Termination Strategy
Circuit configuration used at the ends of a transmission line to match impedance while providing a path for common-mode noise filtering. The split termination topology replaces a single resistor with two resistors of half the value and a capacitor tied to ground. This arrangement improves the electromagnetic compatibility of differential buses like Controller Area Network.
Impedance Matching
Resistive elements provide the necessary load to prevent signal reflections. By using split termination topology, the differential impedance remains at the standard one hundred and twenty ohms, but the center tap creates a low-pass filter. This filter shunts high-frequency common-mode noise to ground before it can radiate from the cable.
Filter Characteristic
Selection of the capacitor value determines the corner frequency of the common-mode filter. A split termination topology must balance noise suppression with the need to avoid loading the bus excessively at high speeds. Variations in the resistor values or the capacitor tolerance can degrade the balance of the filter.
If the two resistors are not closely matched, the termination itself can cause mode conversion. This circuit is a standard feature in high-reliability industrial networks.
Placement Rule
Effectiveness depends on locating the components as close to the physical end of the bus as possible. Using split termination topology at every node is generally avoided to prevent excessive DC loading.
