5.8 A 9.3nW all-in-one bandgap voltage and current reference circuit

Ultra-low-power (ULP) sensor technologies for the future internet of things have presented challenges in ULP implementation of reference circuits while keeping traditional requirements of stable performance. For voltage reference circuits, as an essential block in SoCs to generate various internal supply voltages, the bandgap voltage-reference (BGVR) scheme has been widely used since it provides a well-defined value with strong immunity to process/voltage/temperature variations. Nanowatt-consuming BGVR circuits have been recently proposed using a capacitor network and a leakage-based proportional-to-absolute-temperature (PTAT) circuit. On the other hand, the current reference circuit that is required to set internal bias current still presents difficulties in achieving both stable performance and ULP consumption. The general approach to building a current reference is to use a BGVR with additional resistors for V-to-I conversion. Though it can provide a well-defined stable current reference, it also requires excessively large resistance for ULP consumption. Another approach is a CMOS-based current reference circuit that tries to make the exponential term in the subthreshold current equation constant or temperature-independent, hence reducing process and temperature dependencies. While CMOS reference circuits have achieved ULP implementations, the current is still determined by a number of process and design parameters, resulting in large sensitivity to process variations. This paper presents a sub-10nW bandgap-reference (BGR) circuit that implements both voltage and current references in one circuit. The BGR circuit is implemented with a 0.18μm CMOS process and generates voltage and a current references of 1.238V and 6.64nA while consuming 9.3nW. The voltage and current references show standard deviations of 0.43% and 1.19% with temperature coefficients of 26ppm/°C and 283ppm/°C, respectively.