Low voltage cmos bandgap with new trimming and curvature correction

Abstract

A bandgap circuit for generating an accurate and stable reference voltage at low power supply voltages. Stacking of bipolar devices allows for a lower opamp closed-loop gain, which in turn reduces the error voltage contribution to the output due to opamp offset. A CMOS opamp having NMOS input reference transistors coupled with a new bandgap architecture allows a 1.2 v reference (unlike other stacked architectures) without sacrificing low voltage operation. A new trimming method provides for very efficient trimming of bandgap output voltage. Instead of fine tuning the output voltage by trimming ratioed resistors, the output voltage is trimmed by either changing the area of ratioed bipolar transistors, or changing the magnitude of ratioed currents in equally sized bipolar transistors. Therefore, very fine trimming resolution is possible because of the logarithmic function defining the current or transistor size ratios. A new curvature correction method reduces curvature without requiring additional circuitry. Curvature can be drastically reduced by using resistors with negative temperature coefficient.