outputreferred

Output-referred is a term used in electronics and signal processing to describe quantities and metrics expressed at the output of a system rather than at its input. It is useful when comparing devices with different gains or when evaluating the overall behavior of a signal chain, since the reference point is the system’s final output. The concept helps unify performance assessments across components and stages by anchoring measurements to the output that the system actually delivers.

Calculation and interpretation: In linear systems, the relation between input and output is described by a transfer function or gain G, with output X_out = G X_in. An input-referred quantity e_in can be mapped to the output domain as e_out = G e_in. Conversely, an output quantity Q_out can be referred back to the input by dividing by G, provided the gain is constant over the signal band. If the gain varies with frequency, refer quantities at the frequencies of interest using the corresponding gain. For nonlinear or time-varying systems, the mapping may depend on operating point or signal level, complicating direct reference.

Applications: Output-referred metrics are common for noise, distortion, and spur analyses. Examples include output-referred noise (the noise at the output) and output-referred distortion figures. In RF and microwave design, quantities such as the output third-order intercept point (OIP3) are inherently output-referred, while their input-referred counterparts (IIP3) describe the same nonlinearity at the input.

Caveats: Nonlinearities, saturation, and bandwidth-dependent gain can complicate mapping between input- and output-referred quantities. For time-varying or multi-port systems, refer to the appropriate transfer functions across the relevant frequencies or operating points.

See also: input-referred, transfer function, noise figure.