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The patented TruTrace feature of Gould Instrument Systems' new four-channel, 200-MHz-bandwidth Classic 6000 DSO ($6195) is the latest in the trend toward making digital scopes emulate analog scopes (see "Color DSOs mimic analog displays," EDN, Oct 10, 1996, pg 20). The TruTrace display technology operates in both single-shot and repetitive-sampling modes and does not affect the way the scope acquires waveforms. TruTrace adds a third dimension to the DSO display. In TruTrace mode, the scope provides a faithful emulation of an analog scope's Z-axis or intensity modulation. This approach is a way not just of distinguishing infrequently occurring anomalies from normal waveforms, but also of revealing details in long waveform records that a DSO's minimum/maximum or peak-detection mode normally renders invisible. To achieve its computational power, TruTrace uses a Texas Instruments TMS-320C40 DSP.
In a deep-memory scope, such as the Classic 6000, whose waveform records can contain as many as 200,000 points/channel, each column of pixels on the screen must act as a surrogate for multiple digitized samples. With a 500-pixel-wide display and a 200,000-point record, each column represents 400 samples. To prevent aliasing, the scope cannot discard samples; it must use the minimum/maximum mode, in which the scope determines the highest and lowest values in the group of 400 samples and illuminates a band of pixels between those values. In this mode, the scope illuminates all points with equal brightness, however.
To present more information in the 400 samples without horizontally expanding the display, the scope constructs a histogram of the frequency of occurrence of each Y-axis value. It quantizes this histogram into eight levels and intensity-modulates the display accordingly. The result is an effective emulation of the Z-axis modulation of analog-scope displays. Unlike other schemes for providing Z-axis information in DSO displays (color grading, for example), TruTrace works even with single-shot data.
Aside from TruTrace, the Classic 6000 features 100M-sample/sec waveform capture on each channel, an internal 500-Mbyte hard drive, a PC-compatible 3.5-in. floppy-disk drive, and both IEEE-488 and RS-423 ports. Other features include display scaling in engineering units; the use of a full-color, active-matrix LCD that operates in monochrome in the TruTrace mode; and the ability to segment the capture memory into multiple short records and to accept an internally mounted thermal printer.—by Dan Strassberg, edited by Fran Granville
Gould Instrument Systems Inc, Valley View, OH. (216) 328-7000, fax (216) 328-7400. Circle No. 460
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