5.4 A 32nW bandgap reference voltage operational from 0.5V supply for ultra-low power systems

Most systems require a voltage reference independent of variation of power supply, process, or temperature, and a bandgap voltage reference (BGR) often serves this purpose. For ultra-low power (ULP) systems, the BGR may constitute a significant component of standby power, and the system start-up voltage is often determined by the voltage, Vin, at which the BGR becomes operational. Lowering Vin can also allow an ULP system to continue operation longer as its battery or energy harvested input voltage decreases. The minimum Vin for state-of-the-art BGRs is restricted by VEB+VDS [1], where VEB is the emitter-base voltage of a pnp transistor, and VDS is the drain-source saturation voltage of a MOS transistor. Recent work brings the Vin voltage down to 700mV [2]. There is a need to reduce the standby power and Vin of a BGR to increase the lifetime of ULP systems. This paper presents a BGR circuit with measured minimum operating Vin of 500mV, reducing the Vin of [2] by 1.4x. Further, the power consumption of the proposed circuit is 32nW, which is 1.6x lower than the non-duty cycled BGR reported in [2]. A 2x-charge pump based bandgap core, a switched-capacitor network (SCN), and a current controlled oscillator and clock doubler circuit enable a BGR with a temperature variation of 75ppm/°C and power supply rejection (PSR) of up to -52dB at DC.