active filter design made easy with webench® active filter
TRANSCRIPT
Active Filter Design Made Easy With WEBENCH® Active Filter Designer
Custom Active Filter Designs Including Spice Simulation
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WEBENCH® Active Filter Designer: Active Filter Designs Within Minutes!
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1. Choose a Sensor &
Signal Bandwidth1. Select a Filter Type 2. Design Frequency response 3. Analyze with SPICE
Accessing Filter Designer
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ti.com/webenchfilters
Select your
filter type
Start Design
NEW Filter Designer Requirements page
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Changes to specifications
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Gain units → V/V Gain = 20 V/V
-3 dB = 5 kHz
fs = 25 kHz
NEW Visualizer page
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Choose 0.5
dB
Chebyshev
filter
Filter Design Summary page
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Note Min
OpAmp GBWP
values
Note
OpAmp
Bandwidth –
10MHz
Filter Design adjust gain values
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Change
Gain = 10
Update
Note Min OpAmp GBWP =
2.104 MHz
Change
Gain = 2
Update
Note Min OpAmp GBWP =
3.032 MHz
Note OpAmp GBWP =
4.0 MHz
Electrical SimulationSelect Sim TypeClick to Run Sim
Closed Loop Frequency Response,
Sine Wave Response,
Step Response
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Everything old is new
• Is live today
• Big changes in Filter Type (page 1)
• Bigger changes in Visualizer (page 2)
• ti.com/filterdesigner
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Hands-on Exercise
Generate a filter
What is the output ripple of a 1V input sine
wave at 1kHz?
How can this be improved?
Customer would like a bandstop filter at
1000kHz with the following constraints:
Type: Bandstop
Center Frequency: 1kHz
Gain: 1
Passband Bandwith: 1kHz
Stopband Attenuation: -45 dB
Stopband Bandwidth: 100Hz
Dual Supply: +/- 5V
Filter transfer function: Linear phase .05deg, 6th order
Design Problem: Goals:
Hands On Problems
• Go to hands on problem set for Signal Chain
• Work the problems from the following:
• Active Filter Designer
– 10kHz Low Pass Filter
– Optimize Low Pass Filter
– Anti-aliasing filter
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Active Filter Design Made Easy With WEBENCH® Active Filter Designer
Custom Active Filter Designs Including Spice Simulation
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Common Filter Applications
Band limiting filter in a
noise reduction application
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Common Filter ApplicationsA
na
log
In
pu
t
A.) RAW SIGNAL
f1 f3 f4f2
Nyquist Sampling
An
alo
g I
np
ut
B.) AQUIRED SIGNAL
f1 f2
Nyquist SamplingfC
Anti-aliasing
Filter
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Filter Types
• A lowpass filter the bandwidth is equal to DC to fc
• A highpass filter has a single stop-band DC to fc, and pass-band f >fc
• A bandpass filter has one pass-band, between two cutoff frequencies fL and
fu>fL, and two stop-bands 0<f<fL and f >fu . The bandwidth = fu-fL
• A bandstop (band-reject) filter is one with a stop-band fL<f<fu and two pass-
bands 0<f<fL and f >fu
Lowpass, Highpass, Bandpass, and Bandstop Filters
Adopted from: Introduction to Filter Theory – by David E. Johnson16
Filter Types1-kHz Lowpass filter gain vs. frequency
fc defines
LP bandwidth
Frequency (Hz)
10 100 1k 10k 100k
Gai
n (d
B)
-60
-40
-20
0
20
Low-Pass Filter
fc defines
LP bandwidth
Ideal brick wall
response
Stop-bandPass-band
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Filter Types1-kHz highpass filter gain vs. frequency
fc cutoff
frequency
Frequency (Hz)
10 100 1k 10k 100k
Gai
n (d
B)
-60
-40
-20
0
20
fc cutoff
frequency
High-Pass Filter
Pass-bandStop-band
Ideal brick wall
response
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Filter Types1-kHz bandpass filter gain vs. frequency
fl cutoff
frequency
fh cutoff
frequency
Frequency (Hz)
100 316 1k 3k 10k
Gai
n (d
B)
-50
-40
-30
-20
-10
0
10
bandwidth
BW = fh-fl
fh cutoff
frequency
Band-Pass Filter
Stop-band
bandwidth
fl cutoff
frequencyPass-band
Stop-band
Ideal brick wall
response
The required level of
attenuation is specified
at the stop-band BW
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Filter Types1-kHz bandstop, or band-reject filter gain vs. frequency
fh cutoff
frequency
fl cutoff
frequency
Frequency (Hz)
100 1k 10k
Gai
n (d
B)
-80
-60
-40
-20
0
20Band-Stop Filter
Stop-band
Pass-band Pass-band
fl cutoff
frequency
fh cutoff
frequency
bandwidth
BW = fh-fl
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Filter Order
Gain vs. frequency behavior for different lowpass filter orders
Frequency (Hz)
10 100 1k 10k 100k 1M
Gai
n (d
B)
-80
-60
-40
-20
0
20
-160dB/dec
-120dB/dec
-80dB/dec
-40dB/decFilter Order
2nd
4th
6th
8th
Pass-band Stop-band
Frequency (Hz)
250.00 538.61 1.16k 2.50k
Gai
n (d
B)
-12
-9
-6
-3
0
3
fC (-3dB) 1kHz
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Filter Order
Frequency (Hz)
1 10 100 1k 10k 100k 1M
Gai
n (d
B)
-100
-80
-60
-40
-20
0
20
-2 slope
(-40dB/dec)
-1 slope
(-20dB/dec)
+2 slope
(40dB/dec)
+1 slope
(20dB/dec)2nd-order Band-pass
2nd-order High-pass2nd-order Low-pass
2nd-order lowpass, highpass and bandpass gain vs. frequency slopes
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Why Active Filters?
• Inductor size, weight and cost for low
frequency filters may be prohibitive
• Inductor magnetic coupling considerations
• Active filter size is small and low in cost
• R and C values are easily scaled in active
filters
RS1 1k L1 225m
C1 220n
-
+ Vpas
RL1 1k
R1 2.72k R2 19.8k
-
+
IOP1
C1 10n
C2 47n
-
+ Vact
+
VG1
-
+
-
+
VCV1
RL2 1k
1kHz Passive LP
1kHz Active LP
Source
Impedance
Load
Impedance
Vact
Vpas
Passive and Active
reponses are identical
Frequency (Hz)
10 100 1k 10k 100k 1M
Gai
n (d
B)
-100
-80
-60
-40
-20
0
20
Gain vs. FrequencyPassive and Active
reponses are identical
Vact
Vpas
Frequency (Hz)
10 100 1k 10k 100k 1M
Pha
se [d
eg]
-180
-135
-90
-45
0
Phase vs. Frequency
Vact
Vpas
A comparison of a 1kHz passive and active 2nd-order, lowpass filter
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Popular Active Filter Topologies
Pass Z1 Z2 Z3 Z4 Z5
Low R1 C2 R3 R4 C5
High C1 R2 C3 C4 R5
Band R1 R2 C3 C4 R5
2nd-order Active filter topologies used by WEBENCH
Active Filter Designer
Pass Z1 Z2 Z3 Z4 Z5
Low R1 R2 C3 C4 na
High C1 C2 R3 R4 na
Component type for each filter topology
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Filter Responses
Response Considerations
• Amplitude vs. frequency
• Phase vs. frequency
• Step and impulse response characteristics
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Filter ReponsesCommon active lowpass filters - amplitude vs. frequency
Frequency (Hz)
100 1k 10k 100k
Gai
n (d
B)
-80
-60
-40
-20
0
20
1kHz, 4th-order low-pass
responses, Av = +5V/V
Bessel
Butterworth
Chebyshev (2dB)
Gaussian
Linear Phase (0.5deg)
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Time (s)
0.0 500.0u 1.0m 1.5m 2.0m 2.5m
Outp
ut
-500.0m
0.0
500.0m
1.0
1.5
100us pulse
Bessel
Butterworth
Chebshev (2dB)
Gaussian
Linear phase (0.5deg)
Frequency (Hz)
100 1k 10k 100k
Phase [
deg]
-360
-270
-180
-90
0
Bessel
Butterworth
Chebyshev (2dB)
Gaussian
Linear phase (0.5deg)
Filter ReponsesCommon active lowpass filters – other responses
Phase vs. frequency Impulse response
Group Delay
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Specify Filter Requirements
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Select
Filter
Program
FrequenciesClick to
Continue
Performance
Graphs
Select Filter
Approximation
View / Select Filter Response
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Optimizer
Dial
Topology and
Component
Specifications
Tweak
Design
Share
or Copy
Design
Current
Design and
Design
Notes
Design Summary: Modify your Design
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Electrical SimulationSelect Sim TypeClick to Run Sim
Closed Loop Frequency Response,
Sine Wave Response,
Step Response
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Hands-on Exercise
Optimize the amplifier bandwidths to be as
low as possible.
Design a low pass filter with fast falling after
the cut-off frequency.
Filter
Low pass
Gain = 20 V/V
-3db = 5000 Hz
Stop band frequency = 25000
Hz
Stop band attenuation = - 45 dB
Chebyshev –
allowable ripple <= 0.5 dB
Design Problem: Goals:
Filter Designer Landing Page (http://ti.com/filterdesigner )
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Start Design
Demo
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Optimizer Knob
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Modify Constraints
Change inputs
and click
“Recalculate”
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Refine Results
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Optimization
Chart
Filter
Response
Solutions
Performance
Graphs
View/Optimize Filter Response Solutions
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Optimization Graph
ModifyAxis
Parameters
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Charts
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Select a Filter Response
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Design Summary: Filter Topology ConfigurationUpdate
per stageFilter Stage
Schematic
Filter Stage
BOM
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Update Gain/Topology per stage
Click to
update
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Filter Stage Schematic: View Component Values
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Filter Stage: Bill of Materials
Select
Alternate Part
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Select Alternate Part
Select Alternate Part
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Optimizer
Dial
Topology and
Component
Specifications
Tweak
Design
Share
or Copy
Design
Current
Design and
Design
Notes
Design Summary: Modify your Design
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Optimization Knob
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Filter Topology Specification
Select Topology
for all stages
Cap seed
and
tolerances
Select
Alternative
Amplifier
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Tweak Design
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Design ID
Notate and Share
Share Design
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Electrical Simulation
Click to Simulate
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Electrical SimulationSelect Sim TypeClick to Run Sim
Closed Loop Frequency Response,
Sine Wave Response, Step
Response
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Electrical Simulation
Simulation ResultsWaveform List
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Electrical Simulation
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Review Past Simulations
Export to External Simulator
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1) Click export
2) Choose sim type and
export format
3) Schematic opens in Tina or Altium
(Altium requires v14 and TI plug in)
Design Report
View and Print PDF Report
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