Reduced Termination Loss by Active Synthesis of Output Impedance

Abstract: In high-speed transmission-line applications, it is important to match the output impedance of a line driver to the line. While this is achieved usually with a resistor, an active impedance synthesis has advantages. Thisapplication note describes how to use positive feedback around an op amp to create the desired output impedance. Equations and circuit examples are given for low-noise audio, and video op amps driving 50Ω to 600Ω loads.