Motorola 24-Bit Digital Signal Processor, DSP56000 manual Analog Signal Processing

ORIGIN OF DIGITAL SIGNAL PROCESSING

ANALOG FILTER

Rf

	x(t)
x(t)	Ri
INPUT
FROM
SENSOR
	t

				Cf
		-
		+
		R f
y(t )			1
-x--(t)------	= –------ ----------------------------1 + jw R f C -f
		Ri

y(t)

y(t)

OUTPUT

TO

ACTUATOR

GAIN

FREQUENCY CHARACTERISTICS

IDEAL

FILTER

f

fc

FREQUENCY

Figure 1-1 Analog Signal Processing

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:

1- 4 DSP56K FAMILY INTRODUCTION MOTOROLA