DC termination circuit for 2B1Q line-coded basic rate ISDN.

摘要

A DC termination circuit meeting the 2B1Q basic rate physical layer line code protocol for bilateral switch operation has a trigger circuit for switching the termination circuit from a high impedance to a low impedance circuit. The trigger circuit is connected in parallel with a switch that when activated effectively shorts the trigger circuit out of the DC termination circuit providing reduced power dissipation. Activation of the switch connects low impedance, low power dissipation load into the DC termination circuit. A hold-up current source is provided to maintain circuit operation during momentary losses of a test voltage. In a further embodiment of the DC termination circuit, a fold-back current limiter is included that further reduces the current through the DC termination circuit when the test voltage exceeds a predetermined value set by the 2B1Q standards. <IMAGE>