Baseband and IF Sampling

Operational "How to" GuidesSummaryBaseband and IF Sampling Different Ways to Get your Signal BitsDescriptionBaseband and IF Sampling - Different ways to get your signal bits       In this architecture, the signal is downconverted and band-limited before being digitized. Sampling is performed on the intermediate frequency (IF) stage output.   In signal analyzers, the sampling frequency is related to the maximum bandwidth required to represent the signal under test. That frequency is usually low compared to the center frequency of the signal under test, and there is no need to change it with changes in signal center frequency. The alternative, called baseband sampling, involves direct sampling of the entire signal under test, from DC to at least its highest occupied frequency: CF + ½ OccBW.   Here, the signal undergoes minimal processing before being digitized. The lowpass filter ensures that frequencies above the ADC’s Nyquist sampling criterion do not produce false or alias products in the processed results.   The signal under test is completely represented by baseband sampling and any type of analysis can be performed. Narrowband analysis as performed with a spectrum/signal analyzer—in the time, frequency, and modulation domains—is achieved by implementing filters, mixers, resamplers, and demodulators in DSP. Keysight’s 89600 VSA software is the primary tool for these tasks and many others, and it runs on a variety of sampling platforms.   We thus have two paths to the signal analysis we need. The best sampling choice is determined by performance requirements, the operating frequencies and bandwidths involved, and the resulting demands on sample rate.   The architecture of IF sampling allows for analog downconversion and filtering to dramatically reduce the required sample rate. This process has been thoroughly optimized in performance and cost, and focuses ADC performance on the essential signal. Other frequencies are excluded, and the limited bandwidth allows for ADCs with the best resolution, accuracy, and dynamic range.   With baseband sampling, frequency conversion and filtering are done in DSP, requiring a vast amount of digital data reduction to focus analysis on the band in question. This must precede processing for signal-analysis results such as spectrum or demodulation. The spectrum analysis and demodulation are generally performed using IF sampling. The technological evolution explains the increasing use of baseband sampling for RF and microwave signal analysis.    See AlsoKeysight’s 89600 VSA software X-Series Signal Analyzer Infiniium Z-Series Oscilloscopes