Environmental Engineering Reference
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This is clearly a big advantage, as compared with active filters realized
using diffusion resistors.
The bottom plate of the capacitors usually has a large parasitic capac-
itance to the substrate, particularly if the capacitors are implemented us-
ing poly-diffusion capacitors. To minimize the effect of the parasitic bot-
tom plate-substrate capacitance of switched capacitor networks, stray-
insensitive switched capacitor techniques shown in Fig.1.2 were pro-
posed. Consider the circuit in Fig.1.2a, in phase 1 where
the two terminals of the bottom plate-substrate capacitor are shorted to
ground. In phase 2 where they are connected to both
the ground and the virtual ground of the following operational ampli-
fier. As a result, this parasitic capacitor has no effect on the operation
of the network. Fig.1.3 shows the basic configurations of inverting and
non-inverting stray-insensitive switched capacitor integrators [3].
The basic switched capacitor integrators can be combined to form
more complex switched capacitor networks, such as the biquad shown in
Fig.1.4.
3. Switched Current Techniques
The implementation of switched capacitor networks requires linear
capacitors that are realized using two floating conducting layers. These
floating conducting layers, however, do not exist in standard digitally-
oriented CMOS technologies in which most digital CMOS circuits are
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