Agilent 5989-5732EN English 2014-08-04 PDF 7.28 MB c20140812 [18] free download

File name 5989-5732EN English _ 2014-08-04 _ PDF 7.28 MB c20140812 [18].pdf

Keysight Technologies Evaluating Oscilloscope Sample Rates vs. Sampling Fidelity Application Note Introduction How to Make the Most Accurate Digital Measurements Digital storage oscilloscopes (DSO) are the primary tools used today by digital designers to perform signal integrity measurements such as setup/hold times, eye margin, and rise/fall times. The two key banner specifications than affect an oscilloscope's signal integrity measurement accuracy are bandwidth and sample rate. Most engineers have a good idea of how much bandwidth they need for their digital measurements. However, there is often a lot confusion about required sample rates--and engineers often assume that scopes with the highest sample rates produce the most accurate digital measurements. But is this true? When you select an oscilloscope for accurate, high-speed digital measurements, sampling fidelity can often be more important than maximum sample rate. Using side-by-side measurements on oscilloscopes with various bandwidths and sample rates, this application note demonstrates a counterintuitive concept: scopes with higher sample rates can exhibit poorer signal fidelity because of poorly aligned interleaved analog-to-digital converters (ADCs). This application note also will show how to easily characterize and compare scope ADC sampling fidelity using both time-domain and frequencydomain analysis techniques. Let's begin with a discussion of minimum required sample rate and a review of Nyquist's sampling theorem. Table of Contents Introduction ... 2 Nyquist's Sampling Theorem ... 3 Interleaved Real-Time Sampling ... 7 Testing for Interleave Distortion ... 9 Effective number of bits analysis ... 9 Visual sine wave comparison tests ... 10 Spectrum analysis comparison tests .. 13 Summary ... 16 Related Keysight Literature ... 16 Glossary ... 17 03 | Keysight | Evaluating Oscilloscope Sample Rates vs. Sampling Fidelity - Application Note Nyquist's Sampling Theorem How much sample rate do you need for What Nyquist calls f MAX is what your digital measurement applications? Nyquist Sampling Theorem we usually refer to as the Nyquist Some engineers have total trust For a limited bandwidth signal with frequency (f N), which is not the same in Nyquist and claim that just 2X a maximum frequency fMAX, the as oscilloscope bandwidth (f BW ). If an sampling over the scope's bandwidth is equally-spaced samp