TABLE OF CONTENTS When you review the different topologies, the available products within each topology, and their specifications, you would probably agree that there is a convergence, as the best of each topology attempts to compete with the most exotic specifications first established by the buried-zener. Generally, the other topologies are becoming far more accurate, irrespective of whether they are shunt or series types. Over the past decade, the constant need to support higher-resolution A/D and D/A converters in a myriad of digitally based products has fueled the growth and improvement of the precision monolithic voltage reference. Although many converters incorporate their own on-board (bandgap) voltage reference, this is limited to about 12-bit resolution, even though the converter may be capable of much higher resolution. For the most part it is convenient and enables a design to get off the ground faster. In order to achieve true 12-bit resolution and higher, it forces one to use a high-performance external voltage reference. Remember that for 1/2 LSB error in a 12-bit resolution system over a 100 C temperature span, the maximum allowable tempco is only 1.22 ppm/ C (along with an allowable noise spec of less than 60 ?V pk-pk).
The 1-ppm/ C tempco specification over a product's temperature range has become the industry-wide benchmark for series references. Besides some buried-zener products, only a few other products have yet broken through this 1-ppm/ C barrier and reached that milestone. These are precision super-bandgaps like Maxim's MAX6325 and Thaler's VRE4100...
