Dynamic Range

Before a system can be designed, the dynamic range of the inputs and outputs

must be known. The dynamic range defines the precision that must be applied to

measuring the inputs or generating the outputs. This in turn drives other parts

of the design, such as allowable noise and the precision that is required of the

components.

A simple microprocessor-based system might read an analog input voltage and

convert it to a digital value (how this happens will be examined in Chapter 2).

Dynamic range is usually expressed in decibels (dB) because it is usually a

measurement of relative power or voltage. However, this does not cover all the

things that a microprocessor-based system might want to measure. In simplest

terms, the dynamic range can be thought of as the largest value that must be

measured compared to (or divided by) the smallest. In most cases, the essential

number that needs to be known is the number of bits of precision required to

measure or control something.

As an example, say that we want to measure temperatures between 0 _C and

100 _C. If we want to measure with 1 _C accuracy, we would need 100 discrete

values to accomplish this. An 8-bit analog-to-digital converter (ADC) can divide an

input voltage into 256 discrete values, so this system would need only 8 bits

 of precision. On the other hand, what if we want to measure the same temperature

range with 0.1 _C accuracy? Now we need 100/.1, or 1000 discrete values, and

that means a 10-bit ADC (which can produce 1024 discrete values).