Baker's Best; Will the right voltage reference please stand up?

March 28, 2014 // By Bonnie Baker, Texas Instruments
This is the scenario. You have a good idea about your application needs, and you have finally zeroed in on the correct analogue-to-digital converter (ADC). The next step is to feed the ADC with the proper voltage reference chip and driving amplifier. In this article, we will talk about how to choose your voltage reference (Figure 1).

Figure 1 (above) Block diagram of an ADC/Voltage reference configuration. The voltage reference output (VOUT) determines the full-scale range of the ADC.

For some converters the full-scale range is equal to the voltage reference’s output voltage, or VOUT. For other converters the full-scale range is equal to twice VOUT. You can find this relationship between the ADC’s full-scale range (FSR) of the voltage reference chip’s (VOUT) output value in the ADC’s product data sheet.

In a perfect world, that is all you have to do as you find the IC chip with the correct output voltage for your ADC. However, in our non-perfect world the voltage reference chip has initial output errors, and an inherent inability to drive the ADC’s reference pin directly. If you want to learn about voltage reference driving circuitry, refer to references 1 and 2. But first let’s come to terms with the reference’s initial output errors.

When it comes to the voltage reference output errors, what you should be concerned about is initial accuracy, temperature drift, and noise. Part of this evaluation is to convert all of these errors to units of volts.