This set of Optical Communications Multiple Choice Questions & Answers (MCQs) focuses on “High Performance Receivers”.
1. How many design considerations are considered while determining the receiver performance?
Explanation: Three main considerations are utilized for determining the receiver performance. Noise performance is a major design consideration providing a limitation to the sensitivity. Other two considerations are bandwidth and dynamic range.
2. FET preamplifiers provide higher sensitivity than the Si-bipolar device.
Explanation: At low speeds, the FET preamplifiers provide higher sensitivity than the Si-bipolar device. It is apparent that below 10Mbits-1the Si MOSFET preamplifier provides a lower noise performance than GaAs MESFET.
3. What is the abbreviation of HBT?
a) Homo-junction unipolar transistor
b) Homo-junction bipolar transistor
c) Hetero-junction bipolar transistor
d) Hetero-Bandwidth transcendence
Explanation: HBT is abbreviated as Hetero-junction bipolar transistor. It comprises a selectively doped hetero-junction FET. It is a high-speed, low-noise transistor device.
4. What type of receivers are used to provide wideband operation, low-noise operation?
a) APD optical receivers
b) Optoelectronic integrated circuits (OEICs)
c) MESFET receivers
d) Trans-impedance front-end receivers
Explanation: A strategy for the provision of wideband, low-noise receivers involves the use of p-i-n photodiode detector along with the monolithic integration of the device with semiconductor alloy FETs. It has an operating wavelength of 1.1 to 1.6 μmranges.
5. ___________ circuits extends the dynamic range of the receiver.
c) Automatic Error Control (AEC)
d) Automatic Gain Control (AGC)
Explanation: AGC circuit extends the dynamic range by diverting excess photocurrent away from the input of the receiver. The receiver dynamic range is an important performance parameter as it provides a measure of the difference between the sensitivity and its overload level.
6. The sensitivity of the low-impedance configuration is ____________
d) Same as that of high-impedance configuration
Explanation: A receiver saturation level is determined by the value of the photodiode bias resistor. The photodiode bias resistor valve is indirectly proportional to the sensitivity but is directly proportional in low impedance configuration. The low resistor value provides less sensitivity in the low-impedance configuration.
7. What is generally used to determine the receiver performance characteristics?
c) Dynamic range & sensitivity characteristics
Explanation: Dynamic range and sensitivity characteristics involve a graph of received power level and the value of feedback resistor. The high value of photodiode bias resistor in the high impedance front end causes high sensitivity and a narrow dynamic range. These factors prove useful for determining the performance characteristics of receiver.
8. The __________ technique eliminates the thermal noise associated with the feedback resistor in the trans-impedance front end design.
b) Resonating impedance
d) Optical feedback
Explanation: The optical feedback strategy proves most useful at low transmission rate. The use of optically coupled feedback has demonstrated dynamic ranges of around 40 dB for p-i-n receivers operating at modest bit rates. It removes thermal noise associated with the feedback resistor.
9. The removal of the feedback resistor in the optical feedback technique allows reciever sensitivity of the order of _______________
a) -54 dBm at 2Mbit/sec
b) -12 dBm at 2Mbit/sec
c) -64 dBm at 2Mbit/sec
d) -72 dBm at 2Mbit/sec
Explanation: The removal of feedback resistor in the optical feedback technique allows low noise performance. Low noise performance, in turn, affects sensitivity. The receiver sensitivity gets high of the order of -64 dBm at 2Mbit/sec transmission rates.
10. The optical feedback technique is useful at low transmission rates.
Explanation: The optical feedback technique is useful at low transmission rates because in this case the feedback resistors employed are smaller than the optimum value for low-noise performance. This is done to maintain the resistor at a practical size of 1MΩ. Large values of feedback resistor limits the dynamic range.
11. How many types of optical amplifier technologies are available.
Explanation: There are two basic optical amplifier technologies available. They are semiconductor optical amplifiers and fiber amplifiers. Both these devices are utilized in the pre-amplification role.
12. The optimum filter bandwidth is typically in the range ________________
a) 0.1 to 0.3 nm
b) 0.5 to 3 nm
c) 0.1 to 0.3 μm
d) 0.5 to 3 μm
Explanation: The optimum fiber bandwidth is determined by detector noise, transmission rate and the transmitter chirp characteristics. It is typically in the range of 0.5 to 3 nmas it depends upon the filter insertion loss.
Sanfoundry Global Education & Learning Series – Optical Communications.
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