Abstract: Input current is applied to the emitter electrode of a first transistor, of a first conductivity type, to cause a base current response. This base current response is applied to the base electrode of a second transistor, of a second conductivity type complementary to the first conductivity type, to cause a collector current response. This collector current response is applied to the emitter electrode of a third transistor of the second conductivity type to cause another base current response. This latter base current response is applied to the base electrode of a fourth transistor, of the first conductivity type. The fourth transistor responds with an emitter current flow of opposite sense to the input current, but directly proportional thereto without substantial alpha-dependent or beta-dependent errors.

Abstract: An input terminal of two differential amplifiers, one employing PNP transistors and the other NPN transistors having a different gain (beta) than the PNP transistors, connect in common to a terminal of a signal source. The operating currents to these amplifiers are maintained at different levels such that the base current flowing into the input terminal of one amplifier in its balanced condition is equal to that flowing from the input terminal of the other amplifier in its balanced condition.

Abstract: At least two current mirrors, both responsive to the same input current, the output transistor of the first serving as a current sink for the output current supplied by the second. At least the first mirror is a two-ratio mirror, its output current demand increasing at a rate within the output current supply capacity of the second in a first input current range and increasing at a rate faster than the rate of increase of the output current of the second mirror in a second input current range. A signal detector coupled to the output circuits of both mirrors indicates when the input signal current reaches a given level by detecting when current demanded by said sink exceeds the output current of the second mirror.

Abstract: A current mirror amplifier circuit with an input current path and an output current path is further provided with a sensing means responsive to the cessation of current flow in the output current path such that the cessation of current flow in the output current path causes the current flow in the input current path to be discontinued.

Abstract: Unbalance currents in a-c power line conductors are sensed by a differential current transformer. They are then synchronously detected at the line frequency. A substantial direct current component in the detected signal is indicative of a resistive ground-fault and distinguishes such a fault from other types of unbalanced loading of the a-c power line conductors, such as unbalanced-capacitance-to-ground conditions.

Abstract: A diode OR gate permits trigger circuits of an array of SCR's to share the same integrating capacitor for suppression of short-lived transients, which might otherwise cause false triggering of the SCR's. The SCR's are switching and latching elements in a telephone cross-point switch array.

Abstract: Two transistors, the emitter of the first joined to the collector of the second via a resistor and two bases joined by an element such as a diode. When the input signal applied to the base electrode of the first transistor is less than a given value, neither transistor conducts; when it exceeds a second value close to this given value, substantially constant voltages develop across the diode and resistor, respectively, and the two transistors conduct a constant current.