A 4.6nW Subthreshold Voltage Reference with 400x Current Variation Reduction and 64-Step 0.11% Output Voltage Programmability

This paper presents a nanowatt subthreshold voltage reference that achieves significant reduction of temperature-induced current variation and with fully digital programmability of its output voltage, for the first time. The proposed circuit uses a clock reference to achieve adaptive duty cycled operation and reduce current variation in different temperature conditions. In addition, it integrates a programmable DC-DC converter for a tunable reference voltage and compensates for the die-to-die voltage variation. Fabricated in a 0.18 mu m CMOS process, the proposed voltage reference achieves a temperature coefficient of 176ppm/degrees C while consuming 4.6nW, and reduces the current variation between temperatures to 2.75%/degrees C, a 400x improvement over prior work. It also provides a 64-step output voltage programmability with 1.2mV LSB voltage step.