The Realization of an Area-Efficient CMOS Bandgap Reference Circuit with Less than 1.25 V of Output Voltage Using a Fractional VBE Amplification Scheme

This paper describes a CMOS voltage reference circuit which occupies small die area and has less than 1.25 V of output voltage. The reference voltage is determined by a resistor ratio, and it is possible to set the reference voltage from zero to near the supply voltage with the same temperature independence as those of Widlar’s and Brokaw’s bandgap voltage references. The temperature-independent reference voltage is formed by adding two voltages: the amplified fractional VBE (base-toemitter voltage) of a bipolar transistor with a negative TC (temperature coefficient) and the amplified VT (thermal voltage) with a positive TC. When a reference voltage smaller than 1.25 V is required, the voltage gain of the amplifier for VBE becomes less than one, and the voltage gain of the amplifier for VT becomes small. This enables the size of bipolar transistors for VT generation to be small. The proposed voltage reference circuit was implemented in a standard 0.35-um CMOS technology. A temperature-independent current source was also obtained from the same circuit. The results were a TC (temperature coefficient) of 46 ppm/◦C over 130◦C change, a line regulation of 2.2 mV/V for the 0.5 V reference voltage with 8.7 uA of current consumption in the voltage reference part, and a 6 % change over 130◦C change for the 13 uA current source. key words: Voltage reference, low reference voltage, small diode area, VBE amplification, CMOS