User's Guide
SBFA001C – June 1991 – Revised February 2011
FilterPro™ User's Guide
..................................................................................................................
High-Performance Analog
ABSTRACT
Although active filters are vital in modern electronics, their design and verification can be tedious and
time-consuming. The FilterPro program is designed to aid in the design of active filters implemented with
the multiple feedback (MFB) and Sallen-Key topology. This user's guide describes the information the
designer must enter into the program and what the program delivers.
Contents
1
2
3
4
5
6
7
8
9
10
11
12
Filter Type Definitions
......................................................................................................
3
Filter Responses
............................................................................................................
7
Circuit Implementation
......................................................................................................
8
Using FilterPro Desktop v3.1
............................................................................................
11
Changing Components in FilterPro Desktop
...........................................................................
22
Capacitor Selection
........................................................................................................
23
Op Amp Selection
.........................................................................................................
23
The UAF42 Universal Active Filter
......................................................................................
25
Design Tools
...............................................................................................................
25
Migrating Designs from FilterPro v2.0
..................................................................................
31
Important Notes
............................................................................................................
32
Conclusion
..................................................................................................................
37
List of Figures
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Low-Pass Filter Response
.................................................................................................
3
High-Pass Filter Response
................................................................................................
4
Bandpass Filter Response
.................................................................................................
5
Band-Reject or Bandstop Filter
...........................................................................................
6
Response vs Frequency of Even-Order (Four-Pole), 3dB Ripple Chebyshev Filter Showing Cutoff at
0dB
............................................................................................................................
7
Response vs Frequency of Odd-Order (Five-Pole), 3dB Ripple Chebyshev Filter Showing Cutoff at
–3dB
..........................................................................................................................
7
Real Pole Section (Unity-Gain, First-Order Butterworth; f
–3dB
= 1/2·π·R
1
·C
1
)
........................................
9
Second-Order Low-Pass Filter
............................................................................................
9
Third-Order Low-Pass Filter
...............................................................................................
9
........................................
9
Odd-Order Low-Pass Filter using Cascaded Complex Pole-Pair Sections Plus One Real-Pole Section
.......
9
MFB Complex Pole-Pair Section (Gain = – R
2
/R
1
)
....................................................................
10
Sallen-Key Complex Pole-Pair Section, Unity-Gain (Gain = 1)
.....................................................
10
Sallen-Key Complex Pole-Pair Section (Gain = 1 + R
4
/R
3
)
..........................................................
10
Using the FilterPro Design Wizard
......................................................................................
12
Filter Specification Entry Screen
........................................................................................
13
Filter Response Selection Screen
.......................................................................................
15
Filter Topology Selection Screen
........................................................................................
16
Even-Order Low-Pass Filter using Cascaded Complex Pole-Pair Sections
FilterPro is a trademark of Texas Instruments.
Microsoft, Windows, Excel are registered trademarks of Microsoft Corporation.
All other trademarks are the property of their respective owners.
SBFA001C – June 1991 – Revised February 2011
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© 1991–2011, Texas Instruments Incorporated
FilterPro™ User's Guide
1
www.ti.com
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Main Screen, Schematic Tab
............................................................................................
17
Data Tab
....................................................................................................................
18
...................................................................................................................
Comments Tab
............................................................................................................
Design Report Tab
........................................................................................................
File Menu
...................................................................................................................
File Save Directory Dialog
................................................................................................
Design List
..................................................................................................................
Design List: My Designs
..................................................................................................
Changing Component Values
............................................................................................
Component Tolerance Selection
........................................................................................
Example Fully-Differential MFB Filter Designed by FilterPro 3.1
...................................................
Export to Excel Button
....................................................................................................
Print a Design Report Through the Printer Icon in the Upper Left Toolbar Area
..................................
Save a Design from the
File
Menu
......................................................................................
Save As...
Dialog
..........................................................................................................
Selecting a Design from the Design Manager
.........................................................................
Opening a Design from the
File
Menu
..................................................................................
Opening a Design from the Toolbar Icon
...............................................................................
Design Manager Contextual Menu
......................................................................................
Rename Dialog
............................................................................................................
Open Design from
File
Menu
............................................................................................
Specifying and Opening FilterPro v2.0 Format Files
.................................................................
Windows 7 Desktop Properties Selection
..............................................................................
Setting Privilege Level in Desktop Properties
.........................................................................
Correct Look of Filter Design Wizard
...................................................................................
Incorrect Look of Filter Design Wizard
..................................................................................
Selecting Properties from Desktop Contextual Menu
.................................................................
Settings Button in System Properties
...................................................................................
Selecting Performance Options
..........................................................................................
BOM Tab
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35
Gain vs Frequency for Fifth-Order 20kHz Butterworth, Chebyshev, and Bessel Unity-Gain MFB
Low-Pass Filters, Showing Overall Filter Response
..................................................................
36
Gain vs Frequency for Fifth-Order 20kHz Butterworth, Chebyshev, and Bessel Unity-Gain MFB
Low-Pass Filters, Showing Transition-Band Detail
...................................................................
36
Step Response of Fifth-Order, 20kHz Butterworth Low-Pass MFB Filter
..........................................
37
Step Response of Fifth-Order, 20kHz Chebyshev Low-Pass MFB Filter
..........................................
37
...............................................
Measured Distortion for the Three 20kHz MFB Low-Pass Filters
...................................................
Step Response of Fifth-Order, 20kHz Bessel Low-Pass MFB Filter
37
37
2
FilterPro™ User's Guide
© 1991–2011, Texas Instruments Incorporated
SBFA001C – June 1991 – Revised February 2011
Submit Documentation Feedback
www.ti.com
Filter Type Definitions
1
Filter Type Definitions
Electronic filters are applied in applications where a specific amplitude versus frequency behavior is
required from a circuit. Other applications exist where a specific phase shift, or time delay, needs to be
incorporated in a circuit and a filter may be used in those applications as well. FilterPro has been
designed to synthesize filters that purposely affect the frequency or time characteristics of a signal.
The Texas Instruments FilterPro™ program makes it easy to design low-pass, high-pass, bandpass, band
reject, and all-pass active filters. These five filter types are defined in this section.
1.1
Low-Pass Filters
Low-pass filters are the most widely applied filter type. They are designed to readily pass all frequencies
extending from dc to a set cutoff frequency, f
c
; refer to
Figure 1.
This region where the frequencies readily
pass through the filter is called the
passband,
and f
c
is defined as the filter
bandwidth.
Passband
f
c
defines
LP bandwidth
Stop band
Ideal
brick wall
response
Figure 1. Low-Pass Filter Response
Once the cutoff frequency is reached, the filter begins to attenuate any frequency higher than f
c
. The
region above f
c
is called the
stopband.
Most often the attenuation increases, or rolls off, and achieves very
high levels which are limited only by the non-ideal electronics used to construct the filter. These include
the stray and lead inductance of the capacitors, non-ideal operational amplifier limitations, and circuit
parasitics associated with the physical circuit layout.
SBFA001C – June 1991 – Revised February 2011
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© 1991–2011, Texas Instruments Incorporated
FilterPro™ User's Guide
3
Filter Type Definitions
www.ti.com
1.2
High-Pass Filters
The high-pass filter, as shown in
Figure 2,
has a passband where all frequencies above the cutoff
frequency (f
c
) pass with little to no attenuation. Below f
c
, within the filter's stop-band, the signals are
attenuated at ever greater levels as the frequency moves lower.
f
c
cutoff
frequency
Stop band
Passband
Ideal
brick wall
response
Figure 2. High-Pass Filter Response
4
FilterPro™ User's Guide
© 1991–2011, Texas Instruments Incorporated
SBFA001C – June 1991 – Revised February 2011
Submit Documentation Feedback
www.ti.com
Filter Type Definitions
1.3
Bandpass Filters
The bandpass filter has a passband that allows a select band of frequencies that fall within the passband
to pass with little, or no, attenuation; refer to
Figure 3.
An upper (f
H
) and lower (f
L
) cutoff frequency define
the bandwidth of the filter (f
H
to f
L
). Frequencies beyond the passband lie in the two stopbands and receive
greater attenuation as the frequency moves further away from the passband in either direction.
f
L
cutoff
frequency
Passband
Stop band
f
H
cutoff
frequency
Bandwidth = (f
H
- f
L
)
Stop band
Bandwidth
Ideal
brick wall
response
Figure 3. Bandpass Filter Response
SBFA001C – June 1991 – Revised February 2011
Submit Documentation Feedback
© 1991–2011, Texas Instruments Incorporated
FilterPro™ User's Guide
5
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