Figure la and Figure lb depict two common transmission-line scenarios: series termination and end termination, respectively. Both drivers are fast with negligible series output resistance. The capacitive loads represent the input capacitances of the CMOS receivers. In the series-terminated case, a step edge from the driver proceeds to the right, interacts with the load, and reflects back toward the driver. The capacitive load may create a strange-looking reflection, and it may distort the appearance of thernreceived signal, but whatever bounces off the load returns to the driver termination and dies, never to be seen again. As a result, the receiver sees one step edge, possibly distorted but with no lingering aftereffects. Of all the things that could go wrong with a circuit, this distortion is not too bad.rnFigure 1 illustrates an equivalent-endpoint circuit that defines the nature of instantaneous signal distortion at the receiver. The equivalent circuit comprises two components: a series resistance equal to the line impedance, and a shunt capacitance representing the input capacitance of the receiver (Reference 1).
展开▼
