Northern Telecom Limited

Other

Douglas C Wadsworth

Terence N Thomas

Marc E Bonneville

A FET bidirectional switching arrangement comprises first and second FETs, and a limiting arrangement connected to the FETs. The FETs are operable in response to a first bias condition to pass current in series through the FETs in either of two opposite directions, and operable in response to a second bias condtion to block current through the FETs in both of the two opposite directions. The limiting arrangement senses the direction of current flowing through the FETs and limits a forward bias on a first pn junction of the first FET when the current flows in a first direction of the two opposite directions to limit undesired current flow through the first pn junction of the first FET. When the current flows in a second direction of the two opposite directions, the limiting arrangement limits a forward bias on a first pn junction of the second FET to limit undesired current flow through the first pn junction of the second FET.

FET bidirectional switching arrangements and methods for preventing pn

In a loudspeaker telephone, improved power transfer is achieved by connecting the drive circuit for the loudspeaker in parallel with the input and output of the usual series regulator, the output of the regulator and one of the power supply connections of the drive circuit being connected, in common, to supply other circuitry in the telephone set. This other circuitry might comprise a microprocessor and other signal processing circuitry. Such a configuration means that the current passing through the speaker drive circuit also passes through the other circuitry. In effect, it is 're-used' instead of being added, as would be the case if the drive circuit were connected in parallel with the other circuitry. In the case of a positive series regulator, the series regulator supplies current when the current requirement of the other circuitry exceeds that received from the drive circuit. When the current from the drive circuit exceeds that required by the other circuitry, the series regulator is arranged to sink the excess current. A suitable push-pull regulator may comprise a power operational amplifier.

Speaker drive arrangement for loudspeaker telephone

In the class of electronic circuits known as current conveyors, limitations in the areas of frequency bandwidth, transient response, output impedance, distortion, accuracy, and suitability for integration are overcome by means of a current conveyor comprising a Wilson current mirror of one polarity type cross-coupled with a second Wilson current mirror of the opposite polarity type. The first Wilson current mirror is connected to an input port and a reference port. The second Wilson current mirror is supplied with current by a current-splitting circuit which also supplies an output port with a currrent that is proportional to, preferably half, the current supplied to the second current mirror. An emitter de-generation compensation scheme may optimize the transient response and stability of the mirrors. The current splitter may also comprise current mirrors. A voltage-to-current converter may be realised by connecting suitable resistors in series with the input and reference ports, respectively.

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Manotick, Canada

Douglas C Wadsworth