LC Filter Design Tool

The LC Filter Design Tool is a free, feature-rich web-based application from Marki, a leader in filter circuit development, providing robust synthesis capabilities for lumped LC filters. This user-friendly tool allows engineers to calculate circuit values for low-pass, high-pass, band-pass, and band-stop responses with filter orders up to 20.

Users can select from six classic filter function types, including Chebyshev, Elliptic, Butterworth, Bessel, Legendre, and Inverse Chebyshev. The document outlines the key trade-offs, such as the monotonic passband and constant group delay of the Bessel filter versus the superior roll-off rate achieved by the Elliptic type. The tool supports advanced customization, including arbitrary input and output impedances and multiple topologies.

A critical feature is the option to limit component selection to practical E-series standard values (E6 through E96), which helps model the filter’s sensitivity to real-world manufacturing tolerances.

For advanced analysis, the tool offers one-click synthesis and robust export options. Filters can be exported directly to popular circuit simulators like LTSpice and Qucs for in-depth testing. This enables users to perform S-parameter analysis, transient response analysis, and simulate non-ideal conditions. Specifically, the LTSpice export supports modeling for finite Q inductors (using r=2πfQ​L/Q) and Monte Carlo analysis to assess the impact of random component variations on filter performance.