Subject :- VLSI Design

Topic :- Data Path Design

Difficulty :- High

• The dynamic power is the power associated with switching. To a first order approximation, in any CMOS circuit like those described above, the output of the circuit (NAND, Nor, etc.) is connected to a wire that is usually connected to the input of other circuits. This wire and inputs to other circuits (which are usually gate electrodes) can be modeled as capacitive loads to the circuit.

• When the circuit has to switch from a high voltage to a low voltage (or vice versa) then this capacitance has to be charged or discharged. This takes a certain amount of energy and if you repeat this billions of times every second, it becomes a continuous or AC power.

• As the other respondent mentioned, there can also exist in circuits an intermediate position where in the process of switching, there can appear a direct path in the circuit between voltage and ground which can cause a switching current that is resistive and therefore different than the capacitive power just described.

• This resistive current can be managed somewhat with good device and circuit design and non overlapping clocks in latch design, but this power may also be considered an dynamic power as it only occurs when circuits are switching.