A temperature-insensitive current controlled CMOS output driver

Abstract

A current controlled CMOS output driver was designed by using a temperature-insensitive reference current generator. It eliminates the need for overdesign of the driver transistor size to meet the delay specification at high temperature. Comparison with the conventional CMOS output driver with the same transistor size showed that the ground bounce noise was reduced by 2.5 times and the delay time was increased by 1.4 times, at 25 degrees C for 50pF Load. The temperature variations of the DC pull-up and pull-down currents of the new output driver were 4% within the temperature range from -15 degrees C to 125 degrees C compared to the variations of 30 and 60% for pull-up and pull-down respectively for the conventional output driver. The temperature insensitivity of the reference current generator was achieved by multiplying two current components, one which is proportional to mobility and the other which is inversely proportional to mobility, by using a CMOS square root circuit. The temperature variation of the DC output current of the reference current generator alone was 0.77% within the entire temperature range from -15 degrees C to 125 degrees C.