The HP 53310A Modulation Domain Analyzer

Market Backgrounder

With the trend in modern electronic design toward greater use of complex modulation techniques in everything from cellular telephones and garage door openers to advanced weapons and radar systems, design engineers need a corresponding instrument capable of giving them a quick, qualitative insight into the performance of their designs during the prototype phase and beyond. Traditional instruments like the oscilloscope and spectrum analyzer are no longer sufficient to design and test the growing number of systems that either incorporate complex modulation techniques or are troubled with unintentional modulation or jitter.

In addition to the increasing use of modulation techniques, the margins for error these systems can tolerate keep getting smaller as performance demands increase. Communications channels must carry more information more quickly, radar systems need greater resolution, computer systems need to process more data faster. The requirement to design circuits to increasingly demanding tolerances is pushing up against the limits of traditional measurement techniques to characterize them and determine potential sources of error.

A New Measurement Technology

Modulation Domain Analysis was developed by Hewlett-Packard in the mid-1980s to address the need for a way to quickly and accurately characterize the behavior of these complex circuits and provide insight into potential sources of error. Made possible by HP's patented continuous count technology, modulation domain technology is based on a new meaurment method developed at HP called phase digitizing. Phase digitizing is ideally suited to measuring the time, phase-encoded, or frequency-encoded signals engineers are turning to to solve their design requirements.

Until now, however, the use of modulation domain technology has been limited to solving very specific, high-end problems by a fairly small number of users. First-generation modulation domain analyzers were costly, required extensive training to learn to use, and were cumbersome to operate. Even so, several hundred users found these instruments invaluable in solving problems that were either too difficult or impossible to attempt using traditional methods.

With the introduction of the HP 53310A Modulation Domain Analyzer, Hewlett-Packard Company has brought time-dependent frequency and time-interval measurements within reach of thousands of design engineers. Its breakthroughs in speed, cost, and ease of use have made this second-generation instrument ideal for gaining quick, qualitative insight into the operation of complex circuits used in a broad range of modern electronic systems.

Applications

In its simplest form, modulation domain analysis measures and displays the variation in a signal's frequency continuously over time, called modulation. It also can detect time deviations between digital pulses, called jitter. Because modulation domain analysis is in its infancy, however, the scope of its applicability has not been fully realized. Engineers now are only beginning to appreciate the benefits this new technology has to offer them. Even so, there already exists several specific areas where modulation domain analysis is making significant contributions.

Voltage controlled oscillators (VCOs) are finding their way into the heart of more electronic systems every day. They are used increasingly in radios and televisions, computer disk drives, radar systems, and a host of consumer, military, and commercial products. Because the overall performance of these products are often limited by the performance of the VCO, designers of these systems must have a complete understanding of the VCO's operation to optimize product performance. In fact, the cost of testing VCOs used in military applications (to guarantee they meet specifications) is the single greatest cost of producing them.

To properly characterize a VCO, however, it must be tested in the manner in which it will be used. Most applications require the VCO to operate at one frequency, and then quickly step to another and stay there, sometimes changing frequencies at a rate of several thousand times per second. Other applications require it to change once a minute or less. Designers need to know precisely how this transition occurs; what the frequency change looks like over the time it's changing.

Ideally, a designer would like to be able to capture a single transition and study it because averaging data over many transitions would hide valuable information. Traditional measurement techniques, however, fail to accurately characterize these "single-shot" transitions. And so other more costly and time consuming techniques have been used, unitl now.

The HP 53310A Modulation Domain Analyzer is able to quickly and easily capture and display a VCO's "step response" in a single shot, exactly the way the device operates. It does this by directly making up to 64,000 back-to-back frequency measurements every 500 nanoseconds. The resulting frequency versus time display is actually a plot of the VCO step, making it easy for designers to observe the operation of the VCO under test.

In many applications, changes in a signal's frequency are a source of concern, and can degrade a system's performance. With new digital communications technologies such as Integrated Systems Digital Network (ISDN) and Synchronous Optical Network (SONET) rapidly entering the mainstream telephone systems, transmission rates have reached the limits of traditional test instruments' ability to accurately depict transmission signals.

Jitter, a form of unintentional modulation, is a major source of transmission errors in these types of digital communications sytems. Designers of the line repeaters, mulitplexers, digital switches and other communications equipment used in these systems must verify that jitter is not excessive, and be able to sectionalize problems to find sources of jitter. For example, if a designer can determine the jitter is predominantly at 60 or 120 cycles per second, power supplies can be examined as potential sources of the problem.

Modulation domain analysis is the only technique available today that can directly display jitter as a function of time. In this case, the HP 53310A can be thought of as a "jitter oscilloscope" directly displaying jitter as a function of time, enabling the amplitude to be measured and strong periodic elements to be identified. The ultra-fast hardware histogram capability of the HP 53310A can quantify statistics of the jitter to help determine possible source depending on whether the jitter is random or not.

The HP 53310A

Modulation domain analysis provided by the HP 53310A can provide a clearer understanding of problems in a number of mechanical systems becuase of its unique real-time display of frequency variations. It's invaluable in developing higher resolution, faster laser printers, where accurately characterizing the rotating mirror at the heart of these systems is critical. The anti-lock braking systems, adjustable suspension systems, and other high-tech additions to automobiles rely on faster, more accurate motion control systems, all particularly well-suited to the HP 53310A's abilities.

With its unique ability to directly display complex signals in real time, affordability, and ease-of-use features, the HP 53310A Modulation Domain Analyzer now is ready to take its place beside the designer's other established test instruments.

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