RF and Analog Filter Design — Complete Guide

Butterworth filters offer maximally flat passband response; Chebyshev filters achieve a steeper roll-off at the cost of passband ripple. For most RF applications, a 0.5 dB Chebyshev gives a good balance. Use the filter designer tool to compute component values for both topologies from cutoff frequency and order alone.

Passive LC ladders are the workhorse of RF filtering because they handle high power with low loss. The prototype element values are normalized to 1 Ω and 1 rad/s, then frequency- and impedance-scaled. The LC resonance calculator helps you verify tank frequencies and choose standard component values. The filter designer tool also exports a KiCad schematic for direct PCB layout.

Active Sallen-Key and multiple-feedback (MFB) topologies implement poles using op-amps, resistors, and capacitors — no inductors. The RC time constant calculator establishes the single-pole corner frequency, while the op-amp bandwidth calculator confirms the op-amp has sufficient gain-bandwidth product at the filter corner.

Crystal resonators achieve Q factors of 10,000–100,000, enabling extremely narrow bandwidth filters impossible with LC or RC networks. Proper load capacitance is critical for on-frequency operation. The crystal load capacitance calculator computes the required external capacitors from datasheet CL and board parasitics.

A phase-locked loop synthesizer requires a low-pass loop filter to set loop bandwidth and suppress reference spurs. The PLL loop filter calculator solves the passive second- and third-order charge-pump filter from phase margin and bandwidth targets. Narrow loop bandwidth improves VCO phase noise suppression at the cost of slower lock time.