Investigation of Base Transport Mechanism in Silicon-Germanium Heterojunction Bipolar Transistor Operating over Wide Temperature Range

A high breakdown voltage silicon-germanium heterojunction bipolar transistor operated over a wide temperature range from 300 K to 10 K has been investigated. The measured Gummel characteristics illustrate that the collector current and base current both shift to the higher voltage as the temperature decreases. The fT/fmax are extracted to be 23/40 GHz at 300K, 28/40 GHz at 90 K, and 25/37GHz at 10K, respectively. The effective amplification range becomes narrow as the temperature decreases. And the ideality factor of base current in the low current region is shown to be temperature-dependent and its value is much larger than 2 at cryogenic temperatures. This phenomenon indicates that the base current is not only contributed by drift, diffusion, and Shockley-Read-Hall recombination, but also by trap-assisted tunneling. The Hurkx local trap-assisted tunneling has been used to analyze the non-ideal base transport mechanism. And a calibrated TCAD device model is developed to further verify this non-ideal transport mechanism.

Computation of Lightning Current from Electric Field Based on Laplace Transform and Deconvolution Method

A method for computation of the lightning channel base current from the corresponding vertical component of lightning electric field was presented. The algorithm was developed by applying Laplace transform. The lightning current was estimated from its deconvolution with a special transfer function. The transfer function includes information about geometry and physical properties of entire lightning impulse generation system. The method was verified for a Heidler-type base current and a MTLL model of its propagation within the lightning channel. Research was done for close, middle, and far distance to the lightning strike point. Optimum performance was obtained for the middle distance of several kilometers where the electrostatic, induction, and radiation components of the transfer function were of the same range. An analysis was done for input electric field with and without noise superimposed on its time domain waveform. Relative uncertainties for the electric field and calculated lightning channel base current were similar each other. The presented approach can substantially increase a number of lightning current parameters which can be identified on the basis of its electric field signature. This method can be applied by the lightning location systems using preprocessing which increases the timing efficiency of the transfer function estimation.

Dynamic Modeling and Parametric Analysis of the Magnetic Stiffness on a Radial Heteropolar Rotor Magnetic Bearing (RMB)

This paper presents both the dynamic modelling and the study of the variation of certain physical parameters (pole area, gap and base current) that change the magnetic stiffness of a radial heteropolar Rotor Magnetic Bearing (RMB) aiming at the analysis of the magnitude of its control current for three different equilibrium points. The RMB is modelled as a fully uncoupled symmetric active 8-pole magnetic bearing. The analysis is performed using spectral cubes for a better visualisation of the posed problem. The saturation analysis of the RMB is also performed. At last, it is shown that a control current with the same magnitude as the base current is reached with minimum pole area and air gap s0 = 528 um.

Modified Transmission Line Model with a Current Attenuation Function Derived from the Lightning Radiation Field—MTLD Model

In return strokes, the parameters that can be measured are the channel base current and the return stroke speed. For this reason, many return stroke models have been developed with these two parameters, among others, as inputs. Here, we concentrate on the current propagation type engineering return stroke models where the return stroke is represented by a current pulse propagating upwards along the leader channel. In the current propagation type return stroke models, in addition to the channel base current and the return stroke speed, the way in which the return stroke current attenuates along the return stroke channel is specified as an input parameter. The goal of this paper is to show that, within the confines of current propagation type models, once the channel base current and the return stroke speed are known, the measured radiation field can be used to evaluate how the return stroke current attenuates along the channel. After giving the mathematics necessary for this inverse transformation, the procedure is illustrated by extracting the current attenuation curve from the typical wave shape of the return stroke current and from the distant radiation field of subsequent return strokes. The derived attenuation curve is used to evaluate both the subsequent and first return stroke electromagnetic fields at different distances. It is shown that all the experimentally observed features can be reproduced by the derived attenuation curve, except for the subsidiary peak and long zero-crossing times. In order to obtain electromagnetic fields of subsequent return strokes that are in agreement with measurements, one has to incorporate the current dispersion into the model. In the case of first return strokes, both current dispersion and reduction in return stroke speed with height are needed to obtain the desired features.

A 5.43 nV/√Hz Chopper Operational Amplifier Using Lateral PNP Input Stage with BJT Current Mirror Base Current Cancellation

This paper presents a low-noise chopper operational amplifier using a lateral PNP input stage with bipolar junction transistor (BJT) current mirror base current cancellation. The BJT has a lower noise characteristic than the metal–oxide–semiconductor (MOS) transistor, where low-noise characteristics can be achieved by implanting the BJT to the input stage of the amplifier; however, the base current of the BJT input stage causes low input impedance of the amplifier. The BJT current mirror base current cancellation technique is implemented to enhance the input impedance of the BJT input stage by canceling the base current. BJT current mirror base current cancellation is implemented with a simple scheme using NPN transistors with deep n-well in a generic complementary metal–oxide–semiconductor (CMOS) process. For further noise reduction with the BJT input stage, a chopper amplifier scheme is adopted to reduce low-frequency components such as 1/f noise terms in the low-frequency range. The prototype chip is fabricated in a 0.18-μm CMOS process. The active area of the prototype amplifier is 0.213 mm2. The measured input-referred noise is 5.43 nV/√Hz. The measured input base current of the amplifier with base current cancellation is 67.971 nA. The total amplifier current consumption is 278.3 μA, with a power supply of 3.3 V.

Effect of Collector Voltage on the Large and Small Signal Modulation Characteristics of 980 nm Transistor Laser

Theoretical analysis of Transistor Laser is carried out and the static and frequency responses for different collector voltages, under common emitter configuration are determined. The threshold current (Ith) is observed as 33mA and it increases linearly with reverse collector to base voltage (VCB). Meanwhile, the output optical power is found to decrease proportionately when VCB is increased. A maximum of 18.7GHz modulation bandwidth is observed when an input base current of 95 mA is applied at a fixed value of VCB (1V). The modulation bandwidth is found to decrease with increase in reverse VCB. The turn on delay increases with collector voltage. However, it decreases with increase in base current.