Active filters are vital in modern electronics; every data acquisition systems need them for bandwidth-limiting signals before analog-to-digital converters as anti-aliasing filters, or after digital-to-analog converters as anti-imaging filters. Instrumentation relies on them for accurate signal measurements. Active filters are used for cutoff frequencies that range from sub -1 Hz to 10 MHz, where passive filter designs would require prohibitively large component values and sizes. Their design and verification can be tedious and time consuming.
WEBENCH® Filter Designer lets you design, optimize, and simulate complete multi-stage active filter solutions within minutes. Create optimized filter designs using a selection of TI operational amplifiers and passive components from TI's vendor partners.
SELECT from Lowpass, Highpass, Bandpass, and Bandstop filter types. Specify performance constraints for attenuation, group delay, and step response. Choose from a variety of filter responses such as Chebyshev, Butterworth, Bessel, transitional Gaussian to 6 dB, transitional Gaussian to 12 dB, linear phase 0.05°, and linear phase 0.005°. Determine the filter response best suited for your design by optimizing for pulse response, settling time, lowest cost, pass-band ripple, and stop-band attenuation.
DESIGN your filter using Sallen-Key, multiple feedback, and Bainter topologies. Select the best operational amplifiers for your design by evaluating gain bandwidth vs. current vs. cost and other parameters. Specify your resistor/capacitor tolerances between ideal, 0.1%, 1%, 2%, and 5% values. Experiment with user-defined capacitor seed values. Optimize your filter topologies for sensitivity, lowest cost, and smallest footprint.
ANALYZE your design by running SPICE electrical simulation with closed-loop frequency response, step response, and sine-wave response analysis options.
To access the WEBENCH Filter Designer, click on the Filters tab and your desired filter type (Lowpass, Highpass, Bandpass, or Bandstop) then click Start Filter Design.
Welcome to WEBENCH Filter Designer. The Filter Designer Requirements page is the first view you will see. See the figure to the right and read the text that follows.
The top portion of this page shows the ideal gain, phase, group delay, and step response of the members in the solutions table below. If you hover your mouse over these curves, the approximation type, order, x-axis and y-axis values appear. The zooming function with these graphs is enabled by dragging from low to high.
In the bottom portion of the page, a table with columns Select, Filter Response (or approximation), Color, Order, No. of stages, Max Q and Abs appear. Here is a description of these columns.
|Filter Type||Order||# Poles||# Zeros|
The possible lowpass and highpass filter orders are 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10.
The possible bandpass and bandstop filter orders are 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20.
Once you find the filter that you want to build, click on the green Select button to proceed to the Schematic page.
There are six sub-windows to help you zero in on your final filter design. Let’s start with the bottom three sub-windows.
The solutions table has the same columns as Simple mode. Please refer to that description of the solutions table in the section above.
Charts also has the same ideal graphs as described for Simple mode; gain, phase, group delay, and step response. As in the Simple mode, the Advanced mode lets you zoom in on the curves to achieve more granularity.
Advanced Charting allows you to see the solutions table’s active filters graphically. The x-axis, y-axis, and bubble sizes represent the specification in the solutions table columns. For instance, in the figure above the assignments are:
Now we will discuss the top sub-windows.
The Optimizer knob allows you to sort the filters in accordance to their characteristics. Notice that the order of the filters in the solutions table will re-sort with the best selection for your criteria on top. These characteristics are:
Modify your original constraints by entering values in the Change Inputs fields and click Recalculate to immediately see the results of those modifications.
The Additional Specs (Optional) button takes you to a page where you can control parameters and limits for group delay and step response. Your limits will determine whether the ideal filter calculations in the solutions table are within your specifications.
You will see in the solutions table for Group Delay that green means pass and red means fail.
The Refine Results sliders provide another way to sort the filters. Click and move the sliders to narrow down the filter response choices.
Once you find your filter, click on the green Select button to proceed to the Design Summary page showing the schematic.
Now that you have selected your filter response, you can see your complete circuit, including real amplifiers, resistors and capacitors.
In the center portion of the screen, there are three sections which describe a single stage’s characteristics: a section where you can update the gain and filter topology, the schematic and the bill of materials (BOM) table.
At the top of the page there is information about the individual stage such as the stage topology, gain, cut-off frequency, Q, and minimum required bandwidth for the amplifier. You have the option to change the gain and the topology of each individual stage.
On the left side of this page, there are topology specifications, a design summary, and an option to share your design with others.
The topology specification area allows you to change the amplifier, topology, capacitor seed and tolerances.
Select Alternate allows you to change the amplifier.
You can adjust the filter system topology, capacitor seed value, resistance tolerance and capacitor tolerances in the Filter Topology section.
If you make changes in this area, make sure you click the green Update button to implement your changes.
At the top of this page, you can:
If you click Sim , you will enter the simulation environment.
In the right center of this page, you will see the complete circuit diagram. At the left center you will see the simulation results. At the top right, the simulation options available are Closed Loop Response, Sine Wave, and Step Response. Click on the input or output component to modify the stimulus. Click Start New Simulation to run the simulation.
View the simulation results on the right.
You can get an Electrical Simulation Report by clicking on the Print icon at the top of the page. This report contains the filter circuit diagram, a BOM, graphical simulation results, and a list of design inputs.