This set of Software Defined Radio Interview Questions and Answers focuses on “RF and IF Processing Tradeoffs – 2”.

1. RF integrated circuits generally comprise of _____
a) resonators and resistors
b) resistors
c) diodes
d) resonators and capacitors

Explanation: RF integrated circuits consist of off-chip resonators, inductors, and capacitors. Each device increases the production cost which is linear function of number of components.

2. RF MEMS gives _______ alternative to electronic switching circuits.
a) an electromechanical
b) a mechanical
c) an electro-dynamic
d) an interconnected

Explanation: RF MEMS gives an electromechanical alternative to electronic switching circuit. RF MEMS can aid in the reduction of size, weight and power.

3. Which of these is not a technique used to induce sharp resonance in resonators?
a) Rigidity
b) Bulk
c) Acoustic
d) Piezoelectric

Explanation: Resonator achieves sharp resonance by using bulk, acoustic and piezoelectric effects. By adapting the mentioned effects, quality factor in the range of 10,000 can be achieved.

4. In resonators with nanoscale I-beams, which factor does not affect the mechanical frequencies of I-beams?
a) Size
b) Density
c) Stiffness
d) Distance between beam and bottom of the cavity

Explanation: In resonators with nanoscale I-beams suspended over the cavity, the mechanical frequencies of I-beam are determined by size and stiffness of I-beam, and the distance between the beam and bottom of the cavity.

5. The industry standard figure of merit for an RF switch is ______
a) R0C1
b) R1C0
c) C0R1
d) C1R0

Explanation: The industry standard figure of merit for an RF switch is R1C0. It is given by the product of ON-resistance and OFF-capacitance. It is measured in femtoseconds.

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6. RF MEMS allows selection of ____ and ____, increasing the degree of freedom in design process.
a) digital circuit and reverse engineering
b) analog circuit and reverse engineering
c) digital circuit and reengineering
d) analog circuit and reengineering

Explanation: RF MEMS allows the selection of switches from a collection of analog circuit and components. This is the direct implementation of MEMS in the design. Reengineering and selection of analog circuits are according to the programmability requirements of software defined radio.

7. Superconducting analog filters can reduce noise and interference introduced by wide bandwidth of SDR architecture.
a) True
b) False

Explanation: Superconducting analog filters can reduce noise and interference introduced by wide bandwidth of SDR architecture. The combined use of superconducting filter and regular anti-aliasing filter can offer better spectral purity.

8. Superconductors use ____ to maintain working temperature near _____
a) heat sinks, 70K
b) open cooling system, 80K
c) forced air, 75K
d) closed cooling system, 70K

Explanation: Superconductor analog filters make use of closed cooling system, and thermo-electric coolers to maintain working temperature near 70K.

9.RF amplifiers tend to be ____ amplifiers.
a) class A
b) class B
c) class C
d) class AB

Explanation: RF amplifiers operate in saturated mode (class C). It non-linearly distorts the waveform. Class A, class B, and class AB are linear amplifiers. The output signals are linearly related to input signals.

10.Which of the following modulation type is incompatible with class C operation?
a) Frequency modulation
b) BPSK
c) QPSK
d) QAM

Explanation: Class C operation is incompatible with amplitude sensitive modulation type such as QAM. However it does not face any complication with amplitude insensitive modulation type such as FM.

11. Electronically Programmable Analog Components are also called as ____
a) FPGA
b) FPAA
c) Gate Array ASIC
d) Cell based ASIC

Explanation: Electronically Programmable Analog Components (EPACs) are also called as Field Programmable Analog Array (FPAAs). FPAAs combine conventional analog circuit such as filter, amplifier with programmable interconnect.

12. Which of the following is not a challenge to RF/IF conversion stage in military application?
a) Low phase noise
b) Tunable pre-selector
c) Single RF/IF up-down conversion
d) Fast tuning synthesizers

Explanation: Tunable pre-selector is required for co-site rejection. Low phase noise and fast tuning synthesizers are required for JTIDS and EPLRS. Single RF/IF up-down conversion is a commercial application challenge.

13. ____ fixes the input power dynamic range such that there are no sinusoidal RF conversion artifacts in the output.
a) Noise Figure
b) Two tone intermodulation product
c) Harmonics
d) SFDR

Explanation: Spurious Free Dynamic Range (SFDR) fixes the input power dynamic range such that there are sinusoidal RF artifacts in the output. The artifacts tend to mask weak signal.

14. The Nyquist criterion states that the sampling frequency of a band limited analog waveform must be at least ______ component to properly reconstruct the signal.
a) half the maximum frequency
b) twice the maximum frequency
c) half the minimum frequency
d) twice the minimum frequency

Explanation: The Nyquist criterion states that the sampling frequency of a band limited analog waveform must be at least twice the maximum frequency component to properly reconstruct the signal. Aliasing can be overcome by meeting Nyquist criterion and using filters.

15. The useful dynamic range applicable for antenna, RF/IF conversion, and ADC’s is given by the ratio of smallest processable signal to the smallest detectable signal.
a) True
b) False

Explanation: The useful dynamic range is given by the ratio of largest processable signal to the smallest detectable signal. It is applicable for antenna, RF/IF conversion, and ADC’s. Dynamic range is one of the controlling parameters in the design of software defined radio.

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