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Study material
Photodiode How do you reverse bias a photodiode? Reverse biasing a photodiode is accomplished by setting the cathode of the detector at a higher electric potential than the anode's. In another words, applying a negative voltage to anode.
What is meant by photodiode? Does dark current change over time? The surface dark current component can change over time due to ambient moisture. It is also susceptible to surface cleanness, surface contamination, i.e. sodium from hand grease could increase the dark current significantly. The bulk dark current should not increase over time.
What is the output signal of a photodiode? Photodiode operates as a voltage source as well a current source in response to the incident light in the wavelength range of 200 nm to 1100 nm. The current measurement is preferred since the output current changes linearly with incident light power. The voltage output, however, changes logarithmically with incident light power.
What is the difference between the Photoconductive (PC) and photovoltaic (PV) modes? In the photovoltaic mode, the photodiode is neither operated with nor biasing. It is simply acting like a solar call, which converts light into electricity. In the Photoconductive mode, however, the photodiode can be Reversed Biased by voltages up to the specified maximum reverse voltage.
What happens if the photodiode is biased with a voltage larger than the specified maximum reverse bias? A device may experience reverse bias breakdown if biased over the maximum value we specify, a high current will flow through the device which could lead to the destruction of the photodiode. We do not recommend that you operate this device in this manner.
s there a specific type of power supply used to bias the photodiode? A stable DC voltage source is all that is required to reverse bias a photodiode. The supply's current requirements are minimal, since the device produces its own current.
How much reverse bias should I apply ? Apply a sufficiently high reverse bias only to get the bandwidth you but low enough to avoid the risk of reaching the reverse breakdown voltage. Increasing the reverse voltage increases the response speed of the photodiode, by reducing the junction capacitance.
MOSFET FET is a ______________ operated device. 2. Define pinch off voltage. vo ltage. 3. Why is FET called a unipolar device?
4. How can a FET be used as a voltage controlled resistor? 5. Why are FETs are more advantageous than BJT? 7. Give the relation between transconductance gm , drain resistance rd and amplification factor µ of a FET. 8. Differentiate between depletion mode and enhancement mode. 9. Input impedance of FET is _________ than that of junction transistor. 12. Draw the symbol for n-channel and p-channel MOSFET. 14. Write the applications for MOSFET. 15. What are the advantages of MOSFET? How the constructional features of MOSFET differs from JFET? 30. Explain some application of MOSFET&JFET. How does the gate capacitance of MOSFET affect the performance?
What is the difference between a source and a drain of a MOSFET? What is the difference between an n-type and a p-type MOSFET? What is the difference between an enhancement and a depletion MOSFET? Which device has most positive threshold voltage a depletion mode p-type MOSFET or an enhancement mode p-type MOSFET? Which device has the highest drain current in saturation at zero gate voltage, a p-type enhancement MOSFET or an n-type depletion MOSFET? Why is the electron layer of an n-MOSFET called an inversion layer? Why is there no current in a MOSFET when the device is biased in accumulation? What is the difference between the linear and the quadratic MOSFET model? Does the body effect affect CMOS circuits? Explain. How does the oxide thickness and substrate doping affect the threshold voltage of a MOSFET. Plot the threshold voltage as a function of the oxide thickness for different doping densities. What is the advantage of a poly-silicon gate technology? What is channel length modulation? What is punchthrough?
