Fast a.d. convertor using a digital discriminator and a v.c.o.

The letter suggests that a simple fast digital encoder can be formed from the combination of v.c.o. and digital discriminator, automatically eliminating the complex logic processes of conventional fast baseband a.d. convertors. The technique is suitable for encoding video signals to 8 bits.     

Efficient algorithm for determination of a.r. part of a.r.m.a. model

A fast recursive scheme is given for the solution of the Yule-Walker equations to obtain the a.r. part of an a.r.m.a. model. A lattice equivalent to the predictive filter is also included. This new structure requires what is subsequently called an adjoint model. The algorithm can be used in the evaluation of the a.r. and m.a. parsimonious orders.     

Analogue-computer model for a gallium-arsenide l.s.a. diode

A 1-dimensional analogue-computer model of an l.s.a. diode is described. The model yields new results concerning space-charge growth and decay. Investigations of the output power dependence on the load resistance are made. In addition to n0/f = constant, a constant n0R product is necessary for constant time dependence.     

Quasilinear analysis of a nonlinear a.c. channel

The letter shows how the response to a sinusoidal and/or Gaussian input for an a.c. channel containing a modulator, nonlinearity and demodulator in cascade can be obtained. Results for the modified nonlinearity and the equivalent gain to the signal are tabulated for various situations.     

Conditions for jitter-free timing in a p.a.m. timing recovery circuit

The problem of error-free timing recovery is discussed for a p.a.m. timing recovery scheme. The general conditions were carried out by considering the timing signal as narrow-band-pass process and searching for a condition when the component of phase modulation does not exist.     

Magnetostatic resonances in a y.i.g. rod containing a turning point

The observation of large resonances is reported when the magnetoelastic resonances become saturated. The theoretical analysis allowed these resonances to be attributed to the existence of an important magnetostatic wave reflected at the branch point.     

VDS voltage capabilities of a diffused j.f.e.t. with a vertical-channel arrangement

In the letter, it is shown that the VDS voltage limitation in a j.f.e.t. with a vertical-channel arrangement in the off state is due, not to the breakdown voltage of the gate-drain junction, as for a classical j.f.e.t., but to the field-effect lowering of the potential barrier created in the channel by the polarisation of the gate. The analysis is based on the 2-dimensional numerical solution of the general semiconductor equations.     

New s.a.w. time-inversion system

A new s.a.w. time-inversion system is described. It requires fewer chirp-filter elements than those required with the common method of cascading two Fourier or Fresnel transformations. This new method is based on the fact that the Fourier transform of a linear f.m. signal whose envelope is modulated by a given time function has (approximately) the time-inverted function as its amplitude. Theoretical discussion and some experimental results are included.     

Efficient miniature s.a.w. convolver

We report the development of a miniature s.a.w. convolver with bandwidth 90 MHz, interaction time 12 ?s, and high efficiency, the output power being ?73 dBm for 1 dBm inputs. The overall size is 80 × 14 × 5 mm.     

Room-temperature 1.3 ?m c.w. operation of a glass-clad Nd:y.a.g. single-crystal fibre laser end pumped with a single l.e.d.

Room-temperature c.w. laser action at 1.3 ?m wavelength has been obtained using single-crystal glass-clad Nd:y.a.g. fibres end pumped with a single high-radiance l.e.d. The fibres were 0.5 cm long, 50 ?m in diameter and had a cladding 3 ?m thick. Threshold in a nonoptimum configuration was less than twice that at 1.06 ?m. Application of a transparent, adherent glass cladding to the crystalline fibre is described.     

High-peak-power 2nd-harmonic l.s.a. sources

Results are presented which indicate that the upper frequency range of l.s.a. oscillators can be extended by extracting power at the 2nd-harmonic frequency. By selectively loading the 2nd-harmonic frequency of an X-band l.s.a. oscillator, up to 170 W peak power with 4.8% efficiency at 17.5 GHz has been obtained.     

Scattering loss of s.a.w. resonators

A theory is outlined that predicts the scattering loss into bulk waves of high-Q-factor s.a.w. resonators. The theory applies to an isotropic medium. Nevertheless, experimental results on LiNbO3 are interpreted by the theory.     

Superposition and separation of a u.h.f. wave and a fast-risetime pulse

Arrangements using one or two 3 dB 90° coaxial hybrid couplers with bandwidths of one octave allow the superposition or separation of a u.h.f. wave and a fast-risetime pulse without disturbing the pulse risetime.     

Coupled slot waveguide s.a.w. resonators

Grooved-grating, waveguided s.a.w. resonators are coupled by the evanescent fields of single-mode slot waveguides formed by layers of MgO on SiO2 substrates. Except for higher out-of-band levels, the transfer characteristics of these devices compare favourably with alternative monolithically coupled s.a.w.-resonator geometries. A 4-pole response with a 3 dB bandwidth < 20 kHz and insertion loss < 6 dB is illustrated at 131.5 MHz.     

Phosphor-doped silica cladding v.a.d. fibres

Loss reduction of v.a.d. (vapour-phase axial deposition) fibres at wavelengths of 1.3 ?m and 1.6 ?m was investigated. The infrared absorption loss was reduced by applying SiO2-P2O5 cladding instead of SiO2-B2O3 cladding and by minimising the waveguide imperfection loss. The minimum losses of the fabricated v.a.d. fibre were 0.5 dB/km and 0.28 dB/km at wavelengths of 1.3 ?m and 1.6 ?m, respectively. This fact indicates that fibres fabricated by the soot process, like those made by the vapour-phase axial-deposition process, can be used as long-wavelength optical transmission media. We have also found the OH absorption abnormality at wavelengths of 0.95, 1.24 and 1.39 ?m, and the loss peak values are different from those reported.     

GaAs m.a.o.s.f.e.t. memory transistor

A new non-volatile memory device is reported. This device is a GaAs m.o.s.f.e.t. with charge storage in the gate in which is a double oxide structure of aluminium oxide and GaAs native oxide, both oxides are grown anodically. The fabrication of the device is described and the results of initial measurements on the charging and charge retention properties are presented.     

Novel circuit implementation of current conveyors using an o.a. and an o.t.a

A novel three-port active R circuit is proposed which is capable of implementing all the four forms of current conveyors (namely c.c.I+, c.c.I?, c.c.II+ and c.c.II?) through appropriate adjustments, by employing an operational amplifier, an operational transconductance amplifier and only two resistors.     

Hall-effect analogue a.c.-ratio computer

A fully transistorised a.c.-ratio computer using a thin-film indium antimonide Hall probe is described. The output signal of the divider is proportional to the ratio of an input voltage and the magnetising current of the Hall multiplier. The characteristics of the computer are presented, and its dynamic range of operation is discussed.     

Relaxation l.s.a. mode in InP

What are believed to be the first convincing observations of relaxation l.s.a.-mode operation in InP are reported. Devices fabricated from vapour-phase epitaxial material have shown the characteristic `signatures? of the mode in oscillators operated in S- and X-bands. So far, conversion efficiencies have not exceeded those for comparable samples in GaAs, almost certainly owing to remaining material limitations in the relatively thick active layers. The significance of the results lies, in practical terms, in the promise of high-peak-power sources with acceptable efficiencies, and, in diagnostic terms, in the derived information on the magnitude of the fundamental transferred-electron characteristic peak/valley ratio in InP and in achievable material quality factors for thick epitaxial layers.