Mitel Corporation

Mitel Canada Limited

Mitel Corporation of Kanata

Michael C Cowpland

Patrick R Beirne

Raymond J Whitbread

Jacob Cepelinski

Paul S Wilker

Guido Panizzon

A trunk circuit comprises a first lead pair for carrying two-way signals, a second lead pair for carrying two-way signals, a circuit for electrically coupling an incoming signal from the second lead pair to the first lead pair, a first transformerless circuit for applying an incoming signal from the first lead pair to the second lead pair, and a second transformerless circuit for preventing signals from the first circuit applied to the first lead pair from being reapplied to the second lead pair and for preventing signals from the first transformerless circuit applied to the second lead pair from being reapplied to the first lead pair. Preferably the coupling circuit is comprised of a transformer having a primary winding connected in a low impedance voltage source circuit to the second lead pair, and having a secondary winding connected in a very high impedance-to-direct-current circuit for applying the incoming signal from the second lead pair to the first lead pair. Due to the resulting very low current levels in the transformer, the effective bandwidth of the transformer is substantially increased, allowing use of an inexpensive transformer which can readily be incorporated on a plug-in printed circuit board.

Trunk circuit with single coupling transformer

A telephone line circuit includes balanced tip and ring leads for connection to a telephone set and an unbalanced line output lead. A first differential amplifier has its input terminals connected through individual equal-valued resistors to the tip and ring leads, the values of each resistor being at least 10 times the off hook impedance of the telephone set. The output of the first differential amplifier is connected in a circuit path to a line output lead, for applying outgoing signals thereto. A second differential amplifier has its input connected in a circuit path to a line input lead for receiving incoming signals, and its output connected in a circuit path to one of the tip or ring leads, and connected by a further resistor to the input of the first differential amplifier which is connected to the other of the tip or ring leads. The value of the further resistor is selected to apply sufficient output signal from the second differential amplifier to the other input of the first differential amplifier so as to substantially cancel signals within the first differential amplifier appearing at its input terminals which were applied from the output of the second differential amplifier to the tip and ring leads.

Telephone line circuit

A multifrequency dialing tone to 2/8 decoding circuit which does not require individual filters for distinguishing individual tone frequencies. The circuit converts the period of each of the received multifrequency signals to individual voltage amplitudes which corresponds thereto, then compares the voltage amplitudes with a predetermined plurality of voltage ranges. Correspondence of a voltage amplitude level with one of the ranges causes production of an output signal, signifying the presence of a particular acceptable multifrequency tone. Individual correspondence signals operate latches which apply signals to decode leads which carry the decoded output signal.

Tone decoding circuit

A station set interface circuit for connection to a multi-party line, for prohibiting connection of a party line subscriber's set to the party line in the event the line is in use and for returning busy tone to the subscriber's set. A hookswitch flash by the subscriber causes the circuit to connect the subscriber's set to the party line for a predetermined period, while applying a warning tone to the party line for transmission to the parties of the call in progress at the beginning and end of the period.

Partyline subscriber interface circuit

A transformerless two-way trunk circuit particularly useful for interconnecting a balanced lead pair and an unbalanced lead pair, with complete control over sidetone and signal level. The balanced lead pair is terminated with a first matching A.C. impedance and a second D.C. resistance means. A first transformerless circuit means applies an incoming signal from the unbalanced lead pair to the balanced lead pair, and a second transformerless circuit means applies an incoming signal from the balanced pair to the unbalanced lead pair. A third transformerless circuit means cancels signals from said first circuit means applied to the balanced lead pair to prevent them from being reapplied to the unbalanced lead pair, and a fourth transformerless circuit means cancels signals from said second circuit means applied to the unbalanced lead pair to prevent them from being reapplied to the balanced lead pair.

Transformerless trunk circuit

A transformerless bidirectional amplifier useful in a balanced two wire to single wire line circuit, which blocks common mode signals and allows full control of signal levels, impedances, etc. A differential amplifier circuit is connected to the balanced wires, and has its output connected through a buffer amplifier to a single unbalanced wire. A second differential amplifier has its respective input terminals connected to the input and output of the buffer amplifier. The output of the second differential amplifier is connected to one of the balanced wires, and through a resistor to one of the inputs of the first differential amplifier which is connected to the other of the two balanced wires. The value of the latter resistor is such as to apply sufficient output signal from the second differential amplifier to the first differential amplifier so as to cancel a signal from the second differential amplifier which is applied to the first differential amplifier via the first wire of the balanced pair. The second differential amplifier exhibits different gains for the respective two signals applied to its individual inputs which are from the output of the first differential amplifier, whereby they are cancelled.

Transformerless telephone line circuit

A modified Sallen and key active filter useful for generating tones in a tone generator which can be connected to a telephone line. The modification allows a broad range of frequencies to be generated with a relatively constant output amplitude, the output signal of which can be usefully employed for D.T.M.F. or interoffice multifrequency signal generation.

Tone generator

A regulator which can be used in combination with equipment connected to a telephone type line. The regulator senses the amount of direct current being passed by the line and adjusts its internal AC impedance in inverse relationship thereto. This will shunt alternating current signals more severely when connected to short line loops having relatively small insertion loss, protecting a central office from excessive signal amplitudes.

Growing community of inventors

Ottawa, Canada

Michael C Cowpland