Abstract: A telephone station subscriber line interface circuit for connecting a telephone subscriber station to a telecommunications transmission line comprises a loop current sensing circuit for providing an output signal proportionately representative of DC resistance in the telecommunications transmission line. A ring-side driving circuit is coupled to the loop current sensing circuit and is responsive to the output signal for providing an alternating current voltage source and a direct current voltage source to a transmit amplifier in periods of high constant DC resistance in the telecommunications transmission line, the ring-side driving circuit maintaining the output of the alternating current voltage source constant to the transmit amplifier and automatically transferring from a constant direct current voltage source to a constant direct current current source in the event of a decrease in the DC resistance in the telecommunications transmission line sensed by the loop curent sensing circuit.

Abstract: An electron beam tester (11) utilizes a source (13) of stored electrons to produce a probing beam (14) of short pulses and high intensity. The high intensity improves the signal-to-noise ratio of the potential being measured and is especially suited for measuring potentials in high speed integrated circuits (19) while they are operating. The cyclotron principle is adapted for storing the electrons in an orbital configuration wherein the electrons are clustered in bunches having substantially the same energy level. These characteristics of the electrons in a beam facilitate its operation and control in an electron beam tester for contactless monitoring of voltage potentials in an operating high speed integrated circuit.

Abstract: A lead frame and method for processing the lead frames from a continuous strip of lead frames. A first insulation support member and a second insulative support member are first molded to the lead frame. After the support members are formed, the positioning member for supporting the leads within the lead frame is stamped from the lead frame. After an integrated circuit (IC) is connected to the leads, the IC can be tested within the lead frame since the leads are electrically isolated from the lead frame and each other. Finally the IC can be encapsulated and the leads severed from the lead frame assembly.

Abstract: A modulation-doped field effect transistor includes an undoped semiconductor layer and an arrangement for supplying charge carriers into a region of the semiconductor layer adjacent one side. An arrangement is provided for locally modulating hole and electron density in another region adjacent the other side of the semiconductor layer in a repeating pattern of alternations so as to inhibit current flow in the direction of the alternations.

Abstract: Processing techniques for various surface mount modular components provide various structures for single device components (10) and multiple device components (FIGS. 6 and 7) suitable as character displays. The technique beings with a slab of substrate material 12 patterned on both sides. Plated through holes (33, 43) connecting back side terminals (19, 20) to front side connective strips (22, 24) are formed. Devices (15, 16) are mounted to land areas (13, 34) and wire bonded to connecting pads (14). The front side is coated with epoxy to encapsulate the devices in a layer having an outer surface formed into optional lenses (262, 263). The slab is then separated to provide the modular components.

Abstract: A security unit is disclosed for controlling access to a main computer system. The security unit provides a comprehensive mechanism for detecting and inhibiting sophisticated attackers. A method of operation and special purpose hardware for implementing this operation are disclosed.

Abstract: A modulation-doped field effect transistor comprises a gate recess through a top insulating layer, having a cross-section in a semiconductor layer increasing down to an interface with a further semiconductor layer and thereafter having a cross-section in the further semiconductor layer decreasing down to the bottom of the recess in the further semiconductor layer. A gate electrode is formed in the recess.

Abstract: A process of making an integrated injection logic (I.sup.2 L) semiconductor structure is disclosed which is particularly advantageous for implementation in a group III-V compound semiconductor such as gallium arsenide. By use of "regrowth" techniques, the base region of the lateral transistor is made extremely thin (less than one-tenth micron). Utilization of a Schottky collector in a vertical transistor simplifies the structure.

Abstract: A voice switched gain system is disclosed for loudspeaking telephone and hearing aid applications involving electret microphones. A voice switched gain circuit comprises an audio pre-conditioning circuit for providing a conditioned audio input referenced to an unconditioned audio input to a compandor circuit. A linear gain level reference generator circuit generates a level for comparison with the audio input level. A decision circuit then controls the compandor operation based on the result of the comparison. The decision circuit either maintains the audio output of the compandor in a compressed state or expands the audio input signal to a higher level expanded state for transmission. Two such circuits are provided in a loudspeaking telephone system, one circuit for maintaining a preemptive near end control through appropriate timing of the dual decision process. Far end control is provided by the other voice switched gain circuit.

Abstract: A beam (2) of collimated light is directed towards a printed circuit board (4). The light beam is displaced as reflected from a point of incidence in a path including surfaces having different heights above the printed circuit board when detected at an angle oblique to the surface. From the variation of displacement which is portional to height, the overall profile of the circuit board including components present thereon is determined along the path (56) or line (64) the beam is incident. Various photodetectors (14) are utilized and the addition of a ramp filter (58) enables a single cell integrating photodetector to provide an output intensity indicative of the displacement. An arrangement (FIG. 11) is presented for compensating for variations in surface reflectivity using normalization or feedback.

Abstract: A patient trolley has a tiltable upper body support which is hydraulically lifted to a raised "heart" position and which is immediately lowered by a quick release valve so that a patient may be quickly treated in a horizontal position. Two cylinders are mounted on trunnions with distal ends of pistons interconnected to upper body supports so that the cylinders extend downward and toward a head end of the trolley from the trunnions. As the upper body support is lifted the cylinders rotate on the trunnions toward the head end of the trolley. In the down position of the upper body support the cylinders and trunnions may be lifted and held in an inactive position for clearance of hospital equipment. Levers and linear bearings enable the upper body support to be raised to substantially perpendicular position and to be quickly lowered.

Abstract: A highly aligned optical device which includes an optical element with an optical surface to which are attached electrodes in which is installed in a housing which includes a transparent enclosure for defining a lens. The optical element is very carefully aligned in three dimensions within the transparent enclosure lens and the lens surface is specially contoured to optimize the mechanical/optical characteristics of the device. The device may be an emitter in which case the device is instrumental for generating a very narrow collimated beam of LED rays, or a detector with a special lens which receives the narrow beam of LED rays and focuses the beam to fill the optically active area of detectors to maximize and optimize the current transfer ratio between the emitter and the detector over distances.

Abstract: An integrated injection logic (I.sup.2 L) semiconductor structure is disclosed which may be advantageously implemented in a group III-V compound semiconductor such as gallium arsenide. The base region of the lateral transistor is made extremely thin (less than one-tenth micron) by use of "regrowth" techniques. The structure of the vertical transistor is simplified by using a Schottky collector.

Abstract: A microprocessor has on-chip hardware for protecting software against unauthorized use. The microprocessor includes a decoder for deciphering software instruction codes prior to their execution by the microprocessor. The instruction codes are enciphered in a unique way so that they can only be executed by the specific microprocessor for which they are intended.

Abstract: The invention relates to a transmission testing arrangement for executing performance tests for a telecommunication system which includes a central switch to the common control unit, a switching network, and line interface units internally connected to the switching network and adapted for connection to a corresponding line circuit. The testing arrangement includes a bus-oriented microprocessor system for synthesizing and analyzing test signals, a program memory, a main memory, and first and second interface modules.

Abstract: Apparatus is disclosed for accumulating (counting) the occurrences of different types of events (such as trips travelled by an automobile) and storing these counts in substantially permanent form. The apparatus includes a logic element for determining both the occurrence of an event (trip travelled) and the type of event (length of trip), and a non-volatile memory such as a "fusable-link" PROM or UV-erasable PROM, associated with and connected to the logic element, for accumulating and substantially permanently storing the statistical information.

Abstract: A bistable multivibrator circuit responds to the voltage across a device to be protected. The circuit changes its state when this voltage drops below a predetermined value.

Abstract: Apparatus is disclosed for testing an electrical circuit by means of signature analysis. Responses to a sequence of test patterns from the circuit under test are supplied to a linear feedback signature register (LFSR) which produces a signature signal at its output representing its current state in dependence upon its prior state and the received response signal. A programmed read-only-memory is addressed by these state signals of the LFSR and produces, at its output, a logical "1" signal if the current signature represents a permissible state of the LFSR and a logical "0" if the state is not permissible. This checking occurs throughout and during the testing sequence in contrast to conventional signature analysis wherein the comparison only occurs at the end of the testing sequence.

Abstract: A clock pulse generator system for providing a highly stable clock signal consists of two separate redundant clock signal generators which are controlled to operate in dead synchronization with each other. A microprocessor controlled digital phase lock loop operates to control each of the two clock signal generators and selects among a plurality of operating states such that the average dynamic phase difference in the two clock pulse signals generated is practically zero. Furthermore, the instantaneous dynamic phase difference does not exceed the phase noise of the voltage controlled crystal oscillators of the phase lock loops and, in one embodiment, is normally less than ten pico seconds, each phase lock loop comprising means for performing a fine, as well as coarse, phase comparison among internally or externally generated reference signals, only one of which is the highly stable clock signal output.