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CCD is a array of MOS-diode structure that was proposed in 1969
by George smith & Willard boyle.
A charge-coupled device (CCD) is a device for the movement of
electrical charge, usually from within the device to an area where
the charge can be manipulated
The CCD/CTD can move the charges in the MOS diode along a
predetermined path under the control of clock pulses
Types of CCD’s
SCCD (Surface channel CCD)
BCCD (Buried channel CCD)
JCCD (Junction CCD)
SCCD/BCCD stores and transfer the charges on the surface/interior of
JCCD stores and transfer the charge packet at the PN-junction.
Under control of externally applied gate voltage ,the potential
wells and the charge packets can be shifted from one well to
adjacent one rapidly through entire CCD structure.
Three operational mechanism allow the charge packets to move
1) Self –induced drift
2) Thermal diffusion
3) Fringing field drift
A surface channel CCD is basically an MOS diode structure.
Its energy Band diagram is shown in figure. b and c.
There are two cases for the creation of a charge packet under deep depletion
Case I: Zero Signal Charge(Qsig=0)
Gate voltage and surface potential are related by
Vfb =flat band voltage
Vi =voltage across the insulator
Hence We obtain :
Case II: Stored Signal Charge(Qsig>0)
Surface Potential equation is given by :
The maximum charge density that can
be stored on an MOS capacitor is
approximately given by :
Charge transfer efficiency(ƞ) is defined as the fraction of charge
transferred from one well to the next in a CCD .The fraction left
behind is the transfer loss(Ɛ)
If a single charge pulse width an initial amplitude (Po) transfer
down a CCD register after n transfers(phases), the amplitude
The maximum achievable transfer efficiency depends upon two
1. How fast the free charge can be transferred between
2. How much of the charge gets trapped at each gate location
by stationary states
Frequency Response: There are upper and lower frequency
limitation for CCDs. The maximum frequency is limited by the
channel length L.
Power Dissipation per bit is given by
Signal processing : The CCD can perform several analog and
digital signal processing function such as delay, multiplexing,
demultiplexing, transversal filtering, recursive filtering,
integration, analog memory, digital memory and digital logic.
Thus CCD are being used widely in special application for the very
large scale integration (VLSI) circuit.
Infrared detection and imaging : CCD is capable of detecting and
imaging the infrared light from a target by forming charge packets
that are proportional to light intensity of target. These packets
are shifted to detector point for detection, read-out, multiplexing
and time and delay integration(TDI)
Semiconductor devices: Physics and technology, 2nd
Edition, Wiley India Edition, By S M Sze
Microwave devices and circuits, 3rd Edition ,PHI , By Samuel y.