Electronic Design

Real-Time Scope Breaks Into 4-GHz Territory With Fast SiGe Technology

This instrument promises to give designers more insight into signal behavior than ever before.

Just when you thought real-time oscilloscopes might be reaching the end of the bandwidth line, along comes the Tektronix TDS7000 Series. The flagship model in this series, the TDS7404, boasts an impressive 4-GHz bandwidth, as well as a host of other banner specs. These include a 20-Gsample/s real-time sample rate, a record length of up to 32 Mbytes, and a signal capture rate of 500 kwaveforms/s.

The TDS7404 employs silicon germanium (SiGe) technology, which was developed by IBM Corp., in its front end, composed of the pre-amplifier, amplifier, and track-and-hold circuits (Fig. 1). These critical components were previously considered the bottleneck for accurately acquiring faster signals in real time. By using the SiGe process, the designers at Tektronix achieved a significant increase in performance. Bandwidth was boosted by 33 percent and the real-time sample rate doubled.

According to the company, the high level of integration afforded by SiGe gives the TDS7404 front end excellent signal integrity. In addition, the Tektronix design team was able to maintain the low noise floor of previous amplifier designs while at the same time, as mentioned, substantially increasing bandwidth.

To gain the benefits of this cutting-edge technology, Tektronix invested more than $14 million to fuel SiGe development for use in its oscilloscopes, and a broad range of future instrumentation applications.

The TDS7000 Series—the TDS7054, the TDS7104, and the TDS7404—are all digital phosphor oscilloscopes (DPOs). Pioneered by Tektronix, this architecture dedicates unique ASIC hardware to the task of acquiring signal data. The company believes DPOs give design engineers an unmatched ability to view signals and circuit behavior.

The TDS7000 family's signal capture rate of 500,000 waveforms/s is more than double that of the previously available 200,000 waveforms/s. This, the company says, provides insight into signal behavior that was never before seen in digital oscilloscope. It provides designers with a much better chance to view the transient signal-integrity problems that occur in digital systems. These could be jitter, runt pulses, glitches, or transition errors.

Though the company admits that today's trigger systems might already detect such anomalies, it believes that DPOs accelerate the process. This is accomplished by showing the engineer millions of waveforms in just seconds, while also providing analysis capabilities that translate the waveform data into useful information at the touch of a button or the click of a mouse.

Furthermore, this oscilloscope series marks a new chapter in user interface technology for Tektronix. The company has carefully crafted an interface that gives users a choice. Classic analog-style control knobs exist for anyone who prefers the right-side control panel. Alternatively, a 10.4-in. touch-sensitive display can access the instrument's capabilities through a button-driven or a Microsoft Windows pull-down menu style interface. A USB port is available for mouse and keyboard afficionados. Regardless of the mode of operation, users can manipulate graphical controls to quickly access and apply both standard and sophisticated features (Fig. 2).

The Windows-based nature of the series extends beyond the user interface. Engineers are able to customize the oscilloscope with any Windows-compatible software package. They don't need any special assistance or integration performed by Tektronix. An engineer can launch WordPad from the Windows start menu, for example, and develop documentation by simply copying and pasting the active screen images into a document.

In addition, the TDS7000 Series can be expanded to include such peripherals as storage devices, a modem, or a wireless LAN connection. Once networked, users are able to share files, access print resources, browse the Web, and exchange e-mail directly from the oscilloscope. Using the dual-monitor mode supported by Windows, designers can refer to and exchange information, while simultaneously making measurements on the scope. This feature really takes advantage of the computing power of modern scopes.

The TDS7000 Series supports many standard and optional analysis features. Application-specific measurements, like the company's enhanced Java-based measurement packages, the TDSJIT2 and the TDSDDM2, can be added. By doing so, users can create focused tools. The TDSJIT2 allows jitter measurements on contiguous clock cycles from single-shot measurements. With the TDS7404's hardware precision and software techniques, repeatability in jitter measurements is less than 1.5-ps rms.

The TDSDDM2 disk-drive measurement package adapts the instrument for disk-drive design analysis. Basic characterization measurements (like TAA and PW50), and advanced measurements (including NETS and SNR) can be made with the package.

Another analysis feature is a new math system. Engineers can create sophisticated algebraic expressions using a simple engineering-style calculator approach. Signals, measurement results, and other expressions can be used to create new analysis capabilities. Plus, frequency-domain analysis is controlled in terms that are familiar to spectrum analyzer users. Some examples include "center frequency," "span," and "resolution bandwidth." The company states that this frees the engineer from the idiosyncrasies of the fast-Fourier transform algorithm that's normally presented in oscilloscopes, and it ensures greater confidence in the analysis.

Cranking the bandwidth of a scope up to 4 GHz inevitably leads to questions regarding probes. To give engineers complete access to the breakthrough performance of the TDS7404, Tektronix has developed both single-ended and differential probes. The P7240 is a 4-GHz active probe with a 120-ps rise time. It features the new TekConnect interface, which preserves signal integrity to 10 GHz and beyond to meet present and future bandwidth needs. This probe is well suited for high-speed acquisition in computer systems, datacomm applications, and a broad range of low-voltage logic designs.

The P7330 is a 3-GHz differential probe, also with the TekConnect interface. A compact form factor, high bandwidth, and low noise performance make this probe suitable to the increasingly common differential signals found in applications ranging from high-speed computer systems to communications technologies.

Price & Availability
The TDS7000 Series oscilloscopes range in price from $18,000 to $60,000. Currently, the TDS7054 and TDS7104 are available for order and will be delivered within four weeks. The TDS7404 will be later this year.

Tektronix Inc., P.O. Box 3960, Portland, OR 97208-3960; (800) 426-2200 (request code 1195); fax (503) 222-1542; Internet: dpo.tektronix.com.

TAGS: Components
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