Biomedical Engineering Reference
In-Depth Information
A plot of the magnitude versus frequency is shown in the following figure. As can be seen, the
cutoff frequency gives a value of magnitude equal to 3.53 at 500 Hz, which is the design goal.
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
0
200
400
600
800
1000
1200
1400
Frequency (rad/s)
None of the filters in Example Problems 9.28-9.30 have the ideal characteristics of
Figure 9.36. To improve the performance from the pass-band to stopband in a low-pass fil-
ter with a sharper transition, one can cascade identical filters together—that is, connect the
output of the first filter to the input of the next filter and so on. The more cascaded filters,
the better the performance. The magnitude of the overall filter is the product of the individ-
ual filter magnitudes.
While this approach is appealing for improving the performance of the filter, the overall
magnitude of the filter does not remain a constant in the pass-band. Better filters are avail-
able with superior performance, such as a Butterworth filter. Two Butterworth filters are
shown in Figure 9.38. Analysis of these filters is carried out in Exercises 53 and 55.
9.14 BIOINSTRUMENTATION DESIGN
Figure 9.2 described the various elements needed in a biomedical instrumentation sys-
tem. The purpose of this type of instrument is to monitor the output of a sensor or sensors
and to extract information from the signals that are produced by the sensors.
Acquiring a discrete-time signal and storing this signal in computer memory from a
continuous-time signal is accomplished with an analog-to-digital (A/D) converter. The
A/D converter uniformly samples the continuous-time waveform and transforms it into
a sequence of numbers, one every
t k seconds.
The A/D converter also transforms the
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