the array eventually develops a detailed map of the signal intensity, similar to an ART, except with the benefit of storage.

Creating this detailed image of a waveform's activity and intensity in hardware allows a real-time response similar to an ART. The acquisition engine continuously samples at the maximum rate, triggering and building image after image with minimal dead time between acquisitions. A new snapshot of the digital phosphor is sent to the display every 1/30th of a second, creating an image that responds to waveform activity in real time. Even when the display is updated, the digital phosphor continues to gather new samples. The parallel architecture and hardware-based processing enables the DPO to capture all the details and anomalies that occur in today's complex, dynamic signals and to display them as fast as the human eye can assimilate them.

This real-time processing is what sets the DPO apart from post-processing modes found in today's DSOs, such as persistence. The post-processing in a DSO is executed in software on the normally acquired waveforms, and requires acquisition over a long period of time to build up the display, thus prohibiting instantaneous feedback. The time for creating this display is further exaggerated as multiple channels are turned on, since they use the same microprocessor. Plus, during this processing time, the DSO is no longer acquiring new information and is forced to miss salient details on dynamic waveforms and important aperiodic events, often the very behavior an engineer is hoping to uncover and examine. DSOs are consequently limited to capturing infrequent snapshots of less than 1% of the available signals.

In contrast, like an ART, the DPO's display delivers all the details on a signal's behavior, only better. Figure 2 shows how its display capabilities are superior to those of an ART, with intensity information in color and superior horizontal resolution. And remember, all of this qualitative performance is combined with waveform storage, in-depth analysis and comprehensive automatic measurements. That means a DPO's complete display can be saved and printed, enabling designers to make a host of measurements on the most complex waveforms. Even advanced

analytical operations, such as histograms and statistical analysis can be performed on the data. Unlike an ART, its bandwidth is not limited by CRT technology, and it is able to support sophisticated triggering.

ART	DSO	DPO

The benefits of using a DPO in electronic design, debug and test are dramatic. By providing a third dimension of information, engineers gain new and important insights into the behavior of complex signals, enabling them to accurately interpret signal dynamics, including the mode of changes in the signal and the frequency of occurrence of signal phenomena. Instead of using two instruments—an ART to see all the nuances on the waveform and a DSO to capture, measure and analyze signal behavior—they can use one powerful tool. This will undoubtedly lead to more effective debug and performance verification, thereby helping to streamline overall design and maintenance tasks.

DPX^TM Waveform Imaging Processor Makes DPOs a Reality

Tektronix' first entrant into the DPO era is a flagship family of digital phosphor oscilloscopes enabled by a patented waveform imaging processor called DPX. This family currently includes seven DPO models with up to 2 GHz bandwidth on four channels.

The proprietary DPX waveform imaging processor was designed by Tektronix specifically for acquiring and managing the three dimensions of waveform information of a DPO. Captured in 0.65 micron CMOS, this highly pipelined processor with 1.3 million transistors is tailored for high-speed image acquisition and memory management. To ensure maximum throughput, it has distributed internal control and works independently of the other processors in the oscilloscope.

The DPX waveform imaging processor is completely dedicated to the acquisition and database management process. It includes an acquisition rasterizer and the digital phosphor three-dimensional database array that emulates the behavior of chemical phosphorescence to provide a real-time intensity-graded display. The basic operation of the DPX waveform imaging processor involves its drawing repeated images in the digital phosphor, controlling the rate of image decay, and periodically sending snapshots of that information to the oscilloscope's display system. (See Figure 3)

The gigabyte per second acquisition memory of the TDS oscilloscope is harnessed by the DPX waveform image processor to create an image that is composed of multiple waveforms. The first DPO solutions from Tektronix are capable of acquiring up to 200,000 records per second—an astounding number—and up to 500,000 samples in a single acquisition. As a result, Tektronix' DPO display provides up to 1000 times more signal data than DSOs, giving designers unprecedented insight into the subtle patterns and behavioral variations of their complex signals. Such a super abundance of samples virtually eliminates the threat of aliasing and ensures that all the details on even the most dynamic signals are captured and displayed.

The DPX waveform image processor accomplishes this remarkable feat by incorporating a full 21 bits of gradation information in the digital phosphor's 500x200 array, an array that represents each pixel on the display. The information is compressed to 4 bits on the display and shown as 16 levels of intensity grading. This depth is what enables DPX to retain so much waveform information and show the distribution of the signal over time. Each time the oscilloscope triggers and draws a new waveform into the array, the data is used to update the 21 bits for every point that describes the waveform. (See Figure 4)

In histogram mode, the DPX engine extends each point in the digital phosphor to be 32- or 64- bits deep. This enables the oscilloscope to build a statistically significant database in just a few seconds. It is also makes it possible, for example, to characterize long-term drift in communication applications and high-speed jitter in microprocessor-based development. The deeper bit level ensures that the digital phosphor does not saturate or overflow even if the designer is examining signal behavior over a period of days. In addition, any portion of the histogram, whether live or stored, can be examined to determine the distribution of the waveform data.

The digital phosphor contents can also be exported from the DPO to a PC for 3-D plots using common application software such as Excel or Mathcad. The result is a unique representation of the waveform that provides further insight into the behavior of the signal over time (See Figure 5).

Tektronix' DPO display is especially powerful in XY and XYZ mode. It works much like a scan converter in these modes, continuously drawing samples at a rate of 10.4 Msamples/sec into the digital phosphor and scanning that information out serially to the display at 1 Mpixels/sec. The effect is a display analogous to a 10.4 million-point electron ART, with no rearming dead time. This continuous acquisition enables a dynamic and accurate XY display. The benefits of this approach are obvious when compared to the XY display of a DSO, which does not provide sufficient sample density or continuous acquisition. (See Figure 1)

Depending on the time/div setting, the DPX waveform imaging processor automatically selects record length and sample rate to maximize the data density. As a result, the DPX acquisition capabilities can compress record lengths of up to a half-million samples or as few as 500, enabling it to present the most accurate, detailed representation of the signal at any sweep speed.

Creating the Third Dimension

The biggest benefit of the DPO is its ability to provide three full dimensions of signal information—amplitude, time and distribution of amplitude over time. The DPX waveform imaging processor simultaneously employs three different methods for creating the digital phosphor and resulting real-time intensity-graded display—repeated drawing, compression and slew-rate weighting.

Repeated drawing: This approach for creating the signal intensity in the digital phosphor is used by the oscilloscope at all but the slowest sweep speeds. Because the oscilloscope can trigger at a much faster rate, the DPX waveform imaging processor repeatedly draws the acquisitions into the digital phosphor, accumulating the brightest intensities where the signal overlaps most frequently. By relying on multiple acquisitions, the DPX display is able to build intensity and statistical information about the waveform.

Compression: At all but the fastest sweep speeds, the DPX engine has time to gather up to 500,000 samples on a single acquisition. To show the viewer all this information in one display, it compresses the data into the 500 columns that make up the digital phosphor array. As a result, multiple points in time are compressed in the display and the resulting intensity reveals areas where the signal spends most of its time. This ability to show a large amount of signal activity in a single display is ideal for complex waveforms such as packetized data in telecommunication signals, and disk drive and video signals. Now, instead of painstakingly scrolling through enormous waveform records, engineers can view a complete sector of a disk drive sequence in one display and immediately see any anomalies. They can even gather all the information on a composite TV signal in one display.

Slew-Rate Weighting: When drawing vectors, the DPO display emulates an analog scope's display, showing dimmer fast edges and brighter signal peaks. This varying intensity indicates that the signal is spending more time at the top and the base of the waveform and less time at the transitions. This is especially useful when examining envelope-type waveforms. Now the viewer can immediately tell the difference between a sine, square or triangle waveform by merely looking at the intensity of the edge and peaks.

See it, Believe it

It may be hard to believe that the decades-old dream of blending the strengths of an ART with the compute and storage power of a DSO is actually a reality with DPO. But one look at the remarkable Tektronix DPO display, storage, and analysis capabilities should convince even the most skeptical of engineers. This is truly a case where seeing is believing.

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