LowPassFilter

LowpassFilter is a circuit or algorithm that passes signals with frequencies below a chosen cutoff while attenuating higher frequencies. It reduces high-frequency noise and smooths signals in measurement, audio, and communications, and it prepares data for sampling by limiting bandwidth.

In analog form, the simplest low‑pass is an RC network: a resistor in series with a capacitor to ground. The transfer function is H(s) = 1/(1 + sRC), and the cutoff is fc = 1/(2πRC). First‑order filters have a slope of −20 dB/decade beyond fc, while higher‑order designs provide steeper attenuation by adding poles.

Active low‑pass filters use an op‑amp to gain and buffer stages. Common topologies include Sallen‑Key and multiple‑feedback. They realize higher order, better passband flatness, and tunable corner frequency and Q.

Digital low‑pass filters implement the same idea in software or hardware. They use convolution or difference equations to approximate a target response. Realizations include FIR (linear phase) and IIR filters, with design choices balancing sharpness, latency, and stability.

Design considerations include cutoff frequency, stopband attenuation, passband ripple, and phase response. In analog designs, the source and load impedances and temperature can affect behavior; in digital designs, sampling rate and numerical precision are important.

Applications include audio filtering, anti‑aliasing for ADCs, sensor data smoothing, and image or communications systems.