Abstract: An optic fiber interface device includes an optical transducer mounted on a first portion of a mounting board, a housing mounted over the optical transducer having a bore aligned with the optical transducer for accommodating an optic fiber and having a cavity on its underside. A lens is mounted in the bore between the optical transducer and the optic fiber. An electronic interface circuit is mounted on a second portion of the mounting board folded up relative to said the portion so that the second portion abuts the housing with the electronic interface circuit located in the cavity. The housing can be mounted on the board using surface mount technology.

Abstract: An image reject mixer for a radio receiver comprises transconductors 21 and 22, mixer stages 30 and 23 and a phase shift and combiner circuit 26. The transconductors 21 and 22 provide differential output current signals to their respective mixer stage 30 and 23. Capacitors 28 and 29 are connected between equivalent outputs of the transconductors 21 and 22 respectively. The capacitors 28 and 29 have the effect of correlating the output noise of the transconductors 21 and 22 and correlating the noise generated by the mixer stage transistors which is leaked to the inputs of the mixer stages 30 and 23, the image frequency components of which noise are thereby cancelled by the operation of the mixer stages 30 and 23 and the phase shift and combiner circuit 26. The capacitors 28 and 29 also compensate the second harmonic of the local oscillators which leak through to the inputs of the mixer stages 30 and 23. Overall, gain, noise figure and linearity can all be improved without an increase in current consumption.

Abstract: Circuit 200 comprises an input amplifier stage 290, phase-splitters 292, 293 and mixer cores 294, 295. An input signal is applied to terminal 220, a local oscillator signal applied to terminals 230, 231 and a 90° shifted local oscillator signal is applied to terminals 232, 233. The In-phase differential signal is output at terminals 240, 241 and the quadrature signal is output at terminals 240, 233. Phase-splitters 292, 293 comprise base-coupled transistors 202, 203, 205, 206 which are biased by a potential applied to terminal 262. As these phase-splitters are driven by input amplifier stage 290, which acts as a current source, the arrangement has very good noise properties. Degeneration inductor 280 reduces the noise figure of the circuit further because it is a noiseless component.

Abstract: A variable transconductance amplifier comprises transistors and whose emitters are connected via resistors and to a constant current source to form a differential or long tail pair. A feedback amplifier whose transconductance is controllable has inputs connected to the collectors of the transistors and outputs connected to the emitters thereof. The feedback amplifier thus supplies a differential current to the emitters of the transistors which corresponds to the product of the differential output signal of the transistors and the variable transconductance of the feedback amplifier.

Abstract: A method of fabricating a semiconductor device having active components grown on a substrate, involves providing a semiconductor substrate on which the active components are grown, and doping the semiconductor substrate to render it non conductive and thereby reduce parasitic capacitance between active components thereon. The components typically comprise a VCSEL and monitor. The doped substrate reduces parasitic capacitance.

Abstract: A vertical cavity surface emitting laser diode (VCSEL), includes top and bottom electrically non-conductive mirrors defining a first laser cavity containing a laser medium and designed to resonate at a first wavelength. A second laser cavity is designed to resonate at a second wavelength less than the first wavelength. The second laser cavity is optically coupled to the first laser cavity so as to pump the laser medium and create laser action in the first laser cavity. The second laser cavity is normally provided by a VCSEL stacked below the first laser cavity.

Abstract: A voltage to current converter comprises a first long tail pair comprising transistors whose emitters are connected via equal value resistors to a constant current source. The first long tail pair forms a main transconductance stage. A subsidiary or corrector transconductance stage is connected in anti-phase with the main stage. The corrector stage is based on another long tail pair comprising transistors whose emitters are connected via resistors to another constant current source. The linear part of the transconductance of the corrector stage is substantially less than that of the main stage but the non-linear part is substantially equal to that of the main stage. Thus, non-linear distortion can be substantially reduced.

Abstract: A MOS-controllable power semiconductor trench device has a gate in the form of a trench which extends through a region of p type silicon into an n type region of low conductivity. A discontinous buried p layer below the bottom of the trench forms part of a thyristor which in operation is triggered into conduction by conduction of a PIN diode which is produced when an accumulation layer is formed in the n type region adjacent to the trench under the action of an on-state gate signal. The device has a high on-state conductivity and is protected against high voltage breakdown in its off-state by the presence of the buried layer. An off-state gate signal causes removal of the accumulation layer and conduction of the PIN diode and the thyristor ceases in safe, reliable and rapid manner.

Abstract: A synchronous single port random access memory comprises a core 2 of memory cells 3 arranged as rows and columns. The rows are addressed by a row decoder 5 and the memory cell outputs are connected as columns to a column decoder and multiplexer 7. The decoder and multiplexer 7 selects groups of memory cells 3 from the addressed row and connects these to sense amplifiers 8. Changes in address are propagated immediately to the core 2 so that the selected memory cells 3 are connected as quickly as possible and without any fixed delays to the sense amplifiers 8. Similarly, a read clock “rclk” enables the sense amplifiers 8 immediately upon becoming active.

Abstract: An adapter for coupling optical and electronic circuits, has a housing including a first portion for mating with an optic fiber termination device, and a second portion for mating with an electronic termination device. At least one electro-optical transducer in the housing has an optical interface for coupling with the optical termination device and an electronic interface for coupling with the electronic termination device. The adapter converts signals between optical and electronic form.

Abstract: A number of npn and pnp bipolar transistors is formed in a single chip of silicon, so that some of the transistors have a greater frequency response than others. The higher frequency transistors have their emitters located closer to the collectors, by positioning a collector, or emitter, of a transistor in a recessed portion of the surface of the chip. The recess is formed in an accurate and controlled manner by locally oxidizing the silicon surface, and subsequently removing the oxide to leave the recess.

Abstract: A device for generating light with the aid of a semiconducting material consisting of two electrically conducting contact layers and at least one layer, arranged therebetween, of semiconducting material which comprises a light-emitting semiconducting layer which is divided into at least two permanently parallel-connected sub-regions, delimited by semiconducting material with a higher energy gap than the light-emitting layer or delimited by ion-implanted semiconducting material, wherein the delimiting material shall prevent the propagation of dislocations between the sub-regions.

Abstract: A low power pulse amplifier with low duty cycle errors. The amplifier provides several differential amplifier stages with a biasing and canceling network. To minimize duty cycle errors for large input signals, cascode transistors are added between the drains of the differential amplifiers and the outputs. The result is an amplifier having a duty cycle error of less than 5% at amplitude input ranges from 5 millivolts to the supply voltage.

Abstract: A semiconductor memory, for example of the ROM type, has columns of memory cells with a bitline for each column connected to the cells of the column. The bitlines are connected via multiplexers to the input of a sense amplifier. Before column selection, the bitlines are held uncharged. When a column is selected, its bitline is connected to a charging voltage by a pull up transistor.

Abstract: A method of reducing the amount of unwanted radiation emitted from a semiconductor laser device involves coating a transparent portion the device intended to transmit radiation with a partially reflective layer.

Abstract: A variable attenuator comprises bipolar transistors Q1 and Q2 connected in reverse parallel between a point 1 and ground potential G. The base electrodes of the transistors Q1 and Q2 are biased independently by a control circuit 3. The collector of transistor Q1 and the emitter of transistor Q2 are commonly connected to a bias voltage provided by resistor R2 and voltage source Vr. The attenuator provides means by which the linearity, gain, power handling capabilities and noise figure of a front-end receiver can be altered. The attenuator is susceptible to integration in, for example, a radio receiver front-end.

Abstract: An assembly for use in transferring optical signals from an array of surface-emitting lasers to an array of optical fibers. The laser diodes are mounted on a lead frame type structure in an arrangement which corresponds to the position of optical fibers mounted in an optical fiber ferrule. Complementary alignment means in the lead frame and optical fiber ferrule provides proper positioning of the optical fibers in relation to the laser array when assembled.

Abstract: A phase detector determines an error value dependent on the relative phase between a local oscillator signal, used as the system clock, and an input signal received over a PR (a, b, a) channel. The phase error value is used to control a phase locked loop (FIG. 1, not shown). The received signal is sampled at regular intervals dependent on the local oscillator signal. A threshold slicer 22 selects an ideal sample value for a sampling point by comparing the sampled value to three thresholds provided on respective ones of slicer threshold inputs 23, 24 and 25. A subtracter 27 determines a difference value corresponding to a difference between the ideal sample value and the actual sample value for that sampling point. A delay register 28 and a subtracter 29 operate to determine the sense of change to the current ideal sample value from an ideal sample value for a preceding sample point.

Abstract: A frequency tracking arrangement in which a frequency tracking circuit utilizes a continuously variable analogue first order all-pass filter circuit as a controllable phase-shift element in a closed-loop system which produces a control signal to control the phase shift circuit to introduce a 90.degree. phase shift of a received reference frequency signal when the circuit is tracking that reference frequency. The control signal may then be utilized to slave the cut-off frequency of a filter and/or the delay time introduced by a delay line.

Abstract: An optical emission device includes a laser source having an emitting surface, and a sensor laterally adjacent the laser source generating an output signal dependent on the amount of light falling on its detection surface. A transparent waveguide is located in front of the emitting surface and extends generally parallel thereto such that light striking the waveguide in a direction normal to the emitting surface passes straight through the waveguide. A coupling medium is placed between the emitting surface and the waveguide. A light dispersant in the coupling medium causes a fraction of the laser light to strike the waveguide at an oblique angle so that it can enter the waveguide and be carried thereby to the sensor. An important advantage of the invention is that is uses inexpensive passive parts. The assembly process easy to implement, and the parts are stable during temperature changes. As a result only a small tracking error occurs.