3.4 Conclusions

The need for multimode operation makes it necessary to develop a programmable analogue baseband chain that can serve the stringent and often widely varying performance requirements of 2G and 3G wireless communication standards. To reduce the design cycle time, it would be helpful to have a single active block, which can be repeatedly used in realising required filters and variable gain amplifiers. This chapter introduces a third-order Sallen–Key filter section based on a single high-performance fully balanced differential difference amplifier based buffer. A sixth-order filter is implemented by cascading two third-order blocks. Triode region transistors in parallel with polysilicion resistors are used for tuning the filter characteristics. The same structure is modified by adding current sensing at the output of the buffer to realise a variable gain amplifier with offset control. The gain is set by the ratio of resistors and is independent of the bandwidth. Techniques to reconfigure the baseband chain for satisfying different system-level specifications constructed out of these elements are discussed. Measured results indicate that the proposed chain meets the performance specifications of GSM, IS-95 and WCDMA wireless standards.