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As IS-95 gains worldwide acceptance, higher levels of integration is desirable to reduce cost, board space, and power. Previous baseband signal processors for digital cellular communications integrate only the digital functions, while the baseband data conversion functions reside in a dedicated analog CMOS IC or are merged with the IF functions in a BiCMOS IC. However, analog processes typically have feature sizes that are generations behind digital CMOS. Since even data conversion functions need a variety of digital circuits such as digital filters for voiceband processing, /spl Delta//spl Sigma/ decimation, and various random logic for decoding and register file control, the use of older analog processes leads to larger area and power in addition to the extra package cost. Moreover, chip-to-chip communication consumes power and creates unnecessary board noise. Thus, it is desirable to integrate the analog functions with the digital signal-processing elements to take advantage of the rapid advances in digital CMOS and the integrated form factor. Due to the difficulty of mixed-signal integration, there is no previous report of successful integrated mixed-signal baseband processors that have gained type-approval and gone into high-volume production. The authors report on the design of a 3 V mixed-signal baseband processor IC implemented in CMOS technology for IS-95 applications.
Date of Conference: 9-9 Feb. 2000