Abstract
The design of the power switch which turns on and off power supply to the logic gates is essential to low-voltage high-speed circuit techniques such as multi-threshold voltage CMOS (MTCMOS). This is because this switch influences the speed, area, and power of an low-voltage LSI. This paper describes the influences of the power switch on the circuit performance in detail, and proposes a systematic method for designing a power switch which takes them into consideration for the first time. The main feature of this method, called the average-current method, is the use of the average current consumed in an LSI to determine the power switch size. This makes it easy for designers to determine the minimum size of the power-switch needed to satisfy the required speed, which results in minimizing the area penalty and the standby power. Useful analytical formula and the practical determination flow are also described. Measurement of an actual 0.25-μm MTCMOS/SIMOX 290-Kgate LSI operating at 1 V confirmed the effectiveness of this method. This method well estimated the required power-switch width, and as a result it reduced the area penalty and standby current by about 80% compared to the conventional design scheme.