Direct digital frequency synthesizer
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A frequency synthesizer is an electronic system for generating any of a range of frequencies from a single fixed timebase or oscillator. They are found in many modern devices, including radio receivers, mobile telephones, radiotelephones, walkie-talkies, CB radios, satellite receivers, GPS systems, etc. Direct Digital Synthesis (DDS) is a kind of frequency synthesizer that uses electronic method for digitally creating arbitrary waveforms and frequencies from a single, fixed source frequency. Direct Digital Frequency Synthesis (DDFS) is a mixed signal part i.e. it has both digital and analog parts. DDFSs digital part is also known as Numerically Controlled Oscillator (NCO), which consists of Phase Register, Phase Accumulator (PA) and ROM. Analog part has Digital-to-Analog Converter and a filter. NCO is a digital computing block which renders digital word sequences in time at a given reference clock frequency , which thereafter are converted into analog signals to serve as a synthesizer. The phase accumulator (PA) clocked with , generates the phase value sequence. Application of DDFS ranges from instrumentation to modern communication systems, which employs spread-spectrum and phase shift-keying modulation techniques. The focus of this thesis is on design, analysis and simulation of DDFS, using tools like Xilinx and Cadence. Traditional designs of high bandwidth frequency synthesizers employ the use of a phase locked- loop (PLL). DDFS provides many significant advantages over the PLL approaches, such as, fast settling time, sub-Hertz frequency resolution, continuous-phase switching response and low phase noise.