David Megaw
National Semiconductor
Voltage references are a key building block in data conversion systems, and understanding their specifications and how they contribute to error is necessary for selecting the right reference for an application.
In the application of a voltage reference in a simple analog-to-digital converter (ADC) or digital-to-analog converter (DAC), the reference voltage (VREF) acts as a very precise analog 'meter stick' against which the incoming analog signal is compared or the outgoing analog signal is generated. While many ADCs and DACs incorporate an internal reference, beyond 8 to 10 bits it is rare to find one with sufficient precision. In most cases, the internal reference can be overdriven by an external one to improve performance. Terms such as "high precision" and "ultra-high precision" are common in reference datasheets, but do little to help designers in their selection. This paper seeks to provide an explanation of common reference specifications, rank their relative importance, and show how a designer can use them in some simple calculations to narrow his or her search.
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