ADC vs DAC: Understanding the Key Differences

This article explains the difference between Analog-to-Digital Converters (ADCs) and Digital-to-Analog Converters (DACs). You’ll also find links to more comparisons of various technologies.

ADC - Analog to Digital Converter

An ADC is an electronic integrated circuit that transforms a signal from its analog (continuous) form into a digital (discrete) form. Analog signals are directly measurable quantities, while digital signals only exist in two states: binary 0 and binary 1. The ADC is at the heart of any data acquisition system.

Digital systems require discrete digital data to function. Here’s why we use Analog-to-Digital conversion:

• Processors perform arithmetic operations on digital signals.
• Digital signals are less susceptible to noise.
• The ADC provides a crucial link between the analog world (of transducers) and the digital world (of data and signal processing).

Here are some common types of ADCs:

• Counter type (the simplest)
• Successive Approximation
• Flash ADC
• Sigma Delta

Applications of ADC:

1. Digital Voltmeter: Measures voltage (analog) and converts it to digital for display.
2. Mobile Phone: Analog voice is converted to digital for processing (speech compression, encoding, etc.) before being converted back to analog for transmission.
3. Scanner: When taking a photo, the scanner uses an ADC to convert the analog information from the picture into digital data.
4. Voice Recorder: It uses an ADC to convert analog voice information into digital data. Modern VOIP (Voice over Internet Protocol) solutions also use this principle.

DAC - Digital to Analog Converter

A DAC is used to convert digital values into an analog voltage. It performs the inverse operation of an ADC.

The analog output is calculated as:

Analog output = ( Digital Input / (2^N - 1) ) * Reference Input

There are two main types of DACs:

• Weighted Resistor
• Resistive Divider

The following specifications are crucial for designing, developing, and selecting a DAC:

• Resolution
• Reference Voltages
• Settling Time
• Linearity
• Speed
• Errors

Applications of DAC:

• Modems: Need DACs to convert data to analog form so that it can be transmitted over telephone lines.
• Video Adapters: Also use DACs, often called RAMDACs, to convert digital data into analog signals for display on a monitor.
• Digital Motor Control
• Printers
• Sound Equipments
• Function Generators or Oscilloscopes
• Digital Audio