Syllabic companding filters with emphasis on wireless applications.

摘要

This dissertation investigates the use of syllabic companding to implement analog continuous time filters with wide dynamic range and low power dissipation. A simple, CMOS compatible, technique is proposed where the dynamic range of the filter is divided in sub-ranges, each covered by a different filtering path optimized specifically for this sub-range. This results in small admittance levels for the individual filtering paths, and correspondingly small power dissipation and chip area. The system provides undisturbed output during range switching.; A potential application of syllabic companding is in the area of channel selection filters, which are typically used in wireless receivers to reject large out-of-band interferers before analog to digital conversion. Issues relating to the design of syllabic companding channel selection filters are identified, and possible solutions are proposed.; A general technique is presented for optimizing the dynamic range of an arbitrary continuous time filter while keeping the power dissipation to a minimum. The developed optimization algorithm covers, as a special case, the design of channel selection filters. The distortion performance of the filter is assumed to be dominated by weak third order nonlinearities. The validity of the algorithm is verified with simulations.; A very accurate circuit is proposed for setting the g_m of a transconductor to a prescribed reference value despite temperature and process variations. Also, the idea of using unity gain buffers to achieve common mode stabilization in fully differential circuits is proposed, and related practical issues are addressed. This scheme is shown to provide satisfactory performance with very small power dissipation.; A chip implementing the ideas of this dissertation was fabricated in a 0.25 um standard CMOS process. The intended application of the filter is channel selection in an 802.11a/Hiperlan2 Wireless Ethernet receiver. The chip dissipates 9 mA, occupies an area of 0.7 mm2, and maintains a Signal/(Noise + IM3 Distortion) ratio of at least 33 dB, over a 48 dB signal range, with good blocker immunity. This performance represents at least an order of magnitude improvement over existing channel selection filters.