Vector signal analysis of digital baseband and if signals within an FPGA

Abstract

This paper introduces novel techniques for analyzing digital signal and modulation quality inside of field programmable gate arrays (FPGAs). This convergence of innovations in logic analysis with those in vector signal analysis can provide designers of digital baseband and IF signal processing systems as well as analog-to-digital and digital-to-analog converters with the ability to make key measurements where they were previously unavailable or difficult to make. As FPGAs continue to make larger contributions in DSP for wireless and satellite communications, the increasing dominance of digital baseband and IF signals presents a challenge to designers of radio and satellite systems. DSP circuit designers constantly make tradeoffs between design complexity (bit precision, number of filter taps, etc), power consumption, and signal quality. Key measurements like error vector magnitude can be used to gauge the performance implications of these tradeoffs. Previously, vector signal analysis measurements have been either directly integrated into RF test instruments, or written as custom software by baseband designers. With entire sections of a radio being implemented digitally, and integrated inside a single chip, new methods are needed to characterize the individual subsystems in a digital radio. This paper presents the combination of a dynamic FPGA probe, which enables routing of signal groups within an FPGA to a logic analyzer for measurement through a small number of physical package pads, with an FFT-based vector signal analysis software package. This combination provides simultaneous measurement of time domain, frequency spectrum, and modulation quality on digital signals inside an FPGA. It also provides the quick selection of various internal nets for signal analysis without time-consuming redesigns of the FPGA