Consider the following statements : (A) The charge coupled device (CCD) is a linear scanning system Choose the most appropriate answer from the options given below :
(B) The charge coupled device is a non linear scanning system
(C) A charge coupled devices is used as a shift register
(D) A charge coupled device can not be used as a photo detector
(A) and (C) Only
Statements (A) and (B) are direct opposites, so exactly one of them is true — and (D) is refuted by the CCD's best-known application. The answer is (A) and (C), option 1.
(C) — the CCD is a shift register, and that is what it was invented as. Boyle and Smith conceived it in 1969 as an analogue memory. A row of MOS capacitors sits over a common substrate, and clocking their gate voltages in a repeating pattern moves a packet of charge from one well to the next:
\(\phi_{1}\rightarrow\phi_{2}\rightarrow\phi_{3}\rightarrow\phi_{1}\ldots\)
Each charge packet is passed along the chain and read out at the end — a shift register that stores an analogue quantity rather than a bit, which is exactly why it suits imaging.
(A) — why the scanning is linear. Charge is transferred serially, one well at a time, in strict order along the register. The output therefore reproduces the spatial order of the pixels faithfully, and the charge collected in each well is very nearly proportional to the light that fell on it — a CCD's response is famously linear over four or five decades of illumination. Both senses of "linear" hold, which is why (A) is true and (B) false.
(D) is contradicted by the device's principal use. A CCD is the classic image sensor: photons absorbed in the silicon under each gate generate electron-hole pairs, and the electrons collect in the potential well. It is not merely usable as a photodetector but was the dominant one in astronomy, spectroscopy and cameras for three decades — work that earned Boyle and Smith a share of the 2009 Nobel Prize in Physics.
| Statement | Verdict |
|---|---|
| (A) Linear scanning | ✓ |
| (B) Non-linear scanning | ✗ Contradicts (A) |
| (C) Used as a shift register | ✓ Its original purpose |
| (D) Cannot be a photodetector | ✗ Its most important use |
What decides the answer quickly : since (A) and (B) are mutually exclusive, and (C) is unambiguously true, the answer must pair (C) with one of them — leaving options 1 and 2. (D)'s falsity then confirms which.
Why CMOS sensors displaced CCDs is worth noting: a CCD must shift every packet through the whole register, which costs power and forbids random access, whereas a CMOS sensor amplifies at each pixel and can be read in any order — but the CCD retains an edge in uniformity and low noise for scientific work.
Hence, the correct statements are (A) and (C).
Similar Questions
Consider the following statements for photo diode (PD) and Avalanche Photo Diode (APD)
A. The response time of APD is larger than PD
B. Photo current is a diffusion current for PD and APD
C. APD can handle greater amount of power in comparison to PD
D. Photo current is a minority carrier current for PD and APD
E. compare to ordinary pn diode, power handling capacity of PD is higher.
Choose the correct answer from the options given below :
In a p-i-n photodiode the depletion region thickness can be tailored to
(a) optimize the quantum efficiency
(b) optimize the frequency response
(c) optimize the quantum efficiency but not the frequency response.
(d) optimize the frequency response but not the quantum efficiency.
Out of these
In case a reverse biased photodiode is kept in dark condition, the current flowing through the device corresponds to:
Given below are two statements :
Statement I : In case a reverse biased photodiode is kept in a open light, the current flowing through the device corresponds to value of reverse saturation current.
Statement II : Photovoltaic emf of semiconductor photodiode is that voltage at which the resultant current flowing the device becomes zero.
In the light of the above statement, choose the most appropriate answer from the options given below :
Assertion (A) : Those semiconductor materials that have practically no thermally generated current carriers at room temperature are used as photoconductors.
Reason (R) : These materials are essentially insulators in the dark and carriers generated by the absorption of light cause maximum possible change in the resistivity of the cell.
Select your answer using the codes given below.
Assertion (A) : In PIN photodiodes, an intrinsic layer is there, which is slightly doped with n type material.
Reason (R) : It disables us to increase the width of the depletion region to a value which is far lesser what it could be in a PN diode.
Select your answer using the codes given below.
Photodiode can be used as :
(a) as a detector in forward biased
(b) as a detector in reverse biased
(c) as an LDR
(d) it generates solar energy
Which of the above statements are correct ?
The carrier velocity in a silicon p-i-n photodiode with 25 μm depletion layer width is 3 × 104 m/s. The maximum response time for the pin diode is given by :
Important Questions from Photodetectors - Teaching
Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: In a photodetector, it is desired that the width of the depletion region W be large enough so that most of the photons are absorbed within W rather than in the neutral n and p regions.
Reason R: A wider width W results in small junction capacitance.
In the light of the above statements, choose the most appropriate answer from the options given below
Consider the following statements for photo diode (PD) and Avalanche Photo Diode (APD)
A. The response time of APD is larger than PD
B. Photo current is a diffusion current for PD and APD
C. APD can handle greater amount of power in comparison to PD
D. Photo current is a minority carrier current for PD and APD
E. compare to ordinary pn diode, power handling capacity of PD is higher.
Choose the correct answer from the options given below :
In a p-i-n photodiode the depletion region thickness can be tailored to
(a) optimize the quantum efficiency
(b) optimize the frequency response
(c) optimize the quantum efficiency but not the frequency response.
(d) optimize the frequency response but not the quantum efficiency.
Out of these
In case a reverse biased photodiode is kept in dark condition, the current flowing through the device corresponds to:
Given below are two statements :
Statement I : In case a reverse biased photodiode is kept in a open light, the current flowing through the device corresponds to value of reverse saturation current.
Statement II : Photovoltaic emf of semiconductor photodiode is that voltage at which the resultant current flowing the device becomes zero.
In the light of the above statement, choose the most appropriate answer from the options given below :
