Abstract: In an ISDN communications system, a remote station power detector circuit comprises a capacitor connected between center taps of transformers on the receive and transmit pairs of conductors. The capacitor stores energy delivered from a central DC power source. Two serially-connected opto-couplers form a discharge path for the capacitor. The first opto-coupler is periodically driven on to partially complete the discharge path. If the capacitor charge exceeds a predetermined minimum, the second opto-coupler will then be driven on, providing a logic level output usable by the remote station. Power consumption is minimized by the use of large resistors in series with the capacitor while reliable power detection is achieved by detecting accumulated charge on the capacitor. Dielectric isolation is provided through the use of opto-coupler circuits.

Abstract: A laser source suitable for driving single mode and multimode fiber communication lines. The driver circuit includes a photo diode that, in multimode operation, responds to the laser light and causes the laser's output amplitude and wavelength to rapidly fluctuate thus producing the incoherent light required to drive multimode fiber. In single mode operation, the photo diode is disabled and the laser produces the requisite coherent light.

Abstract: An equalizer circuit suitable for selectively equalizing a transmission media operating at one of a number of different data rates has a number of equalizers, one for each data rate, connected in parallel to the media and a selectively operable means for disabling all but one of the equalizers.