**WELLOG
****ANALOG TO DIGITAL**

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ANALOG TO
DIGITAL CONVERSION:

Analog to
digital conversion is done in a number of different ways.

Single slope
conversion

Dual slope
conversion

Flash
conversion

Successive
approximation Conversion

SUCCESSIVE
APPROXIMATION CONVERSION:

Successive
Approximation Registers (SAR) are the most common type of analog to digital
converters. Successive approximation is similar to the process of using weights
on a balance scale to determine an unknown weight.

Successive
Approximation example:

We have an
unknown weight and eight known weights. We can use successive approximation to
determine the amount of the unknown weight.

The process
is as follows;

We place the unknown
weight on the left side of the scale.

We place a
known 128 ounce weight on the right side of the scale.

We decide if
the 128 ounce weight is greater than the unknown weight. If it is, we take it
“off”. Else we keep it “on”.

We continue
the process using weights each having one half of the previous weights.

When
finished, we add the weights that remain “on” the scale. That is our
approximation of the unknown weight.

Actual case:

We have an
unknown weight of 84 ounces.

Which weights
will remain on the scale and what are their binary equivalents?

Weights:

128 ounce
“off” = 0

64 ounce “on”
= 1

32 ounce
“off” = 0

16 ounce “on”
= 1

8 ounce” off”
= 0

4 ounce “off” = 0

2 ounce “on”
= 1

1 ounce “off”
= 0

The result
is:

LSB
MSB

01010010

A/D in
microcontrollers:

Successive
approximation Analog to digital Converters are found
in many microcontrollers. Microchip Technologies produces a line of PIC
Microcontrollers

that include A/D conversion.
Many of the available microcontrollers operate at speeds of 10 million
instructions per second. The A/D converter can perform

one million conversions per
second.

Revised
11-07-2016 © 2007-2016 WELLOG All Rights Reserved