CIRCUIT TO DETECT THE HOOK STATUS AND RINGING AT THE CPE END OF A TELEPHONE NETWORK

摘要

A circuit for indicating the status of a telephone line at the CPE end, where the status is either on-hook ringing, or off-hook is disclosed. The telephone line is the normal two-wire telephone line. First, a transconductance amplifier converts a floating voltage difference between the two-wire telephone line into a current. The current is proportional to the voltage difference. Next, a current to voltage converter converts the current from the transconductance amplifier to a single ended ground referenced voltage. The single ended voltage is proportional to the current from the transconductance amplifier, thus the single ended voltage is proportional to the voltage difference across the two-wire telephone line. A voltage controlled switch is turned ON when the single ended voltage is greater than a predefined value indicating the on-hook status. When the single ended voltage is below the predefined value, the voltage switch is turned OFF indicating the off-hook status. Finally, the ringing status is detected when the voltage controlled switch is turned ON and OFF with a repetitive cycle proportional to the frequency of the ringing.