Abstract: A subscriber line interface circuit has a battery-powered, high voltage analog section, that drives tip and ring lines of a subscriber loop, and a mixed signal (low voltage and digital signal processing) section, that monitors and controls the high voltage analog section. An input signal receiving unit of the high voltage analog section conditions input voice and low voltage signaling and ringing signals from the mixed signal section, for application to a dual mode, programmable gain, tip/ring amplifier coupled to the loop. A sense amplifier at the output of the tip/ring amplifier is through an auxiliary amplifier to an analog feedback monitor port for closing a loop to synthesize the circuit's output impedance.

Abstract: A mode-dependent, battery-coupling switch for a subscriber line interface circuit (SLIC) selectively adjusts its current requirements to provide optimal current handling capability irrespective of the mode of operation of the SLIC. Where current demands of the SLIC are relatively minimal (e.g., on-hook idle mode), the bias is set at a relatively small, default value. During high current demand, such as ringing and off-hook signaling, the bias is set at a relatively large value, to maintain a low voltage drop across the battery-coupling switch.

Abstract: A first thin film resistor formed by direct etch or lift off on a first dielectric layer that covers an integrated circuit in a substrate. A second thin film resistor comprised of a different material than the first resistor, formed by direct etch or lift off on the first dielectric layer or on a second dielectric layer over the first dielectric layer. The first and second thin film resistors are interconnected with another electronic device such as other resistors or the integrated circuit.