Nonlinearity and noise modeling of operational transconductance amplifiers for continuous time analog filters

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Title: Nonlinearity and noise modeling of operational transconductance amplifiers for continuous time analog filters
Author: Ramachandran, Arun
Abstract: A general framework for performance optimization of continuous -time OTA -C (Operational Transconductance Amplifier -Capacitor ) filters is proposed . Efficient procedures for evaluating nonlinear distortion and noise valid for any filter of arbitrary order are developed based on the matrix description of a general OTA -C filter model . Since these procedures use OTA macromodels , they can be used to obtain the results significantly faster than transistor -level simulation . In the case of transient analysis , the speed -up may be as much as three orders of magnitude without almost no loss of accuracy . This makes it possible to carry out direct numerical optimization of OTA -C filters with respect to important characteristics such as noise performance , THD , IM3 , DR or SNR . On the other hand , the general OTA -C filter model allows us to apply matrix transforms that manipulate (rescale ) filter element values and /or change topology without changing its transfer function . The above features are a basis to build automated optimization procedures for OTA -C filters . In particular , a systematic optimization procedure using equivalence transformations is proposed . The research also proposes suitable software implementations of the optimization process . The first part of the research proposes a general performance optimization procedure and to verify the process two application type examples are mentioned . An application example of the proposed approach to optimal block sequencing and gain distribution of 8th order cascade Butterworth filter (for two variants of OTA topologies ) is given . Secondly the modeling tool is used to select the best suitable topology for a 5th order Bessel Low Pass Filter . Theoretical results are verified by comparing to transistor -level simulation withCADENCE . For the purpose of verification , the filters have also been fabricated in standard 0 .5mm CMOS process . The second part of the research proposes a new linearization technique to improve the linearity of an OTA using an Active Error Feedforward technique . Most present day applications require very high linear circuits combined with low noise and low power consumption . An OTA based biquad filter has also been fabricated in 0 .35mm CMOS process . The measurement results for the filter and the stand alone OTA have been discussed . The research focuses on these issues .
URI: http : / /hdl .handle .net /1969 .1 /3925
Date: 2006-08-16

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Nonlinearity and noise modeling of operational transconductance amplifiers for continuous time analog filters. Available electronically from http : / /hdl .handle .net /1969 .1 /3925 .

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