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U. Glaeser

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FIGURE 15.4 MT-CMOS balloon circuit [7].<br />

FIGURE 15.5 The VRC scheme [9].<br />

written into the balloon latch. During the standby state, TG1 is on to keep the information. When the<br />

system wakes up, TG1 and TG2 briefly turn on so that the held data can be written back into the low-V th<br />

circuit. The balloon can be made of minimum size transistors, so it can be designed to occupy a small<br />

area. The third method is IPS. The IPS supplies power in about 20 ms intervals in the idle state to maintain<br />

voltage on the V ddV line. The IPS acts similarly to the refresh operation of DRAM. The VRC circuit, as<br />

shown in Fig. 15.5, does not need extra circuits to maintain the data in the standby state. While the power<br />

switches MPSW and MNSW are disconnected, V ddV and GNDV voltage variations are clamped by the<br />

built-in potential of diodes DP and DN. The voltage between V ddV and GNDV keeps data in memories.<br />

MT-CMOS has been applied to reduce the power consumed by a digital signal processor (DSP) [10].<br />

The DSP includes a small processor named power management processor (PMP) that handles signalprocessing<br />

computations for small amounts of data. Idle power is reduced to 1/37 of its original value<br />

by the MT-CMOS leakage reduction. Operating power is decreased by 1/2 because loads with small<br />

amount of data are processed by the PMP instead of the DSP. Therefore, total power is reduced to 1/9<br />

of its original value.<br />

Dynamic Voltage Scaling<br />

The active power is in proportion to , as shown in Eq. (15.1). The Vdd reduction substantially reduces<br />

power. On the other hand, a low Vdd increases the CMOS circuit propagation delay, as shown in Eq. (15.2).<br />

Fixed supply voltage reduction is applied to a DRAM [11]. The supply for the memory array is reduced<br />

© 2002 by CRC Press LLC<br />

Logic<br />

circuit<br />

i1<br />

2<br />

Vdd Balloon<br />

memory<br />

B1 B2<br />

TG2<br />

B A<br />

TG3<br />

N<br />

V dd V<br />

internal<br />

circuits<br />

GNDV<br />

TG1<br />

i2<br />

/CS<br />

CS<br />

V dd<br />

GND<br />

MPSW<br />

MP1<br />

MN1<br />

DP<br />

DN<br />

MNSW

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