University Of Vaasa
Telecommunications Engineering
Automation Seminar
Signal Generator
By Tibebu Sime
Email:
t94778@student.uwasa.fi
13th December 2011
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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.
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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.
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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.
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• 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
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Example of typical Sine wave
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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.
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Steps to generate the signal
1st : the development of different waveform
signals which can be selected
2nd: the development of selecting different
frequencies for the waveform output
3rd: to transfer these signals to Digital-to-Analog
Converter (DAC) which then output to the
Oscilloscope.
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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
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The Model
Onboard
Memory
Waveform
Generation
Engine
Output
Digital
Gain
Analog
Filter
Digital
Filter
DAC
Clock
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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.
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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.
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Xilinx’s Spartan-3A FPGA Development
Kit Board
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Signal General model with FPGA
50 MHz
Oscillator
FPGA
Frequency
switches
Waveform
Switches
DAC
Oscilloscope
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• 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.
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FPGA programming process
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• 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.
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Conclusion
• An FPGA based Signal Generator is able to
generate any types of waveforms with good
performance.
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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/Fieldprogrammable_gate_array#cite_note-history2
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