Transistor Characteristics and Applications

Introduction to Transistors

  • Transistors are critical components in electronics, functioning as switches and amplifiers.

  • They are used to generate signals that transport information in various applications, such as radio communication.

Circuit Transfer Function

  • Signals can encode information in voltage (V) or current (I).

  • The circuit transfer function processes or amplifies these signals.

Signals and Semiconductors

AM Radio Example /

  • Carrier Signal: The primary signal used for transmission.

  • Modulating Sine Wave Signal: Effects the modulation of the carrier signal to embed information.

Diode as Transfer Function

  • A diode's I-V characteristics indicate its resistance and conductivity.

    • Shallower I-V curve = Higher resistance (lower conductivity)

    • Steeper I-V curve = Lower resistance (higher conductivity)

Small Signal Equivalent Circuits

  • Small signal resistance (rd) of a diode is critical for understanding its behavior in circuits.

Example Calculation

  • Given $ rac{ΔI}{A_V} = rd$

  • Example parameters:

    • $ΔI = 360 ext{ μA} - 271 ext{ μA}$

    • $V = 538 ext{ mV}$

    • Small signal resistance calculated as $rd = 146 ext{ Ω}$.

Transistor History

  • 1925: Julius Edgar Lilienfeld proposes field-effect transistor (FET).

  • 1947: Invention of point-contact transistor by John Bardeen and Walter Brattain.

  • 1948: William Shockley develops bipolar junction transistor (BJT).

  • 1954: Texas Instruments produces the first commercial transistors.

  • 1958: Jack Kilby invents the integrated circuit (IC).

  • 1969: Development of the Intel 4004 microprocessor.

Transistors: Functionality

Switching and Amplification

  • Transistors can function as either switches or amplifiers.

  • A control voltage ($V{control}$) can turn a switch on/off, while an input signal ($V{sig}$) can be amplified to produce an output current.

BJT Construction

  • BJT Structure: Consists of three regions: Collector (C), Base (B), and Emitter (E).

  • When $V_B$ is high enough, current can flow from collector to emitter.

BJT Modes

  1. When the BJT is OFF (not conducting):

    • $V{CE}$ ~ $V{supply}$

  2. When the BJT is ON (fully conducting):

    • $V_{CE}$ ~ 0.2V (saturated condition)

BJT Graphs

  • Key relationships:

    • $IB = f(V{BE})$

    • $IC = f(V{BE})$

    • $IC = f(V{CE})$

  • $V_{BE}$ controls collector current and offers trans-conductance gain.

Equivalent Circuits

  • The BJT can be represented using passive components for analysis.

  • The base current ($I_B$) controls the operation of the transistor.

FET vs BJT

FET Switch Model

  • FET offers higher input impedance ($V_{GS}$) compared to BJT's base current.

  • Useful in applications requiring high input resistance and fast switching speeds due to the absence of input current.

Modern Applications of Transistors

  • Advances in transistors include those in mobile phones (10-20 billion transistors) and flash memory (1000 billion transistors).

  • GaN (Gallium Nitride):

    • Offers faster switching speeds and higher efficiency compared to silicon.

    • Potential applications in electric vehicles, data centers, and renewable energy technology, improving efficiency and reducing energy loss.