26 September 2007

Variable Threshold CMOS (VTCMOS) Circuits

One of the efficient methods to reduce power consumption is to use low
supply voltage and low
threshold voltage without loosing speed performance. But increase in
the lower threshold voltage devices leads to increased subthreshold
leakage and hence more standby power consumption.

Variable Threshold CMOS (VTCMOS) devices are one solution to this
problem. In VTCMOS technique threshold voltage of the low threshold
devices are varied by applying variable substrate bias voltage from a
control circuitry.


VTCMOS technique is very effective technique to reduce the power
consumption with some drawbacks related to manufacturing of these
devices. VTCMOS requires either twin well or triple well technology to
achieve different substrate bias voltage levels at different parts of
the IC. The area overhead of the substrate bias control circuitry is
negligible.

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