# Microwave Engineering Questions and Answers – Non – Linear Distortion – 1

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This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Non – Linear Distortion – 1”.

1. Active devices like diodes and transistors become non-linear at high power levels due to:
a) Instability of transistor
b) Thermal noise
c) Gain compression
d) None of the mentioned

Explanation: All practical components become non-linear at high power level operations. Active devices like diode and transistor become non-linear at high power levels due to effects such as gain compression or the generation of spurious frequency components due to device non-linearities, but all devices ultimately fail at very high power levels.

2. The ________property of devices like diodes and transistors is responsible for their usage in amplifiers and frequency convertors.
a) Symmetry
b) Non linearity
c) Linearity
d) None of the mentioned

Explanation: Non linearity is of great utility for desirable functions such as amplification, detection and frequency and frequency conversion. But non-linearities in these devices lead to undesirable effects like gain compression and generation of spurious frequency components.

3. The output response of a non-linear circuit is given by the expression:
a) V0=a0+a1Vi1+a2Vi2+a3Vi3
b) 0=a0+a1Vi1
c) V0=a2Vi2+a3Vi3
d) V0=a0

Explanation: The output of non-linear devices in terms of the applied output voltage is given as the Taylor series in terms of the input signal voltage. This expansion is given by V0=a0+a1Vi1+a2Vi2+a3Vi3….
And higher order terms. The constant term leads to rectification converting an AC input signal to DC.

4. As the degree of non-linearity of a transistor or a diode increases, the power gain of the device:
a) Increases
b) Decreases
c) Remains a constant
d) None of the mentioned

Explanation: Let V0cosωt be the input signal applies to a non linear device. The output of the device is given by V0=a0+a1Vi+a2Vi2+a3Vi3. Considering only up to power of 3 and expanding, we get terms, whose constants of third degree and higher order are negative. This results in fall in gain when the input signal levels are high.

5. The fall in gain of a device due to non-linearities is called:
a) Gain compression
b) Gain saturation
c) Impedance mismatch
d) None of the mentioned

Explanation: The fall in gain of a device due to non-linearities is called gain compression. Physically, this is usually due to fact that the instantaneous output voltage of an amplifier is limited by the power supply voltage used to bias the active device.

6. 1 dB compression point is defined as the power level for which the output power of the non-linear device is 1 dB
a) True
b) False

Explanation: 1 dB compression point is defined as the power level for which the output power is decreased by 1dB from the ideal linear characteristic. This power level is represented as P1dB and can be stated in terms of either input power or output power.

7. In a non-linear device, for a single input frequency the output will consist of:
a) Single frequency component
b) Harmonics of the input frequency
c) Constant gain
d) None of the mentioned

Explanation: Let V0cosωt be the input signal applies to a non linear device. The output of the device is given by V0=a0+a1Vi1+a2Vi2+a3Vi3. Substituting in this equation gives higher frequency components which is associated with higher order terms in the expansion. When the input consists of only one frequency component the higher frequencies are filtered out using band pass filter.

8. When the input frequency consists of more than one closely spaced frequency, it results in:
a) Intermodal distortion
b) Gain compression
d) Signal attenuation

Explanation: When the input frequency consists of more than one frequency, due to the non-linear effect of the device, higher frequency components are generated. When the two different frequencies are close enough to each other, due to the interference of multiple frequency components, intermodal distortion occurs.

9. Third-order intercept point is defined as the point at which the gain of a non linear device is 3 dB less than the maximum gain.
a) True
b) False

Explanation: Third-order intercept point is defined as hypothetical intersection point at which the first order and third order powers would be equal is called the third-order intercept point.

10. The relation between an intercept points referenced at the input versus the output is given by the relation:
a) OIP3=G (IIP3)
b) (IIP3) = G (OIP3)
c) OIP3=G (IIP3)2
d) None of the mentioned

Explanation: The relation between an intercept points referenced at the input versus the output is given by the relation OIP3=G (IIP3). Here OPI3 is the output third order intercept point; OIP3 is the input third order intercept point. G is the conversion loss in the device.

Sanfoundry Global Education & Learning Series – Microwave Engineering.
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