Because of the huge bandwidth of Ultra-Wideband (UWB) systems, in-band narrowbandinterference may hinder receiver performance. In this dissertation, sourcesof potential narrowband interference that lie within the IEEE 802.15.3a UWB bandwidthare presented, and a solution is proposed. To combat interference in Multi-BandOFDM (MB-OFDM) UWB systems, an analog notch filter is designed to be includedin the UWB receive chain. The architecture of the filter is based on feed-forwardsubtraction of the interference, and includes a Least Means Squared (LMS) tuningscheme to maximize attenuation. The filter uses the Fast Fourier Transform (FFT)result for interference detection and discrete center frequency tuning of the filter. Itwas fabricated in a 0.18 ????m process, and experimental results are provided. This isthe first study of potential in-band interference sources for UWB. The proposed filteroffers a practical means for ensuring reliable UWB communication in the presense ofsuch interference.The Operational Transconductance Amplifier (OTA) is the predominant buildingblock in the design of the notch filter. In many cases, OTAs must handle inputsignals with large common mode swings. A new scheme for achieving rail-to-railinput to an OTA is introduced. Constant gm is obtained by using tunable levelshifters and a single differential pair. Feedback circuitry controls the level shiftersin a manner that fixes the common mode input of the differential pair, resulting in consistent and stable operation for rail-to-rail inputs. As the new technique avoidsusing complimentary input differential pairs, this method overcomes problems suchas Common Mode Rejection Ratio (CMRR) and Gain Bandwidth (GBW) productdegradation that exist in many other designs. The circuit was fabricated in a 0.5????mprocess. The resulting differential pair had a constant transconductance that variedby only ????0.35% for rail-to-rail input common mode levels. The input common moderange extended well past the supply levels of ????1.5V, resulting in only ????1% fluctuationin gm for input common modes from -2V to 2V.
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