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blocks using analog or mixed-mode IC technologies, as they are much
more costly as compared with standard digitally-oriented CMOS tech-
nologies. Instead, it is highly desirable to realize analog blocks using
standard digitally-oriented CMOS technologies. Switched current tech-
niques emerged in the late 1980s [3] provide such a solution. Shown in
Fig.1.5 are the first generation and second generation switched current
memory cells. It is seen that switched current memory cells make use
of the gate capacitance of the sampling transistor to hold the sampled
input current, in the form of charge stored in and then exports it to
the output in the subsequent clock phase in the form of current. Note
that in these implementations, no linear capacitors are needed. Only
MOS transistors are used. Switched current techniques are therefore
fully compatible with and can be implemented using standard digitally-
oriented CMOS technologies.
Using the basic memory cells, other building blocks, such as integra-
tors, can be realized conveniently using switched current techniques, as
shown in Fig.1.6 [4].
The basic switched current integrators can be combined to form more
complex switched current networks, such as the biquad shown in Fig.1.7.
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