A curvature-compensated CMOS voltage reference using Vth2 characteristics

A novel technique for the design of very low temperature coefficient (TC) voltage references in a CMOS standard process is presented. The proposed circuit uses an all CMOS technique to generate a low TC voltage reference over a wide temperature range. A self-biased VthVth (threshold voltage) generator circuit creates a voltage equal to the VthVth of a CMOS transistor; this voltage is used to generate a current proportional to Vth2 that, when forced into another transistor, creates a voltage which presents a negative non-linear temperature coefficient. A voltage with a positive TC, which can be controlled by the aspect ratio of a pair of transistors, is generated by a current mirror asymmetrically degenerated with a high-poly resistor. A curvature correction, provided by a current proportional to Vth2, is used to modify the thermal behaviour of this positive TC voltage. By adding the positive and negative TCs voltages, a very stable reference voltage can be obtained. The circuit was designed to be implemented in a standard CMOS process (AMS 0.35μm), and simulated results indicate that a variation of only 2.5ppm/∘C is expected over the temperature range of 0–90∘C.