Agilent Technologies' distortion test suite helps optimize linearity of multichannel power amplifiers

1/14/2003 - Agilent Technologies Inc. (NYSE: A) introduced a software application for its spectrum analyzer families, which allows multichannel power amplifier (MCPA) designers to achieve the lowest possible distortion and highest linearity with the least amount of effort and complexity.

The Agilent 89604A distortion test suite can be used with Agilent ESA-E or PSA Series spectrum analyzers or 89600 Series vector signal analyzers. When used with a spectrum analyzer, the ESG or PSG Series digital signal generator, and a PC running any current Windows(r) operating system, the 89604A delivers the processed (delay-corrected and amplitude normalized) signal files designers need to program advanced curve fitters that control the linearity of MCPAs. The test suite also graphically shows the incremental signal degradation contributed by the MCPA, as well as many other characteristics useful for optimizing amplifier performance.

The test suite and its accompanying instruments use stimulus signals that are very similar to those the amplifier will experience in service, which is one of the most important factors for the solution's measurement accuracy. Traditional techniques use a single swept CW signal or multiple CW signals as a stimulus, which do not accurately imitate the complexity of today's broadband digital modulation schemes. As a result, amplifiers optimized using these stimulus signals can perform poorly. In contrast, the distortion test suite works with real-world signals provided by a base station, test signals produced by a signal generator, or even Additive White Gaussian Noise (AWGN). Thus, MCPAs characterized with the distortion test suite are much more likely to meet or exceed tight telecommunications industry standards.

This PC-based software also provides complete, time-aligned stimulus/response data, resampled to match user needs, for input to the predistortion curve fitter, which the designer would otherwise need to compile manually.

The 89604A distortion test suite uses complex modulated "real-world" signals to accurately measure AM/AM and AM/PM distortion with up to 36 MHz of measurement bandwidth (depending on the instruments used), ensuring that even subtle distortion mechanisms such as memory effects and component heating are stimulated and measured. The results are displayed together with an ideal performance line for reference and a curve fit to the results. This helps evaluate how far from ideal the MCPA moves as it approaches saturation, which occurs when the amplifier reaches beyond the highest input level it can withstand and still produce a clean signal.

The distortion test suite provides other useful information as well. The gain compression display scales the AM/AM gain curve to emphasize variations in gain, and the probability density function (PDF) curve lets the designer examine the stimulus and response signals to ensure that they have the expected distribution around their means. The complementary cumulative distribution function (CCDF) curves show how much headroom is available in the design. The distortion test suite can also show how error vector magnitude (EVM) contributed by the MCPA degrades the modulation of the signal. Finally, the distortion test suite provides a results display of the polynomial coefficients used by the AM/AM and AM/PM curve-fitting algorithm, which can then be used to set up the predistortion curve fitter.

Measurement setup is simple: Once a few connections are made, the user enters center frequency, measurement span, number of measurement channels, input range, and values of external attenuators, then presses start. The distortion test suite and instruments do the rest.

The 89604A distortion test suite can be used with any ESA-E or PSA Series spectrum analyzer or the 89600 Series VXI-based vector signal analyzer. Two-channel measurements can be made (greatly reducing measurement test) when the test suite is used with the PSA Series or 89600.

Additional information about the Agilent 89604A distortion test suite is available at

U.S. Pricing and Availability
The Agilent 89604A distortion test suite is available now for approximately $2,000.

About Agilent Technologies
Agilent Technologies Inc. (NYSE: A) is a global technology leader in communications, electronics and life sciences. The company's 36,000 employees serve customers in more than 110 countries. Agilent had net revenue of $6 billion in fiscal year 2002. Information about Agilent is available on the Web at

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