TABLE OF CONTENTS Today's bandgap-based reference technology has brought about lower cost, smaller package sizes, better initial accuracy ( %), lower tempco, and lower power. The bandgap reference is available in either the three-terminal series format or the two-terminal shunt format. The shunt type, which we will look at first, is for low-cost, low-voltage, small space, and less demanding applications. Unlike the low-voltage zener diode, which it was designed to replace, the bandgap has a lower voltage with a sharper knee, at low current levels. Shunt bandgaps are usually available over the voltage range of between 1.2 volts to 5 volts. Many devices have an initial accuracy of less than 0.2%, along with a temperature coefficient of less than 100 ppm/ C, over the industrial temperature range (some new devices have much lower tempcos). In terms of digital resolution, the shunt type would typically be used for 8- to 10-bit accuracy, with a few new devices capable of 12-bit accuracy. In many instances, today's shunt bandgap is a low-power device, with a low quiescent current often below 100 ?A. Most of the bandgap reference's noise is caused by the use of resistor compensation networks for curve and tempco compensation, resulting in low-frequency noise levels of between about 5 and 100 ?V peak-to-peak (pk-pk). Many shunt bandgaps are now available in tiny surface-mount packages like the SOT-23 and the SC70, which makes them attractive for low-power/portable, limited space applications.
The shunt reference (like the zener diode that it...
