All terminators are not created equal

摘要

Variations in physical construction can cause resistors that are de-equivalent to have drastically different electrical characteristics at radio and microwave frequencies. The 56 signers of the Declaration of Independence declared on July 4, 1776 that "... all men are created equal . . ." It's too bad that the same cannot be said of termination resistors for RF and microwave transmission lines. The same resistors or networks that perform termination functions adequately at lower frequencies can often exhibit poor performance at higher frequencies due to unwanted capacitance and inductance present in the various package designs. Measuring how far from "ideal" the resistor performance these devices exhibit will predict how they will behave in a high-frequency design. If there are sufficient changes in the impedance of line terminators at RF and microwave frequencies, the resulting mismatch can cause signal reflections on the transmission lines.