Abstract: An electrostatic discharge protection circuit that includes a first terminal, a second terminal, an electrostatic discharge device coupled between the first and second terminals, and an active device coupled to the electrostatic discharge device and controlling an electrostatic current to the electrostatic discharge device.

Abstract: The system has two units for transferring a telephone circuit from an old pair to a new pair between two locations. Each unit has a carrier amplitude measuring circuit to determine which location has the larger carrier amplitude and therefore which is the upstream location. Each unit has a charge switch, two transfer switches in the form of an old pair switch and a new pair switch and a controller for controlling the switches. One of the units closes its charge switch to charge the new pair to the dc level of the old pair. Then, the upstream unit operates its two transfer switches at the same time to switch from the old pair, by opening the old pair switch, to the new pair, by closing the new pair switch. The upstream unit transmits a signal to the downstream unit on a third pair. When the downstream unit receives the signal, it operates its two transfer switches at the same time to complete the transfer from the old pair to the new pair.