Adaptive CMOS output driver with a wide range of loading conditions

Abstract

In this paper, the output driver that has adaptive characteristics with a wide range of loading conditions is proposed, designed, fabricated using 0.35-micron CMOS process, packaged in chip-on-board, measured with two kinds of measurement setups. The proposed output driver can detect its loading condition directly and can change its size to be optimal with respect to the detected loading condition. The proposed scheme can control the optimal rise time by changing the level of the reference voltage. This controllability can be obtained, of course, with the adaptive characteristics. We have demonstrated that the rise time is maintained to about 2 ns with 2.5pF~22pF of loading conditions and the rise time is varied from 2.1 ns to 4.2 ns by changing the level of the reference voltage. We have also demonstrated low parasitics in the chip-on-board package. Using the low impedance setup in measurement, we can get the digital waveform with 250 ps falling time. And we can observe the reflected wave from the discontinuity on the PCB. The simple design guideline of determining two parameters, the reference driver size and the stage to meet a range of loading conditions has been proposed.