Notes on Electronic Circuits Lecture 1

Introduction to Electronics

• Instructor: Behzod Razavi
• Course Objective: Build the foundation for analysis and design of electronic circuits.
• Electronics is prevalent in daily life and influences various aspects of our lives.

Course Outline

1. Semiconductor Physics
   • Importance of understanding semiconductor physics for electronic design.
2. Electronics Components
   • Review of basic circuit theory: KVL, KCL, Norton Equivalent.
   • Basic components: Resistors, capacitors, inductors.
   • New components in electronics:
     • Diodes
     • Bipolar transistors
     • MOS transistors
     • Operational amplifiers (op amps)
   • These components allow for complex and sophisticated circuits.

Semiconductor Physics

• Need for Understanding: Essential for designing and analyzing electronic devices.
• Topics Covered:
  • Concepts from physics and chemistry relevant to semiconductor devices.
  • Doping as a method to modify semiconductor properties.

Introduction to Wireless Communication (Cell Phone Example)

• Basic Structure:
  • Transmitter: Converts electrical signals into electromagnetic waves.
  • Receiver: Receives and processes the transmitted signals.
• Components in Transmitter:
  1. Microphone: Converts sound to electrical signal.
  2. Amplifier: Boosts weak signals.
  3. Carrier Signal: A high-frequency signal used to transmit information.
  4. Modulator: Combines audio signal with carrier for transmission.
  5. Power Amplifier: Increases signal strength for long-distance transmission.
  6. Antenna: Radiates the signal into the air.

Receiver Components

• Antenna: Captures electromagnetic waves.
• Low Noise Amplifier: Amplifies weak received signals.
• Demodulator: Retrieves original information from the modulated signal.
• Speaker: Converts the processed signal back to sound.

Semiconductor Concepts

• Atoms and Electrons:
  • Atoms consist of a nucleus and electrons in shells.
  • Valence electrons are critical for semiconductor behavior.
  • Example Atoms:
    • Sodium: 1 valence electron (highly reactive)
    • Neon: 8 valence electrons (noble gas, non-reactive)
    • Silicon: 4 valence electrons (moderately reactive).

Conductivity of Silicon

• Intrinsic Silicon: Conductivity at room temperature due to thermally freed electrons.
• Free Electrons: At absolute zero, no electrons are free; at higher temperatures, some electrons gain enough energy to escape their bonds.
• Electric Current: Movement of free electrons constitutes electric current in semiconductors.

Key Questions in Semiconductor Physics

1. Where do charge carriers come from?
   • Free electrons result from thermal energy breaking bonds in silicon.
2. What types of charge carriers are present?
   • Electrons are primary carriers; holes (absence of electrons) also conduct current.
3. How can we modify the density of charge carriers?
   • Through doping with elements such as phosphorus (donor) or boron (acceptor).
4. How do charge carriers move?
   • Electrons move freely; holes move by electron redistribution.

Bandgap Energy

• Definition: Energy needed for an electron to break free from its bond.
• Equation for Free Electron Density:
  • N = 5.2 x 10^15 * T^(3/2) * exp(-EG/2kT)
  • Where EG is the bandgap energy, k is Boltzmann's constant, and T is temperature.
• Values:
  • Silicon: EG = 1.12 eV
  • Germanium: EG = 0.67 eV
  • Diamond: EG = 2.5 eV (excellent insulator).

Introduction to Doping

• Doping: Introducing impurities (e.g., phosphorus) into silicon to increase charge carrier density.
  • Phosphorus has 5 valence electrons and donates free electrons.
  • Resulting material is called n-type silicon (more electrons than holes).
• Doping Levels: Typically between 10^15 to 10^17 atoms/cm³.
• n and p Relationships:
  • For n-type, n (electron density) ≈ nD (donor density).
  • The relationship n * p = ni² holds, where p (hole density) decreases due to increased n.*

Summary

• Understanding semiconductor physics is foundational for electronic circuit design and analysis.
• The concepts of doping and charge carriers are critical for manipulating semiconductor properties for various applications.