Analog-to-Digital Converters (ADC) Used in NI DAQ Devices

Overview

This article describes the Analog-to-Digital Converters (ADC) used in National Instruments Multifunction (MIO) DAQ, DSA or SC Express devices and modules.

Contents

Success-Approximation-Register (SAR) ADC Usage

The successive-approximation-register (SAR) Analog-to-Digital Converter (ADC) is the type used in most National Instruments Multifunction DAQ devices (not necessarily the case for modular instruments and USB devices). This includes the following:

  • NI 63xx X Series devices and modules
  • NI 62xx M Series devices and modules
  • Some NI 61xx S Series devices and modules
  • NI 60xxE E Series devices


The Successive-Approximation-Register (SAR) Analog-to-Digital Converter (ADC) takes in a continuous analog signal into a discrete format utilizing an approximation register. The Successive-Approximation-Register (SAR) Analog-to-Digital Converter (ADC) utilizes a binary algorithm to convert continuous analog waveforms into much smaller discrete outputs. This means that each analog point is checked for being greater than or less than a digital reference point. If greater, the digital bit is set to high, or 1 in binary, then moved to the next bit. If low, the digital bit is set to low, or 0 in binary, then moved to the next bit. This continues until the conversion of the analog point is complete.

Note: Most S Series devices use a pipelined ADC, with an intrinsic pipeline depth. This depth will be specified in the device's specifications manual.

Delta-Sigma ADC Usage

Additionally, the Delta-Sigma Analog-to-Digital Converter (ADC) used in:

  • Some NI 92xx C Series modules
  • NI 44xx Dynamic Signal Analyzer (DSA) devices and modules
  • Some NI 43xx SC Express modules


The 24-bit Delta-Sigma utilize oversampling, decimation filter, and noise shaping to create high resolution and great antialiasing filtering applications. Additionally, the Delta-Sigma Analog-to-Digital Converter (ADC) is free-running meaning it’s being sampled prior to any trigger conditions. These features allow the Delta-Sigma Analog-to-Digital Converter (ADC) to be used for vibration and audio signal analysis as well as strain and pressure measurement.