Analogue and digital signals

Signals, sampling and LC filters

An analogue signal varies continuously; a digital one has discrete levels. Digitising samples the signal at least twice per cycle of its highest frequency, and an $n$-bit sample has $2^n$ levels; bit rate $=$ samples per second $\times$ bits per sample. An LC circuit resonates at $f_0=\frac1{2\pi\sqrt{LC}}$, picking out one band of frequencies; its sharpness is $Q=\frac{f_0}{f_B}$.