Digital Frequency Synthesis Demystified

Digital Frequency Synthesis DemysTIfied: This text deals with emerging modern digital techniques used to generate and modulate sine wav e s. These waveforms are used in almost all radio applicaTIons, communicaTIons, radar, digital comm u n i c a t i o n s, electronic imaging, and more. Such tech n i q u e s either build the waveform from the “ground up” digitally (i.e., generate all the signal parameters such as phase, frequency, and amplitude digitally) and deal with the very fundamental nature of the waveform and its features (direct digital synthesis) or are part of the digital heart of modern p h a s e - l o cked loop (P L L) synthesize r s. This might seem, and is indeed, a common and known subject. Sine waves are truly natural waveforms and trigonometric funcTIons that are well known and have been researched for a long t i m e. Furthermore, frequency synthesis is quite a mature technology with extensive literature and comprehensive coverage in the professional meetings. Why another text on the subject? What is new besides application-specific integrated circuit (A S I C) technologies and silicon densities, geometry, and integration? While the above statements are true, there is a continuous evolution in the tech n o l o g y. The generation of accurate wav e f o r m s p l ays a crucial role in almost all electronic equipment, from radar to home entertainment equipment, so the importance of the subject is cl e a r. Clearly, the most important reason for the utilization of the now extremely popular PLL synthesizers in consumer elec- tronics and other very popular applications at extremely low cost (and the popularization of frequency synthesis from consumer products all the way to complex requirements) is the advance of digital technology; integrated, high densities; and low-cost silicon single-PLL chips and ASICs. However, parallel to the advance of traditional PLL synthesis, there emerged other synthesis techn iques, mainly digital in nature, direct digital synthesis (D D S) and fractional-N PLL synthesis. Thus, the classical PLL synthesizer is now being supplemented with a sizable element of digital technology and digital signal processing (DSP). Indeed the application of DSP techniques to frequency synthesis is still at an early stage.