Mar 30, 1992 - ments in GaAs FETs is presented. Apparatus and methodical provision for the nondestructive control of the isothermal current instability and ...
Reference 3, Fig. 2d). The circuit has been tested using the current conveyor realisation of Huertas [4]. Although this current conveyor realisation is imperfect, highly stable, good quality oscillations have been successfully obtained. An alternative oscillator circuit can be derived from that of Fig. la by replacing all resistors by capacitors and vice versa [3]. In this version, shown in Fig. \b, the frequency and the condition of oscillation are given, respectively, by
2C 3 C 4
(1)
and (2) Thus the frequency of oscillation is independently adjustable through a single variable capacitor C 4 . 30th March 1992 M. T. Abuelma'atti (King Fahd University of Petroleum and Minerals, Box 203, Dhahran 31261, Saudi Arabia)
(5) The nonlinear internal mechanism of the current mirrors ensures the existence of a stable limit cycle. (6) The self-start is guaranteed for a value of R2 (see Fig. 1 in Reference 1) slightly lower than its nominal value. (7) The minimum distortion must be adjusted at the higher frequency of the full span to guarantee oscillating behaviour. These above seven points summarise the ideas reported in Reference 1. Obviously, such considerations must be taken into account in any practical design. 1st June 1992 S. Celma, P. Martinez and A. Carlosena (Universidad de Zaragoza, Dpto de Ingenieria Electrica e Informatica, Ciudad Universitaria, E-50009 Zaragoza, Spain) Reference 1
CELMA, s., MARTINEZ, P., and CARLOSENA, A.: 'Minimal realisation
for single resistor oontrolled sinusoidal oscillator using a single CCIF, Electron. Lett., 1992, 28, (5), pp. 443-444
References 1
CELMA, s., MARTINEZ, P. A., and CARLOSENA, A.: 'Minimal realisation
for single resistor controlled sinusoidal oscillator using single CCII\ Electron. Lett., 1992, 28, pp. 443-444 2
ABUELMA'ATTI, M. T., and HUMOOD, N. A.: 'Current-conveyor sine-
wave oscillators', Electronics & Wireless World, March 1988, 94, (1625), pp. 282-284 3
ISOTHERMAL CURRENT INSTABILITY AND LOCAL BREAKDOWN IN GaAs FET N. A. Kozlov, V. F. Sinkevitch and V. A. Vashchenko
ABUELMA'ATTI, M. T., and HUMOOD, N. A.: 'New low-component
single current-conveyor RC oscillators'. Proc. Int. AMSE Conf. 'Modelling & Simulation', Istanbul, Turkey, 29th June-lst July 1988, Vol. 2B, pp. 9-18 4 HUERTAS, j . L. : 'Circuit implementation of current conveyor', Electron. Lett., 1980,16, pp. 225-226
REPLY The authors regret the unintentional omission of two related References by Abuelma'atti in their Letter [1] and appreciate his Comment. The oscillator proposed in Reference 1 has been independently obtained by the authors from an original synthesis procedure. We do recognise that we were not aware that the oscillator in question had been reported in the literature. In any case, the aim of our work was to demonstrate the characteristics and the performance of a practical implementation of a CCII SRCO rather than merely claim the novelty of a circuit. The authors would like to take this opportunity to mention some relevant aspects of the proposed oscillator that Abuelma'atti did not mention in his papers. These features motivated the choice of this structure out of a wider catalogue. (1) The CCII is biased in its linear range and the structure is a latch-up free sinusoidal oscillator circuit. (2) The structure in question corresponds to a single resistor controlled sinusoidal oscillator (SRCO). (3) The circuit is truly canonic, and uses the minimum number of resistors and capacitors for realising a second order RC active VFO. (4) The configuration has the property of independent control of oscillation frequency and oscillation condition using two single resistors. Moreover, the following are some peculiarities of the practical realisation exclusively based on a voltage opamp with supply current sensing: ELECTRONICS LETTERS 18th June 1992 Vol. 28 No. 13
Indexing terms: Field-effect transistors, Semiconductor devices and materials Results of experimental observations of the S-shaped I-V characteristic and current avalanche injection isothermal filaments in GaAs FETs is presented. Apparatus and methodical provision for the nondestructive control of the isothermal current instability and irreversible breakdown of the FET are proposed.
It was established [1] that the irreversible breakdown of GaAs FETs during an active operation takes place as result of 50 ns drain-source voltage pulses. The authors suggested that this phenomenon is caused by increase of drain current in the isothermal-mode of avalanche injection resulting in the heating of the structure, local thermal breakdown and consequent FET structure destruction. However a clear picture of this phenomenon and the evidence for the leading role of avalanche injection in the irreversible breakdown of the FET are absent. Nevertheless, to date no experimental observation of the S-shaped I-V characteristic and isothermal current filaments in GaAs FETs has been presented. This Letter is devoted to the solution of the above problem. GaAs Schottky gate FETs of various types and test structures with gate widths from 0 1 5 to 10-8 mm were studied. Using modified methods [2, 3] the output pulse I-V characteristics in a common drain circuit at a generator pulse duration of 20 ns were measured. The voltage generator pulses of rectangular waveforms of high relative pulse duration were applied to the transistor drain, which maintained a constant gate bias Ugs (Fig. la). To control the electroluminescence intensity distribution over the crystal surface under pulsed conditions a scanner of 1 fim space resolution was used. The scanner comprised a slit optical microscope and photomultiplier tube [4] with SS-20 photocathode sensitive to the 0-4-0-9 /im wavelength band. The electroluminescence intensity was indicated by optical bandpass filters in two wavelength bands: near infra-red (0-81-2;im) and visible light (0-4-0-7/im). The first band allows the recombination radiation of electrons and holes, not heated by field to be recorded, and the second luminescence of carriers, heated by an intensive electric field. It was established that the FET pulsed I-V characteristic (drain current Id and drain-source voltage Uds dependence measured at the pulse end at constant gate-source voltage) was S-shaped (Fig. \b). As voltage Uds was increased, before
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