This paper explores advanced voltage reference designs with extremely low power consumption, specifically under one microwatt. These designs are crucial for portable electronic systems that rely on minimal power. The paper categorizes these voltage references based on the types of devices used to generate temperature-proportional or complementary signals. It also provides key design examples to illustrate these concepts. Additionally, the paper enhances understanding by conducting a comparative analysis of performance metrics, including power consumption, temperature coefficient, physical size, and resistance to variations in the manufacturing process.

This paper proposes a low-power relaxation oscillator for low-power high-temperature IoT systems. It generates a 959 Hz clock signal from −40 to 170°C, consuming 6.75 nW at 0.65 V. A proposed switch-leakage compensation scheme nullifies the effects of body diode and subthreshold leakages on oscillator output frequency at high temperatures, thereby obtaining a wide operating temperature range. The oscillator implemented in a 180 nm CMOS process achieves a temperature coefficient of 40 ppm/°C from −40 to 170 °C at 0.65 V and a line sensitivity of 0.5 %/V from 0.65 to 2.4 V at room temperature, in simulation. Compared with state-of-the-art sub-$\mu\mathrm{W}$oscillators, this circuit obtains the highest operating temperature and the maximum temperature range.