25-08-2016, 11:43 AM
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Abstract:-
This paper reflects the computer-based method to calculate the parasitic series resistance Rs for Ku-band packaged IMPATT diode for 4H-SiC and Diamond© from small signal conductance-susceptance characteristics. The calculation of parasitic series resistance Rs has been done at the threshold condition when the small signal conductance of the packaged diode just becomes negative and the device susceptance becomes positive. Rsfor 4H-SiCand Diamond is calculated and compared for Ku band frequency.
Introduction:-
The oscillation in IMPATT diode is due to its negative resistance. Crucial device parameter that limits the output power to RF circuit and efficiency of an IMPATT diode is its parasitic series resistance (Rs) [17].In this paper author has concentrated on RF output power. As the negative resistance that develops in an IMPATT diode is very small thus the positive series resistance (Rs) should not cross the value of the negative resistance, otherwise the oscillations will cease or stop. The parasitic positive series resistance of an IMPATT diode come into existence due to the substrate, the metal semiconductor contact, undepleted epitaxial layer and a small part arise from device package. Thus an appropriate technology is required to reduce the value of this positive resistance, so that the oscillation can sustain and maximum output power can result from the oscillator.
Estimation of Series Resistance (Rs) Numerically:-
The circuit shown in the Fig. 1 [14] below represent equivalent circuit for IMPATT diode Where, G and B represent the diode conductance and susceptance respectively. We can determine the magnitudes of G and B from simulation by using values of ionization rate and drift velocities of charge carriers for 4H-Sic and Diamond taken from[20-22]. Rs is the series resistance of the device, g is the load conductance and L is the circuit inductance. Cp and Lp are the package capacitance and package inductance respectively. By using [8] Impedance of the packaged device is given,
Computer Based DC and Small Signal Analysis:-
A generalise DDR (n+ n p p+ type ) IMPATT diode has been designed for operation in Ku-band, through double iterative dc and small signal computer analysis. The following assumptions are made in dc and small signal computer analysis of IMPATT diodes [9-10]. (a) One dimensional model of the p-n junction has been considered, (b) The electron and hole velocities have been taken to be saturated and independent of the electric field throughout the space charge layer, and © Carrier diffusion has been neglected. In this method the computation starts from the field maximum near the metallurgical junction. The distribution of the electric field and carrier currents in the depletion layer are obtained by the double-iterative computer method, which involves iteration over the magnitude of field maximum and its location in the depletion layer. The method is used for a simultaneous solution of Poisson and Carrier continuity equations