Arbitrary waveform generators (AWGs) are flexible, powerful tools for creating any kind of waveform imaginable. Their broad range of capabilities, however, can make these instruments intimidating to learn and time consuming to use. Today's advanced AWGs, though, minimize the intimidation and simplify their use by offering new, user-friendly interfaces and advanced editing features.
In reality, most waveforms don't follow precisely defined functions, such as sine, square, triangle, and pulse. While many waveforms may display a predictable sequence, they also tend to exhibit arbitrary behavior that, at best, can only be described in very complex terms. This behavior may stem from random activity or the complex combination of various segments or functions. Some of this is the result of careful design—like a TV broadcast signal—while other behavior is the product of glitches, drift, noise, and other anomalies or failures.
AWGs let designers precisely create these "real-world" signals, whether analog or mixed signal. An AWG then becomes an indispensable tool during the design, test, and manufacture of electronic components and systems, especially for simulating worst-case conditions during design verification. The AWG accepts a wave-shape definition, stores the digitized image in its memory, and outputs the analog equivalent via its digital-to-analog converters (DACs). It doesn't care about periodicity, binary logic levels, or operational cycles. It simply puts out a continuously changing series of voltage levels at a fixed clock rate—each equivalent to a point stored in its memory—to create any imaginable waveform or bit pattern.
The most advanced AWGs deliver high-speed clock rates of up to 2.6 Gsamples/s, with up to 8 Mpoints of waveform memory. This deep memory allows for high signal fidelity and long signal-playback times. AWGs also can have anywhere from one to four analog output channels with up to 14 digital output channels. Depending on the instrument, the AWG can support up to 10-V p-p output and 14 bits of vertical resolution.
Engineers rely on AWGs in a variety of design arenas. Semiconductor application engineers employ them for high-performance, mixed-signal, functional test and device characterization to test the effects of real-world signal conditions on a device. In physical layer communications, designers use them to create transient spikes and subthreshold "runt" pulses on complex telecom signals. To support the demands of the communications industry, many AWGs provide special telecom-oriented test features that make troubleshooting faster, easier, and more repeatable.
Application-Specific Editors
These features include application-specific graphical editors for creating network data signals such as OC-48, gigabit Ethernet, and Fibre Channel; combining an AWG's digital-marker outputs with the main digital output to perform high-speed mixed-signal testing for network semiconductors; and software applications for creating complex digitally modulated or baseband signals. AWGs also are heavily used in disk-drive manufacturing to simulate the jitter effects on the disk drive, as well as amplifier noise, sample-clock jitter, quantization error, and interpolation error.
While AWGs excel at producing mixed-signal waveform shapes that mirror the arbitrary nature of real-world conditions, creating and editing these signals can appear difficult at first glance. New users of these programmable waveform generators approach them with a mixture of fear, uncertainty, and doubt.
As a result, AWG manufacturers have gone to great lengths to make them more user friendly by incorporating graphical user interfaces in some of the more advanced units. These screen-based control panels are linked to soft keys that access such functions as range and mode selection, display format, and marker placement. Scrolling, cut/paste selection, cursor position, and file selection are controlled by front-panel knobs and buttons. And, every pertinent function, status, and value is available on screen only a menu away.
Some AWGs offer several ways to create and edit wave shapes. These capabilities can include a standard waveform library, the ability to capture waveforms from a digital-phosphor oscilloscope (DPO) or a digital-storage oscilloscope (DSO), graphical waveform editing, digital timing entry, an equation editor, and a sequence editor.
If the AWG has a standard waveform library, the fastest way to create a waveform is to select a wave shape from the library. A waveform library typically includes the basic sine, square, triangle, ramp, pulse, and dc wave shapes. Some instruments offer more advanced signal shapes such as video-sync and color-burst signals, disk read-/write-head signals, and a variety of modulated communication waveforms including AM, FM, PSK, PWM, FSK, and QPSK. Even noise is a standard wave shape in some libraries. These wave shapes can be used directly, or they can be modified with one of the editors to create the desired real-world signal.
Another way to quickly create a signal is to capture waveforms from a digital oscilloscope (either a DPO or a DSO). Newer AWGs have built-in controller capabilities, making it easy to read waveforms directly from a DPO or DSO via a GIPB interface. This is an extremely powerful feature when troubleshooting, since the actual signal conditions causing a problem can be captured and immediately transferred to the AWG.
Some examples of waveforms an engineer might want to capture include a noise spike on a power line, a runt or missing pulse in a digital pattern, or perhaps excessive noise caused by some external source. Once the waveform is transferred to the generator, it can be saved and modified using any of the on-board editing features.
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