Analog to Digital Converters (A/Ds)
What Are They?
Some Properties Of A/D Converters
Where Do You Use A/Ds?
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A/D Converters

Analog-to-Digital converters - a.k.a. A/D converters - are widely used by many engineers and scientists of all types, often without their realizing it.  Whenever they make a measurement of a voltage, and that measurement is taken into a computer, an A/D is used.

If you're going to take measurements - and just about every engineer will do a lot of that - then you will be better off if you understand some of the basic ideas behind A/D converters.  There are two simple goals for this lesson.

Given an A/D converter with a given range and number of bits,
To be able to calculate the resolution of the converter.
Given an A/D converter in the laboratory,
To be able to determine the resolution of the converter and the number of bits used in the converter.

What Are A/D Converters?

A/D converters are electrical circuits that have the following characteristics.

• The input to the A/D converter is a voltage.
• A/D converters may be designed for voltages from 0 to 10v, from -5 to +5v, etc., but they almost always take a voltage input.  (Some rare exceptions occur with current inputs!)  In any event, the input is an analog voltage signal for most cases.
• The output of the A/D converter is a binary signal, and that binary signal encodes the analog input voltage.  So, the output is some sort of digital number.
A comparator can be used as a simple one-bit A/D converter.  Although a converter with just one bit isn't particularly useful, you can begin to see how an A/D converter works by puttering with it for a moment.  If you read the lesson on comparators you encountered a simluation of a comparator.  That simulator is reproduced below.  Click here if you want to read the lesson on comparators.

Comparator Simulator

Sim1  Here is the comparator simulator.  You can think of a comparator as a one-bit A/D converter.  The input is an analog signal, and the output is a one bit digital representation of the analog signal.  In the simulator, you can control a simulated voltage source that is the input the the comparator, and the digital output bit is indicated with a simulated LED.  Notice the following.

• The input can range from zero (0) to ten (10) volts.
• When the input voltage goes above five (5) volts, the output is a binary one (1) and the LED lights.  When the input voltage is less than five volts, the output is a binary zero (0) and the LED does not light.