Types of Termination

There are several forms of line termination, including parallel, series, and differential.

Parallel termination matches the characteristic impedance of the medium at the end of the line, squelching the wavefront at the destination (Z_t = Z₀).

Differential termination is a variation of parallel termination used for differential transmission lines. Many electrical standards, such as emitter-coupled logic (ECL) and LVDS, require that traces are routed differentially. As such, parallel termination is used between the two modes of the differential trace.

Series termination places series impedance equal to the characteristic impedance at the source of the transmission line. This termination prevents the source from re-reflecting any reflections from an unterminated transmission line. It also prevents reflections from the transmission line to the source at the entry (Z_S = Z₀).

Practically, termination at only one end of the transmission line is often adequate and is more commonly used.