High leakage current in deep-submicrometer regimes is becoming a significant contributor to power dissipation of CMOS circuits as threshold voltage, channel length, and gate oxide thickness are reduced. Consequently, the identification and modeling of different leakage components is very important for estimation and reduction of leakage power, especially for low-power applications. This paper reviews various transistor intrinsic leakage mechanisms, including weak inversion, drain-induced barrier lowering, gate-induced drain leakage, and gate oxide tunneling. Channel engineering techniques including retrograde well and halo doping are explained as means to manage short-channel effects for continuous scaling of CMOS devices. Finally, the paper explores different circuit techniques to reduce the leakage power consumption.

Leakage current mechanisms and leakage reduction techniques in deep-submicrometer CMOS circuits

1-V power supply high-speed low-power digital circuit technology with 0.5-/spl mu/m multithreshold-voltage CMOS (MTCMOS) is proposed. This technology features both low-threshold voltage and high-threshold voltage MOSFET's in a single LSI. The low-threshold voltage MOSFET's enhance speed performance at a low supply voltage of 1 V or less, while the high-threshold voltage MOSFET's suppress the stand-by leakage current during the sleep period. This technology has brought about logic gate characteristics of a 1.7-ns propagation delay time and 0.3-/spl mu/W/MHz/gate power dissipation with a standard load. In addition, an MTCMOS standard cell library has been developed so that conventional CAD tools can be used to lay out low-voltage LSI's. To demonstrate MTCMOS's effectiveness, a PLL LSI based on standard cells was designed as a carrying vehicle. 18-MHz operation at 1 V was achieved using a 0.5-/spl mu/m CMOS process. >

1-V power supply high-speed digital circuit technology with multithreshold-voltage CMOS

This paper investigates the effect of lowering the supply and threshold voltages on the energy efficiency of CMOS circuits. Using a first-order model of the energy and delay of a CMOS circuit, we show that lowering the supply and threshold voltage is generally advantageous, especially when the transistors are velocity saturated and the nodes have a high activity factor, In fact, for modern submicron technologies, this simple analysis suggests optimal energy efficiency at supply voltages under 0.5 V. Other process and circuit parameters have almost no effect on this optimal operating point. If there is some uncertainty in the value of the threshold or supply voltage, however, the power advantage of this very low voltage operation diminishes. Therefore, unless active feedback is used to control the uncertainty, in the future the supply and threshold voltage will not decrease drastically, but rather will continue to scale down to maintain constant electric fields.

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Supply and threshold voltage scaling for low power CMOS

A five-fold increase in leakage current is predicted with each technology generation. While Dynamic Voltage Scaling (DVS) is known to reduce dynamic power consumption, it also causes increased leakage energy drain by lengthening the interval over which a computation is carried out. Therefore, for minimization of the total energy, one needs to determine an operating point, called the critical speed. We compute processor slowdown factors based on the critical speed for energy minimization. Procrastination scheduling attempts to maximize the duration of idle intervals by keeping the processor in a sleep/shutdown state even if there are pending tasks, within the constraints imposed by performance requirements. Our simulation experiments show that the critical speed slowdown results in up to 5% energy gains over a leakage oblivious dynamic voltage scaling. Procrastination scheduling scheme extends the sleep intervals to up to 5 times, resulting in up to an additional 18% energy gains, while meeting all timing requirements.

Leakage aware dynamic voltage scaling for real-time embedded systems

A 4 mm/sup 2/, two-dimensional (2-D) 8/spl times/8 discrete cosine transform (DCT) core processor for HDTV-resolution video compression/decompression in a 0.3-/spl mu/m CMOS triple-well, double-metal technology operates at 150 MHz from a 0.9-V power supply and consumes 10 mW, only 2% power dissipation of a previous 3.3-V design. Circuit techniques for dynamically varying threshold voltage (VT scheme) are introduced to reduce active power dissipation with negligible overhead in speed, standby power dissipation, and chip area. A way to explore V/sub DD/-V/sub th/ design space is also studied.

A 0.9-V, 150-MHz, 10-mW, 4 mm/sup 2/, 2-D discrete cosine transform core processor with variable threshold-voltage (VT) scheme

This paper proposes a new multithreshold-voltage CMOS circuit (MTCMOS) concept aimed at achieving high-speed, ultralow-power large-scale integrators (LSI's) for battery-driven portable equipment. The "balloon" circuit scheme based on this concept preserves data during the power-down period in which the power supply to the circuit is cut off in order to reduce the standby power. Low-power, high-speed performance is achieved by the small preserving circuit which can be separated from the critical path of the logic circuit. This preserving circuit is not only three times faster than a conventional MTCMOS one, but it consumes half the power and takes up half the area. Using this scheme for an LSI chip, 20-MHz operation at 1.0 V and only a few nA standby current was achieved with 0.5-/spl mu/m CMOS technology. Moreover, this scheme is effective for high speed and low-power operation in quarter-micrometer and finer devices.

A 1-V high-speed MTCMOS circuit scheme for power-down application circuits

A new MTCMOS concept is proposed for power-down applications. This concept realises a new circuit scheme to hold data during the power-down period in which the power is not supplied. Low-power, high-speed performance are achieved by separating the holding circuit from the critical path. A scan register has been developed based on this concept. Using this scheme for an LSI chip, 20-MHz operation at 1.0 V and only a few nA standby current was achieved with 0.5-/spl mu/m CMOS technology.

A 1-V high-speed MTCMOS circuit scheme for power-down applications

A 1-V power supply low-power and high-speed 16-b fixed-point digital signal processor using a 0.5-/spl mu/m process has been developed for mobile phone applications. A 1-V multithreshold-voltage CMOS (MTCMOS) technology that uses both high-threshold-voltage and low-threshold-voltage transistors is one key to attaining low power consumption, keeping processing throughput high. A maximum operating frequency of 13.2 MHz and an energy consumption of 2.2 mW/MHz were achieved at 1 V. The second key to low-power operation is a power management scheme that uses a secondary embedded microprocessor. This proposed scheme minimizes the standby power in the waiting state by effectively controlling the sleep mode in the MTCMOS design. We confirmed that the standby leakage current was reduced three orders of magnitude and that the energy consumed in the waiting state was less than 1/10 of that consumed by conventional CMOS circuits with lowered supply voltage and threshold voltage but without power management.

A 1-V multithreshold-voltage CMOS digital signal processor for mobile phone application

A low-power digital signal processor (DSP) is the key component for battery-driven mobile phone equipment since a vast amount of data needs to be processed for multimedia use. Reduced supply voltage is a direct approach to power reduction. This 1 V DSPLSI with 26 MOPS and 1.1 mW/MOPS performance adopts a multi-threshold-voltage CMOS (MTCMOS) technique. A small embedded power-management processor decreases power during waiting periods.

Yasuyuki Matsuya

Papers

1-V power supply high-speed digital circuit technology with multithreshold-voltage CMOS

A 1-V high-speed MTCMOS circuit scheme for power-down application circuits

A 1-V high-speed MTCMOS circuit scheme for power-down applications

A 1-V multithreshold-voltage CMOS digital signal processor for mobile phone application

A 1 V multi-threshold voltage CMOS DSP with an efficient power management technique for mobile phone application