A resistor-less bandgap reference with improved PTAT generator for ultra-low-power LSIs

A resistor-less bandgap reference (BGR) for ultra-low power large-scale integrations (LSIs) is proposed in this paper. The BGR consists of a nano-ampere current reference circuit, a complementary-to-absolute-temperature (CTAT) voltage generator based on a diode connected MOSFET operating in subthreshold region, and a proportional-to-absolute-temperature (PTAT) voltage generator. A new topology that combines two mechanisms to generate PTAT voltage is proposed for the first stage of the PTAT generator, which can achieve higher slope in the voltage-temperature characteristics. Therefore, only 3 sub-stages are required in the PTAT generator, and both power dissipation and chip area can be reduced. The BGR is designed in a 0.35-μm CMOS process. Simulated results show that the BGR achieves a 1.1-V reference voltage with best temperature coefficient of 35 ppm/°C, while consuming only 40-nA under a 3.3 V power supply.