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Active filter designer

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NATIONAL Semiconductor, represented in Australia by Arrow Electronics , has released the Webench active filter designer. It is an online design tool that speeds the creation of filters for data acquisition and signal conditioning applications. It lets users design customised filters for all standard filter types, including low pass, high pass, band pass and band stop.

Users can create a theoretical filter in minutes and implement it with real world models moments later. They can sample the amplifiers, download the automatically generated documentation, use the custom assembly diagram and build a filter.

To view a demonstration showing how to create a ninth-order low-pass filter with Bessel response in 30 seconds, see http://filterdemo.national.com/.

Designers may use the Webench active filter designer to develop more than 200,000 customised low-pass filters using any of 180 op amps. It uses a component selection tool that rapidly searches among the company’s portfolio of operational amplifier products (each with hundreds of different electrical parameters) and immediately configures the necessary bill of materials for every design. The active filter designer and its simulators are available at http://webench.national.com.

It contains an embedded expert filter handbook. Visitors are guided through the process of creating a complete filter. The theory is provided in a simple, integrated flowchart. The user can specify performance by frequency response, group delay or step response. The filter designer then creates all of the potential filter options (order and approximation) that meet the user’s requirements and presents them as alternatives for comparison. Chebyshev, Bessel, Butterworth and elliptical transfer functions are offered with up to ninth-order accuracy. Alternatively, the user can specify a set of ideal filters to be compared or even create an advanced filter from scratch.

Performance curves for each of the recommended filters are calculated and presented. The filter designer then guides the user through the selected filter implementation, including selection of the best op amp to be used in the design, and selection of each filter stage’s topology, including Sallen-key, multiple feedback, and state variable types. Simulation, free samples and automatically generated documentation are also available.

The Webench environment is useful for both the expert and the novice. It eliminates the need for a design engineer to perform tedious hand calculations and includes extensive online tutorials in analogue design. The tools offer instant access to the latest Spice models, parametric data and package information, enabling designers to simultaneously compare the performance of multiple devices in multiple applications.

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