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Agilent pattern/pulse stimulus generator spans 150MHz to 7GHz

Posted: 27 Jul 2005 ?? ?Print Version ?Bookmark and Share

Keywords:fiber channel? pci Express? sata? agilent technologies? model 81141a?

Agilent's new <a href=pulse generator" ALIGN="RIGHT">If you're adopting a leading-edge serial transmission technology such as Fiber Channel, PCI Express, and S-ATA, or perhaps designing an ultra-wideband RF system, characterizing your hardware at speeds between 4GHz and 6GHz can be a daunting task. If, however, you're armed with the right test equipment, you can make stimulus/response measurements of either single elements or complete systems. The trick is to have the right test gear at hand.

That's where Agilent Technologies's new Model 81141A pulse generator comes in. While Agilent's previously available pulse Model 81133A generator topped out at about 3.3GHz, the company's latest 81141A instrument, with its memory-based pattern generator, can be used all the way up to 7GHz (and down to 150MHz).

Regardless of frequency, the Windows XP-based 81141A can provide low-voltage differential or single-ended signals, sequencing for protocol data, and handle things such as 8b/10b encoding, thanks to its 32-Mbit memory length. Sequencing and looping of up to four blocks are available to address the needs of protocol emulation for S-ATA and PCI Express. More on the unit's pattern ion capabilities in a moment.

Multiple formats
The company's press release emphasizes the instrument's variety of data formats, supporting R1 and NRZ, and RZ for bandwidth tests. Not mentioned is that parameters such as pulse width and duty cycle are completely configurable. You can even adjust cross points while making sensitivity tests.

Another item not mentioned in Agilent's notes, but worth pointing out here, is that the new 81141A includes an IEEE-488/GPIB interface, as well as interfaces for operation on a LAN. It also includes four USB 2.0 (Universal Serial Bus) ports, one USB 1.1 port, a printer port, and a VGA display port.

Finally, the press release fails to mention the 81141A's sparkling 8-inch touchscreen LCD. Of course, you can also poke in settings with a numeric keypad, and navigate using Up/Down arrows, a dial knob, or even a mouse.

No adverse instrumentation effects
As you perform characterization and validation, you can also be reasonably sure that the 81141A will let you test your devices without any adverse effects generated by the source. That means you can focus on your test set-up, and be assured that the results will be repeatable. That's because intrinsic jitter is typically less than a picosecond (rms), and the unit's clock is stable to within 15ppm. Transition times are also less than 20ps.

The instrument also touts a 500MHz jitter modulation bandwidth. Digital stimulus and response testing probably couldn't be easier. Imagine being able to have injected jitter modulated with a sinewave or a square wave, or perhaps modulated by Gaussian noise. The screen image here is that of a signal's jitter modulated by a sinewave.

You can use the 81141A to check for jitter tolerance, receiver sensitivity, timing skew, and PLL (phase locked loop) bandwidth. The 81141A will let you control a data stream to generate realworld signals for stress testing. The 81141A can also simulate worst-case scenarios, stressing a DUT (device under test) to its limits. Delaying data relative to the clock can let you generate high-frequency low-amplitude jitter. You can even apply an FM clock to generate higher amounts of jitter at lower frequencies (wander).

Published standards
The system's protocol data capability also means you can support most published standards, using the box's fast set-up scheme to initialize sequences and patterns (many pre-defined patterns are also supplied). The unit's hardware supports long high-speed pseudo-random binary sequences.

User-defined or software generated patterns, representing any type of arbitrary data, can be loaded into the unit's memory. You can also connect a hard disk to the unit's USB port if you wish to store patterns and data.

Software generated patterns can also be modified with variable mark density to stress a DUT or system; the larger the pattern the greater the stress. Patterns can also be repeated, a feature that can come in handy when evaluating predictability.

The 81141A can also switch between two equal-length user-programmable patterns, each up to 16Mb in length. That's accomplished from the unit's front panel, or via an auxiliary input, or using the system's IEEE-488/GPIB control. Changeover is synchronous with the end of a pattern, with and two methods of controlling pattern changeover available: one shot and alternative.

Triggering choices
The 81141A also packs extensive triggering hooks; these can be especially useful when the generator is used with other instruments. A Trigger In mode lets you select and run different pulses or data streams based on pre-defined signals or edges. You can, for example, define a trigger to start a data or pulse sequence, or perhaps to suppress the generator's output.

A Trigger Out mode lets the data generator send out a trigger sequence to an external instrument or devices, such as an oscilloscope. The trigger can also be divided by the clock signal to indicate the start of a data pattern.

The 81141A includes many gold-plated SMA connectors for things such as Trigger Out signals, Delay Control inputs, a 10MHz reference input and output, clock inputs, and sub-rate reference clock outputs.

An external trigger can, for example, insert a single-bit error in the generator's output. The Delay Control uses an external signal to vary the delay between data output and a clock output, which can generate jittered test signals. Nifty.

- Alex Mendelsohn

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