Motivated by emerging battery-operated applications that demand intensive computation in portable environments, techniques are investigated which reduce power consumption in CMOS digital circuits while maintaining computational throughput. Techniques for low-power operation are shown which use the lowest possible supply voltage coupled with architectural, logic style, circuit, and technology optimizations. An architecturally based scaling strategy is presented which indicates that the optimum voltage is much lower than that determined by other scaling considerations. This optimum is achieved by trading increased silicon area for reduced power consumption. >

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Low-power CMOS digital design

Recently reported logic style comparisons based on full-adder circuits claimed complementary pass-transistor logic (CPL) to be much more power-efficient than complementary CMOS. However, new comparisons performed on more efficient CMOS circuit realizations and a wider range of different logic cells, as well as the use of realistic circuit arrangements demonstrate CMOS to be superior to CPL in most cases with respect to speed, area, power dissipation, and power-delay products. An implemented 32-b adder using complementary CMOS has a power-delay product of less than half that of the CPL version. Robustness with respect to voltage scaling and transistor sizing, as well as generality and ease-of-use, are additional advantages of CMOS logic gates, especially when cell-based design and logic synthesis are targeted. This paper shows that complementary CMOS is the logic style of choice for the implementation of arbitrary combinational circuits if low voltage, low power, and small power-delay products are of concern.

/pdf/low-power-logic-styles-cmos-versus-pass-transistor-logic-40lwlx0imm.pdf

Low-power logic styles: CMOS versus pass-transistor logic

It is shown that clock frequencies in excess of 200 MHz are feasible in a 3- mu m CMOS process. This performance can be obtained by means of clocking strategy, device sizing, and logic style selection. A precharge technique with a true single-phase clock, which increases the clock frequency and reduces the skew problems, is used. Device sizing with the help of an optimizing program improves circuit speed by a factor of 1.5-1.8. The logic depth is minimized to one instead of two or more, and pipeline structures are used wherever possible. Experimental results for several circuits which work at clock frequencies of 200-230 MHz are presented. SPICE simulation shows that some circuits could work up to 400-500 MHz. >

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High-speed CMOS circuit technique

Processors used in portable systems must provide highly energy-efficient operation, due to the importance of battery weight and size, without compromising high performance when the user requires it. The user-dependent modes of operation of a processor in portable systems are described and separate metrics for energy efficiency for each of them are found to be required. A variety of well known low-power techniques are re-evaluated against these metrics and in some cases are not found to be appropriate leading to a set of energy-efficient design principles. Also, the importance of idle energy reduction and the joint optimization of hardware and software will be examined for achieving the ultimate in low-energy, high-performance design.

Processor design for portable systems

Efficient charge recovery logic (ECRL) is proposed as a candidate for low-energy adiabatic logic circuit. Power comparison with other logic circuits is performed on an inverter chain and a carry lookahead adder (CLA). ECRL CLA is designed as a pipelined structure for obtaining the same throughput as a conventional static CMOS CLA. Proposed logic shows four to six times power reduction with a practical loading and operation frequency range. An inductor-based supply clock generation circuit is proposed. Circuits are designed using 1.0-/spl mu/m CMOS technology with a reduced threshold voltage of 0.2 V.

An efficient charge recovery logic circuit

Differential cascode voltage switch (DCVS) logic is a CMOS circuit technique that has potential advantages over conventional NAND/NOR logic in terms of circuit delay, layout density, power dissipation, and logic flexibility. A detailed comparison of DCVS logic and conventional logic is carried out by simulation, using SPICE, of the performance of full adders designed using the different circuit techniques. The parameters compared are: input gate capacitance, number of transistors required, propagation delay time, and average power dissipation. In the static case, DCVS appears to be superior to full CMOS in regards to input capacitance and device count but inferior in regards to power dissipation. The speeds of the two technologies are similar. In the dynamic case, DCVS can be faster than more conventional CMOS dynamic logic, but only at the expense of increased device count and power dissipation.

/pdf/a-comparison-of-cmos-circuit-techniques-differential-cascode-54lr3glj6k.pdf

A comparison of CMOS circuit techniques: differential cascode voltage switch logic versus conventional logic

Differential cascode voltage switch (DCVS) logic is a CMOS circuit technique which has potential advantages over conventional NAND/NOR logic in terms of circuit delay, layout density, power dissipation, and logic flexibility. Two procedures are presented for constructing DCVS trees to perform random logic functions. The first procedure uses a Karnaugh mapping technique and is a very powerful pictorial method for hand-processing designs involving up to six variables. The second procedure is a tabular method based on the Quine-McCluskey approach and is suitable for functions with more than six variables. Both of these procedures are considerably easier to implement than a recently proposed algebraic technique which relies upon decomposition and factorization of Boolean expressions. Several DCVS circuits that have been synthesized by the Karnaugh map (K-map) and tabular procedures are presented.

K.M. Chu

Papers

A comparison of CMOS circuit techniques: differential cascode voltage switch logic versus conventional logic

Design procedures for differential cascode voltage switch circuits