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Advanced Circuit Design
- Adaptive VDD and VTH control -
To manage both active and standby power consumption, the UltimateLowPower scheme includes circuit technologies that monitor and control a variety of power-related parameters (Figure 1).
- VDD/VTH independent optimization using circuit delay monitor
- VTH control using ISW/ILEAK monitor
- VTH control using ISUBTH-IGIDL monitor
Control During Active Mode
In active mode, the circuits independently optimize VDD and VTH by monitoring circuit delay and comparing switching and leakage currents (ISW, ILEAK) to maintain the desired ISW/ILEAK current ratio. These circuits constitute the world's first practical ASIC/ASSP subsystem for monitoring and controlling VDD and VTH voltages independently (Figure 2). This independent control method minimizes active power consumption with excellent stability, while maintaining maximum LSI performance.
Control During Standby Mode
In standby mode, the circuits achieve the lowest possible standby power by comparing subthreshold leakage and gate-induced drain leakage (GIDL), and modulating VTH to maintain the point at which the two leakage currents are equivalent. Tests show that the control circuits detect the optimum point within 20 percent accuracy.
VDD / VTH Monitor Circuit Operation Flow
Figure 3 shows the control flow for the circuits, and Figure 4 gives an overview of the circuits involved.
In combination with new device structures, the Adaptive VDD and VTH control technology from NEC Electronics provides further reductions in both active and standby power consumption.
