Hubbell Limited

Winston M Gadsby

Jeffery M Davis

Dmitry Levitan

Roger A Nightingale

Makan Abousaeedi

An apparatus and method for automatically selecting an amount of build-out capacitance to be applied to a hybrid in a telecommunications circuit to balance or substantially balance the hybrid. The apparatus measures voltages of signals being transmitted on telecommunication lines to which the hybrid is coupled, and based on the measured voltages, automatically selects any number of a plurality of capacitive elements to be coupled to the balance port of the hybrid as the build-out capacitance. The apparatus is further controllable to operate in a manual mode in which the capacitive elements to be coupled to the hybrid are manually selected by switches.

Apparatus and method for automatic and adaptive adjustment of build-out capacitance to balance a hybrid

A tone generating circuit comprises a counter circuit having a clock input for receiving a clock signal and a plurality of outputs which generate sequential binary values in response to transitioning of the clock signal; a multiplexer having several inputs, a number of select lines connected to the counter circuit outputs, and at least one output; and a resistor divider network connected to the multiplexer inputs. The multiplexer select lines select one of the multiplexer inputs in accordance with the binary value received from the counter circuit. The multiplexer inputs are connected to different taps on the resistor divider network. The counter selects multiplexer inputs on the falling edge of the clock signal, while the output signal level transitions before the rising edge of the clock signal.

Pulse amplitude modulated tone generator

A two-wire channel unit or line card for use in a digital loop carrier (DLC) telephone system is disclosed. The channel unit is provided with a loopback test capability by using relays to open-circuit or short-circuit the input terminals of the hybrid circuit that couples the two-wire subscriber line to the separate two-wire transmit and receive paths within the channel unit. When open-circuited or short-circuited in this manner, the hybrid circuit couples voice frequency test signals between the receive and transmit paths of the channel unit, thereby allowing loopback testing to be carried out without providing a dedicated loss/gain circuit in the channel unit. An additional relay may be provided to vary the gain of an amplifier stage in the transmit or receive path of the channel unit during operation in the loopback test mode, in order to control the overall gain of the channel unit during loopback testing.

Two-wire channel unit with loopback test capability

A correction circuit for use with a subscriber line interface circuit (SLIC) to control the level of a DC voltage supplied to the tip and ring wires of a telephone circuit includes a current sink with a differential operational amplifier. The amplifier output terminal is connected through an output resistor to a control input of the SLIC which influences the DC voltage level. The non-inverting input terminal of the amplifier is connected to the tip or ring wire, or both, and the inverting input terminal is connected to the output resistor and a DC reference circuit. The level of the voltage supplied by the SLIC is a function of the current supplied by the correction circuit.

Tip-ring voltage correction circuit

On-hook VF transmission through a channel unit to a subscriber telephone instrument is provided by a control unit which generates control signals for the channel unit. The control unit responds to receipt of an 'idle' code by creating commands which establish a VF path through the channel unit regardless of whether the subscriber instrument is on-hook or off-hook.

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Herndon, VA, United States of America

Winston M Gadsby