Ansys Launches RF Filter Design Software

Article By : Maurizio Di Paolo Emilio

The RF filter software aids in the design, synthesis and optimization of RF, microwave and digital filters, thereby lowering development costs while boosting performance.

Ansys, the simulation software specialist, has added software designed to spin up RF filters. The RF filter software aids in the design, synthesis and optimization of RF, microwave and digital filters, thereby lowering development costs while boosting performance.

The Nuhertz FilterSolutions workflow starts by entering filter performance specifications used by the tool to synthesize both ideal and physical filter layout. The tool automatically sets up filter analysis and optimization in the company’s HFSS 3D high frequency electromagnetic (EM) simulator software.

Filter design is complex, especially for high-performance microwave and millimeter-wave  designs. RF and microwave filters are prone to EM cross-coupling, which is often a source of inaccuracies in traditional circuit modeling approaches. EM software often proves inadequate for the optimization of high-end filters. An accurate prototype design can help.

Filter designs lacking accuracy often translate into a long, expensive tuning phase requiring consideration of component tolerances. An CAE-based approach can provide a tuning-free design independent of manufacturing or component tolerances.

“It is difficult to find RF designers who are acquainted with and have the expertise for filter design,” said Shawn Carpenter, Ansys product manager for Nuhertz FilterSolutions. The new tool is “used it as a front-end to our electromagnetic simulation suite, the ANSYS HFSS software, in order to provide a tool able to design, synthesize, virtually test, tune and optimize filters, making them suitable for manufacturing tolerances”.

A FilterQuick interface (below) allows also non-expert users to design and synthesize filters, with all the controls available in a single panel. The design can then be pushed to HFSS for validation.

FilterQuick interface.

The modeling and simulation tool also: automates filter design and synthesis; provides virtual prototyping of filters via physics simulation; and assesses yields, process tolerances and relevant effects such as electrical loss, heating, mechanical deformation and stress. The tool also eliminates the need for multiple prototype stages, Carpenter said.

Filter design
Filter categories that can be designed and synthesized by the new tool include:

  • RF and microwave filters: widely used in electronics applications to pass or block some signal components in the RF spectrum. They are also used in RF transmitters and receivers to improve selectivity and sensitivity by removing undesired frequencies, and in ADC and DAC conversions. For planar filters, the Ansys tool offers geometries relevant to the type of filter chosen and predicts the filter response as each is selected. Planar geometry generated by the tool can be exported to Ansys HFSS for prediction and optimization of filter performance. The figure below shows the geometry of a low-pass filter in Ansys HFSS.
  • Passive and lumped filters: lumped-element filters, a combination of capacitors and inductors (LC) tuned to resonate at a specific frequency or in a band of frequencies, are essential to suppress harmonics and reduce distortion affecting power systems. The tool provides a LC schematic synthesis matching the filter specifications, allowing tuning and optimization of each element
  • Distributed filters: the synthesis of a planar transmission line and distributed filters allows designers to synthesize microstrip, stripline, suspended stripline, asymmetric stripline, and surface-lumped components with planar transmission line interconnects
  • Active filters: the tool allows the synthesis of active filters, normally based on op-amps. The netlist of active filters can be exported in SPICE format
  • Switched capacitor filters: normally used within integrated circuits, where capacitors and MOSFETs are available, less costly and less bulky than resistors or inductors, they emulate the behavior of a filter whose value is a function of the switching frequency used to drive the circuit. The tool provides a library of switched cap digital filter realizations, including IIR and FIR realizations with Z-transforms and Monte Carlo analysis for sensitivity
  • Digital filters: widely used in embedded processors and digital signal processors, FIR and IIR digital filters can be synthesized, providing filter architecture and coefficients for implementation. The digital filter synthesis module can also export C code for the generated filter, making it ready for inclusion in a DSP system.
  • Zmatch: starting with complex load definitions, the module synthesizes a matching network for maximum power transfer. It includes both discrete frequency and broadband match modes, and provides optimal matching networks in lumped, distributed and hybrid realizations.
Geometry of a low-pass filter in Ansys HFSS, generated by the Ansys tool.

The new package has been added to the Ansys academic bundle, making it available to research and education institutions. It is also available in the Ansys education bundle with the HFSS software.

The tool “has the ability to synthesize pieces of software subroutines or code that could be used in a digital signal processor,” said Carpenter. It also “creates C code for an IIR or a FIR filter through the many topologies that exist to realize this filter, and filters can be created using active components like op-amps, or individual gain stages transistors. And we have the ability to synthesize them.”

This article was originally published on EE Times.

Maurizio Di Paolo Emilio holds a Ph.D. in Physics and is a telecommunication engineer and journalist. He has worked on various international projects in the field of gravitational wave research. He collaborates with research institutions to design data acquisition and control systems for space applications. He is the author of several books published by Springer, as well as numerous scientific and technical publications on electronics design.


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