Online ISSN
1350-911X
Print ISSN
0013-5194
Electronics Letters
Volume 29, Issue 8, 15 April 1993
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Volume 29, Issue 8
15 April 1993
Monolithic integration of InGaAsp/Inp lasers and heterostructure bipolar transistors by selective area epitaxy
- Author(s): X. An ; H. Temkin ; A. Feygenson ; R.A. Hamm ; M.A. Cotta ; R.A. Logan ; D. Coblentz ; R.D. Yadvish
- Source: Electronics Letters, Volume 29, Issue 8, p. 645 –646
- DOI: 10.1049/el:19930432
- Type: Article
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The Letter describes the use of selective area epitaxy to prepare monolithically integrated lasers and heterostructure bipolar transistors based on InGaAsP/InP. Selective growth offers a versatile method of lateral integration of structurally dissimilar devices with the different device structures grown side by side in different growth cycles. Individual devices can be optimised separately without any performance compromise. Bipolar transistors grown on the semi-insulating current blocking layers of the buried heterostructure lasers show high gain, high breakdown voltage and excellent high current stability. Laser threshold is reached at a base current as low as 160μA and the light output is linear with current to 10mW.
Frequency modulation locking in 980 nm strained quantum well lasers
- Author(s): S.R. Chinn ; C.A. Wang ; G.A. Evans
- Source: Electronics Letters, Volume 29, Issue 8, p. 646 –648
- DOI: 10.1049/el:19930433
- Type: Article
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The fundamental and second-harmonic spectral characteristics of frequency modulation locking have been observed in strained-layer InGaAs quantum well Fabry-Perot ridge-waveguide lasers emitting at 980 nm.
60 GHz reflection gain based on superlattice negative differential conductance
- Author(s): M. Hadjazi ; J.F. Palmier ; A. Sibille ; H. Wang ; E. Paris ; F. Mollot
- Source: Electronics Letters, Volume 29, Issue 8, p. 648 –649
- DOI: 10.1049/el:19930434
- Type: Article
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The negative differential conductance originating from miniband negative effective mass has been characterised at high frequencies in two GaAs/AlAs superlattice devices. High reflection gains reaching 10 dB at 38 GHz have been observed up to 60 GHz. These results demonstrate the excellent potentialities of superlattices for millimetre-wave oscillator applications.
Medical ultrasound imaging using pulse compression
- Author(s): N. Rao and S. Mehra
- Source: Electronics Letters, Volume 29, Issue 8, p. 649 –651
- DOI: 10.1049/el:19930435
- Type: Article
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Pulse compression techniques can play a major role in improving image quality in medical ultrasound. A prototype imaging and digital signal processing system incorporating this technique is described. Feasibility studies were performed and system resolution was evaluated with experiments on tissue mimicking phantoms.
Thermal stability of Al/AlGaAs and Al/GaAs/AlGaAs (MBE) Schottky barriers
- Author(s): A. Bosacchi ; S. Franchi ; E. Gombia ; R. Mosca ; F. Fantini ; S. Franchi ; R. Menozzi
- Source: Electronics Letters, Volume 29, Issue 8, p. 651 –653
- DOI: 10.1049/el:19930436
- Type: Article
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Outstanding stability has been observed in and Al/GaAs/AlxGa1−xAs (x = 0.25) Schottky barriers prepared by depositing Al in situ by MBE on annealing up to 400°C. Conventionally evaporated barriers have been fabricated and compared with epitaxial ones. The changes in barrier height and ideality factor induced by annealing are reported.
Defect level for non-equiprobable faults in digital ICs
- Author(s): F. Corsi ; D. Del Console ; C. Marzocca
- Source: Electronics Letters, Volume 29, Issue 8, p. 653 –654
- DOI: 10.1049/el:19930437
- Type: Article
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Common measures of test efficiency are the fault coverage and the defect level for a given product yield. An extension of the well known formula relating these three quantities to the case of general non-equiprobable faults has been derived by exploiting the concept of critical area. This also leads to a more meaningful definition of fault coverage.
AlGaInP/GaInAs strained quantum well lasers
- Author(s): I. Yoshida ; T. Katsuyama ; J. Hashimoto ; H. Hayashi
- Source: Electronics Letters, Volume 29, Issue 8, p. 654 –655
- DOI: 10.1049/el:19930438
- Type: Article
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AlGaInP cladding layers have been applied for the first time to GaInAs strained quantum well lasers oscillating around 0.98μm. The device has lower threshold current and larger T0 than a device with GaInP cladding layers. This was expected from a larger bandgap difference between active and cladding layers.
Distributed amplifier signal shaping strategy for multigigabit digital optical transmission
- Author(s): P.M.R.S. Moreira ; I.Z. Darwazeh ; J.J. O'Reilly
- Source: Electronics Letters, Volume 29, Issue 8, p. 655 –657
- DOI: 10.1049/el:19930439
- Type: Article
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A novel technique is presented for using the distributed amplifier (DA) as an active pulse shaping/filtering network by effectively constructing a transversal filter. This technique is versatile, and judicious selection of the effective stage delays and gains allows a variety of filtering functions to be implemented. The capability of the technique is illustrated with reference to a GaAs MMIC design for 10 Gbit/s.
Analysis of a reflectarray antenna using microstrip patches of variable size
- Author(s): D.M. Pozar and T.A. Metzler
- Source: Electronics Letters, Volume 29, Issue 8, p. 657 –658
- DOI: 10.1049/el:19930440
- Type: Article
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Microstrip reflectarrays tyically use tuning stubs on each element to adjust the phase of the reflected field. This Letter describes a new approach in which the need for tuning stubs is eliminated and phase control is achieved simply by adjusting the resonant length of the patch elements. The advantages of this approach are described, as are a full-wave analysis technique for computing the phase of the reflected field as a function of patch size and a design curve giving the change in patch size for a desired reflected field phase shift.
Multigigabit/s pulse source based on the switching of an optical beat signal in a nonlinear fibre loop mirror
- Author(s): S.V. Chernikov and J.R. Taylor
- Source: Electronics Letters, Volume 29, Issue 8, p. 658 –660
- DOI: 10.1049/el:19930441
- Type: Article
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A novel technique for the generation of a high repetition rate train of transform-limited pulses is demonstrated. A 32 GHz train of 4.2 ps pulses has been generated.
1-W CW Tm-doped fluoride fibre laser at 1.47μm
- Author(s): Y. Miyajima ; T. Komukai ; T. Sugawa
- Source: Electronics Letters, Volume 29, Issue 8, p. 660 –661
- DOI: 10.1049/el:19930442
- Type: Article
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A 1W CW Tm-doped fluoride fibre laser operating at 1.47 μm and using an upconversion pump scheme is demonstrated. The pump source is an LD pumped Nd : YAG laser operating at 1.064μm. The threshold and slope efficiency are 175mW and 29%, respectively. Tunable operation from 1.445 to 1.51μm is observed.
Effective bandwidth of DSPN signalling for mitigation of fading in dense scatterers
- Author(s): F. Amoroso
- Source: Electronics Letters, Volume 29, Issue 8, p. 661 –662
- DOI: 10.1049/el:19930443
- Type: Article
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The use of direct sequence pseudonoise (DSPN) signalling to mitigate the fading caused by very dense scatterers in the mobile communication environment is explored for the specific case of a rectangular signal spectrum. A very simple and revealing relationship emerges between the variability of the signal strength and the signal bandwidth.
Self-assembly of three-dimensional microstructures using rotation by surface tension forces
- Author(s): R.R.A. Syms and E.M. Yeatman
- Source: Electronics Letters, Volume 29, Issue 8, p. 662 –664
- DOI: 10.1049/el:19930444
- Type: Article
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The authors propose that automatic, parallel and selflimiting operations can be performed to reconfigure microstructures into full three-dimensional geometries, using the surface tension forces provided by molten solder to perform out-of-plane rotation of flexible hinges. Analysis is presented which indicates that the final angle of rotation can be controlled through initial solder volume, and that the forces are easily sufficient for the particular example of silicon micromechanical devices. However, the principle is general and could be applied to other materials.
Broadly tunable InGaAsP/InP vertical-coupler filtered laser with low tuning current
- Author(s): I. Kim ; R.C. Alferness ; L.L. Buhl ; U. Koren ; B.I. Miller ; M.A. Newkirk ; M.G. Young ; T.L. Koch ; G. Raybon ; C.A. Burrus
- Source: Electronics Letters, Volume 29, Issue 8, p. 664 –666
- DOI: 10.1049/el:19930445
- Type: Article
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A tuning range of 48 nm has been achieved with a tuning current of only 40mA in a 1.55μm InGaAsP/lnP multiquantum-well laser based on a grating-assisted vertical coupler intracavity filter. Using a combination of current and voltage tuning, a 55 nm tuning range was demonstrated.
High-performance InP/InGaAs heterojunction bipolar transistors with highly carbon-doped base grown by chemical beam epitaxy
- Author(s): J.-I. Song ; C.J. Palmstrom ; B.P. Van der Gaag ; W.-P. Hong ; J.R. Hayes ; K.B. Chough
- Source: Electronics Letters, Volume 29, Issue 8, p. 666 –667
- DOI: 10.1049/el:19930446
- Type: Article
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InP/In0.53Ga0.47As heterojunction bipolar transistors (HBTs) using a highly carbon-doped base are reported. High carbon doping has been achieved by chemical beam epitaxy (CBE). The resulting hole concentration in the carbon-doped base is as high as 7 × 1019/cm3. To our knowledge, this is the highest doping level reported using carbon. HBTs with 20 Å spacer layer exhibited nearly ideal I-V characteristics with collector and base current ideality factor of 1.018 and 1.037, respectively. Current gain and breakdown voltage BVCEO were 7 and 6 V, respectively.
Temperature-tunable 3.5 μm fibre laser
- Author(s): H. Többen
- Source: Electronics Letters, Volume 29, Issue 8, p. 667 –669
- DOI: 10.1049/el:19930447
- Type: Article
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Use of a Peltier element permits adjustment of fibre temperature over the range 5–41°C, providing a tuning range of 30nm for the 3.5 μm laser. In this temperature range the laser emits nearly 1 mW at 130mW pump power.
CMOS on-chip clock for digital signal processors
- Author(s): P. Nilsson ; M Torkelson ; M. Vesterbacka ; L. Wanhammar
- Source: Electronics Letters, Volume 29, Issue 8, p. 669 –670
- DOI: 10.1049/el:19930448
- Type: Article
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An on-chip clock for frequencies up to 190 MHz is presented. This clock generator can be used for application specific digital signal processors which are clocked faster than the off-chip system clock. It is useful for both processors with a few cycles per sample or for high frequency bit-serial processors which need a large number of cycles.
Miniaturised two-stage balanced Ku-band CPW MMIC amplifier using impedance transforming couplers
- Author(s): M. Gillick ; I.D. Robertson ; J.S. Joshi
- Source: Electronics Letters, Volume 29, Issue 8, p. 670 –671
- DOI: 10.1049/el:19930449
- Type: Article
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A two-stage balanced Ku-band coplanar waveguide amplifier design is presented which has been miniaturised by using impedance transforming couplers which considerably reduce the required matching networks to the MESFETs. The amplifier, measuring only 2 × 1.7 mm2, exhibits a gain of 13.7dB with less than ±0.2dB of ripple over the range 14–16GHz.
Fabrication and performances of delta-doped Si n-MESFET grown by MBE
- Author(s): Q. Chen ; M. Willander ; J. Carter ; C.H. Thaki ; E.R.A. Evans
- Source: Electronics Letters, Volume 29, Issue 8, p. 671 –673
- DOI: 10.1049/el:19930450
- Type: Article
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The fabrication of an Sb delta-doped Si n-MESFET grown by molecular-beam epitaxy (MBE) and a low-energy Sb ion source is reported. The FETs have gate lengths of 2μm and showed a transconductance as high as 28 mS/mm and a gate breakdown voltage of 3.7–4.8 V.
Analysis of optical CDMA communications systems
- Author(s): K. Ben Letaief
- Source: Electronics Letters, Volume 29, Issue 8, p. 673 –674
- DOI: 10.1049/el:19930451
- Type: Article
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The Letter investigates the performance of direct-detection optical code division multiple access (CDMA) systems which employ avalanche photodiode (APD) detectors. In particular, an accurate and extremely computationally efficient importance sampling method for estimating the probability of bit error of such systems is presented.
Dynamic channel assignment with queuing in highway microcells
- Author(s): S.S. Kuek and W.C. Wong
- Source: Electronics Letters, Volume 29, Issue 8, p. 675 –676
- DOI: 10.1049/el:19930452
- Type: Article
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The effects of queuing on an ordered dynamic channel assignment with reassignment (QODCAR) scheme in a highway microcellular environment are studied. Results show that queuing improves channel use by ∼9–43%, and significantly lowers the probability of call failure.
Microwave noise characterisation of poly-emitter bipolar junction transistors
- Author(s): M.J. Deen and J.J. Ilowski
- Source: Electronics Letters, Volume 29, Issue 8, p. 676 –678
- DOI: 10.1049/el:19930453
- Type: Article
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The microwave noise characteristics of poly-emitter bipolar junction transistors have been evaluated in a 0.8μm silicon BiCMOS process, at frequencies between 1 and 5.6GHz, and for collector currents between 0.5 and 15mA. Using a small-signal model for the poly-emitter bipolar junction transistors, very good agreement has been obtained between measurements and calculations of both noise figure (FMIN) against frequency, and FMIN against collector current. It is found that FMIN was 2.3dB at 1 GHZ and 8.3dB at 5.6GHZ for a collector current of 5mA.
1047 nm laser diode master oscillator Nd:YLF power amplifier laser system
- Author(s): A.W. Yu ; M.A. Krainak ; G.L. Unger
- Source: Electronics Letters, Volume 29, Issue 8, p. 678 –679
- DOI: 10.1049/el:19930454
- Type: Article
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A master oscillator power amplifier (MOPA) laser transmitter system at 1047 nm wavelength using a semiconductor laser diode and a diode pumped solid state (Nd : YLF) laser (DPSSL) amplifier is described. A small signal gain of 23 dB, a near diffraction limited beam, 1 Gbit/s modulation rates and >0.6 W average power are achieved. This MOPA laser has the advantage of amplifying the modulation signal from the laser diode master oscillator (MO) with no signal degradation.
Coaxial feed in uniaxial substrate between two finite parallel conductors
- Author(s): G.A.E. Vandenbosch and A.R. van de Capelle
- Source: Electronics Letters, Volume 29, Issue 8, p. 679 –681
- DOI: 10.1049/el:19930455
- Type: Article
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A coaxial feed located in a uniaxial substrate between two finite parallel conductors is reduced analytically into a finite number of voltage sources over the coaxial probe. The procedure used is the same as originally developed for an isotropic substrate. The resulting expressions for both the new sources and the separated admittance component are interpreted by comparison with the isotropic case.
Method for automated waveform analysis of transient responses in digital circuits
- Author(s): S. Simovich ; P.D. Franzon ; M.B. Steer
- Source: Electronics Letters, Volume 29, Issue 8, p. 681 –682
- DOI: 10.1049/el:19930456
- Type: Article
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A simple but powerful computer-aided technique is presented for the waveform analysis of transient responses in digital circuits. The technique is targeted towards automatic simulation-based timing and signal integrity analysis and design of digital circuits and interconnects.
Modified packet reservation multiple access protocol
- Author(s): K.C. Chua and W.M. Tan
- Source: Electronics Letters, Volume 29, Issue 8, p. 682 –684
- DOI: 10.1049/el:19930457
- Type: Article
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A modified packet reservation multiple access (PRMA) protocol is proposed to minimise premature loss of reservations when the protocol operates in real radio channels where noise and fading errors are prevalent. The proposed protocol is shown to yield significant improvements in performance over PRMA in the presence of channel fading errors.
Long wavelength quantum well lasers with InGaAs/InP superlattice optical confinement and barrier layers
- Author(s): A. Ginty ; J.D. Lambkin ; L. Considine ; W.M. Kelly
- Source: Electronics Letters, Volume 29, Issue 8, p. 684 –685
- DOI: 10.1049/el:19930458
- Type: Article
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Long wavelength, separate confinement heterostructure, ridge waveguide laser diodes using InGaAs/InP short period superlattices and InGaAs quantum wells have been demonstrated. The short period superlattices replace the more conventional quaternary alloys. These lasers have threshold current densities of 1.9kA/cm2, device efficiencies of 0.16mW/mA and a characteristic temperature T0 of 56 K.
Multichannel coherent FSK transmission at 622 Mbit/s with synchronous intra-bit sinusoidal polarisation spreading
- Author(s): N. Caponio ; J. Zhou ; F. Delpiano ; P. Gambini ; M. Puleo ; V. Seano ; E. Vezzoni
- Source: Electronics Letters, Volume 29, Issue 8, p. 685 –687
- DOI: 10.1049/el:19930459
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The feasibility of polarisation insensitive multichannel coherent FSK transmission with synchronous intra-bit sinusoidal polarisation spreading has been experimentally demonstrated at 622 Mbit/s for the first time, complying with a front-end bandwidth of 3.2 GHz. Results evidenced an optimum IF filter bandwidth of four times the bit rate, and a minimum channel spacing of 11 GHz.
Proposal of new ring access control and connection admission control method
- Author(s): K. Kubota ; H. Yokota ; T. Tanaka
- Source: Electronics Letters, Volume 29, Issue 8, p. 687 –688
- DOI: 10.1049/el:19930460
- Type: Article
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A new ring access control method is proposed for an ATM ring network. In this method, higher priority traffic which requires strict quality of service can be transmitted with no cell loss, by executing connection admission control. Lower priority traffic is transmitted using that part of the bandwidth not used for higher priority traffic. In this way, ring use is improved. A simulation is used to demonstrate these characteristics.
Improvement of bidirectional associative memories by using correlation significance
- Author(s): D.-L. Lee and W.-J. Wang
- Source: Electronics Letters, Volume 29, Issue 8, p. 688 –690
- DOI: 10.1049/el:19930461
- Type: Article
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A correlation significance technique is introduced, which uses the significances between the training associations and between the neurons of the different fields, such that the storage capacity of Kosko bidirectional associative memories (BAMs) is improved. Based on the gradient descent method, an error function is constructed such that the maximal number of stored associations which are successfully recalled can be obtained. Finally computer simulations demonstrate that the proposed method has much better storage capacity than the existing methods.
Millimetre wave fibre-optic PSK subcarrier transmission at 35 GHz over 6.3 km using a grating external cavity semiconductor laser
- Author(s): S. Levy ; R. Nagarajan ; R.J. Helkey ; P. Humphrey ; J.E. Bowers
- Source: Electronics Letters, Volume 29, Issue 8, p. 690 –691
- DOI: 10.1049/el:19930462
- Type: Article
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10−9 bit error rates have been achieved over a distance of 6.3 km in a millimetre wave fibre-optic phase shift keying subcarrier transmission system operating at 35 GHz for a 40 Mbit/s narrowband digital signal. Using a grating in the external cavity for wavelength control, the transmission distance was extended from 200 m to 6.3 km.
Integrated optic laser emitting at 906, 1057, and 1358 nm
- Author(s): K.J. Malone ; N.A. Sanford ; J.S. Hayden
- Source: Electronics Letters, Volume 29, Issue 8, p. 691 –693
- DOI: 10.1049/el:19930463
- Type: Article
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Laser oscillation at 906, 1057, and 1358 nm has been achieved in the same neodymium-doped-glass integrated optic laser. This is believed to be the first report of a 906 nm integrated optic laser. High slope efficiency and high output power were observed at 1057 nm. The laser was fabricated by silver ion exchange in a phosphate glass.
Neural learning in analogue hardware: effects of component variation from fabrication and from noise
- Author(s): B.K. Dolenko and H.C. Card
- Source: Electronics Letters, Volume 29, Issue 8, p. 693 –694
- DOI: 10.1049/el:19930464
- Type: Article
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Simulations of backpropagation networks in analogue circuitry with on-chip learning are presented. Forward and backward computations are performed using Gilbert multipliers. Component variations fixed in fabrication are shown to be adapted to and tolerated much better than similar variations due to noise.
Achievable performance of autonomous SIR-based power control
- Author(s): S. Ariyavisitakul
- Source: Electronics Letters, Volume 29, Issue 8, p. 694 –696
- DOI: 10.1049/el:19930465
- Type: Article
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The Letter investigates the achievable performance in a TDMA system of an autonomous power control technique which relies only on a simple fixed-step feedback adjustment algorithm. Simulation results indicate that this simple power control technique can perform nearly as well as ideal signal-to-interference ratio (SIR) balancing/call removal, yielding a possible increase in spectrum efficiency of at least three times compared to a system without power control. The work is targeted towards understanding the traffic capacity and deployment implications to local exchange networks of wireless technology that could provide access to those networks.
1/f noise and interface trap density in high field stressed pMOS transistors
- Author(s): J.L. Todsen ; P. Augier ; R.D. Schrimpf ; K.F. Galloway
- Source: Electronics Letters, Volume 29, Issue 8, p. 696 –697
- DOI: 10.1049/el:19930466
- Type: Article
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Experimental results for pMOS transistors subjected to high field stressing are reported. 1/f noise and interface trap density increase with stress time. A direct relationship between the increase in1/f noise and interface trap density during the high field stressing is observed.
PRMA efficiency in adaptive transceivers
- Author(s): L. Hanzo ; J.C.S. Cheung ; R. Steele
- Source: Electronics Letters, Volume 29, Issue 8, p. 697 –699
- DOI: 10.1049/el:19930467
- Type: Article
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The effects of different speech source rates and various number of modulation levels on packet reservation multiple access (PRMA) efficiency in an adaptive transceiver are investigated under the constraint of fixed channel bandwidth and benign cochannel interference in office type cordless telecommunications (CT) environments. The number of PRMA users supported in a 200 kHz frequency slot ranges from 17 to 103, the required user bandwidth is between 11.8 and 1.94 kHz, and the number of PRMA users per slot is between 1.7 and 1.94, respectively.
Processing of specular echoes from planar reflectors in airborne sonar data
- Author(s): A.M. Sabatini
- Source: Electronics Letters, Volume 29, Issue 8, p. 699 –700
- DOI: 10.1049/el:19930468
- Type: Article
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Airborne ultrasound sensing techniques are widely used for obtaining range information. Research is being carried out to extend the measuring capabilities of sonar ranging systems. The results of an investigation are presented aimed at understanding how a single transducer can be used for estimating the inclination angle of a specular planar reflector.
Low threshold-current, wide tuning-range, butt-joint DBR laser grown with four MOVPE steps
- Author(s): B. Stoltz ; M. Dasler ; O. Sahlén
- Source: Electronics Letters, Volume 29, Issue 8, p. 700 –702
- DOI: 10.1049/el:19930469
- Type: Article
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InGaAsP/InP butt-joint, buried-heterostructure DBR lasers, with 8 mA threshold current at T = 293 K. have been developed, using electron-beam lithography and a four-step MOVPE process with a semi-insulating Fe : InP current-blocking structure. Packaged devices give 5 mW fibre-coupled power. The maximum tuning range is 9.1 nm. The 3 dB modulation bandwidth is 9 GHz.
Bit-rate flexible all-optical demultiplexing using a nonlinear optical loop mirror
- Author(s): D.M. Patrick ; A.D. Ellis ; D.M. Spirit
- Source: Electronics Letters, Volume 29, Issue 8, p. 702 –703
- DOI: 10.1049/el:19930470
- Type: Article
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The nonlinear optical loop mirror is shown to be capable of demultiplexing 20 Gbit/s pulses from a continuous 40 Gbit/s data stream. Bit error rate measurements are presented for a demultiplexed 10Gbit/s channel, and the sensitivity of the error rate to timing jitter between the signal and clock pulses is examined. Bit-rate flexible demultiplexing can be achieved.
Adaptive speech coding with DCT and neural net vector quantisation
- Author(s): L.V. Veleva and R.K. Kunchev
- Source: Electronics Letters, Volume 29, Issue 8, p. 704 –705
- DOI: 10.1049/el:19930471
- Type: Article
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A hybrid method for speech coding is presented based on the discrete cosine tranform (DCT) and neural net vector quantisation (NNVQ). The neural networks are trained off-line using a two stage learning algorithm. During the encoding process, neural net adaptation is carried out. Simulation results show a high compression factor and SNR.
Direct comparison of InGaAs/InGaAlAs and InGaAs/InGaAsP quantum well modulators
- Author(s): B.J. Hawdon ; T. Tütken ; A. Hangleiter ; R.W. Glew ; J.E.A. Whiteaway
- Source: Electronics Letters, Volume 29, Issue 8, p. 705 –707
- DOI: 10.1049/el:19930472
- Type: Article
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Using picosecond pump-probe measurements, InGaAs/ InGaAlAs and InGaAs/InGaAsP quantum well modulator structures are compared directly. It is found that the shortpulse exciton saturation intensity for the Al-based structure is at least 10 times that for the P-based system. The more efficient carrier sweep-out observed in the Al-based modulator is due to the lower valence-band discontinuity, making it by far the more attractive structure for high-power applications.
Hydrogenated amorphous silicon-carbide thin-film light-emitting diode with quantum-well-injection structure
- Author(s): T.-S. Jen ; J.-Y. Chen ; N.-F. Shin ; J.-W. Hong ; C.-Y. Chang
- Source: Electronics Letters, Volume 29, Issue 8, p. 707 –708
- DOI: 10.1049/el:19930473
- Type: Article
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To improve the electroluminescence (EL) intensity of the hydrogenated amorphous silicon carbide (a-SiC : H) pin thin-film light-emitting diode (TFLED), a quantum-well-injection (QWI) structure has been incorporated into the i-layer of an a-SiC : H pin TFLED at the p-i interface. The obtained brightness of this QWI TFLED is 256cd/m2 at an injection current density of 800mA/cm2, which is about three orders of magnitude higher than the brightness of an a-SiC : H pin TFLED. Also, a comparatively lower EL threshold voltage of 6 V was observed for this a-SiC : H QWI TFLED.
Determination of depth of proton exchanged layer in LiNbO3 from laser induced pyroelectric signals
- Author(s): S. Tuli and A.B. Bhattacharyya
- Source: Electronics Letters, Volume 29, Issue 8, p. 708 –710
- DOI: 10.1049/el:19930474
- Type: Article
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A new nondestructive technique for the determination of the depth of the proton exchanged (PE) layer in LiNbO3 is reported. The techniques relies on the difference in phase of measured pyroelectric voltages, induced by a modulated laser beam incident on the exchanged and unexchanged regions. Measurements of PE layer thickness in a Z-cut LiNbO3 sample have been corroborated by prevalent, more elaborate, optical characterisation techniques.
Narrow bandpass single layer frequency selective surfaces
- Author(s): A.C.de C. Lima and E.A. Parker
- Source: Electronics Letters, Volume 29, Issue 8, p. 710 –711
- DOI: 10.1049/el:19930475
- Type: Article
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Single layer arrays of convoluted slots are capable of giving passbands with fractional widths of less than 20% at the –10 dB points, less than a third of those for more conventional structures such as dipole arrays. The transmission curves and insertion loss of an illustrative example are discussed.
Complex modes in circular chirowaveguides
- Author(s): G. Busse and A.F. Jacob
- Source: Electronics Letters, Volume 29, Issue 8, p. 711 –713
- DOI: 10.1049/el:19930476
- Type: Article
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The dispersion equation for circular chirowaveguides is solved for frequencies below cutoff. It is shown that the propagation constants become complex. Some numerical examples are discussed.
Novel sub-100 nm thin film transistors
- Author(s): S. Franssila ; J. Paloheimo ; P. Kuivalainen
- Source: Electronics Letters, Volume 29, Issue 8, p. 713 –714
- DOI: 10.1049/el:19930477
- Type: Article
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A new method is introduced for fabricating metal electrodes for thin film field-effect transistors having a source to drain distance in the sub-100 nm range. The method is based on a liftoff process with sidewall spacers and it is demonstrated by fabricating sub-100 nm polymer transistors. These are to the authors' knowledge the smallest polymer transistors reported.
Formation of optical slab waveguides using thermal oxidation of SiOx
- Author(s): Q. Lai ; J. Schmid ; W. Hunziker ; H. Melchior ; P. Pliska
- Source: Electronics Letters, Volume 29, Issue 8, p. 714 –716
- DOI: 10.1049/el:19930478
- Type: Article
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A novel method for the fabrication of optical slab waveguides is presented. After growth of the base cladding by thermal oxidation and deposition of the core layer of the waveguide by PECVD of SiOx, the top cladding layer is formed from the core layer material by an additional thermal oxidation which transforms SiOx, into SiO2. With this simple technology, contaminations and rough interfaces between core and cladding are avoided. Low propagation losses and good matching to optical fibres are achieved.
Novel calibration technique employing a spread-spectrum tone for mobile satellite systems
- Author(s): G.E. Corazza ; C. Ferrarelli ; F. Vatalaro
- Source: Electronics Letters, Volume 29, Issue 8, p. 716 –718
- DOI: 10.1049/el:19930479
- Type: Article
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A calibration technique based on a low-power spread-spectrum tone to assist demodulation is presented. The technique does not impose any requirements on signal modulation, spectral shaping, nor on channel spacing, and is highly spectrum efficient. The performance is analysed in the presence of cochannel and adjacent channel interference, diffused-multipath fading and additive white Gaussian noise, and results are presented for M-PSK. (M = 2, 4, 8).
Optical pulse generation with high repetition rate by sinusoidally-driven InGaAs/InAIAs multiquantum well modulator
- Author(s): K. Wakita ; I. Kotaka ; O. Mitomi ; H. Asai ; M. Asobe
- Source: Electronics Letters, Volume 29, Issue 8, p. 718 –719
- DOI: 10.1049/el:19930480
- Type: Article
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A 20 GHz optical pulse train was generated by a sinusoidally-driven InGaAs/InAlAs multiquantum well intensity modulator operating at low voltages (from –2 to –3 V DC bias with a 3.2 V peak-to-peak RF signal). An approximately transform-limited optical pulse train width of 8ps and a spectral width of 40 GHz were obtained.
Design of three channel complementary filters as a weighted sum of two allpass sections
- Author(s): S.R. Pillai
- Source: Electronics Letters, Volume 29, Issue 8, p. 719 –721
- DOI: 10.1049/el:19930481
- Type: Article
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The design of power complementary filters for multichannel sub-bands using a minimum number of allpass sections is investigated. In particular it is shown that three power complementary niters, for example a lowpass, a bandpass and a highpass combination, can be generated from two allpass filters. From a hardware design point of view, these new power complementary structures are desirable, because the actual number of filters to be implemented is comparatively small.
Demonstration of all-optical demultiplexing at 1555 nm with an AlGaAs directional coupler
- Author(s): A. Villeneuve ; J.U. Kang ; G.I. Stegeman ; K. Al-Hemyari ; C.N. Ironside ; J.S. Aitchison
- Source: Electronics Letters, Volume 29, Issue 8, p. 721 –722
- DOI: 10.1049/el:19930482
- Type: Article
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All-optical demultiplexing of 500 fs pulses is demonstrated in an AIGaAs nonlinear directional coupler at 1.55 nm.
Low-threshold operation of tensile-strained GaInP/AlGaInP MQW LDs emitting at 625 nm
- Author(s): T. Tanaka ; H. Yanagisawa ; M. Takimoto ; S. Yano ; S. Minagawa
- Source: Electronics Letters, Volume 29, Issue 8, p. 722 –724
- DOI: 10.1049/el:19930483
- Type: Article
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A low threshold current of 47 mA at 20°C has been obtained in a tensile-strained index-guided AlGaInP LD emitting at 625nm, which has an active region consisting of five 8 nm-thick QWs with a lattice mismatch of −0.9%. It is shown that optimisation of the tensile-strained QW structure is very useful in improving the performance of AlGaInP LDs at wavelengths shorter than 630 nm.
Microwave power InP/InGaAs/InP double-heterojunction bipolar transistors
- Author(s): J.-I. Song ; W.-P. Hong ; R. Bhat ; K.B. Chough ; J.R. Hayes ; B. Sugeng ; C.J. Wei ; J.C.M. Hwang
- Source: Electronics Letters, Volume 29, Issue 8, p. 724 –725
- DOI: 10.1049/el:19930484
- Type: Article
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The first demonstration of the microwave power performance of an InP/InGaAs/InP double-heterojunction bipolar transistor (DHBT) is reported. A collector-emitter breakdown voltage in excess of 14 V was achieved with a current gain of 70. A maximum output power density of approximately 1 W/mm emitter length was measured at 5 GHz with a power gain of 8 dB. The results show the significant potential of InP based DHBTs for microwave power applications.
Erratum: Simple method for determining 3-D TLM nodal scattering in nonscalar problems
- Author(s): P. Naylor and R. Ait-Sadi
- Source: Electronics Letters, Volume 29, Issue 8, page: 726 –726
- DOI: 10.1049/el:19930485
- Type: Article
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Erratum: Circuit performance of low temperature CMOS polysilicon TFT operational amplifiers
- Author(s): H.-G. Yang ; P. Migliorato ; C. Reita ; S. Fluxman
- Source: Electronics Letters, Volume 29, Issue 8, page: 726 –726
- DOI: 10.1049/el:19930486
- Type: Article
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Erratum: Reduced intermodulation-free dynamic range in gain-lever lasers
- Author(s): L.D. Westbrook and C.P. Seltzer
- Source: Electronics Letters, Volume 29, Issue 8, page: 726 –726
- DOI: 10.1049/el:19930487
- Type: Article
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Erratum: Variable time delay of microwave signals using high dispersion fibre
- Author(s): S.T. Johns ; D.A. Norton ; D.W. Keefer ; R. Erdmann ; R.A. Soref
- Source: Electronics Letters, Volume 29, Issue 8, page: 726 –726
- DOI: 10.1049/el:19930488
- Type: Article
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