The simplest filter circuit consists of a single pole-pair
subcircuit as shown in Figure 5. More complex filters
consist of two or more cascaded subcircuits as shown in
Figure 6. Even-order filters are implemented entirely with
UAF42 pole-pair sections and normally require no external
capacitors. Odd-order filters additionally require one real
pole section which can be implemented with the fourth
uncommitted op amp in the UAF42, an external resistor, and
an external capacitor. The program can be used to design
filters up to tenth order.
The program guides you through the filter design and gen-
erates component values and a block diagram describing the
filter circuit. The
Filter Block Diagram
program output
shows the subcircuits needed to implement the filter design
labeled by type and connected in the recommended order.
The
Filter Component Values
program output shows the
values of all external components needed to implement the
filter.
L
V
IN
C
V
O
R
FIGURE 4A. n = 2 Band-Pass Filter Using UAF42 (ap-
proximates the response of a series-connected
tuned L, C, R circuit).
L
V
IN
C
R
V
O
SUMMARY OF FILTER TYPES
Butterworth
Advantages:
Maximally flat magnitude
response in the pass-band.
Good all-around performance.
Pulse response better than
Chebyshev.
Rate of attenuation better than
Bessel.
FIGURE 4B. n = 2 Band-Reject (Notch) Filter Using
UAF42 (approximates the response of a par-
allel-connected tuned L, C, R circuit).
Subcircuit 1
In
Out
(2)
V
IN
(1)
V
O
Disadvantages:
Some overshoot and ringing in
step response.
Chebyshev
Advantages:
Better rate of attenuation
beyond the pass-band than
Butterworth.
NOTES:
(1) Subcircuit will be a complex pole-pair (PP1 through PP6)
subcircuit specified on the
UAF42 Filter Component Values
and
Filter Block Diagram
program outputs.
(2) HP Out, BP Out, LP Out, or Aux Out will be specified on the
UAF42
Filter Block Diagram
program output.
Disadvantages:
Ripple in pass-band.
Considerably more ringing in
step response than Butterworth.
Inverse Chebyshev
Advantages:
Flat magnitude response in
pass-band with steep rate of
attenuation in transition-band.
FIGURE 5. Simple Filter Made with Single Complex Pole-
Pair Subcircuit.
Subcircuit 1
In
Out
(2)
Subcircuit N
In
Out
(2)
V
IN
(1)
(1)
V
O
Disadvantages:
Ripple in stop-band.
Some overshoot and ringing in
step response.
Bessel
Advantages:
Best step response—very little
overshoot or ringing.
NOTES:
(1) Subcircuit will be a real-pole high-pass (HP), real-pole low-pass
(LP), or complex pole-pair (PP1 through PP6) subcircuit specified
on the
UAF42 Filter Component Values
and
Filter Block Diagram
program outputs.
(2) If the subcircuit is a pole-pair section, HP Out, BP Out, LP Out, or
Aux Out will be specified on the UAF42
Filter Block Diagram
program output.
Disadvantages:
Slower initial rate of attenua-
tion beyond the pass-band than
Butterworth.
3
FIGURE 6. Multiple-Stage Filter Made with Two or More
Subcircuits.
BURR-BROWN [ BURR-BROWN CORPORATION ]
