University Of Vaasa

learnedbawledΗλεκτρονική - Συσκευές

24 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

78 εμφανίσεις

University Of Vaasa

Telecommunications Engineering

Automation Seminar


Signal Generator


By Tibebu Sime

Email:

t94778@student.uwasa.fi










13
th

December 2011


1

Introduction


Signal generator produces alternating current (AC) of the desired
frequencies and amplitudes with the necessary modulation for
testing or measuring circuits. Users are able to know what state the
circuit is in when the signals are distorted, attenuated or missing
entirely. Therefore, it is important that the amplitude generated by
the signal generator is accurate.




The objective of this
seminar is to highlight how to
design a signal
generator using Field
-
Programmable Gate Array (FPGA) to generate
a few basics waveform such as square waves, triangular waves and
sine waves. These waveforms will be output to
an
oscilloscope since
with just the LCD on the FPGA development board is not able to
display the waveforms.



2

Why do we need?



The application of Field Programmable Gate


Array (FPGA) in the development of power
electronics circuits control scheme has drawn
much attention lately

due to its shorter design
cycle, lower cost and higher density.

3

Categories of signal Generator


Signal Generator is a tool that can produce
various patterns of waveforms at a variety of
frequencies and amplitudes. Basically, a signal
generator is used to generate signal with
precise controlled frequency and amplitude
characteristics to mimic the input signal of the
circuit being tested. It is generally used in
designing, testing and troubleshooting
electronic devices.

4


Signal generators generally fall into one of the two
categories:
function generators
and
arbitrary
waveform
generators

1.Function Generator:

is a device which produces simple
repetitive waveforms
. Such devices contain
an

electronic oscillator, a

circuit that
is capable of
creating a repetitive

waveform.


Modern
devices may use

digital signal processing

to
synthesize waveforms, followed by a

digital to
analog
converter
to produce an analog
output.

Example: Sine, square and triangular waves

5

Example of typical Sine wave

6

2.
Arbitrary wave generators
:
are sophisticated
and
complicated signal
generators which allow the user to
generate arbitrary
waveforms
within published limits
of

frequency

range, accuracy, and output level. Unlike
function generators, which are limited to a simple set
of
waveforms, an
AWG allows the user to specify a
source waveform in a variety of different
ways such as
exponential , cardiac ,sinc function or the combinations


FPGA will come to our rescue in providing
an attractive
platform for these signal generators in
-
terms of
performance, power consumption and flexibility in
configuration.


7

Steps to generate the signal

1
st
:
the
development of different waveform
signals which can be
selected

2
nd
:
the development of selecting different
frequencies for the waveform
output

3
rd
: to transfer these signals to Digital
-
to
-
Analog
Converter (DAC) which then output to the
Oscilloscope.


8

Signal Generator Model

The signal generator may use Digital Signal
Processing (DSP) to synthesize waveforms,
followed by a Digital to Analog Converter to
produce analog output
.
The signal generator
will operate in the audio frequency range,
ranging from 20 Hz to 20 KHz or quantity of
cycles per second. The frequency and the
amplitude are adjustable and must be able to
maintain constancy over the tuning
range


9

The Model






Onboard

Memory

Waveform

Generation

Engine

Digital

Gain

Digital

Filter

DAC

Clock

Analog

Filter

Output

10

VHDL


it allows system’s behaviour to be modelled and
simulated before logic synthesis tools were used



it allows switching between different modelling
of the system.


Verilog
: allows switch
-
level modelling which are
useful for exploring new circuits. And it ensures
that all signals are initialized to “unknown” so
that designers will produce necessary logic to
initialize their design.


11

Overview of HDL


FPGA is a semiconductor device that can be configured
by the customer or designer after manufacturing.
FPGAs are programmed using a logic circuit diagram or
a source code in a Hardware Description Language
(HDL) to specify how the chip will work. The most
common HDL used to program FPGA is Very high speed
integrated circuit Hardware Description Language
(VHDL) and
Verilog.


With the complexity of FPGA design, many specialist
design consultant has his / her own specific tools and
libraries written in VHDL or Verilog.



12

Xilinx’s Spartan
-
3A FPGA Development
Kit Board

13

Signal General model with FPGA

FPGA

50 MHz

Oscillator

DAC

Oscilloscope

Frequency

switches

Waveform

Switches

14


With input from the clock and switches
(frequencies selection and waveform
selection), FPGA will process the data and
transfer to DAC every micro second. This data
will be output to an Oscilloscope.


15

FPGA programming process

16


When the system compiled a HDL code written at
the design entry level, it output a Register
Transfer Level (RTL)
netlist
. When the input HDL is
successfully synthesize at the synthesizer, it
produces a HDL of this gate
-
level code that can
be mapped into the FPGA hardware. Compiling
and simulation of this gate
-
level HDL can be done
at the actual level to avoid any code written at
RTL disappeared at the final gate level
implementation. Thus, debugging of error can be
done at actual level.


17

Conclusion


An FPGA based Signal Generator is able to
generate any types of waveforms with good
performance.

18

References


http://en.wikipedia.org/wiki/Signal_generator


Wong, Yen.
Design a signal generator

using
FPGA
. SIM

University

School of Science and
Technology,2010


http://en.wikipedia.org/wiki/Field
-
programmable_gate_array#cite_note
-
history
-
2




19