Caller ID circuit powered through hookswitch devices

摘要

The communication system disclosed herein allows for the hookswitch devices to draw loop current from the phone line in both on-hook and off-hook conditions. Thus, even though an on-hook condition occurs, current may be obtained through the hookswitch devices. This feature allows circuitry which operates during on-hook conditions to still receive power from the phone line. Moreover because the hookswitch devices are utilized for drawing power in both on-hook and off-hook conditions, the use of additional switches dedicated to drawing the power during on-hook conditions is not required. For example, loop current may be drawn from the phone line through the hookswitch devices to power circuits used to perform the on-hook caller ID function. The powered circuits may include for example analog to digital converters. The technique disclosed herein for drawing current through the hookswitch devices is particularly useful for communications systems which utilize a capacitive isolation barrier system.