Generating Analog Outputs - Intel 8XC196MC User Manual

8XC196MC, MD, MH USER'S MANUAL

10.5.4 Generating Analog Outputs

PWM modules can generate a rectangular pulse train that varies in duty cycle and period. Filter-
ing this output will create a smooth analog signal. To make a signal swing over the desired analog
range, first buffer the signal and then filter it with either a simple RC network or an active filter.
Figure 10-7 is a block diagram of the type of circuit needed to create the smooth analog signal.
®
MCS 96
Microcontroller
PWM
Figure 10-8 shows a sample circuit used for low output currents (less than 100 µA). Consider
temperature and power-supply drift when selecting components for the external D/A circuitry.
With proper components, a highly accurate 8-bit D/A converter can be made using the PWM.
PWM
®
MCS 96
Microcontroller
Consider both ripple and response time requirements when selecting R and C.
Figure 10-8. PWM to Analog Conversion Circuitry
10-10
Buffer
to Make (Passive
Output Swing
Rail Active)
to
Rail (Optional)
Figure 10-7. D/A Buffer Block Diagram
R
74ACxxx
Buffer
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Filter Power
Amp
or
(Optional)
-
+
Op Amp
C
Analog
Output
A2391-01
Analog
Output
A2390-02