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i A PHYSICAL IMPLEMENTATION WITH CUSTOM LOW POWER ...

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To study the impact of the power consumed during the power-on condition, an inverter<br />

with an approximated load capacitance CL of 4.44 pF was used. Any device that allows<br />

switching could be used to model the dynamic power of the device; however, the inverter was<br />

selected due to its simplified modeling. To this device the power enable PMOS device was<br />

added in series. The circuit diagram is shown in Figure 8-7.<br />

Figure 8-7: Inverter with power<br />

gate.<br />

The pow er-up time a nd in particular the delay has<br />

a significant impact on the power<br />

consumed by the memory. For example, with a power<br />

up time, tP = 100 us and an ideal ramp up<br />

of the power enable inputs, t = 0, the average power consumption is approximately 25.5 nW.<br />

D<br />

However, as the power enable delay increases linearly, the power consumption increases<br />

exp<br />

onentially to reach 25.4 uW f or tD = 40 us based on the simulations as indicated<br />

in Figure<br />

8-3.<br />

tD was varied between 26us and 40us to study the peak currents in more detail. The results<br />

are shown in Figure 8-8. For delays exceeding 30 us, there are big spikes initially in supply<br />

149

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