High-order passive low-pass filtering for ultra-low-distortion sine-wave testing

Accurate characterization of low-distortion devices requires sine-wave excitation with extremely low harmonic content. Commercial signal generators exhibit limited spurious-free dynamic range (SFDR), especially in the MHz range, motivating external passive purification techniques. This paper presents a ninth-order passive Chebyshev low-pass filter designed to enhance sine-wave purity for distortion testing. The ladder LC architecture is experimentally validated from 10kHz to 320MHz. Harmonic suppression exceeds 65dB at the second harmonic extending generators SFDR to better than 125dBc in typical laboratory setups. The filter has negligible passband ripple, low insertion loss and return loss better than 25dB. Design equations, tolerance analysis, and measurements demonstrate close agreement with simulations. The proposed two-series-inductor and two-parallel-capacitor implementation enables accurate realization using commercially available components and is scalable across frequency decades.