51419a

M
FilterLab® 2.0
User’s Guide

 2003 Microchip Technology Inc. DS51419A

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DS51419A-page ii  2003 Microchip Technology Inc.

M FilterLab® 2.0
User’s Guide
Table of Contents

General Information
Introduction .......................................................................................... 1
About This Guide ................................................................................. 2
The Microchip Internet Web Site.......................................................... 2
Customer Support ................................................................................ 3
Chapter 1. Dialog Boxes
1.1 Dialog Boxes ................................................................................ 5
Chapter 2. Wizards
2.1 Anti-Aliasing Wizard ................................................................... 19
2.2 Filter Selection Wizard ............................................................... 25
Chapter 3. Toolbar
3.1 Buttons ....................................................................................... 35
3.2 Approximation Combo Box ........................................................ 38
3.3 Frequency Textboxes ................................................................. 39
Chapter 4. Menus
4.1 File ............................................................................................. 41
4.2 Edit ............................................................................................. 44
4.3 View ........................................................................................... 45
4.4 Filter ........................................................................................... 46
4.5 Window ...................................................................................... 47
4.6 Help ............................................................................................ 47

 2003 Microchip Technology Inc. DS51419A-page iii

FilterLab® 2.0 User’s Guide

Chapter 5. Window Views
5.1 Frequency View ..........................................................................49
5.2 Circuit View .................................................................................50
5.3 Spice Listing View ......................................................................51
Appendix A. FilterLab 2.0 to SPICE Interface
A.1 Introduction And Highlights......................................................... 53
Appendix B. Filter Magnitude Templates
B.1 Introduction................................................................................. 57
Appendix C. Group Delay
C.1 Introduction................................................................................. 63
Appendix D. Bessel Filter Response
D.1 Introduction................................................................................. 65
Appendix E. Op Amp Selection
E.1 Introduction................................................................................. 67
Appendix F. Selected References
F.1 Introduction................................................................................. 71
Worldwide Sales and Service ................................................................. 72

DS51419A-page iv  2003 Microchip Technology Inc.

M FilterLab® 2.0
User’s Guide
General Information

INTRODUCTION
FilterLab® 2.0 is an innovative software tool that simplifies active filter design. Available
at no cost from Microchip’s web site (www.microchip.com), the FilterLab 2.0 active filter
software design tool provides full schematic diagrams of the filter circuit with
recommended component values and displays the frequency response.
FilterLab 2.0 allows the design of low-pass filters up to an 8th order filter with Cheby-
chev, Bessel or Butterworth responses from frequencies of 0.1 Hz to 1 MHz. FilterLab
2.0 also can be used to design band-pass and high-pass filters with Chebychev and
Butterworth responses. The circuit topologies supported by FilterLab 2.0 are the Sallen
Key and Multiple Feedback (MFB). The low-pass filters can use either the Sallen Key
or MFB, the band-pass is available with the MFB and the high-pass uses the Sallen
Key.
Users can select a flat pass band or sharp transition from pass band to stopand.
Options (such as minimum ripple factor, sharp transition and linear phase delay) are
available. Once the filter response has been identified, FilterLab 2.0 generates the fre-
quency response and the circuit. For maximum design flexibility, changes in capacitor
values can be implemented to fit the demands of the application. FilterLab 2.0 will
recalculate all values to meet the desired response, allowing real-world values to be
substituted or changed as part of the design process.
FilterLab 2.0 also generates a SPICE model of the designed filter. Extraction of this
model will allow time domain analysis in SPICE simulations, streamlining the design
process.
Further consideration is given to designs used in conjuction with an Analog-to-Digital
Converter (ADC). A suggested filter can be generated by simply inputting the bit
resolution and sample rate via the Anti-Aliasing Wizard. This eliminates erroneous
signals folded back into the digital data due to the aliasing effect.
This section also covers the following topics:
• About This Guide
• The Microchip Internet Web Site
• Customer Support

 2003 Microchip Technology Inc. DS51419A-page 1


ABOUT THIS GUIDE
Document Layout
The User’s Guide layout is as follows:
• General Information – this section describes how to use the FilterLab® 2.0
User’s Guide.
• Chapter 1: Dialog Boxes – this section describes the dialog boxes and their
uses.
• Chapter 2: Wizards – this section describes the Filter Selection Wizard and helps
you design a filter.
• Chapter 3: Toolbars – this section describes the toolbars and their functions.
• Chapter 4: Menus – this section describes the menus and their functions.
• Chapter 5: Window Views – this section describes the window views and how
they are used.
• Worldwide Sales and Service – this section gives the address, telephone and
fax number for Microchip Technology Inc. sales and service locations throughout
the world.

THE MICROCHIP INTERNET WEB SITE
Microchip provides on-line support on the Microchip World Wide Web (WWW) site.
The web site is used by Microchip as a means to make files and information easily
accessible to customers. To view the site, the user must have access to the internet
and a web browser, such as Netscape® Communicator or Microsoft® Internet
Explorer®. Files are also available for FTP download from our FTP site.

Connecting to the Microchip Internet Web Site
The Microchip web site is available by using your favorite Internet browser to connect
to:
http://www.microchip.com
The file transfer site is available by using an FTP program/client to connect to:
ftp://ftp.microchip.com
The web site and file transfer site provide a variety of services. Users may
download files for the latest Development Tools, Data Sheets, Application Notes,
User's Guides, Articles and Sample Programs. A variety of Microchip specific business
information is also available, including listings of Microchip sales offices, distributors
and factory representatives. Other data available for consideration is:
• Latest Microchip Press Releases
• Technical Support Section with Frequently Asked Questions
• Design Tips
• Device Errata
• Job Postings
• Microchip Consultant Program Member Listing
• Links to other useful web sites related to Microchip Products
• Conferences for products, Development Systems, technical information and more
• Listing of seminars and events

DS51419A-page 2  2003 Microchip Technology Inc.


CUSTOMER SUPPORT
Users of Microchip products can receive assistance through several channels:
• Distributor or Representative
• Local Sales Office
• Field Application Engineer (FAE)
• Corporate Applications Engineer (CAE)
• Hot Line
Customers should call their distributor, representative or field application engineer
(FAE) for support. Local sales offices are also available to help customers. See the
back cover for a listing of sales offices and locations.
Corporate Applications Engineers (CAEs) may be contacted at (480) 792-7627.
In addition, there is a Systems Information and Upgrade Line. This line provides system
users a listing of the latest versions of all of Microchip's development systems software
products. Plus, this line provides information on how customers can receive any
currently available upgrade kits.
The Hot Line numbers are:
• 1-800-755-2345 for U.S. and most of Canada, and
• 1-480-792-7302 for the rest of the world


NOTES:


M FilterLab® 2.0
User’s Guide
Chapter 1. Dialog Boxes

1.1 DIALOG BOXES
1.1.1 Filter Design Dialog
The Filter Design dialog enables the user to create a filter by specifying all aspects of
the filter.

1.1.2 Filter Specification Tab
The Filter Specification tab enables the user to specify the approximation type, the
selectivity and the gain. Select any approximation, the selectivity for the approximation
and the overall filter gain. The maximum allowed gain is 10 V/V. After specifying the
approximation, selectivity and gain, select OK or the Filter Parameters tab.

Note: Bessel approximations only support low-pass selectivities. Therefore, when
the Bessel approximation is selected, the only available selectivity will be
low-pass.

FIGURE 1-1: Filter Specification Tab



FIGURE 1-2: Filter Specification Tab with Bessel Selected



1.1.3 Filter Parameters Tab
Figures 1-4, 1-5 and 1-6 demonstrate the location of the pass band and stop band
upper and lower frequencies. For all selectivities, apass and astop represent the pass
band and stop band attenuations. For low-pass selectivities (Figure 1-4), fpass and fstop
represent the pass band and stop band frequencies. For high-pass selectivities
(Figure 1-5), fpass and fstop represent the pass band and stop band frequencies. For
low-pass selectivities (Figure 1-6), fpass upper and fpass lower represent the pass band
and upper and lower frequencies, while fstop upper and fstop lower represent the stop
band and upper and lower frequencies.

FIGURE 1-3: Filter Parameters Tab
The Filter Parameters tab enables the user to modify the filter’s parameters.
Figures 1-4, 1-5 and 1-6 provide a simplified representation of the filter specification
parameters. A detailed discussion of the filter specification is provided in Appendix B,
“Filter Magnitude Templates”.



Attenuation (dB) Transition
Passband Region Stopband

a pass

a stop

Frequency (Hz)
f pass f stop

FIGURE 1-4: Parameter Definitions for Low-pass Selectivity

Attenuation (dB) Transition
Stopband Region Passband

a pass

a stop

Frequency (Hz)
f pass f stop

FIGURE 1-5: Parameter Definitions for High-pass Selectivity



Attenuation (dB) Transition Transition
Stopband Region Passband Region Stopband

a pass

a stop

Frequency (Hz)
f stop lower f pass lower f pass upper f stop upper

FIGURE 1-6: Parameter Definitions for Band-pass Selectivity


1.1.3.1 FILTER ORDER
The Force Filter Order option enables the user to specify the filter order or have the
program calculate the filter order based on the dialog entries. To force the filter order,
select the Force Filter Order checkbox. When the checkbox is selected, the user
specifies the Pass Band Attenuation and the Pass Band frequencies. FilterLab 2.0 then
calculates the Stop Band Attenuation and Stop Band frequencies based on the order.
When the checkbox is not selected, the user specifies the attenuation and all frequency
values. FilterLab 2.0 then calculates the order based on the attenuation and frequency
values.

Note: Bessel approximations only support forced filter orders. When the Bessel
approximation is selected, the Force Filter Order checkbox will be checked
and disabled.

FIGURE 1-7: Filter Parameters Tab with Force Filter Order Selected



FIGURE 1-8: Filter Parameters Tab with Bessel Approximation Selected

1.1.3.2 PASS BAND ATTENUATION
The Pass Band Attenuation is the change in magnitude of the frequencies in the pass
band. The Pass Band Attenuation for each selectivity (low-pass, high-pass, band-pass)
is shown in Figures 1-4, 1-5 and 1-6. The allowable range is -0.01 dB to -3 dB. If a value
beyond this range is entered in the Filter Parameters tab, the error message shown in
Figure 1-9 will appear.

FIGURE 1-9: Error Message


1.1.3.3 STOP BAND ATTENUATION
The Stop Band Attenuation is the minimum reduction in magnitude of the frequencies
in the stop band relative to the pass band. The Stop Band Attenuation for each selec-
tivity is shown in Figures 1-4, 1-5 and 1-6. The allowable range is -10 dB to -100 dB. If
a value beyond this range is entered in the Filter Parameters tab, the error message
shown in Figure 1-10 will appear.


1.1.3.4 PASS BAND FREQUENCY
The Pass Band Frequency is the starting point of the pass band, as shown in
Figures 1-4, 1-5 and 1-6. The allowable range is 0.1 Hz to 1,000,000 Hz. If a value
beyond this range is entered in the Filter Parameters tab, the error message shown in
Figure 1-11 will appear.


1.1.3.4.1 Low-pass
The Pass Band Frequency must be lower than the Stop Band Frequency for low-pass
filters. If a value is entered in the Filter Parameters tab which is larger than the Stop
Band Frequency, the error message shown in Figure 1-12 will appear.



1.1.3.4.2 High-pass
The Pass Band Frequency must be greater than the Stop Band Frequency for
high-pass selectivities. If a value is entered in the Filter Parameters tab that is smaller
than the Stop Band Frequency, the error message shown in Figure 1-13 will appear.


1.1.3.4.3 Band-pass
The Pass Band Lower Frequency must be lower than the Pass Band Upper Frequency
and both Stop Band Frequencies for band-pass selectivities. If a value is entered in
the Filter Parameters tab that is greater than the Stop Band Frequency or Pass Band
Upper Frequency, the error message shown in Figures 1-14 and 1-15 will appear.




1.1.3.5 STOP BAND FREQUENCY
The Stop Band Frequency is the starting point of the stop band, as shown in Figures
1-4, 1-5 and 1-6. The allowable range is 0.1 Hz to 1,000,000 Hz. If a value beyond this
range is entered in the Filter Parameters tab, the error message shown in Figure 1-16
will appear.


1.1.3.5.4 Low-pass
The Stop Band Frequency must be greater than the Pass Band Frequency for low-pass
selectivities. If a value is entered in the Filter Parameters tab that is smaller than the
Pass Band Frequency, the error message shown in Figure 1-17 will appear.


1.1.3.5.5 High-pass
High-pass selectivities. If a value is entered in the Filter Parameters tab that is smaller
than the Stop Band Frequency, the error message shown in Figure 1-18 will appear.



1.1.3.5.6 Band-pass
and both Stop Band Frequencies for band-pass selectivities. If a value is entered in
the Filter Parameters tab that is greater than the Stop Band Frequency or Pass Band
Upper Frequency, the error message shown in Figures 1-19 and 1-20 will appear.





1.1.4 Circuit Tab
The Circuit tab enables the user to modify the circuit topology and component values.

FIGURE 1-21: Circuit Tab

1.1.4.1 RESISTOR SELECTION
The Resistor Selection enables the user to change from standard 1% resistors to the
exact calculated value. Changing the Resistor Selection affects all stages.

1.1.4.2 TOPOLOGY SELECTION
The Topology Selection enables the user to change the topology for Low-pass
selectivities.

Note: Band-pass selectivities only support Multiple Feedback (MFB) topologies,
while the high-pass selectivities only support Sallen Key topologies.
Changing the topology only affects the stage for the active tab.

1.1.4.3 CAPACITOR SELECTION
The Capacitor Selection enables the user to change the value of a capacitor from the
default value calculated by FilterLab 2.0. FilterLab 2.0 automatically scales the other
resistors and capacitors of the filter section to maintain the desired filter specifications.
Changing the capacitor value only affects the capacitor that is selected. The capacitor
combo box is disabled unless a capacitor has been selected (Figure 1-21). To modify
a capacitor's value, select the appropriate stage tab, then select the capacitor to be
modified by left-clicking it with the mouse. When a capacitor is selected, it will be high-
lighted and the capacitor combo box will be enabled (Figure 1-22). Select “Automatic”
from the combo box to automatically calculate the capacitor value. Select a value to
force the capacitor to that value.



FIGURE 1-22: Capacitor Selected

1.1.5 Cancel
To cancel changes made to the Specification, Parameters or Circuit tabs, select
Cancel.

1.1.6 OK
To implement changes made to the Specification, Parameters or Circuit tabs, select
OK.


NOTES:


M FilterLab® 2.0
User’s Guide
Chapter 2. Wizards

2.1 ANTI-ALIASING WIZARD
The Anti-Aliasing Wizard assists the user in designing a low-pass filter used with an
A/D converter. The wizard prompts the user for the bandwidth, the sampling frequency,
the resolution and the signal-to-noise ratio of the A/D converter.

FIGURE 2-1: Anti-Aliasing Wizard



2.1.1 Anti-Aliasing Wizard Filter Bandwidth Page
The Cut-off Frequency (Figure 2-2) determines the bandwidth of the anti-aliasing filter.
The frequency range is limited to values from 0.1 Hz to 1 MHz. If a value outside this
range is entered, the error message shown in Figure 2-3 will appear.

FIGURE 2-2: Filter Bandwidth




2.1.2 Anti-Aliasing Wizard Sampling Frequency Page
Enter the Sampling Frequency of the A/D converter. The Sampling Frequency must be
greater than 2 * cut-off frequency. If a value which is less than 2 * cut-off frequency is
entered, the error message shown in Figure 2-5 will appear.

FIGURE 2-4: Sampling Frequency




2.1.3 Anti-Aliasing Wizard Resolution Page
Enter the Resolution of the A/D converter. The Resolution must be between 8 and
24 bits. If a value outside this range is entered, the error message shown in Figure 2-7
will appear.

FIGURE 2-6: Resolution




2.1.4 Anti-Aliasing Wizard Signal-to-Noise Page
Enter the desired Signal to Noise Ratio. The default value is 6.02 * bits + 1.76.
Decreasing the value will decrease the order of the filter, while increasing the value will
increase the filter order.

FIGURE 2-8: Signal to Noise Ratio



2.1.5 Anti-Aliasing Wizard Completion Page
The completion page summarizes the selections and presents the filter options. If the
previous settings cause a filter to have a higher order than allowed by the program, the
radio button for that option will be disabled.

Note: Filters with an order greater than 8 typically are not practical. If the
calculated filter order is greater than 8, the user should evaluate increasing
the sampling rate.

FIGURE 2-9: Completion Page



2.2 FILTER SELECTION WIZARD
The Filter Selection Wizard allows the specification of the selectivity, attenuation and
frequencies, then presents a table of data showing the order, frequencies and
attenuations for each approximation.

FIGURE 2-10: Filter Selection Wizard



2.2.1 Filter Selection Wizard Selectivity Page
The Filter Selectivity page allows the modification of the selectivity. The response of
the selected selectivity is displayed in the property page.

FIGURE 2-11: Filter Selectivity



2.2.2 Filter Selection Wizard Specification Page
The Filter Specification page allows the modification of the filter parameters, attenua-
tions and frequencies. The values are defined in Figures 1-4, 1-5 and 1-6. The
response of the selectivity is displayed in the property page.

FIGURE 2-12: Filter Specification – Filter Parameters

2.2.2.1 PASS BAND ATTENUATION
The Pass Band Attenuation is the change in magnitude of the frequencies in the pass
band. The Pass Band Attenuation for each selectivity is shown in Figures 1-4, 1-5 and
1-6. The allowable range is -0.01 dB to -3 dB. If a value beyond this range is entered,
the error message shown in Figure 2-13 will appear.



2.2.2.2 STOP BAND ATTENUATION
The Stop Band Attenuation is the change in magnitude of the frequencies in the stop
band. The Stop Band Attenuation for each selectivity is shown in Figures 1-4, 1-5 and
1-6. The allowable range is -10 dB to -100 dB. If a value beyond this range is entered,
the error message shown in Figure 2-14 will appear.


2.2.2.3 PASS BAND FREQUENCY
The Pass Band Frequency is the starting point of the pass band, as shown in
Figures 1-4, 1-5 and 1-6. The allowable range is 0.1 Hz to 1,000,000 Hz. If a value
beyond this range is entered, the error message shown in Figure 2-15 will appear.


2.2.2.3.1 Low-pass
The Pass Band Frequency must be lower than the Stop Band Frequency for low-pass
selectivities. If a value is entered which is larger than the Stop Band Frequency, the
error message shown in Figure 2-16 will appear.



2.2.2.3.2 High-pass
high-pass selectivities. If a value is entered that is smaller than the Stop Band
Frequency, the error message shown in Figure 2-17 will appear.


2.2.2.3.3 Band-pass
and both Stop Band Frequencies for band-pass selectivities. If a value is entered that
is greater than the Stop Band Frequency or Pass Band Upper Frequency, the error
message shown in Figures 2-18 and 2-19 will appear.




2.2.2.4 STOP BAND FREQUENCY
The Stop Band Frequency is the starting point of the stop band, as shown in Figures
1-4, 1-5 and 1-6. The allowable range is 0.1 Hz to 1,000,000 Hz. If a value beyond
this range is entered, the error message shown in Figure 2-20 will appear.


2.2.2.4.4 Low-pass
The Stop Band Frequency must be greater than the Pass Band Frequency for low-pass
selectivities. If a value is entered that is smaller than the Pass Band Frequency, the
error message shown in Figure 2-21 will appear.


2.2.2.4.5 High-pass
high-pass selectivities. If a value is entered that is smaller than the Stop Band
Frequency, the error message shown in Figure 2-22 will appear.



2.2.2.4.6 Band-pass
and both Stop Band Frequencies for band-pass selectivities. If a value is entered that
is greater than the Stop Band Frequency or Pass Band Upper Frequency, the error
message shown in Figures 2-23 and 2-24 will appear.





2.2.3 Filter Selection Wizard Approximation Page
The Filter Approximation page summarizes the filter settings and lists the calculated
Order and Stop Band Attenuation for each approximation.

Note: If the calculated order for either approximation exceeds 8, the
approximation will be disabled. The user should consider modifying either
the pass band or stop band frequencies so that a more practical filter can
be produced.

FIGURE 2-25: Filter Approximation



2.2.4 Filter Selection Wizard Completion Page
The Filter Completion page summarizes all selections made. To implement the filter,
click the Finish button.

FIGURE 2-26: Completion Page


NOTES:


M FilterLab® 2.0
User’s Guide
Chapter 3. Toolbar

3.1 TOOLBAR
The toolbar provides a shortcut to FilterLab 2.0 program settings. Options available on
the toolbar can also be accessed from the menus or dialog boxes.

Filter Filter Overlay Approximation High-pass Zoom Zoom Filter
Design Selection Combo Box Button In Out Order
Wizard Button Button

Circuit Anti-aliasing Low-pass Band-pass
Configuration Wizard Button Button

Filter fSL fPL fPH fSH
Order

FIGURE 3-1: Toolbar

3.2 BUTTONS
3.2.1 Filter Design
The Filter Design toolbar button (Figure 3-2) opens the Filter Design dialog box.

FIGURE 3-2: Filter Design Button

3.2.2 Circuit Configuration
The Circuit Configuration toolbar button (Figure 3-3) opens the Filter Design dialog with
the Circuit tab active.

FIGURE 3-3: Circuit Configuration Button



3.2.3 Overlay
The Overlay button (Figure 3-4) enables the overlay feature. The overlay feature
overlays approximations selected from the toolbar's approximation combo box
(Figure 3-5) in the response view. The overlay button functions as a radio button. When
the overlay feature is enabled, the overlay button will be depressed. To overlay
approximations in the response view, select the first approximation to overlay from the
toolbar's approximation combo box. After the first approximation has been selected,
select the overlay button. Once the overlay button has been selected, any
approximations selected from the toolbar's approximation combo box will be overlayed
with the original approximation. A checkmark will appear next to all approximations that
have been selected to be overlayed. To disable the overlay feature, select the overlay
toolbar button.

Note: Bessel approximations cannot be overlayed. Therefore, if you select the
Bessel approximation from the toolbar's approximation combo box, it will
not be overlayed with the other approximations.

FIGURE 3-4: Overlay Button

FIGURE 3-5: Approximation Combo Box

3.2.4 Low-pass
The Low-pass toolbar button (Figure 3-6) changes the selectivity to low-pass and the
frequencies to the default values with a pass band frequency of 1,000 Hz and a stop
band frequency of 10,000 Hz.

FIGURE 3-6: Low-pass Button



3.2.5 High-pass
The High-pass toolbar button (Figure 3-7) changes the selectivity to high-pass and the
frequencies to the default values with a pass band frequency of 10,000 Hz and a stop
band frequency of 1,000 Hz. The High-pass toolbar button is disabled for Bessel
approximations.

FIGURE 3-7: High-pass Button

Note: Bessel approximations only support low-pass selectivities. The High-pass
toolbar button will be disabled when Bessel approximations are selected.

3.2.6 Band-pass
The Band-pass toolbar button (Figure 3-8) changes the selectivity to band-pass and
the frequencies to the default values with a lower pass band frequency of 1,000 Hz, an
upper pass band frequency of 5,000 Hz, a lower stop band frequency of 100 Hz and
an upper stop band frequency of 50,000 Hz. The Band-pass toolbar button is disabled
for Bessel approximations.

FIGURE 3-8: Band-pass Button

Note: Bessel approximations only support low-pass selectivities. The Band-pass
toolbar button will be disabled when Bessel approximations are selected.

3.2.7 Zoom-In
The Zoom-In button (Figure 3-9) zooms the response view towards the center of the
response. The zoom button has no affect on the Circuit or the SPICE views.

FIGURE 3-9: Zoom-In Button

3.2.8 Zoom-Out
The Zoom-Out button (Figure 3-10) zooms the response view out from the center of the
response. The Zoom-Out button has no affect unless the response has been previously
zoomed with the Zoom-In button (Figure 3-9). The zoom button has no affect on the
Circuit or the SPICE views.

FIGURE 3-10: Zoom-Out Button



3.2.9 Filter Order
The Filter Order button (Figure 3-11) displays the filter's order and modifies that order.
Selecting the Filter Order arrow buttons will increase or decrease the order of the filter.
When the minimum or maximum order of the program is reached, the order will
automatically roll over. If the current design filter had the order automatically calculated
and one of the Filter Order arrow buttons is selected, the program automatically sets
the Force Filter Order flag (Figure 1-7) and forces the filter order to the value in the
Force Filter Order text box. Band-pass selectivities only have even order selectivities.
Therefore, the order will increment by two when a band-pass selectivity is selected.

FIGURE 3-11: Filter Order

3.3 APPROXIMATION COMBO BOX
The Approximation combo box (Figure 3-12) changes the filter approximation.
Selecting All will enable the overlay feature and overlay all approximations, excluding
the Bessel approximation. The Bessel approximation is only available for low-pass
selectivities and forced filter orders. Therefore, when the Bessel approximation is
selected, the selectivity will be changed to low-pass and the Force Filter Order flag will
be enabled.

FIGURE 3-12: Filter Approximation

Note: Bessel approximations only support low-pass selectivities. Choosing a
selectivity other than low-pass changes the selectivity to low-pass and
resets the frequency values.



3.4 FREQUENCY TEXT BOXES
The frequency text boxes provide a shortcut for modifying the pass band and stop band
frequencies. The range of values is limited to 0.1 Hz to 1,000,000 Hz.
The text boxes are enabled and disabled depending on the currently specified selec-
tivity and whether the filter order is forced or calculated by the program. If the frequency
order is forced, there is only one frequency value that can be adjusted for low-pass and
high-pass selectivities and only two frequencies that can be adjusted for band-pass
selectivities. Therefore, only one text box will be enabled for low-pass and high-pass
selectivities and two text boxes will be enabled for band-pass selectivities.

3.4.1 Low-pass
When the Low-pass selectivity is specified, the left-most enabled text box represents
the filter's pass band frequency and the rightmost enabled text box represents the
filter's stop band frequency (Figure 3-13). When the filter order is forced only, the filter's
pass band frequency can be modified. Therefore, only the left most text box is enabled
(Figure 3-14).

FIGURE 3-13: Frequency Text Boxes - Order Unforced

FIGURE 3-14: Frequency Text Boxes - Order Forced

3.4.2 High-pass
When the High-pass selectivity is specified, the leftmost enabled text box represents
the filter's stop band frequency and the right most enabled text box represents the fil-
ter's pass band frequency (Figure 3-15). When the filter order is forced only, the filter's
pass band frequency can be modified. Therefore, only the right most text box is
enabled (Figure 3-16).





3.4.3 Band-pass
When the band-pass selectivity is specified, the left most text box represents the filter's
lower stop band frequency. The second textbox represents the filter's lower pass band,
while the third text box represents the filter's upper pass band. The right most text box
represents the filter's pass band frequency (Figure 3-17). When the filter order is
forced, only the filter's lower and upper pass band frequencies can be modified.
Therefore, only the center text boxes are enabled (Figure 3-18).




M FilterLab® 2.0
User’s Guide
Chapter 4. Menus

4.1 MENUS

FIGURE 4-1: Menu Bar

4.2 FILE

FIGURE 4-2: File Menu

4.2.1 New
The New menu item (Figure 4-2) creates a new project with filter properties that are
independent of the original project. When selected, a new window will open for the new
project.



4.2.2 Open
The Open menu item (Figure 4-2) opens a saved project. Select Open, then select the
previously saved project in the Open Project dialog box (Figure 4-3).

FIGURE 4-3: Open Project Dialog

4.2.3 Close
The Close menu item (Figure 4-2) closes the currently active project.

4.2.4 Save
The Save menu item (Figure 4-2) saves the currently active project and changes the
title bar's file name (Figure 4-5) and spice listing's macro-model title (Figure 4-6), to the
specified file name in the Save File dialog box (Figure 4-4).

FIGURE 4-4: Save Project Dialog



FIGURE 4-5: Title Bar Filename

FIGURE 4-6: SPICE Listing Model Title

4.2.5 Print
The Print menu item (Figure 4-2) prints the active view.

4.2.6 Print Preview
The Print Preview menu item (Figure 4-2) previews the active view.

4.2.7 Print Setup
The Print Setup menu item (Figure 4-2) opens the Print Setup dialog box (Figure 4-7).

FIGURE 4-7: Print Setup Dialog

4.2.8 Exit
The Exit menu item (Figure 4-2) exits the program.



4.3 EDIT

FIGURE 4-8: Edit Menu

4.3.1 Select All
The Select All menu item (Figure 4-8) selects the text in the SPICE listing for copying
and pasting. The Select All menu item is only available when the SPICE view has
focus.

4.3.2 Copy
The Copy menu item (Figure 4-8) copies the active view or SPICE listing to the clip-
board. It is enabled for the Response and Circuit views and is disabled for the SPICE
view unless text has been selected.



4.4 VIEW

FIGURE 4-9: View Menu

4.4.1 Filter Views
The Filter View menu items (Figures 4-9 and 4-10) change the current view.

FIGURE 4-10: Filter View Menu

4.4.2 Group Delay
The Group Delay menu item (Figure 4-9) changes the Response view's auxiliary data
to group delay. The Group Delay menu item is enabled only when the Response view
has focus.

4.4.3 PhaseRadians
The PhaseRadians menu item (Figure 4-9) changes the Response view's auxiliary
data to radians. The PhaseRadians menu item is enabled only when the Response
view has focus.

4.4.4 PhaseDegrees
The PhaseDegrees menu item (Figure 4-9) changes the Response view's auxiliary
data to phase. The PhaseDegrees menu item is enabled only when the Response
view has focus.



4.5 FILTER

FIGURE 4-11: Filter Menu

4.5.1 Design
The Design menu item (Figure 4-11) opens the Filter Design dialog box (Figure 1-1)
with the Filter Specification tab active.

4.5.2 Filter Selection Wizard
The Filter Selection Wizard menu item (Figure 4-11) opens the Filter Selection Wizard
dialog box (Figure 2-10).

4.5.3 Anti-Aliasing Wizard
The Anti-Aliasing Wizard menu item (Figure 4-11) opens the Anti-Aliasing Wizard
dialog box (Figure 2-1).

4.5.4 Overlay
The Overlay menu item is used to display both the frequency and phase or group delay
response of the filter.



4.6 WINDOW

FIGURE 4-12: Window Menu

4.6.1 New Window
The New Window menu item (Figure 4-12) creates a new window for the current
project and changes to the filter design are represented in both windows. When a new
window is created, the title bar will change to [ProjectName]:[Window Number]. The
view listing in the View menu will have a new listing in the form [Project Name]:[Window
Number].

4.6.2 Cascade
The Cascade menu item (Figure 4-12) cascades all windows.

4.6.3 Tile
The Tile menu item tiles all windows.

4.6.4 Arrange Icons
The Arrange Icons menu item (Figure 4-12) arranges the minimized window icons at
the bottom of the main window.

4.7 HELP

FIGURE 4-13: Help Menu

4.7.1 About
The About FilterLab menu item (Figure 4-13) opens the About dialog box.


NOTES:


M FilterLab® 2.0
User’s Guide
Chapter 5. Window Views

5.1 FREQUENCY VIEW
The Frequency View displays the filter response.

Menu available by
right clicking the
mouse button

FIGURE 5-1: Frequency View

5.1.1 Axes
The left axis displays the attenuation of the filter. The default left axis scale is +10 dB
to -80 dB. The right axis displays either the phase in degrees or radians, or the group
delay. The frequency range is automatically set to three decades when the filter order
is forced.



5.1.2 Pop-up Menu
5.1.2.1 PHASE/GROUP DELAY
The Phase/Group Delay pop-up menu item (Figure 5-1) changes the right axis to one
of the three right axis options. These options are:
• Group Delay
• Phase/Radians
• Phase/Degrees

5.1.2.2 SAVE AS JPEG
The Save as JPEG pop-up menu item (Figure 5-1) saves the Response view as a
JPEG file.

5.1.2.3 COPY
The Save as JPEG pop-up menu item (Figure 5-1) copies the Response view image to
the clipboard.

5.2 CIRCUIT VIEW

FIGURE 5-2: Circuit View

5.2.1 Circuit Display
The Circuit View (Figure 5-2) displays the current circuit for the specified filter.



5.3 SPICE LISTING VIEW

Menu available by
right clicking the
mouse button

FIGURE 5-3: SPICE Listing View

5.3.1 Pop-up Menu
5.3.1.1 COPY
The Copy pop-up menu item (Figure 5-3) copies the selected SPICE listing to the
clipboard. The Copy popup menu item is only enabled when spice text has been
selected in the Edit menu.

5.3.1.2 SAVE
The Save pop-up menu item (Figure 5-3) saves the SPICE listing to a text file. The
spice listings model name changes to the name of the file to which the listing is saved.


NOTES:


M FilterLab® 2.0
User’s Guide
Appendix A. FilterLab 2.0 to SPICE Interface

A.1 INTRODUCTION AND HIGHLIGHTS
FilterLab 2.0 provides a net list of the filter circuit that can be imported to a SPICE
simulator. The SPICE output of FilterLab 2.0 and the Microchip operational amplifiers
macromodels are designed to be compatible with PSPICE™ or other SPICE 2G6
circuit simulators. Other simulators may require translation.
The FilterLab 2.0 to PSPICE interface consists of a three-step procedure. First, the
filter is defined using either the Filter Design dialog box or the Filter Selection Wizard.
The second step consists of reviewing the frequency response and schematic of the
filter design. The last step consists of copying the net list filter that is provided in the
SPICE view to the SPICE simulator.

FilterLab 2.0 SPICE Design Example
*****************************************************************************
*****************************************************************************
*1 KHz Low-pass Filter
*2nd Order Butterworth Approximation
*Sallen-Key Circuit Topology
*MPC6001 Operational Amplifier PSPICE Macromodel
*****************************************************************************
*****************************************************************************
* AC Response Test
* Node 10 functions as the input to the filter network
V_IN 10 0 AC 1V
*
* N#pts Start/Stop Freq.
.AC DEC 100 1 10MEG
*
* OP-AMP Power (pin 3 = V+, pin 4 = V-)
V_PWR_PLUS 3 0 2.5V
V_PWR_NEG 4 0 -2.5V

*CALL FILTER_DEMO CIRCUIT
*CONNECTIONS:
* INPUT
* | OUTPUT
* | | POSITIVE POWER SUPPLY
* | | | NEGATIVE POWER SUPPLY
* | | | |
* | | | |
* 1 2 3 4
X1 10 20 3 4 FilterLab1

.PROBE


*****************************************************************************
*****************************************************************************
* SUBCIRCUIT FOR SINGLE SUPPLY LOW-PASS FILTER
* CREATED USING FILTERLAB ON 8/7/2003 AT 14:31:15
* ------------------------------------------------------------
* This model is being supplied as an aid to circuit designs.
* While it reflects reasonable close similarity to the actual
* filter in terms of performance, it is not suggested as a
* replacement for breadboarding. Simulation should be used as
* a forerunner or a supplement to traditional lab testing.
* Neither this model nor any part may be copied without the
* express written consent of Microchip Technology, Inc.
* ------------------------------------------------------------
*
* 4TH ORDER BUTTERWORTH FILTER
* GAIN EQUALS 1
* CONNECTIONS: INPUT
* | OUTPUT
* | | POSITIVE POWER SUPPLY
* | | | NEGATIVE POWER SUPPLY
* | | | |
* | | | |
* 1 2 3 4
.SUBCKT FilterLab1 10 20 3 4

*************** Stage 1 ***************
R11 10 11 7870.000
R12 11 12 14700.000
C11 11 20 0.000000022
C12 12 0 0.00000001
X11 12 20 3 4 20 MCP6001
.ENDS

*****************************************************************************
*****************************************************************************
*PSPICE OPERATIONAL MODELS ARE AVAILABLE AT www.microchip.com

.SUBCKT MCP6001 1 2 3 4 5
* | | | | |
* | | | | Output
* | | | Negative Supply
* | | Positive Supply
* | Inverting Input
* Non-inverting Input
*
*****************************************************************************
* Software License Agreement
*
*The software supplied herewith by Microchip Technology Incorporated (the
*"Company") is intended and supplied to you, the Company's customer, for use
*solely and exclusively on Microchip products. The software is owned by
*the Company and/or its supplier, and is protected under applicable
*copyright laws. All rights are reserved. Any use in violation of the
*foregoing restrictions may subject the user to criminal sanctions under
*applicable laws,*as well as to civil liability for the breach of the terms
*and conditions of this license.
*
*
*THIS SOFTWARE IS PROVIDED IN AN "AS IS" CONDITION. NO
*WARRANTIES, WHETHER EXPRESS, IMPLIED OR STATUTORY,
*INCLUDING, BUT NOT LIMITED TO, IMPLIED WARRANTIES OF
*MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
*APPLY TO THIS SOFTWARE. THE COMPANY SHALL NOT, IN ANY
*CIRCUMSTANCES, BE LIABLE FOR * SPECIAL, INCIDENTAL OR
*CONSEQUENTIAL DAMAGES, FOR ANY REASON WHATSOEVER.


******************************************************************************
**
*
* Macromodel for the MCP6001/2/4 op amp family:
* MCP6001 (single)
* MCP6002 (dual)
* MCP6004 (quad)
*
* Revision History:
* REV A: 21-Jun-02, KEB (created model)
* REV B: 16-Jul-02, KEB (improved output stage)
* REV C: 03-Jan-03, KEB (added MCP6001)
*
* Recommendations:
* Use PSPICE (or SPICE 2G6; other simulators may require translation)
* For a quick, effective design, use a combination of: data sheet
* specs, bench testing, and simulations with this macromodel
* For high impedance circuits, set GMIN=100F in the .OPTIONS
* statement
*
* Supported:
* Typical performance at room temperature (25 degrees C)
* DC, AC, Transient, and Noise analyses.
* Most specs, including: offsets, DC PSRR, DC CMRR, input impedance,
* open loop gain, voltage ranges, supply current, ... , etc.
*
* Not Supported:
* Variation in specs vs. Power Supply Voltage
* Distortion (detailed non-linear behavior)
* Temperature analysis
* Process variation
* Behavior outside normal operating region
*
* Input Stage
V10 3 10 -300M
R10 10 11 6.90K
R11 10 12 6.90K
C11 11 12 115E-15
C12 1 0 6.00P
E12 1 14 POLY(4) 20 0 21 0 26 0 27 0 1.00M 20.1 20.1 1 1
I12 14 0 1.50P
M12 11 14 15 15 NMI L=2.00U W=42.0U
C13 14 2 3.00P
M14 12 2 15 15 NMI L=2.00U W=42.0U
I14 2 0 500E-15
C14 2 0 6.00P
I15 15 4 50.0U
V16 16 4 300M
D16 16 15 DL
V13 3 13 50M
D13 14 13 DL
*
* Noise, PSRR, and CMRR
I20 21 20 423U
D20 20 0 DN1
D21 0 21 DN1
G26 0 26 POLY(1) 3 4 110U -20.0U
R26 26 0 1
G27 0 27 POLY(2) 1 3 2 4 -440U 80.0U 80.0U
R27 27 0 1
*
* Open Loop Gain, Slew Rate
G30 0 30 POLY(1) 12 11 0 1.00K
R30 30 0 1
E31 31 0 POLY(1) 3 4 104 -2.33
D31 30 31 DL


E32 0 32 POLY(1) 3 4 140 -6.07
D32 32 30 DL
G33 0 33 POLY(1) 30 0 0 447
R33 33 0 1
C33 33 0 77.1M
G34 0 34 POLY(1) 33 0 0 1.00
R34 34 0 1.00
C34 34 0 50.2N
G35 0 35 POLY(2) 34 0 33 34 0 1.00 3.00
R35 35 0 1.00
*
* Output Stage
G50 0 50 POLY(1) 57 5 0 2.00
D51 50 51 DL
R51 51 0 1K
D52 52 50 DL
R52 52 0 1K
G53 3 0 POLY(1) 51 0 50.0U 1M
G54 0 4 POLY(1) 52 0 50.0U -1M
E55 55 0 POLY(2) 3 0 51 0 -10M 1 -40.0M
D55 57 55 DLS
E56 56 0 POLY(2) 4 0 52 0 10M 1 -40.0M
D56 56 57 DLS
G57 0 57 POLY(3) 3 0 4 0 35 0 0 1.00M 1.00M 2.00M
R57 57 0 500
R58 57 5 500M
C58 5 0 2.00P
*
* Models
.MODEL NMI NMOS
.MODEL DL D N=1 IS=1F
.MODEL DLS D N=10M IS=1F
.MODEL DN1 D IS=1F KF=146E-18 AF=1
*
.ENDS MCP6001

.END


M FilterLab® 2.0
User’s Guide
Appendix B. Filter Magnitude Templates

B.1 INTRODUCTION
B.1.1 LOW-PASS FILTER MAGNITUDE RESPONSE
The magnitude response of low-pass filters is shown in Figure B-1.

Pass Band
HM
HM - A P

Transition band
Gain (dB)

HM - 3

Stop Band
HM - A S

0
0 fP BW fS

Frequency (Hz)

FIGURE B-1: Low-pass Filter Template.
The nominal filter response is required to stay within the three regions shown (pass
band, transition band and stop band). The relevant parameters for the three regions
and the controlling inequalities are:
• Pass Band
HM = Maximum Pass Band Gain (dB)
A = Attenuation (relative to HM) (dB)
AP * = Pass Band Ripple/Max. Attenuation (dB)
fP * = Pass Band Frequency (Hz)
BW = -3 dB Bandwidth
0 ≤ f ≤ fP
0 ≤ A ≤ AP
* sometimes referred to as cut-off
• Transition Band
fP ≤ f ≤ fS
AP ≤ A ≤ AS


• Stop Band
fS = Stop Band Edge Frequency (Hz)
AS = Minimum Stop Band Attenuation (dB)
fS ≤ f
AS ≤ A

The gain parameter in FilterLab (G) corresponds to the DC gain (for good sensitivity
performance). Thus,
G = HM; Bessel, Butterworth and Chebychev (n = 1, 3, 5, 7)
G = HM - A P ; Chebychev (n = 2, 4, 6, 8)
Note: The Frequency Response plot in FilterLab 2.0 does not show even
order Chebychev responses correctly.
The limits that FilterLab 2.0 enforces on these low-pass parameters are:
0.1 Hz ≤ fP < fS ≤ 1.0 MHz
AP = 3.0 dB, Bessel Filters
0.01 dB ≤ AP ≤ 3.0 dB, Butterworth and Chebychev
10 dB ≤ AS ≤ 100 dB
1V/V ≤ G ≤ 10V/V, (0 dB to 20 dB)



B.1.2 BAND-PASS FILTER MAGNITUDE RESPONSE
The magnitude response of band-pass filters is shown in Figure B-2.

Pass Band
HM
HM - AP

Transition band
Transition band
Gain (dB)
HM - 3

Stop Band Stop Band
HM - AS

0
0 fSL fPL fPU fSU
BWL BWU

Frequency (Hz)

FIGURE B-2: Band-pass Filter Template.
The nominal filter response is required to stay within the five regions shown (pass
band, two transition bands and two stop bands). The relevant parameters for the three
regions and the controlling inequalities are:
• Lower Stop Band
fSL = Lower Stop Band Edge Frequency (Hz)
AS = Min. Stop Band Attenuation (dB)
f ≤ fS
AS ≤ A

• Lower Transition Band
fSL < f < fPL
AP < A < A S

• Pass Band
fPL * = Lower Pass Band Frequency (Hz)
fPU * Upper Pass Band Frequency (Hz)
BWL = Lower -3 dB Bandwidth
BWU = Upper -3 dB Bandwidth
fPL ≤ f ≤ fPU
0 ≤ A ≤ AP
* sometimes referred to as cut-off


• Upper Transition Band
fPU < f < fSU
AP < A < A S

• Upper Stop Band
fSU = Upper Stop Band Edge Frequency (Hz)
fSU ≤ f
AS ≤ A

The gain parameter in FilterLab 2.0 (G) corresponds to the midband gain (for ease of
implementation), where:
f0 = Midband Frequency
= (fPL fPU)1/2

Thus,
G = HM; Bessel, Butterworth and Chebychev (n = 2, 6)
G = HM - A P ; Chebychev (n = 4, 8)
Note: The Frequency Response plot in FilterLab 2.0 does not show
Chebychev response correctly for orders 4 and 8.
The limits that FilterLab 2.0 enforces on these band-pass parameters are:
0.1 Hz ≤ fSL < fPL < fPU < fSU ≤ 1.0 MHz
1.2210 ≤ fPU/fPL ≤ 5.8284
0.01 dB ≤ AP ≤ 3.0 dB
10 dB ≤ AS ≤ 100 dB
1 V/V ≤ G ≤ 10 V/V, (0 dB to 20 dB)
If the ratio fPU/fPL is larger than 5.8284, the wider pass band can be designed by
cascading a low-pass and high-pass filter. If the ratio fPU/fPL is smaller than 1.2210, the
narrow pass band cannot be implemented with this version of FilterLab 2.0.



B.1.3 HIGH-PASS FILTER MAGNITUDE RESPONSE
The magnitude response of high-pass filters is shown in Figure B-3.

Pass Band
HM
HM - A P

Transition band
Gain (dB)
HM - 3

Stop Band
HM - A S

0
0 fS BW fP

Frequency (Hz)

FIGURE B-3: High-pass Filter Template.
The nominal filter response is required to stay within the three regions shown (pass
band, transition band and stop band). The relevant parameters for the three regions
and the controlling inequalities are:
• Pass Band
fP * = Pass Band Frequency (Hz)
BW = -3 dB Bandwidth
fP ≤ f
0 ≤ A ≤ AP
* sometimes referred to as cutoff
• Transition Band
fS < f < fP
AP < A < A S

• Stop Band
fS = Stop Band Edge Frequency (Hz)
f ≤ fS
AS ≤ A


The gain parameter in FilterLab 2.0 (G) corresponds to the high-frequency gain (at
"infinity" for good sensitivity performance). Thus,
G = HM; Bessel, Butterworth and Chebychev (n = 1, 3, 5, 7)
G = HM - A P ; Chebychev (n = 2, 4, 6, 8)
Note: The Frequency Response plot in FilterLab 2.0 does not show even
order Chebychev responses correctly.
The limits that FilterLab 2.0 enforces on these high-pass parameters are:
0.1 Hz ≤ fS < fP ≤ 1.0 MHz
0.01 dB ≤ AP ≤ 3.0 dB
10 dB ≤ AS ≤ 100 dB
1 V/V ≤ G ≤ 10 V/V, (0 dB to 20 dB)


M FilterLab® 2.0
User’s Guide
Appendix C. Group Delay

C.1 INTRODUCTION
Group delay is a measure of time domain response. It focuses on the relative delay
among sine waves of nearly equal frequency. Its usual definition is:
Ω = Radian Frequency (rad/s)
φ(ω) = Phase Response (rad)
= atan(Im{G}/Re{G})
τgd(ω) = group delay (s)
= -dφ(ω)/dω
An equivalent definition, when frequency is in Hz and phase is in degrees, is:
f = Frequency (Hz = cycles/s)
φ(f) = Phase Response (°)
= atan(Im{G}/Re{G})
τgd(f) = group delay (s)
= (1 cycle/360°) (-dφ(f) / df)
Figure C-1 and Figure C-2 illustrate phase and group delay.

360° jump 180° jump
(transmission zero)
φ(0)
Phase (°)

φ(0) - 360°
0 fP fS

Frequency (Hz)

FIGURE C-1: Low-pass Phase Response.



Group Delay (s)
τgd(0)

0
0 fP fS

Frequency (Hz)

FIGURE C-2: Low-pass Group Delay.
Some reasons that group delay has been traditionally used for filter work are:
• It is easier to manipulate mathematically (no arc-tangent functions)
• Group delay is easier to optimize
- Its jump discontinuities are only at transmission zeros on the jω-axis (gain is
zero)
- It is a non-negative function for low-pass filters
• It applies directly to AM modulated signals
- The information is delayed by the group delay (also known as envelope delay)
- It maps directly to group delay at baseband
- The carrier is delayed by a different time (total phase shift divided by carrier
frequency)
• It is a good indicator of low-pass step response quality
- Constant group delay in the pass band, and well into the transition band
(A < 10 dB to 20 dB), indicates a very good step response
- Group delay with peaking (usually near fP) indicates overshoot and ringing


M FilterLab® 2.0
User’s Guide
Appendix D. FilterLab 2.0 Filter Response

D.1 INTRODUCTION
Bessel (low-pass) filters are mainly used for applications that need excellent step
response. The emphasis is on phase and group delay; the frequency selectivity is poor
compared to the other classical filter response functions (e.g., Butterworth). Some
typical applications are: PWM communications channels, instrumentation and simple
anti-aliasing filters for ADCs.
Figure D-1 and Figure D-2 show the normalized frequency response. Increasing the
filter order does not provide a significant improvement in the stop band rejection.
Figure D-3 shows the normalized group delay, Figure D-4 shows the normalized step
response. The step response overshoot is minimal.
FilterLab 2.0 does not allow the user to select Bessel filters based on their frequency
response. Use Figure D-3 and Figure D-4 to choose the order based on group delay
and step response.

0.0
n = 8 (top)
-0.5 through
n = 1 (bottom)
Normalized Gain
= G / HM (dB)

-1.0

-1.5

-2.0

-2.5

-3.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Normalized Frequency = f / fP

FIGURE D-1: Normalized Bessel frequency response in the pass band.



0
-10

Normalized Gain
-20

= G / HM (dB)
-30
-40
-50
-60 n = 1 (top)
through
-70 n = 8 (bottom)
-80
0.1 1 10

FIGURE D-2: Normalized Bessel frequency response in the stop band.

0.55
0.50 n=8
Normalized Group Delay

n=7
0.45 n=6
0.40 n=5
0.35 n=4
= tgd fP

0.30 n=3
0.25 n=2
n=1
0.20
0.15
0.10
0.05
0.00
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

FIGURE D-3: Normalized Bessel group delay.

1.1
1.0
0.9 VIN
Step Response (V)

0.8 VOUT
0.7 n=8
0.6 n=7
0.5 n=6
0.4 n=5
n=4
0.3 n=3
0.2 n=2
0.1 n=1
0.0
-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Normalized Time = t fP

FIGURE D-4: Normalized Bessel step response.


M FilterLab® 2.0
User’s Guide
Appendix E. Op Amp Selection

E.1 INTRODUCTION
E.1.1 OP AMP SMALL SIGNAL BANDWITH
The op amps you select for your filter need to be fast enough to avoid problems with
non-linear distortion and filter response distortion. A crude estimate of the op amp
GBWP (Gain Bandwidth Product) that you need for a filter section is:
GBWP = K 100 fP, low-pass
= K Q 100 fPU, band-pass
= K max {100 fP, fmax}, high-pass
Where:
K = Filter section's gain (V/V)
fP = Low-pass and high-pass filters’ pass band frequency
(Hz)
fPU = Band-pass filter's upper pass band frequency (Hz)
Q = Band-pass filter's overall Q-factor
= 1/"fractional bandwidth"
= (fPL fPU)1/2/(fPU - fPL)
fmax = Maximum pass band/signal frequency for high-pass
response >> fP
Try op amps with different GBWPs to see what you require. Small signal frequency
response (typically VOUT < 100 mVP-P) starts to peak as the GBWP goes too low.
Harmonic distortion also grows as the GBWP goes lower.

E.1.2 OP AMP FULL-POWER BANDWIDTH
The op amps also need to handle large signals. The SR (Slew Rate) specified in our
op amp data sheets is related to the full-power bandwidth as follows.
fFPBW = SR/(π VOUT_P-P) (Hz)
Where:
VOUT_P-P = Filter section's maximum output voltage swing (VP-P)
< VDD – VSS
SR = Slew rate (V/s); data sheets usually give units of V/µs
(1 V/µs = 1,000,000 V/s)
fFPBW op amp full-power bandwidth (Hz)
Sine waves faster than fFPBW will not be faithfully reproduced because their derivative
(slew rate) is too high.


In order to keep harmonic (non-linear) distortion to a minimum, the recommended
minimum SR for all op amps in the filter is:
SR = XFF π VOUT_P-P fP, low-pass
= XFF π VOUT_P-P fPU, band-pass
= XFF π VOUT_P-P fmax, high-pass
Where:
fP = Low-pass and high-pass filters' pass band frequency
(Hz)
fPU = Band-pass filter's upper pass band frequency (Hz)
fmax Maximum pass band/signal frequency for high-pass
response >> fP
XFF = rough fudge factor for distortion performance (relative to
fundamental)
≈ 2, THDSR = -60 dBc
≈ 16, THDSR = -96 dBc
THDSR = Slew Rate induced distortion level (dBc)
Note that non-linear distortion may include a DC offset term.

E.1.3 OP AMP OUTPUT LOADING
Choose the resistance values in your filter so that the op amp is not overloaded. A
compromise among loading, noise and parasitic RC time constants needs to be made.
To scale the resistor values, change the capacitor values in the Filter Design dialog box
within FilterLab 2.0.

E.1.4 MINIMUM GAIN
Most op amps are unity gain stable (G ≥ +1 V/V). A few op amps need to be set at
higher gains to remain stable (e.g., G ≥ +10 V/V for the MCP6141). If you need gain in
your filter, this kind of part can give you the bandwidth and gain you need for less
quiescent current. Note that inverting gains, used in Multiple Feedback (MFB) sections,
have an equivalent "noise gain" that is used to determine stability. It is calculated as:
1 + |G| (e.g., a signal gain of -1 V/V gives a noise gain of +2 V/V).



E.1.5 CURRENT MICROCHIP OP AMPS
The following table shows the Microchip op amps recommended for new designs as of
October 1, 2003. See our web site (www.microchip.com) for the latest information.

TABLE E-1: MICROCHIP OP AMPS

Supply
Op Amp GBWP SR Rail to Rail
# Amplifiers Voltage Comments
Family (Hz) (V/µs) Input/Output
(V)
MCP6041 1, 2, 4 14k 0.003 I/O 1.4-5.5
TC1034 1, 2, 4 90k 0.035 I/O 1.8-5.5 Also TC1026, TC1029, TC1030, TC1035
MCP6141 1, 2, 4 100k 0.024 I/O 1.4-5.5 Gain ≥ 10 V/V
MCP606 1, 2, 4 155k 0.08 O 2.5-5.5
MCP616 1, 2, 4 190k 0.08 O 2.3-5.5 Bipolar (PNP) input
TC7652 1 400k 1.0 O 6.5-16.0 Chopper Stabilized (VOS ≤ ±5 µV)
MCP6001 1, 2, 4 1.0M 0.6 I/O 1.8-5.5
TC913 2 1.5M 2.5 — 6.5-16.0 Chopper Stabilized (VOS ≤ ±15 µV)
TC7650 1 2.0M 2.5 O 6.5-16.0 Chopper Stabilized (VOS ≤ ±5 µV)
MCP6271 1, 2, 4 2.0M 0.9 I/O 2.0-5.5
MCP601 1, 2, 4 2.8M 2.3 O 2.7-5.5
MCP6281 1, 2, 4 5.0M 2.5 I/O 2.2-5.5
MCP6291 1, 2, 4 10.0M 7.0 I/O 2.4-5.5
MCP6021 1, 2, 4 10.0M 7.0 I/O 2.5-5.5


NOTES:


M FilterLab® 2.0
User’s Guide
Appendix F. Selected References

F.1 INTRODUCTION
F.1.1 FILTER TEXTBOOKS AND CLASSIC REFERENCES
[1] Arthur B. Williams and Fred J. Taylor, Electronic Filter Design Handbook, 3rd ed.,
McGraw-Hill, 1995.
[2] Rolf Schaumann, M.S. Ghausi, and Kenneth R. Laker, Design of Analog Filters:
Passive, Active RC, and Switched Capacitor, Prentice Hall, 1990.
[3] Andreas Antoniou, Digital Filters: Analysis and Design, McGraw-Hill, 1979.
[4] Anatol I. Zverev, Handbook of Filter Synthesis, Wiley, John & Sons, 1967.
[5] Rolf Schaumann, Mac E. Van Valkenburg, and Mac Van Valkenburg, Design of
Analog Filters, 2nd ed., Oxford University Press, 2001.

F.1.2 APPLICATION NOTES
[1] Bonnie Baker, Anti-Aliasing, Analog Filters for Data Acquisition Systems,
Application Note 699, DS00699, Microchip Technology Inc., 1999.


M
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DS51419A-page 72  2003 Microchip Technology Inc.

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