Chapter 18: Electronics

• Semiconductors

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  • Materials with electrical conductivity between conductors and insulators.
  • Conductivity increases with temperature.
  • Examples: Silicon (Si), Germanium (Ge).

  • Intrinsic Semiconductors

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    • Pure semiconductors (e.g., pure Si, Ge).
    • Number of free electrons equals number of holes ($n_e = n_h$).
    • Conductivity is low at room temperature.

  • Extrinsic Semiconductors (Doped Semiconductors)

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    • Intrinsic semiconductors with impurities added (doping) to enhance conductivity.

    N-type Semiconductor:

    • Doped with pentavalent impurities (e.g., Arsenic, Antimony).
    • Majority carriers: electrons. Minority carriers: holes.
    • Donor impurity atoms provide extra electrons.

    P-type Semiconductor:

    • Doped with trivalent impurities (e.g., Boron, Aluminum, Indium).
    • Majority carriers: holes. Minority carriers: electrons.
    • Acceptor impurity atoms create holes.

• P-N Junction

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  • Formed by joining a P-type semiconductor with an N-type semiconductor.
  • Depletion region: region near the junction depleted of mobile charge carriers.
  • Barrier potential: voltage developed across the depletion region due to immobile ions.

  • Biasing of P-N Junction

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    Forward Biasing:

    • P-side connected to positive terminal, N-side to negative terminal of battery.
    • Barrier potential decreases, depletion region narrows.
    • Current flows easily.

    Reverse Biasing:

    • P-side connected to negative terminal, N-side to positive terminal of battery.
    • Barrier potential increases, depletion region widens.
    • Very small current (leakage current) flows.

  • Rectification

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    • Process of converting AC to DC.
    • P-N junction diode acts as a rectifier.

    Half-Wave Rectifier:

    • Uses one diode.
    • Rectifies only half of the AC input cycle.
    • Output is pulsating DC.

    Full-Wave Rectifier:

    • Uses two or four diodes (bridge rectifier).
    • Rectifies both halves of the AC input cycle.
    • Output is more stable pulsating DC.

• Transistor

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  • Semiconductor device used for amplification and switching.
  • Consists of three layers: Emitter (E), Base (B), Collector (C).
  • Types: NPN and PNP.

  • Transistor as an Amplifier

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    • Small change in base current produces large change in collector current.
    • Current gain ($\beta$ for common emitter): $\beta = \frac{\Delta I_C}{\Delta I_B}$.
    • Voltage gain: $A_V = \beta \frac{R_C}{R_{in}}$.

  • Transistor as a Switch

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    • Operates in saturation (ON) and cut-off (OFF) regions.
    • Used in digital circuits.

• Operational Amplifier (Op-Amp)

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  • High-gain, direct-coupled, differential amplifier.
  • Ideal characteristics: infinite input impedance, zero output impedance, infinite open-loop gain.

  • Inverting Amplifier

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    • Output is $180^\circ$ out of phase with input.
    • Gain: $A_V = -\frac{R_f}{R_{in}}$.

  • Non-Inverting Amplifier

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    • Output is in phase with input.
    • Gain: $A_V = 1 + \frac{R_f}{R_{in}}$.

  • Adder/Summing Amplifier

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    • Sums multiple input voltages.
    • Output: $V_{out} = -R_f \left( \frac{V_1}{R_1} + \frac{V_2}{R_2} + ... \right)$.

  • Comparator

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    • Compares two input voltages and outputs a high or low voltage depending on which input is greater.

• Digital Electronics (Logic Gates)

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  • Deals with discrete voltage levels (binary 0 and 1).
  • Logic gates: Basic building blocks of digital circuits.

  • Basic Logic Gates

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    AND Gate:

    • Output is HIGH only if ALL inputs are HIGH.
    • Boolean: $Y = A \cdot B$.

    OR Gate:

    • Output is HIGH if ANY input is HIGH.
    • Boolean: $Y = A + B$.

    NOT Gate (Inverter):

    • Output is opposite of input.
    • Boolean: $Y = \bar{A}$.

  • Universal Logic Gates

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    NAND Gate:

    • NOT AND. Output is LOW only if ALL inputs are HIGH.
    • Boolean: $Y = \overline{A \cdot B}$.
    • Can be used to construct all other logic gates.

    NOR Gate:

    • NOT OR. Output is LOW if ANY input is HIGH.
    • Boolean: $Y = \overline{A + B}$.
    • Can be used to construct all other logic gates.

  • Other Logic Gates

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    XOR Gate (Exclusive OR):

    • Output is HIGH if inputs are different.
    • Boolean: $Y = A \oplus B = A\bar{B} + \bar{A}B$.

    XNOR Gate (Exclusive NOR):

    • Output is HIGH if inputs are same.
    • Boolean: $Y = \overline{A \oplus B} = A B + \bar{A}\bar{B}$.

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