TABLE OF CONTENTS Semiconductor voltage references are basic electronic building blocks that are used extensively in OEM circuit board designs, as well as integrated into the designs of many monolithic A/D and D/A converters and voltage regulators. They are created by combining diodes and resistors with either transistors (BJTs and/or FETs) or op amps. Various techniques for creating and optimizing voltage references will be reviewed in this section of this book. While most forms of today's instrumentation use either voltage or current references, the former are far more readily available. Voltage references include discrete zener diodes, temperature-compensated zeners, as well as several different types of integrated circuit devices: bandgap, buried zener, Analog Devices' XFET , and Xicor's FGA types. Of these different types, the zener diode is the oldest (1960s). The bandgap reference is the oldest IC type (early 1970s), as well as the most common, while Xicor's FGA reference is presently the newest. As mentioned, many A/D and D/A converter products contain their own on-board bandgap references. Figure 12.1 shows the voltage reference family tree. We will look more closely at these various types in this and following chapters.
The advantages of using voltage references is their inherent constant voltage outputs, which (ideally) are independent of changes in supply voltage, temperature, load resistance, load current, or aging over time. One could liken the voltage reference to that of a precision, low-noise, low-current voltage regulator. These advantages, when compared...
