A/D and D/A converters

What is ADC ?

An electronic integrated circuit which transforms a signal from analog (continuous) to digital (discrete) form.

  • Analog signals are directly measurable
  • Digital signals only have two states. For
    digital computer, we refer to binary states, 0
    and 1.

Why ADC is needed ?
Microprocessors can only perform complex processing on digitized signals.

  •  When signals are in digital form they are less
    susceptible to the deleterious effects of
    additive noise.
  • ADC Provides a link between the analog
    world of transducers and the digital world of
    signal processing and data handling.

Application of ADC
ADC are used virtually everywhere where an analog signal has to be processed, stored, or transported in digital form.

  • Some examples of ADC usage are digital volt meters, cell phone, thermocouples, and digital oscilloscope.
  • Microcontrollers commonly use 8, 10, 12, or 16 bit ADCs, our micro controller uses an 8 or 10 bit ADC

ADC process
2 steps

  • Sampling and Holding (S/H)
  • Quantizing and Encoding (Q/E)

Sampling and Holding

  1. Holding signal benefits the accuracy of the A/D conversion
  2. Minimum sampling rate should be at least twice the highest data
    frequency of the analog  signal

Quantizing and Encoding

  • Quantizing:
    Partitioning the reference signal range into a number of discrete quanta, then matching the input signal to the      correct quantum.
  • Encoding:
    Assigning a unique digital code to each quantum, then allocating the digital code to the input signal

Accuracy of A/D Conversion
There are two ways to best improve the accuracy of A/D conversion:

  •  increasing the resolution which improves the accuracy in measuring the amplitude of the analog signal.
  • increasing the sampling rate which increases the maximum frequency that can be measured.

Types of A/D Converters
Dual Slope A/D Converter

  • Successive Approximation A/D Converter
  • Flash A/D Converter
  • Delta-Sigma A/D Converter
  • Other
  • Voltage-to-frequency, staircase ramp or single slope, charge balancing or redistribution, switched capacitor, tracking, and synchro or resolver

What is a Digital to Analog Converter?

Digital to analog converting is a process where digital signals that have a few (usually two) defined states are turned into analog signals, which have a theoretically infinite number of states. A Digital to Analog Converter, or DAC, is an electronic device that converts a digital code to an analog signal such as a voltage, current, or electric charge. Signals can easily be stored and transmitted in digital form; a DAC is used for the signal to be recognized by human senses or non-digital systems. Converting a signal from digital to analog can degrade the signal. Therefore details are chosen so that errors are negligible. Due to their cost, digital to analog converters are mostly manufactured on an integrated circuit (IC). DAC architectures may contain different advantages as well as disadvantages. The suitability of a digital to analog converter for a particular application is determined by several attributes such as speed and resolution.

Applications for Digital to Analog Converters:

An example can be found in the processing of computer data by a modem into audio-frequency tones transmitted over a telephone line. The circuit that performs this is a digital to analog converter. In music players, digital to analog converters can be used for generation of audio signals from digital information. In TVs and cell phones, digital video signals are converted into analog in order to display colors and shades. In VoIP applications, the source is first digitized for transmission through an analog to digital converter and is then reconstructed into an analog signal using a DAC at the receiving end.

Try Now – Digital Electronics MCQs