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  • Question

  • Both Impatt and Trapatt devices use avalanche effect


  • Options
  • A. True
  • B. False

  • Correct Answer
  • True 

    Explanation
    An Impatt diode has n+ - p - i - p + structure and is used with reverse bias.

    It exhibits negative resistance and operates on the principle of avalanche breakdown.

    Impatt diode circuits are classified as broadly tunable circuit, low Q circuit and high Q circuit.

    The impedance of Impatt diode is a few ohms. The word Impatt stands for Impact Avalanche Transit Time diode.

    The features of Impatt diode oscillator are : frequency 1 to 300 GHz, Power output (0.5 W to 5 W for single diode circuit and upto 40 W for combination of several diodes), efficiency about 20%.

    Its applications include police radar systems, low power microwave transmitter etc.

    Avalanche diode can also be operated in large signal high efficiency mode called Trapped Avalanche Transit Time mode.

    The Trapatt oscillations depend on the delay in the current caused by avalanche process.

    The avalanche delay makes it possible to increase the diode voltage well above the breakdown voltage.

    Therefore a very rapid multiplication of charge carriers occurs. A Trapatt diode is also a negative resistance device.

    The features of Trapatt diode oscillator are : Frequency 3 to 50 GHz, Power output 1-3 W, efficiency about 25%.

    Its applications are low power doppler radar, microwave beacon landing system etc.

    More questions

    • 1. Performance of a PIN diode switch is represented by

    • Options
    • A. insertion loss when switch is off
    • B. insertion loss when switch is on
    • C. insertion loss when switch is on and isolation loss when switch is off
    • D. insertion loss when switch is off and isolation loss when switch is on
      • Discuss
    • 2. In a single phase full wave converter (M-2 connection) feeding on R - L load, the input voltage is v = Vm sin ?t. The expression for dc output voltage is

    • Options
    • A.
    • B.
    • C.
    • D.
      • Discuss
    • 3. The relation between thermal conductivity K (W/m/°C), heat flow density Q (watt/m2) and dT/dx (°C per metre) is

    • Options
    • A. Q = K(dT/dx)
    • B. Q = - K(dT/dx)
    • C. K = Q(dT/dx)
    • D. dT/dx = - QK
      • Discuss
    • 4. If f is the frequency of electromagnetic wave, fc is cutoff frequency, then in a rectangular waveguide

    • Options
    • A. attenuation is low when f > fc
    • B. attenuation is low when f < fc
    • C. attenuation is high when f < fc
    • D. either (b) or (c)
      • Discuss
    • 5. A parallel polarized wave is incident from air into paraffin having relative permittivity 3, the value of its Brewster angle is

    • Options
    • A. 0°
    • B. 30°
    • C. 45°
    • D. 60°
      • Discuss
    • 6. For a permanent magnetic material

    • Options
    • A. the residual induction and coercive field should be large
    • B. the residual induction and coercive field should be small
    • C. area of hysteresis loop should be small
    • D. initial relative permeability should be high
      • Discuss
    • 7. The sensitivity of a superheterodyne receiver is determined by

    • Options
    • A. the gain IF amplifier
    • B. the gain of RF amplifier
    • C. the noise figure
    • D. all of the above
      • Discuss
    • 8. In a virgin specimen of iron, the direction of spontaneous magnetisation varies from domain to domain.

    • Options
    • A. True
    • B. False
      • Discuss
    • 9. A material which is lightly repelled by a magnetic field is known as

    • Options
    • A. diamagnetic material
    • B. non-magnetic material
    • C. ferromagnetic material
    • D. paramagnetic material
      • Discuss
    • 10. In a specimen of ferromagnetic material, as the flux density is increased from zero to 2.5 T, µr will

    • Options
    • A. increase
    • B. decrease
    • C. first decrease then increase
    • D. first increase then decrease
      • Discuss

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