Laboratory Manual - King Fahd University of Petroleum and Minerals

KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS
DEPARTMENT OF ELECTRICAL ENGINEERING
Electronic Circuits II – EE303
Experiment # 6
Various types of first-order active filters and their
applications
OBJECTIVE
1. To design various type of first-order filters.
2. To measure the characteristics of these filters.
3. To see the high frequency limitation due to op amp limited bandwidth.
4. To cascade first-order sections to design new functions.
BACKGROUND
High order-filters can be realized by cascading first and second order sections. These
filters can be implemented by passive RC or LC circuit. However, using active-RC filters
based on op amps provides several advantages: gain which can be set to a desired value,
independent of some of the filter parameters without affecting others and the output
impedance is very low (ideally zero) allowing cascading. Figure 1 gives summary of
various types of first order filters including the transfer functions, bode plots and op amp
based circuit realizations.
Type T(s) Bode plot Circuit
Low-pass
o
filter Ts ()
a
a
20 log| o
w |
o
|T| dB
20 dB
decade
s wo
0 w o w [log]
R 2
R
C
1
+
V i +
V o
CR
2 = 1 w o
R 2
DC gain =
R1
High-pass
filter
Ts ()
as
1
s w
o
20 log|a 1 |
|T| dB
20 dB
decade
0 w o w [log]
+
V i
C
R 1
R 2
+
V o
CR 1 = 1 w o
R 2
High-frequency gain =
R 1
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