Designing On-Chip Active RC Filters for the Analog Front End (AFE)

Summary form only given. Since the early days of microminiaturization in the 1970´s and 70´s, the design and implementation of filters has presented a special problem. The reason for this is mainly that conventional LCR filters, and in particular, inductors, cannot be miniaturized, let alone integrated, on a chip. Thus, for the last forty years or so, inductorless alternatives to LCR filters that are compatible with microminiaturization and on-chip integration have been developed. This continues to be necessary because, in spite of the ´digital revolution´, the so-called ´analog front end´ (AFE) of most electronic devices, which interface with the real world, is and will continue to be, analog. In this talk, a brief historical overview of the many attempts at finding inductorless filters is first given. The overview ranges from hybrid integrated thin and thick film circuits of the 60´s and 70´s, to switched capacitor and switched current filters of the 80´s and 90´s, and on to the present day continuous time active RC filters that are amenable to mixed mode on-chip implementation. Some of the main present day methods of designing active RC filters for on-chip design are covered. These methods cover signal flow graph simulation of LC ladder filters, multiamplifier biquads, ladder-biquad combinations, and the design of frequency-dependent capacitors and inductors. Examples from the area of high speed wire-bound digital data communication systems (ADSL and VDSL) are given