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Description:
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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 . |