WELLOG                         ANALOG TO DIGITAL

Revised 5-22-2008

© 2007-2008 WELLOG

All Rights Reserved

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 and 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