Performance improvement of low voltage CMOS circuits using body bias approach

Abstract

In the last few decades, the demand for portable electronic devices and implantable newlinemedical devices has grown immensely. For these devices, low voltage and low power newlineoperation is an essential prerequisite to ensure reliable functioning and prevent newlineoverheating. Low voltage operation is desired for possible reduction in the number, newlineweight and size of batteries and low power consumption prolongs the operation period newlinefor battery powered devices. newlineThe shrinking size of MOS transistors in CMOS processes entails the use of newlinelower supply voltages. Since the threshold voltage of MOS transistor is not reduced at newlinethe same rate as the power supply, analog designers face difficulties due to reduced newlinevoltage headroom. At reduced supply voltage, diminishing headroom sets new newlinechallenges to improve or even maintain the circuit performance. One of the solutions, newlinewhich can overcome the difficulties introduced by relatively high threshold voltages, newlineis based on the application of body bias approach. In such a solution, potential is newlineapplied at body terminal of a MOS transistor to adjust its threshold voltage. newlineReconfiguring the MOS transistor in this way extends the applicability of basic analog newlinebuilding blocks to low supply voltages. newlineBody effect in a MOS transistor was considered in the past as an exclusive source of newlineunwanted second order effects. In this research work, it is shown that body bias newlineapproach is an attractive opportunity for exploiting the body effect positively to newlineimprove the performance of low voltage integrated circuits. Also, as the power supply newlinevoltage approaches the transistor threshold voltage, the circuit performance becomes newlineextremely sensitive to process variations and temperature fluctuations. Body bias newlineapproach not only boosts the performance, but also improves the circuit robustness newlineagainst process and temperature variations.The results are compared with the existing circuits in the literature to newlinedemonstrate the performance improvements obtained using body bias approach.