A picopower temperature-compensated, subthreshold CMOS voltage reference

摘要

A voltage reference consisting of only two nMOS transistors with different threshold voltages is presented. Measurements performed on 23 samples from a single batch show a mean reference voltage of 275.4 mV. The subthreshold conduction and the low number of transistors enable to achieve a mean power consumption of only 40 pW. The minimum supply voltage is 0.45 V, which coincides with the lowest value reported so far. The mean TC in the temperature range from 0 to 120 ℃ is 105.4 ppm/℃, while the mean line sensitivity is 0.46%/V in the supply voltage range 0.45-1.8 V. The occupied area is 0.018 mm~2. The power supply rejection rate without any filtering capacitor is - 48 dB at 20 Hz and -29.2 dB at 10 kHz. Thanks to large area transistors and to a careful layout, the coefficient of variation of the reference voltage is only 0.62%. We introduce as a new figure of merit, the voltage temperature parameter (VTP), which gives a direct measure of the overall percentage variation of the reference voltage on the typical 2D domain of supply voltage and temperature. For the proposed circuit, the average VTP is 1.70% with a standard deviation of 0.21 %. In order to investigate the effect of transistor area on process variability, a 4X replica of the proposed configuration has been fabricated and tested as well. Except for LS, the 4X replica doesn't exhibit any appreciable improvement with respect to the basic voltage reference.