Adaptive bus termination apparatus and methods

摘要

Termination impedance of a digital signal bus is adaptively selected as a function of a present or anticipated state of the bus. A variable termination resistor is arranged in series between a termination switch and a common voltage node at the termination end of each bus conductor. Information regarding the current or anticipated bus state is received from an external device such as a bus controller or may be derived by sensing activity on the bus. For example, clock frequency detection logic coupled to clock lines of the bus senses the current operational speed of the bus. A highest-value termination resistance predetermined to be consistent with reliable bus operation under conditions of the current or anticipated bus state is selected for each bus conductor. A bus conductor termination may be taken to a high impedance state by opening the associated termination switch. Decreased average bus power consumption may result.

主权项

1. An adaptive digital signal bus termination apparatus, comprising:
a plurality of termination switches, each termination switch to be singly coupled in series with a bus signal conductor at a receiver end of a digital signal bus furthest from a driver end of the digital signal bus, the termination switch configured to leave the bus signal conductor electrically open at the receiver end of the bus when the termination switch is open; a plurality of variable termination resistors, each variable termination resistor coupled in series between a termination terminal of a corresponding termination switch and a common voltage node, the termination terminal of the termination switch electrically connected to the receiver end of the bus only when the termination switch is closed; and a termination logic module coupled to the plurality of termination switches and to the plurality of variable termination resistors to receive at least one of bus state information or at least one bus termination command and to select a highest termination resistance for each bus signal conductor predetermined to be consistent with reliable operation of the digital signal bus for a bus state indicated by the bus state information or the bus termination command by setting a state of each termination switch and a value of each variable termination resistor.