How Does a Phone Circuit Work?

Telephone circuits are dedicated connections used to transmit voice or data information. Phone circuits rely on a tip-and-ring operation, which form the two sides of a phone's circuit.


Tip
The tip is the positive, or ground, side of the phone circuit. Ground refers to the electrical circuit that uses the earth or ground as a return path or direct connection. The tip side of the phone circuit typically connects to the telephone company.


Ring
The ring is the negative, or battery, side of the phone circuit. Batteries use electrochemical cells to transform chemical energy into electrical energy that is distributed via the circuit. An electrochemical cell facilitates chemical reactions through electrical energy. The ring side carries -48 volts of direct current, or DC voltage, when idle.


Combination
Combining the tip-and-ring line connections creates a phone circuit. Activating, or "ringing," the phone in an incoming call requires about 90 volts of AC, or alternating current, to be sent, or superimposed, over the direct current voltage at the ring side of the circuit.