Lecture 1 - Lecture 1: Introduction to electronic analog...

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Lecture 1: Introduction to electronic analog circuits 361-1-3661 1 THE AIM OF THE COURSE Lumped linear time-invariant (LLTI) electric circuits do not provide any solution to the following five tasks (see Fig. 1), which are very important in Electrical Engineering: 1) It is impossible to control the circuit transfer function ( gain ) by an electrical signal, either voltage or current. 2) It is impossible to implement a circuit with a dc gain greater than one. 3) It is impossible to implement a circuit with a power gain greater than one. 4) It is impossible to implement a current source. 5) It is impossible to implement an oscillator (circuit generating a periodic signal), for example, a sine-wave oscillator. The aim of the course is to solve all the above tasks by using electronic devices: diodes and transistors. To develop and study electronic circuits, we start from elementary circuits, analyze them, and then improve if there is a need. 1. ELEMENTARY ELECTRONIC CIRCUITS WITH A DIODE Our main aim here is to build a circuit with a gain (not necessarily greater than one) that can be controlled by an electrical signal, either voltage or current. Namely we would like to build a voltage-controlled voltage divider and a current- controlled current divider (homework). To reach this goal, we first develop physical, mathematical, and finally a graphical model of the diode. Based on the graphical model, we find equivalent electric circuits to replace a diode in an electronic circuit. This will allow us to analyze single-diode electronic circuit by applying electric circuit theory. 1.1. Diode: symbol, physical structure, analytical model and graphical characteristic The symbol of the diode and its physical structure are given in Fig. 2. To develop a mathematical model of the diode we have to describe the dependence of the diode current, i D , on the diode voltage, v D . Assuming that the n region is much more heavily doped that the p region, n po >> p no , we neglect the diode current due to the holes and consider only that due to the electrons. Neglecting the small effect of the weak electric field within the p region on the electrons, which are the minor charge carriers in this region, we conclude that the diode current is exclusively due to the diffusion current of electrons: A = f ( I,V ) A DC > 1 A P > 1 I v s Fig. 1. Circuits that cannot be implemented by using LLTI components only: resistors, capacitors, and inductances. T
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Lecture 1 - Lecture 1: Introduction to electronic analog...

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