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U. Glaeser

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FIGURE 20.9 A logic gate and its corresponding graph.<br />

both ends of disjointed segments of the path become isolated and assumed to retain their voltage values.<br />

On the other hand, if a conducting path joins the disjointed segments, then all the nodes along the<br />

conducting paths must be updated to a new equilibrium value. If the conducting path to the V supply (V gnd)<br />

exists, then all nodes along the path will be charged (discharged).<br />

The algorithm for path updating process is as follows. When input node i switches from OFF to ON:<br />

1. If a conducting path from the internal node to Gnd exists:<br />

• collect all the node charges along the path<br />

• set all the node voltages to Vlow (Vlow for nodes in NMOS and PMOS are 0 and Vthp, respectively).<br />

2. If a conducting path to Vsupply exists:<br />

• set all the node voltages to Vhigh (Vhigh for nodes in NMOS and PMOS are (Vsupply − Vthn) and<br />

Vsupply, respectively).<br />

Vthp and Vthn are PMOS and NMOS threshold voltage, respectively. The internal nodes in PUN among<br />

PMOS devices will be fully charged to Vsupply, but will only be discharged to Vthp. Similarly, the internal nodes<br />

in PDN among NMOS devices will be fully discharged to Vgnd, but will only be charged to (Vsupply − Vthn). This is because the transistors will be cut-off when the gate to source voltage is less than the threshold<br />

voltage.<br />

Along the discharging path (conducting path to the GND), all the charges in the internal nodes are<br />

added together. The sum of the charges is accumulated over all simulation runs. The normalized power<br />

measure is directly derived from this accumulated sum of charges as = ⋅ /run-time.<br />

© 2002 by CRC Press LLC<br />

A<br />

B<br />

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E<br />

C<br />

D<br />

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F<br />

C1<br />

V dd<br />

C3<br />

C4<br />

C5<br />

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C D<br />

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F<br />

C1<br />

C3<br />

C4<br />

A<br />

B<br />

C2<br />

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V dd<br />

C<br />

V ss<br />

D<br />

E F<br />

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B<br />

E<br />

C5<br />

F<br />

φ internal Q total V supply

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