Basic Electronics
Questions & Answers
In a particular technology, a small BJT operating at BE = 28VT conducts a collector current of 100 µA. What is the corresponding saturation current? For a transistor in the same technology but with an emitter junction that is 32 times larger, what is the saturation current? What current will this transistor conduct at BE = 28V7? What is the base-emitter voltage of the latter transistor at i = 1 mA? Assume active-mode operation in all cases.
Two transistors, fabricated with the same technology but having different junction areas, when operated at a base- emitter voltage of 0.75 V, have collector currents of 0.2 mA in and 5 mA. Find I, for each device. What are the relative junc- tion areas?
The terminal voltages of various npn transistors are measured during operation in their respective circuits with the following results: In this table, where the entries are in volts, 0 indicates the reference terminal to which the black (negative) probe of the voltmeter is connected. For each case, identify the mode of operation of the transistor.
) The material doped with phosphorus is heated to 100°C. A) What is the intrinsic density at this temperature? B) How does this affect the densities of carriers and the position of the Fermi level? Assume that the effective densities of states do not depend on temperature (in fact they do).
) In a slab of silicon, the electron and hole concentration gradients are 1028çarriers m4. A) Calculate the electron and hole currents due to diffusion in this sample, assuming the sample is at room temperature. B) Are the magnitudes of the currents the same? C) Are the signs of the currents the same?
A) Calculate the intrinsic density using the semiconductor equation and other data given above for silicon. B) Find the position of the Fermi level in intrinsic material at room temperature. It can be measured from either the conduction band or the valence band (It is called the intrinsic level.) C) Is the result consistent with the value quoted above?
A causal LTI system is defined in the signal flow graph below which represents a cascade ofa 2nd order system with a first order system. • What is the system function of the overall cascade function? • Is the overall system stable? Explain? • Is the overall system a minimum phase system? Explain. • Draw the signal flow graph of a transposed direct form II implementation of this system.
)You are asked to design a silicon p-n diode in such a way that the conductivity of the n-type and the p-type material is the same. On one side the silicon(5.0 · 1028 atoms m) is doped with one atom in 10 of arsenic (valence5). A) Is this n-type or p-type and why? B) Calculate what the doping on the other side should be and suggest a suitable dopant atom.
