Better Signal Quality Begins At Baseband

rF Or BaseBand engineers often need fast, accurate, and cost-effective signal-analysis measurements in the spectral and time domains. They also need to perform digital-modulation analysis. Such measurements may be made with an oscilloscope and a spectrum analyzer. Using two instruments can introduce errors while raising the cost of test, however. Although single-instrument, higher-end solutions are available, they come at a higher cost. These issues are compounded by the fact that new, more compact, and economical radio-communications devices with higher data rates are constantly being developed. Agilent Technologies, Inc. illustrates how quick, accurate, and cost-effective baseband in-phase/quadrature (I/Q) analysis of radio-communications devices can be performed in "Baseband IQ Analysis."

This four-page application note discusses how baseband I/Q analysis can be performed early in analog baseband development using a general-purpose signal analyzer. Of course, that signal analyzer must support multiple bandwidths and be equipped with analog baseband I/Q inputs. Such analyzers allow engineers to use a range of standard-based measurements like spectrum emission mask and local-oscillator phase noise. In addition, modulation analysis allows the designer to detect, demodulate, and troubleshoot digital signals. With the added feature of the baseband I/Q inputs, these capabilities can be extended to baseband signals.

By just switching the input channels on the signal analyzer, any unexpected degradation in baseband signal quality can be investigated at both RF and baseband. The engineer also can perform complex spectrum and I/Q waveform measurements during analog baseband signal analysis. With complex spectrum, sampled complex data can be shown in the frequency domain. In addition, the marker functions available in the analyzer allow channel power, intermodulation distortion (IMD), and spurious signal measurements to be made. If the signal analyzer offers more sophisticated capabilities like noise and band/interval markers, baseband signals can even be fully characterized.

As an example, the note points to the firm's MXA signal analyzer with option BBA for baseband analysis. Different aspects like the software and probe are recommended and detailed. A two-channel analysis example also is included. The note emphasizes that the successful operation of a radio-communications device depends on signal quality at the baseband as well as RF.

Agilent Technologies, Inc., 5301 Stevens Creek Blvd., Santa Clara, Ca 95051; (408) 345-8886, Fax: (408) 345-8474, internet:

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