Bus through termination circuit

摘要

A system of resistive end termination and transmission line routing is disclosed for matching the impedance of an IC load to that of a signal source and a transmission line. Each integrated circuit has an internal termination resistor designed to match the characteristic impedance of the transmission line and preferably also the impedance of the source. When the source drives multiple IC devices on a printed circuit board, the devices are cascaded in a chain with the internal resistors of all but the last IC device in the chain bypassed by a short circuit underneath the device, so that a continuous transmission line is provided to the last IC device. The last IC in the chain, which does not have a short circuit underneath it, provides the necessary resistive termination by simply connecting the appropriate pin to a common reference in the circuit. The invention is also applicable to differential applications in which first and second complementary signal sources feed each IC device.