Charge coupled device(ccd)
Embed Size (px)
Transcript of Charge coupled device(ccd)
Charge coupled device(CCD)
Charge coupled device (CCD)Presented By:Darshil Shah (IU1241090051)Sachin Jain (IU1241090018)Jainam Patel (IU1241090033)
Surface-Channel charge coupled device (SCCD)
IntroductionCCD is a array of MOS-diode structure that was proposed in 1969 by George smith & Willard boyle.
Acharge-coupled device(CCD) is adevicefor the movement of electricalcharge, usually from within thedeviceto an area where thechargecan 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 CCDsSCCD (Surface channel CCD)
BCCD (Buried channel CCD)
JCCD (Junction CCD)
SCCD/BCCD stores and transfer the charges on the surface/interior of semiconductor respectively.
JCCD stores and transfer the charge packet at the PN-junction.Operational MechanismUnder 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 moveSelf induced driftThermal diffusionFringing field drift
Energy band of MIS diode
Store and transfer of charger packet
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 Here Vfb =flat band voltageVi =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 :DYNAMIC CHARACTERISTICSCharge transfer efficiency() 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()
If a single charge pulse width an initial amplitude (Po) transfer down a CCD register after n transfers(phases), the amplitude (Pn) becomes
The maximum achievable transfer efficiency depends upon two factors:How fast the free charge can be transferred between adjacent gates 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
Photographic camerasSignal 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)
ReferencesSemiconductor devices: Physics and technology, 2nd Edition,Wiley India Edition, By S M Sze
Microwave devices and circuits, 3rd Edition ,PHI , By Samuel y. Liao.