Abstract: A network interface circuit includes an off-hook/on-hook circuit, responsive to the communications network, that provides an off-hook voltage substantially equal to the communications network voltage in an off-hook state and that provides an on-hook voltage in an on-hook state. A voltage controlled current source provides a load current which is proportional to a communications network voltage provided by the communications network. A divider circuit, responsive to the off-hook/on-hook circuit, provides an input voltage and produces an over-voltage, wherein the input voltage is proportional to off-hook or on-hook voltage. A clamping circuit limits the input voltage to one of a first or second predetermined value based on the operating mode and generates a current limited voltage.

Abstract: A communication interface and a design method therefor simultaneously shape a synthesized terminating impedance matching different frequency bands on different connecting communication circuits and a receive path response to prevent frequency roll-off. In some cases, for example based on specified network requirements in a particular country, the terminating impedance presented by the interface must have different frequency characteristics for received signals in different bands of frequencies. A transconductance amplifier and feedback loop provide the terminating impedance for signals received from the communication circuit and serve as a source impedance for signals transmitted by the interface to the telephone line. Signals with different frequencies will generally be received from the telephone line. These different characteristics are realized using different filter networks in the feedback loop.

Abstract: A communication interface and a design method therefor provide a synthesized terminating impedance matching different frequency bands on a communication circuit. In some cases, for example based on specified network requirements in a particular country, the terminating impedance presented by the interface must have different frequency characteristics for received signals in different bands of frequencies. A transconductance amplifier and feedback loop provide the terminating impedance for signals received from the communication circuit and serves as a source impedance for signals transmitted by the interface to the telephone line. Signals with different frequencies will generally be received from the telephone line. These different characteristics are realized using different filter networks in the feedback loop. Each network provides a matching terminating impedance to the communication circuit according to the frequency band applied to the circuit.