The circuit provides DC loop termination for analog trunk lines. The V-I characteristics is equivalent to a fixed voltage drop (zener like characteristic) in series with an external resistance that determines the slope of the DC characteristic. An external low voltage electrolytic capacitor causes the circuit to exhibit a very high impedance to all AC signal above a minimum frequency that is determined by the capacitor itself and by a 20 K nominal resistor integrated on the chip. The Off-Hook status is detected all the time a typic of 8 mA is flowing into the circuit. In this condition a constant current generator is activated to