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

SUMMARY 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 resis-tor ratio, and it is possible to set the reference voltage from zero to near the supply voltage with the same temperature indepen-dence as those of Widlar’s and Brokaw’s bandgap voltage refer-ences. The temperature-independent reference voltage is formed by adding two voltages: the amplified fractional VBE (base-to-emitter voltage) of a bipolar transistor with a negative TC (tem-perature 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 be-comes 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 consump-tion 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 1