Presentation on theme: "BASICS OF DIRECT DIGITAL SYNTHESIS Calen Carabajal EECS 713 12/3/2013."— Presentation transcript:
BASICS OF DIRECT DIGITAL SYNTHESIS Calen Carabajal EECS 713 12/3/2013
WHAT DOES A DDS DO? “Direct Digital Synthesis is a method of producing an analog waveform— usually a sine wave—by generating a time-varying signal in digital form and then performing a digital-to-analog conversion. ” Capable of generating arbitrary waveforms and accomplishing various modulation schemes. High-speed DDS applications include, primarily, radar and communication systems
HOW IT WORKS: THE DDS CORE The core of the DDS is the phase accumulator and a lookup table, which comprise a Numerically Controlled Oscillator N-bit word in frequency control register (Frequency Tuning Word, FTW) is input to adder, added to feedback accumulator output. Truncated output serves as address/input for sin() lookup table. Output word is amplitude for given phase value. Converted to analog.
HOW IT WORKS: FREQUENCY TUNING WORD The FTW determines the jump size on a phase wheel. Each clock cycle, the phase accumulator is updated by the amount given by the frequency tuning word. Output of phase accumulator is a ramp function with slope FTW When accumulator surpasses 2^n, it cycles back to beginning
HOW IT WORKS: PHASE-TO-AMPLITUDE CONVERSION Phase-to-amplitude conversion is a block of memory. Contains values ~2^M values of sine wave amplitude Only needs to contain first 90 degrees, not 360 degrees. Accumulator output bits serve as address
CHIRP GENERATION USING ON-CHIP DIGITAL RAMP GENERATOR
SOURCES Understanding Direct Digital Synthesis (DDS). www.ni.com/white- paper/5516/enwww.ni.com/white- paper/5516/en Ask the Application Engineer—33: All About Direct Digital Synthesis. http://www.analog.com/library/analogdialogue/archives/38- 08/dds.pdf http://www.analog.com/library/analogdialogue/archives/38- 08/dds.pdf Fundamentals of Direct Digital Synthesis (DDS). http://www.analog.com/static/imported-files/tutorials/MT- 085.pdf http://www.analog.com/static/imported-files/tutorials/MT- 085.pdf AD9914 Datasheet. http://www.analog.com/static/imported- files/data_sheets/AD9914.pdfhttp://www.analog.com/static/imported- files/data_sheets/AD9914.pdf