Abstract: A tuneable crystal oscillator arrangement includes a piezo-electric, e.g. quartz, crystal and drive current means therefor. A reactance is arranged in series with the crystal and is fed with a current corresponding to the crystal drive current. The corresponding voltage developed across the impedance is fed via a variable gain amplifier back to the crystal. The reactance comprises a number of impedances, there being current steering means for dividing the current between the impedances. This determines the effective value of the reactance and provides a control or adjustment of the crystal frequency.

Abstract: The temperature of a quartz crystal oscillator is determined by comparison of a pair of inharmonically related overtone oxcillations of the same vibrational type, e.g. a thickness shear mode, and of the same overtone order. The use of inharmonically related signals relaxes the contraints on crystal design. The technique may be employed in a crystal controlled frequency synthesizer to provide a feedback signal for maintaining constant output frequency.

Abstract: A semiconductor structure is configurable via a customizing mask either as a varicap diode or as a polysilicon emitter bipolar transistor. The structure forms part of an integrated circuit providing e.g. a voltage controlled oscillator for a crystal frequency standard.

Abstract: An integrated circuit structure has a number of device areas each of which is configurable in a subsequent customizing process as a field effect transistor, a bipolar transistor or as a pair of those devices. Configuration of the structure is determined by correspondingly selective etching of a polysilicon layer disposed on the structure.

Abstract: In a semi-custom integrated circuit, e.g. a bipolar analogue array, underpass areas are so configured as to permit operation as capacitors by suitable configuration of a user determined interconnection pattern. Typically each underpass comprises a highly doped region disposed over a buried layer. A thin oxide layer is applied to the surface of the underpass. Suitable configuration of polysilicon and metal masks provides either a cross-over or a capacitor.

Abstract: Feedforward of the source signal into the compensation mode of an operational amplifier produces more than an order of magnitude improvement in small-signal capability at high frequencies. The technique is useful for active filters and wideband amplifiers. Further improvement will be available using amplifiers designed for this approach.

Abstract: In a comparator circuit in which the active element is a long-tailed transistor pair the input bias current to at least one input of the pair is maintained constant by providing a supplemental current from a current source. A multivibrator incorporating the comparator is also described.

Abstract: For a voltage follower unity gain amplifier, used, for instance, as a buffer in a transceiver associated with a data bus, the input signal is fed forward to a comparator (T2-T3) to which the output is also applied. The input is also applied via an amplifier stage (T5-T6) to a transistor (T4) in the commoned circuit of the comparator, which is a long-tailed pair. Thus, with a connection from the output of the circuit which includes another transistor (T9), provides negative feedback round the comparator, gives a highly stable current.

Abstract: A temperature compensated crystal oscillator in which the base emitter voltage of transistors in an integrated circuit is used to provide substantially linearly temperature sensitive outputs which are employed to generate a series of polynomial functions of Chebyshev-like form which are summed and used to control a varicap diode in the oscillator feedback path.

Abstract: In a matrix array liquid crystal display on silicon with an a.c. drive involving periodic reversal of the potential of the counter-electrode this reversal is liable to produce a significant r.m.s. error voltage at each reversal. The OFF element error voltage is effectively eliminated by blanking all picture elements at the commencement of each reversal, and the ON error voltage more evenly shared by making this reversal occur after a non-integral number of frame scans.

Abstract: An optoelectronic device comprising a light-sensitive device which produces or modifies an electric current in dependence upon the intensity of light incident thereon, and a light-emitting device arranged to emit light in response to said electric current and so disposed that part of said emitted light is incident upon the light-sensitive device to provide positive feedback.