Gte Communication Systems Corporation

Semiconductor Components Industries, LLC

Robert G Thomson

A circuit (,) for providing TTL logic signals at an output (,) employs dual pull up devices (,) at the output. The first device (,) is a bipolar transistor that acts as an emitter-follower to quickly pull up the output in response to applied logic signals to drive the output to a logic one state. Thereafter, the second device (,) which is a MOS transistor is turned on to drive the magnitude of the high logic output signal to substantially V,, the positive power supply voltage supplied to the circuit (,).

Circuit and method for a transistor-transistor logic (TTL) compatible output drive

A Current Reference for providing a feedback signal to a current driver in a current-series, feedback-controlled current source circuit that includes at least one, but more likely more than one, controlled current source. The Current Reference comprises a current mirror having an input transistor coupled to an output transistor in a current mirror configuration. The input transistor of the current mirror is driven by a constant current source, Icc, so that the current mirror output transistor causes a current substantially equal to Icc to flow out of a summing node. A sensing transistor is coupled to a controlled current source for providing a current into the summing node that is representative of the current delivered by the controlled current source. As a result, the current flowing away from the summing node and into a phase inverter is representative of the difference between the delivered current and Icc. The output of the phase inverter is coupled to the current driver so as to maintain the magnitude of the delivered current at the intended value.

Current reference for feedback current source

An integrated circuit includes an interface circuit for coupling with a relative high-level VOICE circuit and a relatively low-level DIALER circuit to a subscriber line. A first shunt transistor is coupled across the telephone line and has its collector current forced by a current sink driven from the VOICE circuit. A second shunt transistor is coupled in a current mirror configuration to the first shunt transistor and supplies current to the DIALER circuitry. The interface circuit includes a saturation prevention circuit coupled to the current sink and to the second shunt transistor for sensing a tendency of the second shunt transistor toward saturation and for increasing the collector current load on that transistor in response. The saturation prevention circuit includes a voltage offset element and a sensing transistor arranged to form a loop with the collector-to-base junction of the second shunt transistor. As the collector-to-base junction of the shunt transistor approaches a forward-biased condition, the normally nonconducting sensing transistor is biased into conduction so that the collector load on the shunt transistor is increased.

Nonsaturating interface supply

A differential amplifier feedback current mirror includes a feedback current source that provides a correction current to one input of a differential amplifier. The correction current is synthesized by comparing a sample of the current delivered by a string of controlled current sources to a reference current set up by a constant current source. A current driver is included in the differential amplifier feedback loop and a current source buss is driven by the current driver. The feedback configuration assures that the current delivered by the dependent controlled current sources accurately tracks the current established by the reference current source, irrespective of the base current offset attributable to each of the dependent controlled current sources.

Differential amplifier feedback current mirror

Circuitry for supplying power to low-level DIALER portions of a telecommunications integrated circuit device comprises a PNP current sourcing transistor mirrored to a bypass transistor. The bypass transistor is coupled across the TIP and RING terminals of the subscriber line so as to maintain current flow sufficient to prevent the central office from 'dropping out'. A sensing transistor drives a current sink coupled to the current sourcing transistor in order to prevent that transistor from dropping into saturation and degrading the necessarily high impedance level that must be presented across the subscriber line. Saturation is prevented through the operation of a circuit loop that includes the base-collector junction of the current sourcing transistor, the emitter to-base junction of the sensing transistor, and a voltage offset element. When the base-collector voltage of the current sourcing transistor approaches to a predetermined level determined by the voltage offset, the level chosen to be indicative of a tendency toward saturation, the sensing transistor begins to conduct, thereby driving a current sink into conduction and imposing an additional load on the current sourcing transistor. The additional load prevents the current sourcing transistor from falling into saturation.

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Tempe, AZ, United States of America

Robert G Thomson