Page 141 - Understanding Automotive Electronics

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4 MICROCOMPUTER INSTRUMENTATION AND CONTROL

Figure 4.17
Digital-to-Analog
Converter Circuit
Block

FPO

The DAC output voltage can only change in discrete steps. This causes
the analog output voltage to have a staircase appearance as the binary number
at the input is increased one bit at a time from minimum value to maximum
value, as shown in Figure 4.18. This DAC can have any one of 256 different
voltage levels. For many applications, this is a close enough approximation to a
continuous analog signal.
The accuracy of the The DAC output voltage can change only when the computer writes a
DAC’s representation of new number into the DAC data latches. The computer must generate each new
the digital input signal output often enough to ensure an accurate representation of the changes in the
varies with circuit digital signal. The analog output of the DAC can take only a specific number of
design, and with the rate different values and can change only at specific times determined by the
at which the input signal sampling rate. The output of the converter will always have small discrete step
is sampled. changes (resolution). The designer must decide how small the steps must be to

128 UNDERSTANDING AUTOMOTIVE ELECTRONICS