ch03 - 1 Fundamentals of Microelectronics CH1 Why...

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Unformatted text preview: 1 Fundamentals of Microelectronics CH1 Why Microelectronics? CH2 Basic Physics of Semiconductors CH3 Diode Circuits CH4 Physics of Bipolar Transistors CH5 Bipolar Amplifiers CH6 Physics of MOS Transistors CH7 CMOS Amplifiers CH8 Operational Amplifier As A Black Box 2 Chapter 3 Diode Circuits 3.1 Ideal Diode 3.2 PN Junction as a Diode 3.3 Applications of Diodes CH3 Diode Circuits 3 Diode Circuits After we have studied in detail the physics of a diode, it is time to study its behavior as a circuit element and its many applications. CH3 Diode Circuits 4 Diode’s Application: Cell Phone Charger An important application of diode is chargers. Diode acts as the black box (after transformer) that passes only the positive half of the stepped-down sinusoid. CH3 Diode Circuits 5 Diode’s Action in The Black Box (Ideal Diode) The diode behaves as a short circuit during the positive half cycle (voltage across it tends to exceed zero), and an open circuit during the negative half cycle (voltage across it is less than zero). CH3 Diode Circuits 6 Ideal Diode In an ideal diode, if the voltage across it tends to exceed zero, current flows. It is analogous to a water pipe that allows water to flow in only one direction. CH3 Diode Circuits 7 Diodes in Series Diodes cannot be connected in series randomly. For the circuits above, only a) can conduct current from A to C. CH3 Diode Circuits 8 IV Characteristics of an Ideal Diode If the voltage across anode and cathode is greater than zero, the resistance of an ideal diode is zero and current becomes infinite. However, if the voltage is less than zero, the resistance becomes infinite and current is zero. ∞ = = ⇒ = R V I R = = ⇒ ∞ = R V I R CH3 Diode Circuits 9 Anti-Parallel Ideal Diodes If two diodes are connected in anti-parallel, it acts as a short for all voltages. CH3 Diode Circuits 10 Diode-Resistor Combination The IV characteristic of this diode-resistor combination is zero for negative voltages and Ohm’s law for positive voltages. CH3 Diode Circuits 11 Diode Implementation of OR Gate The circuit above shows an example of diode-implemented OR gate. V out can only be either V A or V B , not both. CH3 Diode Circuits 12 Input/Output Characteristics When V in is less than zero, the diode opens, so V out = V in . When V in is greater than zero, the diode shorts, so V out = 0. CH3 Diode Circuits 13 Diode’s Application: Rectifier A rectifier is a device that passes positive-half cycle of a sinusoid and blocks the negative half-cycle or vice versa. When V in is greater than 0, diode shorts, so V out = V in ; however, when V in is less than 0, diode opens, no current flows thru R 1 , Vout = I R1 R 1 = 0. CH3 Diode Circuits 14 Signal Strength Indicator The averaged value of a rectifier output can be used as a signal strength indicator for the input, since V out,avg is proportional to V p , the input signal’s amplitude., the input signal’s amplitude....
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This note was uploaded on 04/05/2010 for the course EE EE taught by Professor Ee during the Spring '10 term at Korea Advanced Institute of Science and Technology.

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ch03 - 1 Fundamentals of Microelectronics CH1 Why...

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