An integrated CMOS telephone line adapter

A novel fully CMOS circuit for electronic telephone line adaption is described. In the on-hook state the circuit operates in micropower condition, dissipates only 5 μA, and is capable of generating the supply voltage required for retention of data stored on external RAM. In the off-hook state the circuit is boosted into the normal operation mode and is able to drive external bipolar transistors to synthesize the line impedance. The dc and the ac line impedances are set with external components, thus permitting the fulfillment of different PTT specifications. The circuit also performs line signal extraction and transmission, both for voice and DTMF. The dc line voltage is monitored, and a supervision block generates a precise reset signal when the line voltage drops out. The circuit has been integrated in a CMOS P-well 3-μm double-poly single-metal technology; the silicon area is 6 mm2.