| OCR Text |
Show 1night want to 1nak it si1npl to r du e ost and ornpl xity f th spr ad-sp trum syst ms an be r c iver orient d or trans1nitt r ri nt on where 1nost of the processing is done. Most syst ms ar Th where the transmitter is simple and the receiver is complex. This way th n twork protocol is simpler and fully connected networks are easier to implement compar d to a TDMA, which needs a master clock and complicates the whole syst m. Spread spectrum communications have been useful for the military(22] for a long period of time. However, during the past 10 years, spread-spectrum use in coininercial applications has been increasing, specially in applications like wireless communications and multiple access communications. Spread spectrum techniques offer several advantages over conventional digital communication methods. Chapter 2 discusses the operation of spread-spectrum systems and advantages of such systems over other methods. Most modern day communication systems make use of A/D conversion to move from analog domain to digital domain. A/D converters play an important role in the performance of the whole system, and the speed of operation of the whole system depends on the speed and accuracy of the A/D converter. Presently the inaccuracies involved in high-speed A/D conversion represent one of the bottlenecks in the development of faster spread-spectrum systems. Among the available A/D conversion techniques, the sigma-delta modulation technique has recently received considerable attention as a promising means of high-speed A/D conversion in VLSI. A/D converters utilizing sigma-delta modulation have many desirable properties when compared to other methods of A/D conversion[3]. One advantage of this approach over other high-speed A/D conversion methods is that a smaller number of circuit components is required. The sensitivity of the components can also be relaxed due to the single-bit nature of the quantization in the sigma-delta unit. Also due to the feedback and error accumulation in the sigma-delta modulator, it is robust against circuit imperfections. Hence the sigma-delta modulation technique is well suited to implementation in VLSI. These advantages make this method of A/D conversion a good practical choice for the implementation of the A/D converter |
