Controlled Impedance Driver (Source Termination) - Controlled Impedance Driver (Source Termination) - UG861

To optimize signal integrity for high-speed or high-performance applications, extra measures are required to match the output impedance of drivers to the impedance of the transmission lines and receivers. Optimally, drivers must have an output impedance matching the characteristic impedance of the driven line, otherwise reflections can occur due to discontinuities. To solve this issue, designers sometimes use external-source series-termination resistors placed close to the pins of high-strength, low-impedance drivers. The resistance values are chosen such that the sum of the output impedance of the driver plus the resistance of the source series-termination resistor roughly equals the impedance of the transmission line.

DCI can provide controlled impedance output drivers to eliminate reflections without requiring the use of an external source-termination resistor. The impedance is derived from the external reference resistor.

The following figure illustrates a controlled impedance driver inside a device.

In HP banks, the use of controlled impedance DCI drivers is triggered by specific standards supporting the controlled impedance driver as shown in the following table.