By Len Staller
Embedded Systems Design
(02/24/05, 05:24:00 PM EST)
Confused by analog-to-digital converter specifications? Here's a primer to help you decipher them and make the right decisions for your project.
Although manufacturers use common terms to describe analog-to-digital converters (ADCs), the way ADC makers specify the performance of ADCs in data sheets can be confusing, especially for a newcomers. But to select the correct ADC for an application, it's essential to understand the specifications. This guide will help engineers to better understand the specifications commonly posted in manufacturers' data sheets that describe the performance of successive approximation register (SAR) ADCs.
ABCs of ADCs
ADCs convert an analog signal input to a digital output code. ADC measurements deviate from the ideal due to variations in the manufacturing process common to all integrated circuits (ICs) and through various sources of inaccuracy in the analog-to-digital conversion process. The ADC performance specifications will quantify the errors that are caused by the ADC itself.
ADC performance specifications are generally categorized in two ways: DC accuracy and dynamic performance. Most applications use ADCs to measure a relatively static, DC-like signal (for example, a temperature sensor or strain-gauge voltage) or a dynamic signal (such as processing of a voice signal or tone detection). The application determines which specifications the designer will consider the most important.
For example, a DTMF decoder samples a telephone signal to determine which button is depressed on a touchtone keypad. Here, the concern is the measurement of a signal's power (at a given set of frequencies) among other tones and noise generated by ADC measurement errors. In this design, the engineer will be most concerned with dynamic performance specifications such as signal-to-noise ratio and harmonic distortion. In another example, a system may measure a sensor output to determine the temperature of a fluid. In this case, the DC accuracy of a measurement is prevalent so the offset, gain, and non-linearity will be most important.
Reference:
- http://www.embended.com/
- http://en.wikipedia.org
