A Nano-Watt MOS-Only Voltage Reference With High-Slope PTAT Voltage Generators

This brief presents an MOS-only voltage reference circuit with high-slope proportional-to-absolute-temperature (PTAT) voltage generators for ultra-low-power applications. Biased by a nano-ampere current reference circuit, the PTAT voltage generator is realized by an asymmetrical differential cell with two additional cross-coupled nMOS/pMOS pairs, which enhance the slope of the PTAT voltage remarkably. As a result, only two cascaded PTAT stages are used to compensate the complementary-to-absolute-temperature voltage generated directly by a diode-connected nMOS in the current reference circuit. Therefore, much power and chip area can be saved. A trimming circuit is also adopted to compensate the process-related reference voltage variations. The experimental results of the proposed reference circuit fabricated in a 0.18-<inline-formula> <tex-math notation="LaTeX">$ {\mu }$ </tex-math></inline-formula> m standard CMOS process demonstrate that the circuit could operate under a minimum supply voltage of 1 V, and generate a reference voltage of 756 mV with temperature coefficient of 74 and 49.6 ppm/°C under 1-V and 1.8-V power supply, respectively. The proposed circuit consumes only 23 nA under a 1-V power supply, and the active area is only 95 <inline-formula> <tex-math notation="LaTeX">$ {\mu }\text{m}\,\, {\times } \,\, 170 ~{\mu }\text{m}$ </tex-math></inline-formula>.