Bidirectional adaptive body bias (ABB) is used to compensate for die-to-die parameter variations by applying an optimum pMOS and nMOS body bias voltage to each die which maximizes the die frequency subject to a power constraint. Measurements on a 150 nm CMOS test chip which incorporates on-chip ABB, show that ABB reduces variation in die frequency by a factor of seven, while improving the die acceptance rate. An enhancement of this technique, that compensates for within-die parameter variations as well, increases the number of dies accepted in the highest frequency bin. ABB is therefore shown to provide bin split improvement in the presence of increasing process parameter variations.

Adaptive body bias for reducing impacts of die-to-die and within-die parameter variations on microprocessor frequency and leakage

Measurements on a 150 nm CMOS test chip show that on-chip bidirectional adaptive body biasing compensates effectively for die-to-die parameter variation to meet both frequency and leakage requirements. An enhancement of this technique to correct for within-die variations triples the accepted die count in the highest frequency bin.

Die-to-Die and Within-Die Parameter Variations on Microprocessor Frequency and Leakage

In order to manage the active power consumption of high-performance digital designs, active leakage control techniques are required to provide significant leakage power savings coupled with fast time constants for entering and exiting idle mode. In this paper, dynamic sleep transistors and body bias are used in conjunction with clock gating to control active leakage for a 32-bit integer execution core in 130-nm CMOS technology. Measurements on pMOS sleep transistor reveal that lowest-leakage state is reached in less than 1 /spl mu/s, resulting in 37/spl times/ reduction in leakage power, while reactivation of block is achieved in less than two clock cycles. PMOS body bias reduces leakage power by 2/spl times/ with no performance penalty, and similar reactivation time. Power measurements at 4 GHz, 1.3 V, 75/spl deg/C demonstrate 8% total power reduction using dynamic body bias and 15% power reduction using a pMOS sleep transistor, for a typical activity profile.

Dynamic-sleep transistor and body bias for active leakage power control of microprocessors

The driving force for the semiconductor industry growth has been the elegant scaling nature of CMOS technology. In this article, we will first review the history of technology scaling that follows Moore's law from the prespective of microprocessor designs. Challenges to continue the historical scaling trends will be highlighted and design choices to address two specific challenges, process variation and leakage power, will be discussed. In nanoscale CMOS technology generations, supply and threshold voltages will have to continually scale to sustain performance increase, limit energy consumption, control power dissipation, and maintain reliability. These continual scaling requirements on supply and threshold voltages pose several technology and circuit design challenges. One such challenge is the expected increase in process variation and the resulting increase in design margins. Concept of adaptive circuit schemes to deal with increasing design margins will be explained. Next, with threshold voltage scaling, subthreshold leakage power has become a significant portion of total power in nanoscale CMOS systems. Therefore, it has become imperative to accurately predict and minimize leakage power of such systems, especially with increasing within-die threshold voltage variation. A model that predicts system leakage based on first principles will be presented and circuit techniques to reduce system leakage will be discussed. It is essential to point out that this article does not cover all challenges that nanoscale CMOS systems face. Challenges that are not detailed in the main sections of the article and speculation on what future nanoscale silicon based CMOS systems might resemble are summarized.

Challenges and design choices in nanoscale CMOS

A shared n-well layout technique is developed for the design of dual-supply-voltage logic blocks. It is demonstrated on a design of a 64-bit arithmetic logic unit (ALU) module in domino logic. The second supply voltage is used to lower the power of noncritical paths in the sparse, radix-4 64-bit carry-lookahead adder and in the loopback bus. A 3 mm/sup 2/ test chip in 0.18-/spl mu/m 1.8-V five-metal with local interconnect CMOS technology that contains six ALUs and test circuitry operates at 1.16 GHz at the nominal supply. For target delay increase of 2.8% energy savings are 25.3% using dual supplies, while for 8.3% increase in delay, 33.3% can be saved.

A shared-well dual-supply-voltage 64-bit ALU

A 32-bit integer execution core containing a Han-Carlson arithmetic-logic unit (ALU), an 8-entry /spl times/ 2 ALU instruction scheduler loop and a 32-entry /spl times/ 32-bit register file is described. In a 130 nm six-metal, dual-V/sub T/ CMOS technology, the 2.3 mm/sup 2/ prototype contains 160 K transistors. Measurements demonstrate capability for 5-GHz single-cycle integer execution at 25/spl deg/C. The single-ended, leakage-tolerant dynamic scheme used in the ALU and scheduler enables up to 9-wide ORs with 23% critical path speed improvement and 40% active leakage power reduction when compared to a conventional Kogge-Stone implementation. On-chip body-bias circuits provide additional performance improvement or leakage tolerance. Stack node preconditioning improves ALU performance by 10%. At 5 GHz, ALU power is 95 mW at 0.95 V and the register file consumes 172 mW at 1.37 V. The ALU performance is scalable to 6.5 GHz at 1.1 V and to 10 GHz at 1.7 V, 25/spl deg/C.

5-GHz 32-bit integer execution core in 130-nm dual-V/sub T/ CMOS

A 32 b integer execution core implements 12 instructions. Circuit and body bias techniques together increase the core clock frequency to 5 GHz. In a 130 nm six-metal dual-V/sub T/ CMOS process, the 2.3 mm/sup 2/ prototype contains 160 k transistors, with RF-ALU units dissipating 515 mW at 1.6 V.

M.R. Stan

Papers

5-GHz 32-bit integer execution core in 130-nm dual-V/sub T/ CMOS

A 25 GHz 32 b integer-execution core in 130 nm dual-V/sub T/ CMOS