A time-slicing ring oscillator (TSRO) which captures time-dependent delay degradation due to periodic transient voltage drop on a power supply network is proposed. An impact of the supply voltage fluctuations, including voltage drop and overshoot, on logic circuit delay is evaluated as a change of oscillation frequency. The TSRO is designed using standard logic cells so that it can be placed almost anywhere in a digital circuit wherein supply voltage fluctuation is concerned. We also propose a new procedure for reconstructing supply voltage waveform. The procedure enables us to accurately monitor time-dependent, effective supply voltages. The -1 dB bandwidth of the TSRO is simulated to be 15.7 GHz, and measured time resolution is 131 ps. Measurement results of a test chip using 90-nm standard CMOS process successfully proved the feasibility of both delay degradation and effective supply voltage fluctuation measurements. Measurement of spatial voltage drop fluctuation is achieved.

Stochastic approaches for effective power distribution network optimization are proposed. Considering node voltages obtained using dynamic voltage drop analysis as sample variables, multi-variate regression is conducted to optimize clock timing metrics, such as clock skew or jitter. Aggregate correlation coefficient (ACC) which quantifies connectivity between different chip regions is defined in order to find a possible insufficiency in wire connections of a power distribution network. Based on the ACC, we also propose a procedure using linear regression to find the most effective region for improving clock timing metrics. By using the proposed procedure, effective fixing point were obtained two orders faster than by using brute force circuit simulation.

An efficient pad assignment methodology to minimize voltage drop on a power distribution network is proposed. A combination of successive pad assignment (SPA) with incremental matrix inversion (IMI) determines both location and number of power supply pads to satisfy drop voltage constraint. The SPA creates an equivalent resistance matrix which preserves both pad candidates and power consumption points as external ports so that topological modification due to connection or disconnection between voltage sources and candidate pads is consistently represented. By reusing sub-matrices of the equivalent matrix, the SPA greedily searches the next pad location that minimizes the worst drop voltage. Each time a candidate pad is added, the IMI reduces computational complexity significantly. Experimental results including a 400 pad problem show that the proposed procedures efficiently enumerate pad order in a practical time.

As semiconductor manufacturing technology advances, power dissipation and noise in scan testing have become critical problems. Our studies on practical LSI manufacturing show that power supply voltage drop causes testing problems during shift operations in scan testing. In this paper, we present a new testing method named MD-SCAN (Multi-Duty SCAN) which solves power supply voltage drop problems, as well as its experimental results applied to practical LSI chips.

Sliding contact behavior is important in the mechanism of collecting current. In this study, the effect of ambient gas including an inert gas on surface film formation and on the contact voltage drop was examined, changing the atmosphere from low pressure to atmospheric pressure. Furthermore, the sliding surface state was observed using SEM, EDX and XPS analyzers after the test operation. As a result, at the sliding contact in an inert gaseous environment (nitrogen and argon), it was confirmed that the contact voltage drop tends to increase. However, it was clarified that any chemically generated surface film is difficult to detect in the inert gas environment by qualitative analysis. On the basis of these results, we suggest the existence of physically adsorbed surface film. The relationship between inert gases and sliding contact phenomena is discussed.

The surface film of a slip ring is important for the sliding contact phenomenon. The surface film is affected by atmospheric temperature, humidity and air pressure. The main objective of our study is to examine the effect of oxygen gas on the sliding contact phenomenon. In the present experiment, we examined the contact voltage drop for continuous sliding when the atmosphere is changed from low pressure to atmospheric pressure by introducing oxygen (O2 20%+N2 80%) or nitrogen gas. As a result, the contact voltage drop increases rapidly with increasing gas pressure, and its fluctuation also becomes large. These phenomena are observed in both cases of oxygen (O2 20%+N2 80%) and nitrogen introduction. The results clearly show that the sudden increase of contact voltage drop is affected by factors other than the oxide film. Actually, the oxide film is not formed in the nitrogen atmosphere. Furthermore, the frictional coefficient of carbon and copper ring is changed at ambient atmosphere. It is inferred from these data that the contact voltage drop may be affected by the frictional coefficient. When the gas pressure decreases again, the contact voltage drop does not suffer from the effect of ambient gas. Therefore, only the resistance of the oxide film appears to affect contact voltage drop. In this paper, the effect of sliding contact phenomenon on the contact voltage drop by gas adsorption and film generation was examined.

At the sliding contact of brush and rotating slip-ring or commutator, it has been recognized that the brush wear is influenced by brush pressure, current density and atmosphere nearby contact part. However, little is known about the relation between brush wear and atmosphere condition in detail. In this paper, the experiments are carried out with a great attention to the effect of surrounding temperature and humidity on brush wear. The sliding part of brush and slip-ring is put on the sealed box and the atmosphere in the sealed box is kept on the specified condition by temperature and humidity control system. The brush wear, contact voltage drop and slip-ring surface morphology are observed after the sliding test. From these results, in both cases of the high humidity (nearby 80%) and low humidity (nearby 20%), the brush wear are large. And the brush wear rate is the lowest around 60% relative humidity. However, the characteristics of brush wear under the 15C is not similar to others. When the surrounding temperature is changed, in case of the 20% humidity, the brush wear increases with increasing surrounding temperature. On the other hand, in case of 80% humidity, the brush wear increases with decreasing surrounding temperature. Consequently, the results clearly shows that the temperature and humidity not only affect the brush wear but also change the condition of the film formation on slip-ring.

Since, in a VLSI circuit, the number of transistors and the clock frequency are constantly increasing, it is important to analyze the voltage drop and current density on a full chip's power networks. We propose a new hierarchical power analysis system named XPOWER. A new reduction algorithm for the resistance and current source network is used in this system. The algorithm utilizes the design hierarchy in nature and is independent of network topology. Networks at each level are reduced into small and equivalent networks, and this reduction is performed recursively from the bottom levels of the design hierarchy. At each step of the reduction, the network under consideration consists of two kinds of objects: (1) reduced child networks, and (2) the interconnection between child networks. After all networks have been reduced, circuit equationa are solved recursively from the top. This allows to decrease the size of the matrix to be solved and to reduce the execution time. Experimental results show that the factor of reduction in matrix size is from 1/10 to 1/40 and execution is six times faster than with flat analysis. The power networks of a 16 bit digital signal processor was analyzed within 15 minutes using XPOWER.