EE 330 Lab 10 Fall 2010

EE 330 Lab 10 Fall 2010 - EE 330 Laboratory 10 Bipolar...

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EE 330 Laboratory 10 Bipolar Devices and Applications Fall 2010 Objective: The objective of this laboratory is to investigate applications of BJTs Discussion: Although the major emphasis in this course has been on integrated devices, discrete transistors are more readily available commercially than integrated devices and will be used in this experiment. Datasheets for discrete transistors were very complete 25 years ago but with the limited use of discrete bipolar transistors today, details provided in the datasheets are often sketchy. In textbooks of the 60s and 70s, the small- signal parameters of the bipolar transistor were generally expressed in terms of h- parameters (hybrid parameters) rather than in terms of the conductance parameters that are more commonly used today. This is still reflected in the datasheets today. The relationship between the conductance parameters and the h-parameters are fe β = h π ie g = h 0o e h m π fe ie g = β hh The key parameter g m is generally not given directly in a datasheet but can be obtained from the expression There is one other small-signal parameter that is given in some of the datasheets, h re . This parameter was not discussed in class and characterizes the small amount of feedback that exists in the bipolar transistor from the collector to the base. By assuming the BJT is unilateral, we have neglected this effect. It was shown in the device models that the small signal parameters g o , g m , and g π are strongly operating point dependent. Unfortunately, most manufacturer’s datasheets do not directly reflect this dependence and simply give the small-signal h-parameters at a single operating point. This limits the usefulness of the small-signal model parameters that are given. Many applications of transistors and diodes are in the greater optoelectronics area whereby light energy is emitted from semiconductor devices or whereby incident light is detected by semiconductor devices. Light emitting diodes (LEDs) and laser diodes are widely used as sources of light and photodiodes, photo-transistors and Darlington phototransistors are widely used as light detectors. Invariably the light sources will emit energy over a rather narrow spectral range and invariably photo-detectors will respond optimally over a limited spectrum and often little if at all at to other wavelengths of light. When transmitting light and detecting light, it is important that the spectral response of the transmitter and detectors be compatible. Optoelectronic devices operate over a wide Page 1 of 5
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EE 330 Lab 10 Fall 2010 - EE 330 Laboratory 10 Bipolar...

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