CE CC CB Amplifiers

• CE Amplifier Characteristic Curve


  • Input Characteristic Curve (CE)
  • Output Characteristic Curve (CE)
  • Transfer Characteristic Curve (CE)
• Quiescent Point


  The point on the characteristic curve where the amplifier operates

  
• DC Blocking Capacitor


  Also known as 'Coupling Capacitor'
• 1. stage CE amplifier


  • First stage provides voltage gain, second stage provides power gain
• Common Collector Amplifier


  • Input is connected to the base, output is taken from the emitter
  • Also known as 'Emitter Follower'
  • Used as a voltage buffer

  
• AC equivalent circuit (CC)

  1. C1 & C2 are DC blocking capacitors

  2. Input is connected to the base, output is taken from the emitter
• AC Current Gain (CC)

  hfc = ie/ib = (ib+ic)/ib = ib/ib + ic/ib = 1 + hfe (hfe ≫1, so hfc ≈ hfe)
• Voltage Gain (CC)


  Vout ≈ Vin, no voltage amplification, used as voltage buffer
• CC Phase Relationship: Output is in phase with input signal
• Common Base Amplifier


  • Input is connected to the emitter, output is taken from the collector
  • No current amplification, used as a buffer
• AC equivalent circuit (CB)


  Input is connected to the emitter, output is taken from the collector

  
• CB Phase Relationship: Output is in phase with input signal
• AC Current Gain (CB)

  hfb = ic/ie = ic/(ic + ib), less than 1, no current amplification, used as buffer
• Amplifier Characteristics


  • Voltage Gain
  • Current Gain
  • Input Resistance
  • Output Resistance

  
• CE Amplifier


  • High voltage gain, high current gain, medium input resistance, high output resistance

  
• CC Amplifier


  • Low voltage gain (<1), high current gain, high input resistance, low output resistance
• CB Amplifier


  • High voltage gain, low current gain (<1), low input resistance, high output resistance
• Multi-stage amplifier


  1. Stage 1 gain

  2. Stage 2 gain

  3. Overall gain = Stage 1 gain x Stage 2 gain
• Multi-stage amplifier


  1. Stage 1 gain = 10

  2. Stage 2 gain = 2

  3. Overall gain = 10 x 2 = 20
• Multi-stage amplifier


  1. Stage 1 gain = 10

  2. Stage 2 gain = 2

  3. Stage 3 gain = 5

  4. Overall gain = 10 x 2 x 5 = 100
• Quiescent Point


  The point on the characteristic curve where the amplifier operates when there is no input signal.
• Characteristic Curve


  A graph that shows the relationship between the input voltage and the output voltage in an amplifier circuit.
• DC Operating Point


  Another term for the quiescent point, representing the DC voltage and current levels in the circuit when no input signal is present.
• Stability


  The importance of maintaining a stable quiescent point to ensure that the amplifier remains in its active region and does not enter saturation or cutoff.
• Biasing Circuitry


  The components used to set the quiescent point in an amplifier circuit, such as the base bias or collector resistors in a BJT amplifier.
• Servomechanisms


  A device which provides a mechanical control by means of an error-sensing feedback
• Objectives of servomechanisms


  • Transducers
  • Open loop & closed loop system
  • Negative feedback & positive feedback
  • Hunting (Oscillation)
  • Deadband
  • Damping
  • Error signal
  • Null point
  • Rate (velocity) feedback
  • Positional feedback
  • Tacho-generator
• Transducer


  A device which converts one type of energy to another (e.g. mechanical energy → electrical energy)
• Open loop servo


  No way to ensure that the output is following changes of the input
• Closed loop servo


  With a negative feedback, the output is more controlled; the output can be ensured to follow any changes of the input
• Negative feedback


  Feeding some of the output back to the input, reduces the output or the gain of a system
• Positive feedback


  No description provided
• Flight Control System


  A servomechanism is part of it
• Error signal


  The difference between the actual value of the output (e.g. angle) and the input
• Null point


  When both rotors R1 and R2 are parallel to each other
• Rate (velocity) feedback


  Negative feedback to reduce hunting (oscillations)
• Topics


  • Properties of a pure semiconductor
  • Properties of a doped semiconductor
  • PN junction
  • Diode parameters and symbol
  • Functional testing of diodes
  • Diodes in rectifier circuit
  • Diodes in voltage doubler and tripler circuits
  • Semiconductor devices

  
• Positional feedback


  Negative feedback to ensure control surfaces move to the demanded position
• Tacho-generator


  Converts mechanical energy into electrical energy, measures the speed of a motor, and provides velocity feedback
• Torque synchros


  Have 3 stator coils spaced by 120° and 2 rotor coils, can be used as transmitters or receivers