1 introduction to electronics.ppt
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electronicsTRANSCRIPT
ELECTRONICSThe word Electronics is derived from Electron Mechanics which means the study of the behavior of an electron under different conditions of externally applied fields.
Electronics is a field of Science and Engineering, which deals with electronic devices and their utilization.
Electronic device is a device in which conduction takes place by the movement of electrons ─ through vacuum, gas or semiconductors.
Applications of Electronics
Communications & EntertainmentsMedical SciencesDefence ApplicationsIndustrial ApplicationsInstrumentations
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Communications and Entertainments
Line CommunicationsTelegraphyTelephonyTelexTeleprinters
Wireless CommunicationsRadio broadcastingTV broadcastingFacsimile (Radiophoto)
Audio SystemsPublic Address (PA) systemsStereo amplifiersRecord playersTape recorders
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Medical Sciences
Electrocardiogram (ECG) Electrotherapy Modern X-rays
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Defence Applications
Radar guided missiles Coded communications
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Industrial Applications
Automatic control systems Heating and welding systems Electron Microscope Computers
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InstrumentationInstrumentation Precision measuring instruments
Cathode Ray Oscilloscope (CRO)Vacuum Tube Volt Meter (VTVM)Digital Volt Meter (DVM)Frequency CountersSignal generatorpH meterStrain gauge
etc.
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Atomic Structure
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Random Movement of Electronsin Aluminium atoms.
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Simplified Representation of Atoms
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Permissible Energy Levels (for an isolated hydrogen atom)
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Types of Materials
Conductors Semiconductors Insulators
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Conductors• Electrical conductivity is excellent.• Concentration of free electrons is very large ~1028
electrons/metre3.• Under the influence of an applied electric field the
electrons may acquire additional energy and move into higher states.
• The conduction and the valence band overlaps with each other.
• Have positive temperature coefficient of resistance, i.e., resistance increases with increase in temperature.
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Insulators
• Very poor conductor of electricity.• Concentration of free electrons is very small ~ 107
electrons/meter3.• Large forbidden band gap separates filled valence
band from the vacant band.• The energy which can be supplied to an electron
from an applied field is too small to carry the electrons from the filled to the vacant band.
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Semiconductors• Conductivity is in between that of conductors and
insulators.• Concentration of free electrons is moderate and is in
between that of conductors and insulators.• Width of the forbidden gap is relatively small ~
1 eV.At 0 K : Eg for Ge ~ 0.785 eV
Eg for Si ~ 1.21 eV • Band gap energy in a crystal is a function of interatomic
spacing and hence depends somewhat on temperature.• Has negative temperature coefficient of resistance, i.e.,
resistance decreases with rise ion temperature.
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Energy Bands
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Materials for Semiconductors
Germanium and Silicon, which has tetravalent atoms are the two most important semiconductors used in electronic devices.
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Review• Electronics.• Applications of Electronics :
– Communications and Entertainments.– Medical Sciences.– Defence Applications.– Industrial Applications.– Instrumentation.Instrumentation.
• Types of Materials :– Conductors.– Insulators.– Semiconductors.
• Atomic Structure : Energy Bands (in Na)
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