This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Metal Oxide Semiconductor FET”.
1. There exists no difference between the construction of GaAs MESFET and silicon MOSFET except for the material used in their construction.
Explanation: There exists a difference between the construction of MESFET and MOSFET. There is a thin insulating layer of silicon dioxide between the gate contact and the channel region. Because the gate is insulated, it does not conduct DC bias current.
2. MOSFETs can provide a power of several hundred watts when the devices are packaged in:
d) None of the mentioned
Explanation: MOSFETs can be used at frequencies into the UHF range and can provide powers of several hundred watts when devices are packaged in parallel. Laterally diffused MOSFETs have direct grounding of the source and can operate at low microwave frequencies with high power.
3. High electron mobility transistors can be constructed with the use of single semiconductor material like GaAs that have high electron mobility.
Explanation: High electron mobility transistor is a hetero junction FET, meaning that it does not use a single semiconductor material, but instead is constructed with several layers of compound semiconductor materials.
4. The curve of IDS v/s VDS of an FET does not vary with the gate to source voltage applied.
Explanation: Curve of IDS v/s VDS of an FET varies with the gate to source voltage applied. As the gate to source voltage applied becomes more positive, the drain to source current goes on increasing for an applied constant gate to source voltage.
5. High-power circuits generally use higher values of:
a) Gate to source current
b) Drain to source current
c) Drain current
d) Gate to source voltage
Explanation: In order to achieve high drain current for high power applications, DC bias voltage must be applied to both gate and the drain, without disturbing the RF signal paths.
6. High drain current at RF levels is achieved with the biasing and decoupling circuitry for a dual polarity supply.
Explanation: High drain current at RF levels is achieved with the biasing and decoupling circuitry for a dual polarity supply. The RF chokes provide a very low DC resistance for biasing, and very high impedance at RF frequencies to isolate the signal from the bias supply.
7. Since multiple layers of semiconductor materials is used in high electron mobility transistors, this results in:
a) High gain
b) Power loss
c) Temperature sensitivity
d) Thermal stress
Explanation: The multiple layers in the high electron mobility transistor result in the thermal and mechanical stress in the layers. To avoid this, the layers usually have matched crystal lattice.
8. A major disadvantage of high electron mobility transistor is that:
a) They have low gain
b) High manufacturing cost
c) Temperature sensitive
d) High driving voltage is required
Explanation: High electron mobility transistors are devices containing multiple layers of different semiconductor materials. This complicated structure of HEMT requires sophisticated fabrication techniques leading to relatively high cost.
9. HEMT fabricated using GaN and aluminum gallium nitride on a silicon substrate can be used in :
a) High power transmitters
b) High power receivers
d) Smart antennas
Explanation: GaN HEMT operate with drain voltages in the range of 20-40 V and can deliver power up to 100 W at frequencies in the low microwave range, making these devices popular for high power transmitters.
10. The scattering parameter S11 for GaN HELMT increases with increase in frequency of operation
Explanation: For GaN, the S11 parameter of the amplifier decreases with increase in frequency of operation. Experimental results have shown that S11 parameter was 0.96 at 0.5 GHz of frequency and 0.88 at 4 GHz of frequency.
Sanfoundry Global Education & Learning Series – Microwave Engineering.
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