Abstract:
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This paper presents an improved modeling of the effect
of random mismatch and current source transient switching
behavior on the performance of current-steering CMOS digital-toanalog
converters (DACs). The work considers two current source
cell topologies, namely a simple cell and a cascoded cell, obtaining
the relation of transistors design parameters to the static and dynamic
models. On the one hand, a mismatching statistical analysis
is applied to all the transistors of the current source circuit,
which allows to define design expressions relating the circuit parameters
to the DAC specifications without the need of arbitrary
design margins or Monte Carlo simulations. On the other hand,
improved analysis of the current source switching characteristics
provides a more realistic modeling of the relation between transistors
sizes and output current settling time. By including these two
improved models into the usual design procedure, circuit sizing for
optimum settling time and proper static behavior can be obtained
analytically, reverting in smaller current source area, and, hence,
in an overall DAC area reduction. |