University Of Vaasa Telecommunications Engineering

1. University Of VaasaTelecommunications Engineering Automation Seminar 13th December 2011 Signal Generator By Tibebu Sime Email: t94778@student.uwasa.fi

2. 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.

3. 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.

4. 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.

5. 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

6. Example of typical Sine wave

7. 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.

8. 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.

9. 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

10. The Model Onboard Memory Waveform Generation Engine Digital Filter Digital Gain Clock DAC Output Analog Filter

11. 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.

12. 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.

13. Xilinx’s Spartan-3A FPGA Development Kit Board

14. Signal General model with FPGA Frequency switches 50 MHz Oscillator FPGA Waveform Switches DAC Oscilloscope

15. 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.

16. FPGA programming process

17. 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.

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

19. References • http://en.wikipedia.org/wiki/Signal_generator • Wong, Yen. Design a signal generatorusing FPGA. SIMUniversitySchool of Science and Technology,2010 • http://en.wikipedia.org/wiki/Field-programmable_gate_array#cite_note-history-2