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U. Glaeser

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FIGURE 15.10 Clustered voltage scaling structure [20].<br />

FIGURE 15.11 Schematic block diagram of threshold voltage controlling circuit for short channel MOS ICs [23].<br />

15.4 Threshold Voltage Management<br />

Substrate Bias Control for Leakage Reduction<br />

When a CMOS circuit is running in low V dd or is made of small technology devices, the V th fluctuation<br />

caused by the fabrication process deviations becomes large [22], and then, circuit performance is degraded.<br />

A V bb control scheme keeping the V th constant is presented in [23]. As shown in Fig. 15.11, the substrate<br />

bias is automatically produced and V th fluctuation caused by the short-channel effect is suppressed. If V th<br />

is lowered to improve performance, subthreshold leakage current grows too large in the standby state.<br />

Another V bb control method is proposed to solve the V th fluctuation and large-subthreshold leakage at the<br />

© 2002 by CRC Press LLC<br />

i1<br />

i2<br />

i3<br />

i4<br />

i5<br />

i6<br />

Reference<br />

voltage<br />

V r<br />

LLC<br />

V dd<br />

high-V dd cluster<br />

low-V dd cluster<br />

Latch with level-conversion function<br />

Reference<br />

MOS-FET<br />

-K<br />

Common<br />

substrate<br />

Lv<br />

V bg<br />

Lever<br />

shifter<br />

o1<br />

o2<br />

o3<br />

o4<br />

o5<br />

Signal input<br />

LLC<br />

LLC<br />

LLC<br />

LLC<br />

Latch<br />

Threshold<br />

Controlled<br />

MOS-IC chip<br />

Signal output

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