In recent years, the demand for low-power design has remained undiminished. In this paper, a pseudo power gating (SPG) structure using a normal logic cell is proposed to extend the power gating to an ultrafine grained region at the gate level. In the proposed method, the controlling value of a logic element is used to control the switching activity of modules computing other inputs of the element. For each element, there exists a submodule controlled by an input to the element. Power reduction is maximized by controlling the order of the submodule selection. A basic algorithm and a switching activity first algorithm have been developed to optimize the power. In this application, a steady maximum depth constraint is added to prevent the depth increase caused by the insertion of the control signal. In this work, various factors affecting the power consumption of library level circuits with the SPG are determined. In such factors, the occurrence of glitches increases the power consumption and a method to reduce the occurrence of glitches is proposed by considering the parity of inverters. The proposed SPG method was evaluated through the simulation of the netlist extracted from the layout using the VDEC Rohm 0.18 µm process. Experiments on ISCAS'85 benchmarks show that the reduction in total power consumption achieved is 13% on average with a 2.5% circuit delay degradation. Finally, the effectiveness of the proposed method under different primary input statistics is considered.

Clock gating is the insertion of control signal for registers to switch off unnecessary clock signals selectively without violating the functional correctness of the original design so as to reduce the dynamic power consumption. Commercial EDA tools usually have a mechanism to generate clock gating logic based on the structural method where the control signals specified by designers are used, and the effectiveness of the clock gating depends on the specified control signals. In the research, we focus on the automatic clock gating logic generation and propose a method based on the candidate extraction and control signal selection. We formalize the control signal selection using linear formulae and devise an optimization method based on BDD. The method is effective for circuits with a lot of shared candidates by different registers. The method is applied to counter circuits to check the co-relation with power simulation results and a set of benchmark circuits. 19.1-71.9% power reduction has been found on counter circuitsafter layout and 2.3-18.0% cost reduction on benchmark circuits.

In this paper, a new heuristic algorithm is proposed to optimize the power domain clustering in controlling-value-based (CV-based) power gating technology. In this algorithm, both the switching activity of sleep signals (p) and the overall numbers of sleep gates (gate count, N) are considered, and the sum of the product of p and N is optimized. The algorithm effectively exerts the total power reduction obtained from the CV-based power gating. Even when the maximum depth is kept to be the same, the proposed algorithm can still achieve power reduction approximately 10% more than that of the prior algorithms. Furthermore, detailed comparison between the proposed heuristic algorithm and other possible heuristic algorithms are also presented. HSPICE simulation results show that over 26% of total power reduction can be obtained by using the new heuristic algorithm. In addition, the effect of dynamic power reduction through the CV-based power gating method and the delay overhead caused by the switching of sleep transistors are also shown in this paper.

CMOS circuits consume great dynamic power in switching. It has been proposed that energy transfer through a rising Vdd dissipates small amounts of energy. In typical power gate circuits, the high-performance PMOS transistors (PSW) that connect the circuit blocks to the power supply reduce leakage power by shutting off outer power (Vdd) to the idle blocks. We expand this technique by utilizing active PSW, which are turned on and off by clock signal. The PSW are fully turned on only for half of each clock cycle. This means that sufficient Vdd is provided to the circuit continuously for half of each clock cycle. In this manner, the circuit charge and discharge actions are cycle occur in different phases, and ramp Vdd is supplied to the designed circuit; we name this technique "CKVdd." CKVdd is a clock-controlled self-stabilized voltage technique, which generates stable ramp voltage to suppress the currents effectively. It is proposed to reduce dynamic power dissipation in conventional CMOS digital circuits. As compared to the conventional circuit, the circuits using CKVdd technique possesses several characteristics that differ from those of the current circuits using constant Vdd power source. First, CKVdd technique combines the power source and clock signal; it is an efficient low power technique. Second, CKVdd propose a feasible method to generate ramp-Vdd and low-Vdd. This technique would be convenient used to design generic low power digital circuits. Third, normal CMOS circuits show the dynamic power consumption increase proportional to the clock frequency. CKVdd results in a lower-than-usual frequency dependency, it is suitable used to design high clock speed circuits. In investigating constant Vdd for MPEG VLD decoders, CKVdd-circuit reduces 48% of the usual power dissipation and 88% of the usual peak current with small delay penalty.

This paper addresses bitwidth optimization focusing on leakage power reduction for system-level low-power design. By means of tuning the design parameter, bitwidth tailored to a given application requirements, the datapath width of processors and size of memories are optimized resulting in significant leakage power reduction besides dynamic power reduction. Experimental results for several real embedded applications, show power reduction without performance penalty range from about 21.5% to 66.2% of leakage power, and 14.5% to 59.2% of dynamic power.