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, V_in, at which the BGR becomes operational. Lowering V_in can also allow an ULP system to continue operation longer as its battery or energy harvested input voltage decreases. The minimum V_in for state-of-the-art BGRs is restricted by V_EB+V_DS [1], where V_EB is the emitter-base voltage of a pnp transistor, and V_DS is the drain-source saturation voltage of a MOS transistor. Recent work brings the V_in voltage down to 700mV [2]. There is a need to reduce the standby power and V_in of a BGR to increase the lifetime of ULP systems. This paper presents a BGR circuit with measured minimum operating V_in of 500mV, reducing the V_in 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.