Electronic Design

Digital Storage Oscilloscopes Are Becoming PC Friendly

Though sampling rates keep rising and avaiable storage capabilities climb, it's the PC-based features that are accelerating their appeal in design and testing applications.

What seems inescapable, the never-ending rise in signal speeds, coupled with the never-ending rise in accelerating time-to-market pressure, is challenging designers and quality-assurance (QA) engineers to do more in less time. In this vein, some recent introductions in the digital storage oscilloscope (DSO) domain are certainly helping out. A trend is evolving where the functionality of DSOs and PCs is becoming more closely linked.

As Pete Cipriani, product marketing manager at Gould Instrument Systems, Valley View, Ohio, points out, "Without a doubt, we are entering into a new generation of oscilloscope instrumentation with the PC offering a whole slew of features for the DSO user." The new generation includes the embedding of a PC into an oscilloscope product. Today, 95% of DSOs regularly move data to a PC. There are good reasons for doing this—a better display, more processing power, and much more powerful analysis capability in the DSO. Much better conductivity is provided with regard to sharing data, archiving data, and report generation.

DSOs have been around since the mid-1970's, and early versions were monochrome. Designers with four signals tended to segment signal viewing into four regions. But now that there are DSOs with screens in full color, designers can make use of the full screen and the full resolution without worrying about losing signals and confusing them with one another because they overlap.

When Hewlett-Packard reorganized the company and broke out its Test & Measurement Group into the newly formed Agilent Technologies, DSOs fell under the latter's umbrella. Recently added features to Agilent's line of Infinium DSOs include voice control and a Windows operating system (Fig. 1). Its line spans bandwidths ranging from 500 MHz to 1.5 GHz, with corresponding sampling rates of 1 to 8 Gsamples/s.

The voice-control feature enables users to free up their hands for other tasks, such as probing multiple signals on a very fine-pitched IC. The response is said to be both speaker and gender independent. This means that there's no need to train the DSO to respond to any particular voice.

Agilent has added a Windows 98 operating system. Also available is a drag-and-drop measurement capability, so measurements may be made on any channel. Users simply drag an icon from the measurement toolbar to the waveform section that they want to measure and then drop it. Furthermore, there's a feature called "easy zooming." It lets users draw a box around the waveform portion that they want to expand and then click inside the box.

A communications test op-tion is available for proving a product's compliance with, for instance, an ANSI and ITU standard. Known as the communications mask test option, it includes a library of templates for compliance tests, as well as a set of adapters for connecting the DSO to the device under test. If a test fails, then the regions of failure are highlighted on the screen.

Gould came out with the very first DSOs over 25 years ago. Today, the company focuses on four-channel, high-performance instruments. Gould's recently introduced Ultima 500 DSO combines the acquisition power of a high-performance, four-channel DSO with the flexibility and features of a PC. It simplifies data handling by moving effortlessly from signal capture to report (Fig. 2). Users will find the Ultima 500's portability especially attractive for those applications where, until now, a separate DSO and a companion PC were required.

The Ultima series offers a 500-MHz bandwidth and up to a 2-Gsample/s sampling rate. Memory is 1 Mbit per channel. The Ultima 500 is supported by an extensive package of trigger tools to qualify the incoming signal for amplitude, time, pulse, gating, and TV. This creates a wide dynamic range in the transient mode with a resolution of 12 bits, at up to 2 Msamples/s.

Featuring a Pentium-class computer and a 10.4-in. SVGA (800- by 640-pixel) color display, the Ultima 500 is easily transformed into a fully configured Windows PC. This enables a direct data interchange with Microsoft Office applications (Word, Excel) as well as other popular analysis and report-generation packages. In addition, this DSO includes a large and flexible data storage capability with an internal 8.4-Gbyte hard-disk drive and removable 1.44- or 120-Mbyte floppy-disk drive alternatives.

"It's the PC embedded in our DSO that allows people to install all of their own software," remarks Cipriani. This is claimed to be a unique arrangement, exclusive to Gould. Embedding the PC eliminates the need for users to move the data, which can be a repetitive and laborious task.

Gould offers what supposedly is the only true 12-bit DSO. "This means that while most other DSOs employ 8-bit converters, the 12-bit capability of the Ultima offers better accuracy—4096 bits for 12-bit conversion quantized values—versus 256 bits for 8-bit conversion quantized values. The input amplifiers are accurate within 0.1%, whereas most DSOs are typically within 2%," states Cipriani.

"A four-channel arrangement is valuable because signal interaction is an integral part of testing. Often, two channels just don't get it done," Cipriani adds.

A dual-mode interface combines the look and feel of both a DSO and PC in a single integrated operating system. Adjustments are accessible via either traditional front-panel controls or a mouse and keyboard. Ease of use is further simplified by implementing the on-board menu editor that enables customization of the user interface. This limits menu selections to those required for any given application.

Plus, the Ultima series provides real-time analysis capabilities, like FFT, differentiation, integration, graphing, histograms, phase correction, and math functions. User-defined, real-time measurements can be developed using the on-board formula editor. The wide range of configurable measurements will track sections of waveforms and measure them in real time.

Ease of operation is further enhanced by a dual-level, page-selection feature. It provides access to basic DSO functions on one page with setup and control of the analysis capabilities on the adjacent page. Up to eight display windows can be viewed simultaneously, enabling main and zoom traces, or user-defined math traces, to be viewed independently and scaled to user-defined units.

The Ultima also supports a range of display capabilities including YT, XY, persistence, and envelope, as well as what's known as the "TruTrace" capability. With this, signal aberrations can be identified and examined in detail.

The addition of internal PCI cards enables modem data transfers, GPIB control, GPS/IRIG timing, and additional storage devices. Windows operation also offers further user benefits by providing the power of connectivity with a high-speed Ethernet for networking.

USB ports are supplied for a mouse and the keyboard. Plus, there are IrDA wireless connections to printers and other devices, standard serial and parallel ports, and a video monitor output.

"Digitizer-On-A-Chip" Helps
LeCroy Corp., Chestnut Ridge, N.Y., has recently introduced its WavePro series of high-performance DSOs, incorporating what's termed "digitizer-on-a-chip" technology. The company says that this enables its DSO series, consisting of three models, to offer a faster sampling rate and a longer memory in the 500-MHz to 2-GHz bandwidth range and at lower prices than other DSOs (Fig. 3).

The DSOs incorporate an-other novel feature. Known as WavePilot, it makes taking shortcuts easy. These include obtaining quick measurements and then displaying the results with graphing tools, so as to obtain insight into signal behavior that's essential for troubleshooting.

The model 940 is a 500-MHz-bandwidth DSO with 250 kpoints of acquisition memory and a 4-Gsample/s sampling rate on each channel. When implementing only one of the two input channels, the WavePro 940 doubles the sampling rate to 8 Gsamples/s and also doubles the acquisition memory length.

The WavePro 950 provides a 1-GHz bandwidth, 250-kpoints of acquisition memory, and a 4-Gsample/s sampling rate on each channel. Like the WavePro 940, the 950 can operate in a two-channel mode at 8 Gsamples/s with a 2X memory length. But, it can go a step further to acquire a single signal at 16 Gsamples/s, loading it into a quadruple-length memory. All WavePro DSOs offer memory options of 1, 4, and 8 Mpoints/channel.

Recently, Tektronix Inc. introduced the TDS7000 series of digital-phosphor oscilloscopes (DPOs). With 4-GHz real-time performance, the company claims that these are the world's fastest real-time oscilloscopes (Fig. 4). They offer the traditional benefits of the DSO architecture, from data storage to sophisticated triggering. But they also answer the need for analog-like characteristics, such as a gray-scale display and real-time behavior.

The TDS7000 series accomplishes this dual role by digitally emulating the chemical phosphorescence process that creates the intensity grading in an analog oscilloscope's CRT. It thereby transforms the digitizing oscilloscope into a universal waveform-acquisition instrument. Based on a new, open Windows platform, the TDS-7000 line combines exceptional performance, including up to 20-Gsamples/s, a real-time sample rate, record lengths of up to 32 Mbits, and up to a 4-GHz bandwidth.

The flagship of this oscilloscope family, the TDS7404, employs SiGe devices, a semiconductor technology developed by IBM, to deliver unusually high performance in signal acquisition. This DPO provides accurate performance at significantly in-creased speeds over standard silicon at similar power levels. Furthermore, this instrument maintains the low noise floor of previous designs, while substantially increasing the bandwidth. Although SiGe is growing in popularity as a semiconductor process, Tektronix claims that it is the first test and measurement manufacturer to adopt the technology to a DSO.

The signal capture rate of the TDS7000 family, greater than 400,000 waveforms/s, is said to be more than double what was previously available. This provides the user with insights into signal behavior that Tektronix believes have never before been seen in DSO instrumentation. It thereby increases the likelihood that designers will witness transient-signal integrity problems occurring in digital systems. These include jitter, runt pulses, glitches, and transition errors.

Although today's trigger systems may already detect such anomalies, engineers need to very quickly determine where to look for and how to classify the type of fault present. Tektronix says that its DPOs will speed this process by showing the engineer millions of waveforms in just seconds. At the same time, they will provide analysis capabilities that translate the waveform data into useful information at the touch of a button or the click of a mouse.

The TDS7000 series user interface lets users "drive" these DPOs according to their personal preferences. Traditional analog-style controls are present for those who like the right-side control panel. A large, 10.4-in. touch-sensitive display offers immediate access to the instrument's capabilities. This touch screen is especially helpful when a cluttered space or a cart makes mouse control a challenge. In addition, a keyboard or mouse can be hot-connected at any time to a USB port for direct control.

Network Connectivity
Unrestricted access to Windows-compatible software and hardware, coupled with network connectivity, is provided by the TDS7000 series DSOs. This "Open Windows" feature enables a user to customize the oscilloscope with any Windows-compatible software package—without special assistance or integration by Tektronix.

For example, the engineer can launch WordPad from the Windows start menu and then develop documentation by simply copying and pasting the active screen images into a document. This concurrent ap-proach reduces the likelihood of error and simplifies the tasks of detailing and communicating measurement results.

Standard interfaces allow expansion of the TDS7000 series to include peripherals. Some examples are storage devices, a modem, or a wireless LAN connection. Once networked, users can share files, access print resources, surf the web for vendor information, such as data sheets, and exchange e-mail directly with the DSO. Also, by employing the dual-monitor mode supported by Windows, the user can refer to and exchange critical information while simultaneously making measurements.

Tektronix claims to have developed the industry's fastest, single-ended and differential probing solutions for connection to the device under test. The company's P7240 4-GHz active probe exhibits a 120-ps rise time. Therefore, it can preserve signal integrity to 10-GHz and beyond. This probe is well suited for high-speed acquisition in computer systems, data communications applications, and low-voltage logic designs. On the other hand, the company's P7330 differential probe provides a 3-GHz bandwidth.

In order to craft focused tools, Tektronix's Java-based measurement packages, TDSJIT2 and TDSDDM2, can be added. The TDSJIT2 package allows jitter measurements to be performed on contiguous clock cycles from single-shot measurements. The package also makes possible 1.5-ps rms repeatability when performing jitter measurements.

The TDSDDM2 is a disk-drive measurement package that adapts the instrument for disk-drive design analysis. This instrument's performance, along with its 3-GHz differential probe, plus the TDSDDM2, combine to create a highly effective analyzer. This package also provides basic characterization measurements, such as TAA and PW50 and advanced measurements, including NLTS and SNR. Other analysis features include a powerful new math system that enables engineers to create sophisticated algebraic expressions using a simple engineering-style calculator approach.

500 MHz At 2 Gsamples
Recently, Yokogawa Corp. of America, Newnan, Ga., introduced the DL7200 DSO (Fig. 5). It extends performance of the company's DL series to a 500-MHz bandwidth at a 2-Gsample/s sampling rate. The DL7200 includes up to 16 Mwords of memory, a fast screen-update rate (30 screens/s), and an all-points display. A new search function should prove helpful when locating hard-to-find problems in a data string.

In Yokogawa's view, although high bandwidth and fast sampling are important, a long memory is essential for capturing high-speed events reliably. With 16 Mwords of memory, it's possible to sample at 2Gsamples/s, even with a time window of 8 ms (16 ms at 1 Gsample/s).

A new pattern-search function makes it easy to find specific signal patterns—up to 64 bits long—anywhere in the long memory. Therefore, the DL7200 is well suited for debugging serial-bus applications.

Both "history memory" and "history search" are standard on the DL7200. These features, which enable the user to look back in time at more than 2000 previous acquisitions, make it possible to identify unexpected conditions not covered by trigger settings. This is useful when trying to understand random behavior in complex circuits.

Logic inputs allow a user to trigger on and view mixed analog and logic signal combinations simultaneously. With its four analog inputs and 16 logic inputs, the DL7200 lets the user establish a correlation between control signals and the analog performance of a circuit with a single DSO and the one display.

It's also possible in the scroll mode, from very slow sweep speeds to 2 Msamples/s, to locate problem areas and see just where the problems are in the total waveform. Additionally, the DL7200 has an easy-to-use zoom function with two independent zoom windows that can be set up and displayed quickly.

Other DL7200 features include the ability to send data to a PC via a network, to output screen data in color to a printer, and to receive error information from remote instruments by utilizing the e-mail function. The designer can select automatic transmissions at scheduled intervals too, on a trigger condition, as the result of a go/no-go determination, or any combination of these conditions. Yokogawa's DL7100 is similar to the DL7200, but it offers a maximum sampling rate of 1 Gsample/s.

No larger than a video tape, the DSO-2102M DSO, manufactured by Link Instruments Inc., Fairfield, N.J., connects to a desktop or a laptop PC. It's based on an earlier version, the 2100 (Fig. 6). For $650, it offers excellent performance at a quite nominal price. Because the 2102M runs from a PC, there's no need to write programs to transfer data or panel settings to disk. Plus, the user can save and recall setup panels by user-defined names for quick setup changes.

To install the 2102M, the de-signer simply plugs it into a printer port and runs the install software. The PC's speed doesn't significantly af-fect the instrument's performance. While the 2102M de-pends on the PC for the user interface and to display the data, the DSO doesn't rely on the PC for high-speed data acquisition.

With the 2102M model, any combination of DSO and spectrum analyzer traces can be displayed at the same time. This includes each of the data channels, memories, waveform functions, horizontal cursors, vertical cursors, trigger position, text, background, and grid.

Standalone oscilloscope display screens usually represent a compromise. Few people would choose a 7-in. or a 9-in. monitor for their PC screen. But because the 2102M is a PC-based instrument, the user is free to select the display monitor's size and type for viewing the data. Plus, PC-industry display peripherals, like VGA overhead projectors, remote monitors, and heads-up displays, can be employed. The display screen can be printed on any Windows-compatible printer.

Each of the two channels can operate at up to 100 Msamples/s with a 32-kbit sample buffer. The 2102M includes a spectrum analyzer (FFT), advanced triggering, and pass/fail testing. It's able to capture single-shot data at 100 Msamples/s on two channels simultaneously, and it contains 32-ksample/channel buffers.

The 2102M has a number of triggering options. They include level trigger with rising or falling slope, TV horizontal, TV vertical, pulse count, trigger on the Nth pulse, pulse width, trigger on a pulse of a certain width, pulse width + count, and trigger on the Nth pulse of a certain width.

With its Autosetup of both channels, a single mouse click will cause the software to analyze incoming data and set up the DSO to capture the data. Rate, voltage/division, offset, and trigger level can all be preset, and then any of these parameters can be modified later.

Deep Acquisition Memory
The deep acquisition memory maintains fast DSO sample rates, even at slow timebase settings. The 2102M contains deep, 32-kpoint/channel data buffers, allowing it to record long data streams. Unlike short-memory DSOs, the 2102M maintains full 0.1% timebase accuracy and 10-ns sampling resolution on long 327-µs events or data streams. This means that it can accurately capture a 1-kHz signal containing up to 50-MHz frequency components—or a 60-Hz signal with 1-MHz glitches riding on top.

After recording the data, a "zoom-and-scroll" feature simplifies both troubleshooting and analysis of digital hardware/software problems and of long analog signals. The display shows the entire recorded waveforms. Also, the user can zoom in (up to 64X) on signal details and scroll through long data records to identify and characterize problems. The "locked all" channel zoom keeps all of the analog waveforms synchronized.

Furthermore, the deep memory lets the user analyze jitter from the beginning of the record to the end. By zooming/scrolling and then measuring with cursors, pulse widths and channel-to-channel timing can be compared at different sections of data streams. This feature enables identification of time-varying problems, such as "power-on" sequences and clock jitter.

The DSO-2102M provides high-accuracy spectrum analysis too. A binary FFT algorithm is used to break down the input signal into its spectral components. Unlike swept spectrum analyzers that require a stable, repetitive signal due to filter settling time, the 2102M can also analyze transient-event spectra. And, the user can control and view both the frequency-domain signal spectrum and its time-domain oscilloscope display, simultaneously.

The recording time of any DSO creates an acquisition window on the signal. It turns out that FFT spectrum analysis works best for transient signals that begin and end at zero, or for repetitive signals that can be depicted as an integral number of cycles within the acquisition window. An FFT analysis on other types of signals creates artificial spectra not present in the original signal. Shorter recording times and fewer spectral bins lead to worse errors. Most low-cost FFT analyzers provide no more than 512 spectral bins, whereas the 2102M offers up to 16,384 bins. This translates as 32 times better accuracy and fewer artifacts.

To further maximize spectral accuracy, the 2102M has five selectable "windowing" functions: Hanning, Hamming, Blackman-Harris, triangular, and rectangular functions. Also, the 2102M enables the user to store an unlimited number of waveforms, timing patterns, and spectra on a floppy-disk drives, hard disks, or PCMCIA cards. At a later date, designers can recall the stored data to the screen for viewing and for comparison with live data. Or instead, the stored waveforms can be processed through the 2102M's spectrum analyzer and waveform-analysis functions.

The 2102M includes software for DOS, Windows 3.x, Windows 95, and Windows 98. Software for winNT and win2000, which Link Instruments regularly upgrades, is available on the company's web site.

Compared to previous models, the latest generation of digital storage oscilloscopes includes a significant number of new features—no matter which model designers choose. Therefore, it's a good idea for engineers to familiarize themselves with these features and the terminology that comes with them (see "The Language of DSOs," p. 104).

Companies That Contributed To This Report
Agilent Technologies
(800) 452-4844

Gould Instrument Systems
(216) 328-7000

LeCroy Corp.
(800) 453-2769

Link Instruments Inc.
(973) 808-8990

Tektronix Inc.
(800) 426-2200

Yokogama Corp. of America
(800) 258-2552

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