Online ISSN
1350-911X
Print ISSN
0013-5194
Electronics Letters
Volume 15, Issue 21, 11 October 1979
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Volume 15, Issue 21
11 October 1979
Room-temperature c.w. operation of InP/InGaAsP/InP double heterostructure diode lasers emitting at 1.55 μm
- Author(s): H. Kawaguchi ; K. Takahei ; Y. Toyoshima ; H. Nagai ; G. Iwane
- Source: Electronics Letters, Volume 15, Issue 21, p. 669 –670
- DOI: 10.1049/el:19790475
- Type: Article
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p.
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–670
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Room-temperature c.w. operation has been achieved for stripe-geometry double heterostructure InP/InGaAsP/InP diode lasers emitting at 1.55 μm. The heterostructures were grown by l.p.e. on (100) InP substrates, and stripes were defined by the conventional planar-stripe structure. The room-temperature (20°C) c.w. threshold current ≃250 mA for a 6 μm wide by 200 μm long cavity.
Decoupled control of robot movement
- Author(s): J.R. Hewit
- Source: Electronics Letters, Volume 15, Issue 21, p. 670 –671
- DOI: 10.1049/el:19790476
- Type: Article
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p.
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–671
(2)
Recently, methods have been proposed for the simultaneous decoupling of the controls of nonlinear dynamical systems and for the assignment of poles in the resulting decoupled linear systems. These methods have been used to obtain decoupled controls for the equations of motion of industrial robot arms and their performance has been gauged by simulation. It is shown here that such decoupling procedures do not guarantee stable controls and that their use, where the mathematical models of the controlled systems may be subject to uncertainty, should be attempted with caution.
Hybrid realisation of an adaptive filter for real-time noise-cancelling applications
- Author(s): T. Schwarz and D. Malah
- Source: Electronics Letters, Volume 15, Issue 21, p. 671 –672
- DOI: 10.1049/el:19790477
- Type: Article
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p.
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An efficient hybrid realisation of an adaptive filter for real-time noise-cancelling applications is described. The filter is based on an analogue tapped delay line but its coefficients are digital and are updated according to a simplified l.m.s. algorithm. A single multiplying d.a. device is used for performing the multiplications. The structure of the filter, its performance and processed examples are presented.
Adaptive filters to improve loudspeaker telephone
- Author(s): C.R. South ; C.E. Hoppitt ; A.V. Lewis
- Source: Electronics Letters, Volume 15, Issue 21, p. 673 –674
- DOI: 10.1049/el:19790478
- Type: Article
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p.
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A loudspeaking telephone is under development which uses two adaptive filters to cancel acoustic and electric coupling in an open-loop or shallow voice-switched system. Measurements indicate that between 15 and 30 dB of echo cancellation is available for a range of conditions.
Improved ohmic properties of Au–Ge Contacts to thin n-GaAs layers alloyed with an SiO2 overlayer
- Author(s): F. Vidimari
- Source: Electronics Letters, Volume 15, Issue 21, p. 674 –676
- DOI: 10.1049/el:19790479
- Type: Article
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p.
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–676
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The contact resistivity of Au–Ge contacts on n-type GaAs was reduced by about one order of magnitude by replacing the usual Ni top layer with an SiO2 layer. Surface coverage and edge definition of the contact areas can be optimised by proper choice of process parameters, making this technology suitable for submicrometre device processing.
Measurements performed on l.e.d. 4-level digital optical-fibre system for 68 Mbit/s
- Author(s): Manfred Rocks
- Source: Electronics Letters, Volume 15, Issue 21, p. 676 –677
- DOI: 10.1049/el:19790480
- Type: Article
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A description is given of the configuration of a 4-level digital optical-fibre system. By means of light-emitting diodes (l.e.d.s), it is possible to transmit an equivalent bit rate of 68.736 Mbit/s (34.368 Mbaud), over a distance of 5.16 km, the signal/noise ratio required for a bit error rate (b.e.r.) of 10–9 being observed.
Strain birefringence in single-polarisation germanosilicate optical fibres
- Author(s): I.P. Kaminow ; J.R. Simpson ; H.M. Presby ; J.B. MacChesney
- Source: Electronics Letters, Volume 15, Issue 21, p. 677 –679
- DOI: 10.1049/el:19790481
- Type: Article
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p.
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Fibres that maintain a fundamental mode with fixed polarisation can be realised by the introduction of a large strain birefringence. A modal birefringence of 3 × 10−4 was achieved by differential thermal expansion in a germanosilicate fibre prepared from a circular preform by the exposed-cladding technique. Measurements of birefringence agree with earlier calculations.
Novel active RC circuit for floating-inductor simulation
- Author(s): Raj Senani
- Source: Electronics Letters, Volume 15, Issue 21, p. 679 –680
- DOI: 10.1049/el:19790482
- Type: Article
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p.
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Whereas existing methods of lossy/lossless floating-inductance simulation would require two to four operational amplifiers or current conveyors and compulsorily require exact matching of some components, this contribution presents a novel circuit which employs only a single current conveyor along with only three passive components to realise a floating-inductor (parallel RL), without any component-matching requirement.
Low-loss high-numerical-aperture optical fibre fabricated by v.a.d. method
- Author(s): N. Shibata ; M. Kawachi ; S. Sudo ; T. Edahiro
- Source: Electronics Letters, Volume 15, Issue 21, p. 680 –681
- DOI: 10.1049/el:19790483
- Type: Article
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p.
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Low-loss high-numerical-aperture optical fibres, consisting of GeO2/P2O5-doped silica core and silica cladding, have been made by the v.a.d. method. The minimum transmission loss of the fibre with an n.a. 0.32 was 0.8 dB/km at 1.55 μm.
Compensation of profile dispersion in graded-index optical fibres
- Author(s): S. Geckeler
- Source: Electronics Letters, Volume 15, Issue 21, p. 682 –683
- DOI: 10.1049/el:19790484
- Type: Article
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p.
682
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As the profile dispersion parameter P of graded-index fibres is wavelength-dependent. Marcatili's condition for achieving high bandwidth is usually satisfied only in a narrow wavelength range, if at all. This behaviour can be compensated by a wavelength-dependent refractive-index profile. This letter presents a profile function that compensates for a broad class of profile dispersions and may become a design criterion for fibres in the future, although its practical applicability is presently restricted by the limited variety of available glasses.
Fine tuning of s.a.w. resonators using argon ion bombardment
- Author(s): S. James and I.H. Wilson
- Source: Electronics Letters, Volume 15, Issue 21, p. 683 –684
- DOI: 10.1049/el:19790485
- Type: Article
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p.
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–684
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High-energy (40 to 240 keV) argon ion beams have been used for fine tuning of the stop/passband frequency (nominally 157 MHz) of Al/quartz Rayleigh wave transmission filters. An increase in frequency (accompanied by a reduction in impedance ratio) occurred for high ion energies and low ion doses, where the dominant effect appears to be amorphisation of the quartz surface with a reduction in mass loading due to swelling. The frequency shift was+120 kHz per 100 keV of bombarding ion energy for an ion dose of 1.5×1016 ions/cm2. A decrease in frequency occurred for low ion energies and high ion doses caused by the difference in sputtering rate between the quartz and the Al digits. The frequency shift in this case was −100 kHz for a dose of 1×1017 ions cm−2
Ray interpretation of the material signature in the acoustic microscope
- Author(s): W. Parmon and H.L. Bertoni
- Source: Electronics Letters, Volume 15, Issue 21, p. 684 –686
- DOI: 10.1049/el:19790486
- Type: Article
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p.
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The output voltage of the reflection acoustic microscope depends on the location on the object surface in a way that is characteristic of its elastic properties. We present a ray model showing that this dependence is due to interference between a narrow bundle of axial rays and rays associated with the leaky Rayleigh wave excited on the surface.
Effect of chromatic dispersion on pulses of arbitrary coherence
- Author(s): D. Gloge
- Source: Electronics Letters, Volume 15, Issue 21, p. 686 –687
- DOI: 10.1049/el:19790487
- Type: Article
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p.
686
–687
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Chromatic signal distortion in fibre waveguides depends on the coherence of the optical carrier. The theory derived here covers carriers of arbitrary coherence and arbitrary dispersion characteristics. It gives simple estimates for the available signal bandwidth.
Groove-guide connection losses at 100 GHz
- Author(s): D.J. Harris and Y.M. Choi
- Source: Electronics Letters, Volume 15, Issue 21, p. 687 –688
- DOI: 10.1049/el:19790488
- Type: Article
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p.
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–688
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Sections of groove guide can be simply connected together with a loss of less than 0.2 dB even at 100 GHz. A gap of up to 1 mm between the sections introduced an additional loss of only about 0.1 dB and alignment tolerances needed to be no better than ±0.5 mm.
Novel capacitor floatation scheme
- Author(s): D. Patranabis and A.N. Paul
- Source: Electronics Letters, Volume 15, Issue 21, p. 688 –689
- DOI: 10.1049/el:19790489
- Type: Article
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p.
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–689
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An earlier suggested ideal floating inductor realisation circuit is extended to a capacitor floatation scheme with the addition of only one operational amplifier. Appropriate comments regarding practical realisability of both floating capacitor and inductor are appended.
Pumped Schottky diodes with noise temperatures of less than 100 K at 115 GHz
- Author(s): Nigel J. Keen ; William M. Kelly ; Gerard T. Wrixon
- Source: Electronics Letters, Volume 15, Issue 21, p. 689 –690
- DOI: 10.1049/el:19790490
- Type: Article
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p.
689
–690
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New Schottky-barrier diodes, with an epitaxial layer thickness of < 1000 Å and doping 2.5×1016 cm−3, yield a mixer noise temperature of 98 K at 115 GHz. The diodes have a diameter of 1.8 μm, and show repeatable performance. Measurements indicate negligible capacitance variation to at least +0.2 V. The noise temperature is competitive with values reported for Josephson and quasiparticle junctions.
Minimisation of incompletely specified sequential machines: the ‘really’ excluded compatibility classes
- Author(s): G. Palama and G.V. Russo
- Source: Electronics Letters, Volume 15, Issue 21, p. 690 –691
- DOI: 10.1049/el:19790491
- Type: Article
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The known methods for the minimisation of incompletely specified sequential machines do not take into consideration the number of unspecified entries in the flow-table of the minimal machine. In this note, we show that the prime compatibility classes (following the definition of Grasselli and Luccio) do not allow such an additional condition. Here we give a more complete definition of the excluded compatibility classes and a method for deriving them.
System reduction by Routh approximation and modified Cauer continued fraction
- Author(s): John Sarasu and R. Parthasarathy
- Source: Electronics Letters, Volume 15, Issue 21, p. 691 –692
- DOI: 10.1049/el:19790492
- Type: Article
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p.
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–692
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An algorithm is proposed for obtaining stable reduced-order models using Routh stability criterion and matching moments and Markov parameters, via the modified Cauer continued fraction.
Insensitive grounded-capacitor simulation of grounded inductors using current conveyors
- Author(s): R. Nandi
- Source: Electronics Letters, Volume 15, Issue 21, p. 693 –694
- DOI: 10.1049/el:19790493
- Type: Article
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p.
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Two new schemes for grounded-inductor simulation with single grounded capacitors using the second-generation current conveyors (c.c. II) are reported. The realised inductors L and their quality factors Q can be independently adjusted and hence are suitable for high-quality applications. L and Q are shown to be quite stable and are practically insensitive to the changes in the active c.c. II parameters.
Comparison of GaAs IMPATT designs for 20 GHz
- Author(s): J.J. Berenz ; M. Vichr ; F.B. Fank
- Source: Electronics Letters, Volume 15, Issue 21, p. 694 –695
- DOI: 10.1049/el:19790494
- Type: Article
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p.
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GaAs IMPATT diodes have been developed to deliver high c.w. powers in K-band. Single-drift and double-drift flat profile and single-drift Read profile designs have been evaluated. The highest conversion efficiencies were obtained with the high/low Read doping profile. A maximum c.w. power of 3.1 W has been measured at 19.6 GHz with 18.6% efficiency for these devices.
Temperature dependence of InGaAsP double-heterostructure laser characteristics
- Author(s): R.E. Nahory ; M.A. Pollock ; J.C. DeWinter
- Source: Electronics Letters, Volume 15, Issue 21, p. 695 –696
- DOI: 10.1049/el:19790495
- Type: Article
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p.
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We report the temperature dependence of threshold for InGaAsP d.h. lasers with wavelengths from 1.23 to 1.53 μm. Our results suggest that a recombination centre, rather than carrier leakage, is responsible for the temperature sensitivity of the thresholds.
Signal-processing operations on A-law companded speech
- Author(s): P. Bylanski
- Source: Electronics Letters, Volume 15, Issue 21, p. 697 –698
- DOI: 10.1049/el:19790496
- Type: Article
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p.
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A method of multiplication and accumulation of A-law companded numbers for signal processing of speech is presented. It is based on conversion of A-law to scientific notation and results in efficient hardware implementation.
Alternative realisations of switched-capacitor floating inductors
- Author(s): U.W. Brugger and B.J. Hosticka
- Source: Electronics Letters, Volume 15, Issue 21, p. 698 –699
- DOI: 10.1049/el:19790497
- Type: Article
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p.
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Several switched-capacitor circuits simulating grounded and floating inductors have been published recently. Several alternative realizations are presented of s.c. inductors using one operational amplifier, which can be derived from a configuration reported previously.
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