active filter design made easy with webench® active filter

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

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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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