Design of Digital Signal Spectrum Analyzer
Based on FPGA
Dewen Qi
1
, Xuan Guo
1
, Weitao Du
1
1
Engineering Center of Digital Audio & Video
Communication University of China
Beijing, China
dewen_qi@cuc.edu.cn
Abstract—This paper presents a hardware software co-design
of embedded digital spectrum analyzer. As a digital hardware
design, it achieves better portability and modularity so that it
could be easily deployed and embedded into other systems as a
module and conduct arbitrary intermediate nodes spectrum
monitoring with ease while such tasks are hard for traditional
spectrum analysis instruments to accomplish since most of them
only provide limited user interface. Besides, this design
implements functions of real-time signal analysis and real-time
spectrum display with VGA port, which traditional embedded
data observation systems, for example SignalTap II Logic
Analyzer, do not have. Furthermore, this design serves as a
sample of hardware software co-design of soft-core processor
based system, which can be used for reference.
Keywords—Spectrum analyzer; FPGA; SOPC; Nios II; FFT
I. INTRODUCTION
Spectrum analyzer is a kind of instrument which analyses
signal spectrum to provide its frequency-domain feature that is
widely used in military, satellite communications, radio
monitoring and other fields. In recent years, the popularity of
digital devices sparked a new revolution in the field of
electronics, and as a result, the spectrum analyzer design also
evolved from conventional analog type to digital type. Among
the digital systems, field-programmable gate array (FPGA), has
advantages of design flexibility, high speed, ease of
modification, low power consumption, which results in its
widespread usage.
There are basically two kinds of methods to observe digital
spectrum. The first approach is using the digital spectrum
analysis instrument, which only provides limited user interface
and not suitable for analyzing system’s internal signal. Another
approach is collecting spectrum data from the embedded logic
analyzer of FPGA or printing spectrum data to personal
computer (PC) through the soft-core processor and then
plotting the spectrum with MATLAB. The second approach
makes it possible for users to assign internal nodes in the
system and monitor the spectrum of them while it is inefficient
and incapable of real-time spectrum analysis. To solve these
problems, this paper proposes a method of embedded digital
spectrum analysis, which not only can analyze signals and
display spectrum in real-time with the help of the fast Fourier
transform (FFT) IP core, but also is so portable that it can be
easily migrated to other systems to monitor spectrum of
intermediate nodes. In conclusion, this design has advantages
of real-time, stability, high reusability and simple peripheral
circuit.
II. S
YSTEM OVERVIEW
A. Overall system Scheme
Based on different approaches of signal analysis, there are
two kinds of spectrum analyzer implementation schemes,
based on the discrete Fourier transform (DFT) of modern
digital signal processing technology or based on the frequency
sweep tuning method, which belongs to traditional heterodyne
signal processing technology. This design chooses the former
approach for the ease of implementing DFT based on digital
devices.
B. System Top-Level Structure
This design mainly consists of three parts: the signal source
for test, FPGA board and video graphics array (VGA) display
as is shown in Fig. 1. The major function of this system is
analyzing input signals and then displaying their spectrum and
energy progress. Besides, this design provides two kinds of
different source signal modes and different FFT processing
modes, as is shown in TABLE I. .
ADC
VGA
Display
Signal
Generator
FPGA Board
Video
DAC
GPIO
FPGA
Chip
Fig. 1. System Block Diagram
TABLE I. S
YSTEM OPTION
Mode Description
External signal mode
Choose external signals through the ADC
circuit to test.
Internal signal mode Choose internal signals from DDS to test.
CFFT mode
Use FFT algorithm in Nios II to perform
FFT.
FFT IP core mode Use FFT IP core to perform FFT.
DDS frequency adjust Range:0.5M-5MHz; stepper:0.5MHz
978-1-4673-9104-7/15/$31.00 ©2015 IEEE
Proceeding of the 2015 IEEE
International Conference on Information and Automation
Lijiang, China, August 2015