ORIGIN OF DIGITAL SIGNAL PROCESSING
1- 4 DSP56K FAMILY INTRODUCTION
MOTOROLA
The equivalent circuit using a DSP is shown in Figure 1-2. This application requires an
analog-to-digital (A/D) converter and digital-to-analog (D/A) converter in addition to the
DSP. Even with these additional parts, the component count can be lower using a DSP
due to the high integration available with current components.
Processing in this circuit begins by band-limiting the input with an anti-alias filter, eliminat-
ing out-of-band signals that can be aliased back into the pass band due to the sampling
process. The signal is then sampled, digitized with an A/D converter, and sent to the DSP.
The filter implemented by the DSP is strictly a matter of software. The DSP can directly
implement any filter that can also be implemented using analog techniques. Also, adap-
tive filters can be easily implemented using DSP, whereas these filters are extremely
difficult to implement using analog techniques.
The DSP output is processed by a D/A converter and is low-pass filtered to remove the
effects of digitizing. In summary, the advantages of using the DSP include the following:
yt()
xt()
--------- Rf
Ri
------ 1
1jwRfCf
+
------------------------------
–=
-
+
y(t)
OUTPUT
TO
ACTUATOR
t
x(t)
INPUT
FROM
SENSOR
x(t)
Ri
Rf
Cf
ANALOG FILTER
FREQUENCY CHARACTERISTICS
IDEAL
FILTER
f
fc
FREQUENCY
GAIN
y(t)
Figure 1-1 Analog Signal Processing