Equalization

Equalization is the art of un-smearing a signal — applying a filter that's the inverse of the channel so that a flattened, blurred bit stream snaps back into crisp, readable pulses. If the channel is a pair of muddy glasses that blur high frequencies, the equalizer is a sharpening lens that boosts exactly those high frequencies back up, restoring the edges. The goal is to flatten the channel's frequency response so every frequency the bits need passes through with equal strength — hence 'equalize'.

There are three workhorses, often stacked together. A feed-forward equalizer (FFE) on the transmitter or receiver pre-shapes the pulse to cancel echoes. A continuous-time linear equalizer (CTLE) is a small analog amplifier that boosts high frequencies relative to low. A decision-feedback equalizer (DFE) uses the bits it has already decided to subtract their trailing echoes — without amplifying noise. Modern 56-112 Gb/s links chain all three, plus adaptive logic that re-tunes the coefficients on the fly as temperature and the channel drift.