DESIGN AND APPLICAATIONS OF CHARGE COUPLED DEVICESA Seminar ReportSubmitted toJAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY,ANANTAPURIn partial fulfillment of the requirement for the award of the degree ofBACHELOR OF TECHNOLOGYInELECTRONICS AND COMMUNICATION ENGINEERINGBy D.DINESH 11691A0424

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERINGMADANAPALLE INSTITUTE OF TECHNOLOGY AND SCIENCE(Approved by AICTE, New Delhi, Affiliated to JNTU, Ananthapur)Madanapalle-517325, Andhra Pradesh.

ABSTRACT :

The charge-coupled device (CCD) is, by far, the most common mechanism for converting optical images to electrical signals. In fact, the term CCD is know by many people because of their use of video cameras and digital still cameras. The CCD has matured over the last thirty years to the point that we can get a reasonable quality picture in an inexpensive toy camera. At the other end of the cost curve, we see spectacular telescope pictures returned from the Hubble Space Telescope (HST). A number of different device architectures have been developed to optimize resolution, sensitivity and various other performance parameters. This paper gives a brief description of how the more common charge-coupled devices work, and it reviews some current developments in CCD technology.

CONTENTS

Chapter No.TitlePage No.

1Introduction011.1 What is CCD?011.2Basic Theory of CCD1.3 Basics of Operation1.4Basic CCD Ops Usage03 2History of CCD 042.1A brief history on Invenctions of ccds 042.2History of Charge Coupled Devices053Inception of Raspberry Pi073.1The Idea to create the Raspberry Pi073.2 Initial Design Considerations084 Hardware094.1Hardware Layout094.2A brief description of the components on the Pi094.3Brief description of System on Chip (SoC) 134.4Accessories155Software175.1 Operating System175.2Boot Process175.3 The NOOBS installer196Applications and comparison206.1 Applications20 6.2Comparison of Raspberry with the competitors23 7Advantages and disadvantages24 7.1 Advantages of the Raspberry Pi247.2Disadvantages25Conclusion26References27

INTRODUCTION

Digital camera systems, incorporating a variety of charge-coupled device (CCD) detector configurations, are by far the most common image capture technology employed in modern optical microscopy. Until recently, specialized conventional film cameras were generally used to record images observed in the microscope. This traditional method, relying on the photon- sensitivity of silver-based photographic film, involves temporary storage of a latent image in the form of photochemical reaction sites in the exposed film, which only becomes visible in the film emulsion layers after chemical processing (development).

Digital cameras replace the sensitized film with a CCD photon detector, a thin silicon wafer divided into a geometrically regular array of thousands or millions of light-sensitive regions that capture and store image information in the form of localized electrical charge that varies with incident light intensity. The variable electronic signal associated with each picture element (pixel) of the detector is read out very rapidly as an intensity value for the corresponding image location, and following digitization of the values, the image can be reconstructed and displayed on a computer monitor virtually instantaneously.Several digital camera systems designed specifically for optical microscopy are illustrated in Figure 1. The Nikon Digital Eclipse DXM1200 provides high quality photo-realistic digital images at resolutions ranging up to 12 million pixels with low noise, superb color rendition, and high sensitivity. The camera is controlled by software that allows the micro scopist a great deal of latitude in collecting, organizing, and correcting digital images. Live color monitoring on the supporting computer screen at 12 frames per second enables easy focusing of images, which can be saved with a choice of three formats:JPG,TIF, andBMP for greater versatility.

The idea of storing and transferring signal charge in an array of closely spaced capacitors on an isolated surface of a semiconductor was first proposed by Boyle and Smith in their search for an electrical analog to magnetic bubble devices.This concept of storing and transferring signal charge is known as v charge coupling and the device is called a charge coupled device (CCD). In view of the potential of this concept for other applications such as signal processing imaging etc., it has been improved further for various applications by other workers Since the conception of this idea of charge coupling a wide variety of charge coupled devices have been built by companies such as Texas Instruments, RCA General Electric Company etc.,Two types of CCDs are commonly in use namely the surface channel charge coupled device (SCCD) and the buried channel charge coupled device (BCCD). The name vsurface or 'buried' associated with the CCD indicates the signal handling operation of the device The Nuclear Instrumentation (NI) group at Durham University has acquired buried channel charge coupled devices (BCCDs) from the General Electric Company(GEC). The BCCDs provided by GEC are of two versions:The bulk and the epitaxial substrate version both types are primarily designed as frame transfer organisation intended for television applications.

1.CCD

A CCD is an electrical device that is used to create images of objects, store information (analogous to the way a computer stores information), or transfer electrical charge (as part of larger device). It receives as input light from an object or an electrical charge. The CCD takes this optical or electronic input and converts it into an electronic signal - the output. The electronic signal is then processed by some other equipment and/or software to either produce an image or to give the user valuable. A CCD chip is a metal oxide semiconductor (MOS) device. This means that its base, which is constructed of a material which is a good conductor under certain conditions, is topped with a layer of a metal oxide. In the case of the CCD, usually silicon is used as the base material and silicon dioxide is used as the coating. The final, top layer is also made of silicon - polysilicon.

Example for Charge Coupled Device Chip

1.1 Basic Theory of a CCD The CCD is a special integrated circuit consisting of a flat, two dimensional array of small light detectors referred to as pixels. The CCD chip is an array of Metal-Oxide-Semiconductor capacitors (MOS capacitors), each capacitor represents a pixel. Each pixel acts like a bucket for electrons.A CCD chip acquires data as light or electrical charge. During an exposure, each pixel fills up with electrons in proportion to the amount of light that enters it.The CCD takes this optical or electronic input and converts it into an electronic signal. The electronic signal is then processed by some other equipment and/or software to either produce an image or to give the user valuable information.1.2 Basics of operation In a CCD for capturing images, there is a photoactive region (anepitaxiallayer of silicon), and a transmission region made out of a shift register(the CCD, properly speaking). An image is projected through alensonto the capacitor array (the photoactive region), causing each capacitor to accumulate an electric charge proportional to thelightintensity at that location. A one-dimensional array, used in line-scan cameras, captures a single slice of the image, whereas a two-dimensional array, used in video and still cameras, captures a two-dimensional picture corresponding to the scene projected onto the focal plane of the sensor. Once the array has been exposed to the image, a control circuit causes each capacitor to transfer its contents to its neighbor (operating as a shift register). The last capacitor in the array dumps its charge into acharge amplifier, which converts the charge into avoltage. By repeating this process, the controlling circuit converts the entire contents of the array in the semiconductor to a sequence of voltages. In a digital device, these voltages are then sampled, digitized, and usually stored in memory; in an analog device (such as an analog video camera), they are processed into a continuous analog signal (e.g. by feeding the output of the charge amplifier into a low-pass filter), which is then processed and fed out to other circuits for transmission, recording, or other processing.1.3 Basic CCD Ops Usage The following process describes operation of CCDOps from a Windows XP environment along with a few useful commands included in the program: 1.Install CCDOps onto a computer that runs Windows before connecting the camera to the computer. a. The process is simple and detailed instructions accompany the software package. b. Make sure that the proper drivers for specific camera are installed.

2. SBIG cameras come equipped with a USB cable that connects the camera to the computer. a. Plug the cameras power supply into the wall and note that the internal fan comes on. b. Connect the USB to the computer and follow instructions provided in the manual and the Found New Hardware Wizard prompts.

3. Once CCDOps is installed and the camera is successfully connected to the computer, run CCDOps. a. The interface will display many commands, functions, and information concerning the camera in use. i. At first, the camera will not show up on the bottom panel of the display. ii. Click the Setup command in the Camera menu. 1. The camera should automatically become connected. a. One can check the bottom right ribbon to verify that a connection has been established. 2. Cooling is an option under Setup. a. A CCD should be cooled to approximately 30-35 degrees below the ambient temperature to reduce noise. b. One can select a temperature for the camera to reach but observe in the bottom right ribbon the percent capacity that is being used to cool camera. c. Once the temperature is reached, the percent capacity should be no more than 60-80 percent, and should never be operating at 100 percent. b. Grab is the command used to collect an image.i.Options under Grab include Integration time, Dark frame (yes, no, only), Special Processing,Exposure Delay, and Image Size.ii.One can set the Integration time for the however long of exposure is required, but some cameras have limitations on how fast of exposure is possible. iii.For example, the ST8300s quickest exposure time is 0.1 seconds. iiii. The longest possible exposure time is 3600 seconds. 3.Under Special Processing, one can take a series of consecutive images using Auto Grab.

i.This is useful when acquiring a set of dark frames at a certain integration time. ii. Another application is to observe changes in an image when one variable is adjusted.d. Saving Imagesi. It is important to save all images with descriptive titles.ii. CCDOps requires that an image be saved before another image is taken or opened.iii. Images must be saved in .fits format to be compatible with IRAF. These are just a few functions that CCDOps exhibits. The program also allows for a certain degree of image processing, mostly aesthetical.2. HISTORY:2.1 Invention of CCD Smith & Boyle 1969As the story goes, George Smith and Willard Boyle were working in a Bell Labs group interested in creating a new kind of semiconductor memory for computers. Also great hope was then held for the video telephone service, which needed inexpensive Solid State cameras. On October 17, 1969 Smith and Boyle mapped out the plan for what was to become the miracle we know of as the CCD. On that fateful day in 1969 Smith and Boyle not only described the basic structure and principles of operation, they also predicted its applications in imaging as well as memory. 2.2 Buried channel CCD Smith & Boyle 1974 Smith and Boyle are also credited with inventing the Buried Channel CCD, which greatly enhanced the performance of the original Surface Channel CCD.As a result of the work of researchers like Smith and Boyle, Bell-Labs now holds many of the relevant patents for charge-coupled devices.Early Video Camera Developments 1970 and 1975 Using the Smith & Boyle CCD, Bell Labs researchers built the world's first solid-state video camera in 1970. In 1975, they demonstrated the first solid-state camera with image quality sharp enough for broadcast television.CCDs Replace Photographic Plates in Telescopes 1983 In the beginning astronomers looked though telescopes with their eyes. Later photographic plates and film generally took over for serious work. In 1983,telescopes were first outfitted with CCD cameras. For the last ten years we have been receiving amazing pictures from the Hubble Space Telescopes CCD cameras.Digital Cameras Invade the Consumer Market 1995 CCD still cameras have been around since about 1985. In 1991 Kodak released the first professional digital camera system (DCS), aimed at photojournalists. It was a Nikon F-3, 35 millimeter, camera equipped by Kodak with a 1.3 mega-pixel CCD sensor. By 1995, inexpensive, high resolution CCDs made possible the consumer digital cameras that are ubiquitous today.

3 .CCD TYPES3.1.Burried Channel Charge Coupled The name of this device derives from the way charge is stored and transferred within it. The basic structure of BCCD . It consists of closely spaced electrodes each of which forms a MOS capacitor each electrode operating in a manner similar to the gate of a MOS transistor.Signal information usually in the form of a quantity of electric charge (electrons and holes) can be stored under the electrodes. These charges are localised under the electrodes (in the n-type layer) with the highest applied voltages because the positive potentials on the electrodes (VG) cause the underlying silicon to be driven into depletion thus attracting the negatively charged electrons. As apparent from the shape of the potential distribution beneath the electrodes the electrons are stored in the depletion region and this region is commonly called a potential well. The BCCD can transfer the charge packets in the potential wells in discrete time increments by controlling the voltages on the electrodes. The technique by which the charges can be transferred from one potential well to the next is called n charge coupling. This technique will be described later in this section. The charge packets can be detected via capacitive coupling at the output of the device. 3.2 A Two Dimensional Area Type Buried Channel Charge Coupled DeviceIn the previous section9 it has been noted that the device can also be built as a two dimensional array. The practicability of imaging with two dimensional charge coupled device was performed by Bell Telephone Laboratory in 1971. Such possibilities have led to this type of device being commercially developed for television applications. This device later became attractive to astronomers because it appears to be a promising detector that can be used in a wide variety of applications. For this reason the following sections will concentrate on the descriptions of the features and limitations of a particular device intended for astronomical work.

3.3 SINGLE CCD CELLOf course a single cell CCD would be an oxymoron! I suppose, the Complementary Metal Oxide Semiconductor (CMOS) imaging device could be considered an array of single-cell CCDs. The chip in a CMOS camera is, in fact, an array of MOS capacitors. Each cell also contains enough CMOS circuitry to both address and readout a digital representation of the quantity of charge left by the light image. With CMOS there is no bucket-brigade movement of charge! One cell of a CCD would just be a MOS capacitor if its function were to just pass along the analog charges by bucket-brigade. The more general cell would be a MOS capacitor that is also light sensitive as in a photodiode (PD). As an element of a CCD the single cell would, in general, be capable of: receiving a quantity of charge from an upstream cell, holding the charge for a time without appreciable loss, and passing the charge to the next cell downstream. In addition, a cell may be required to generate an initial charge in response to someoutside stimulus. A small number (maybe one) of the cells may also be used for the conversion, to electrical signal, process.

3.4 Array of Cells to Form a Device MOSThe simplest, I can think of, CCD would be a few capacitors (not light sensitive) arranged in a single row. At one end, called the input, we could establish, from an electric signa l, the initial charge electrostatically for each time slot. Then at the other end, called the output, we reconvert each charge back to an electric signal. If all goes well, the output electric signal is a reasonable copy of the input electric signal, but it is sampled at discrete points in time. 3.5 Charge Transfer ProcessMany schemes are used to encourage the charge packets to move cell to cell in bucket-brigade style. The goal is to protect the integrity of each charge packet and to move them on down the line. We do not want to leave any charge behind, and we do not want to contaminate any packet with charges from other packets or any external source. The various techniques are named two-phase, three-phase, four phase, and so on. These names bare a correspondence to the type of clock used for the marching orders. Generally, a cell in the phase scheme will have n control wires passing through it. These wires, each connected to one phase of the transfer clock, are used to control the height of the various potential wells.The changing well height is what pushes and pulls the charge packets along the line of CCDs. Of the various charge transfer techniques, I will only describe the three phase process that is similar to the scheme proposed at Bell Labs by Boyle and Smith in 1969. I show two pixels of a linear CCD. The three clocks (c1, c2,c3) have identical shapes, but differ in phase. Note: A high clock signal represents a large electric field, thus a deep potential well. With three-phase charge transfer, we think of the three gates in each pixel, as one storage gate (G2) and two barrier gates (G1 & G2). All the G1s (G2s & G3s) are connected together as phase 1 (2 & 3) or P1 (P2 & P3). Charges move from space A to space B when gate B goes high and gate A ramps low.3.6 Charge generationBefore the MOS capacitors are exposed to light, they arebiasedinto the depletion region; in n-channel CCDs, the silicon under the bias gate is slightlyp-doped or intrinsic. The gate is then biased at a positive potential, above the threshold for strong inversion, which will eventually result in the creation of anchannel below the gate as in aMOSFET. However, it takes time to reach this thermal equilibrium: up to hours in high-end scientific cameras cooled at low temperature. Initially after biasing, the holes are pushed far into the substrate, and no mobile electrons are at or near the surface; the CCD thus operates in a non-equilibrium state called deep depletion . Then, when pair electronholesare generated in the depletion region, they are separated by the electric field, the electrons move toward the surface, and the holes move toward the substrate. Four pair-generation processes can be identified: photo-generation (up to 95% ofquantum efficiency), generation in the depletion region, generation at the surface, and generation in the neutral bulk.The last three processes are known as dark-current generation, and add noise to the image; they can limit the total usable integration time. The accumulation of electrons at or near the surface can proceed either until image integration is over and charge begins to be transferred, or thermal equilibrium is reached. In this case, the well is said to be full. The maximum capacity of each well is known as thewell depth,typically about 105electrons per pixel.

4.DESIGN OF CCD 4.1.Design and manufacturing The photoactive region of a CCD is, generally, anepitaxiallayer ofsilicon. It is lightlypdoped (usually withboron) and is grown upon asubstratematerial, often p++. In buried-channel devices, the type of design utilized in most modern CCDs, certain areas of the surface of the silicon areion implantedwithphosphorus, giving them an n-doped designation. This region defines the channel in which the photo generated charge packets will travel.Simon Szedetails the advantages of a buried-channel device: This thin layer (= 0.20.3 micron) is fully depleted and the accumulated photo generated charge is kept away from the surface. This structure has the advantages of higher transfer efficiency and lower dark current, from reduced surface recombination. The penalty is smaller charge capacity, by a factor of 23 compared to the surface-channel CCD.The gate oxide, i.e. thecapacitordielectric, is grown on top of the epitaxial layer and substrate.Later in the process,polysilicongates are deposited bychemical vapor deposition, patterned withphotolithography, and etched in such a way that the separately phased gates lie perpendicular to the channels. The channels are further defined by utilization of theLOCOSprocess to produce thechannel stopregion.Channel stops are thermally grownoxidesthat serve to isolate the charge packets in one column from those in another. These channel stops are produced before the polysilicon gates are, as the LOCOS process utilizes a high-temperature step that would destroy the gate material. The channel stops are parallel to, and exclusive of, the channel, or "charge carrying", regions.Channel stops often have a p+ doped region underlying them, providing a further barrier to the electrons in the charge packets (this discussion of the physics of CCD devices assumes anelectrontransfer device, though hole transfer is possible).The clocking of the gates, alternately high and low, will forward and reverse bias the diode that is provided by the buried channel (n-doped) and the epitaxial layer (p-doped). This will cause the CCD to deplete, near thep-n junctionand will collect and move the charge packets beneath the gates and within the channels of the device.CCD manufacturing and operation can be optimized for different uses. The above process describes a frame transfer CCD. While CCDs may be manufactured on a heavily doped p++ wafer it is also possible to manufacture a device inside p-wells that have been placed on an n-wafer. This second method, reportedly, reduces smear,dark current, andinfraredand red response. This method of manufacture is used in the construction of interline-transfer devices.Another version of CCD is called a peristaltic CCD. In a peristaltic charge-coupled device, the charge-packet transfer operation is analogous to the peristaltic contraction and dilation of thedigestive system. The peristaltic CCD has an additional implant that keeps the charge away from the silicon/silicon dioxideinterface and generates a large lateral electric field from one gate to the next. This provides an additional driving force to aid in transfer of the charge packets.

4.2 Design and Layout The charge coupled device purchased from the General Electric Company is type P8600 : 385 x 576 pixel area image sensor. This device operates in the buried channel mode. It was chosen because it shows good responsivity towards the red end of the spectrum range especially near the one-micron region and also low readout noise. The one-micron region is the region of interest to look at for the purpose of our astronomical work. Details of this work will be described in chapter The basic design of the CCD type P8600 (385 x 576 pixels). The device consists of an array of polysilicon electrodes with charge transfer channels defined by 'channel stop isolation regions. These polysilicon electrodes are connected in sequence to the bus lines carrying the three phase drive pulses (as described previously) and are grouped in three sections: an upper 'image section a lower ustore section and a line readout section at the bottom of the array to transfer signals to the on-chip charge detection amplifier. The image section consists of 288 vertical by 385 horizontal pixels and is used for imaging (i.e. collecting signal information). The store section comprises 290 vertical by 385 horizontal pixels. The two extra vertical lines are to accowmodate any residual signals that might arise through inefficient charge transfer out of the image section. Ina full frame mode, common connections are made to the image and sections such that the whole array (i.e. 385 x 578 pixels) is used for imaging. However 9 this mode is only possible with long integration times under cooled conditions~ such that the relatively long read out period of this approach does not give rise to significant frame-shift smear (i.e. spurious charge picked up during read out). This operational mode will be considered in the next section. The line read out section or the output register has a total of 400 elements One register element is associated with each of the horizontal pixels in the array; plus eleven extra at the output end of the register and four at its inputo For television applications these fifteen extra registers may be used to establish a black reference level at the start of each line. For our purpose these fifteen extra registers are used as a doc. offset reference level at the start of each line. Therefore the drift of d.c. level with temperature between the start and the end of each line can be monitored in Figure 2.6. There are two identical output circuits incorporated on chip. Each output circuit consists of an output diode connected to a dual gate MOS transistor switch T1 and a second MOS transistor T2 operated in the source follower mode. Only one of the output circuits is used for charge detectiono The other output circuit is called a 'dummy' output because it receives no signal charge. The reason for this dummy output being incorporated will be described later in this chapter. The device is supplied in a 0.9 inch wide 30 pin DIL package with an optical window.

4.3 ARTICTUREThe CCD image sensors can be implemented in several different architectures. The most common are full-frame, frame-transfer, and interline. The distinguishing characteristic of each of these architectures is their approach to the problem of shuttering.In a full-frame device, all of the image area is active, and there is no electronic shutter. A mechanical shutter must be added to this type of sensor or the image smears as the device is clocked or read out. a frame-transfer CCD, half of the silicon area is covered by an opaque mask (typically aluminum). The image can be quickly transferred from the image area to the opaque area or storage region with acceptable smear of a few percent. That image can then be read out slowly from the storage region while a new image is integrating or exposing in the active area. Frame-transfer devices typically do not require a mechanical shutter and were a common architecture for early solid-state broadcast cameras. The downside to the frame-transfer architecture is that it requires twice the silicon real estate of an equivalent full-frame device; hence, it costs roughly twice as much.The interline architecture extends this concept one step further and masks every other column of the image sensor for storage. In this device, only one pixel shift has to occur to transfer from image area to storage area; thus, shutter times can be less than a microsecond and smear is essentially eliminated. The advantage is not free, however, as the imaging area is now covered by opaque strips dropping thefill factorto approximately 50 percent and the effectivequantum efficiencyby an equivalent amount. Modern designs have addressed this deleterious characteristic by adding micro lenses on the surface of the device to direct light away from the opaque regions and on the active area. Micro lenses can bring the fill factor back up to 90 percent or more depending on pixel size and the overall system's optical design. CCD MpixelsAPS-C1.8" (23.98 x 16.41mm) sensor side The choice of architecture comes down to one of utility. If the application cannot tolerate an expensive, failure-prone, power-intensive mechanical shutter, an interline device is the right choice. Consumer snap-shot cameras have used interline devices. On the other hand, for those applications that require the best possible light collection and issues of money, power and time are less important, the full-frame device is the right choice. Astronomers tend to prefer full-frame devices. The frame-transfer falls in between and was a common choice before the fill-factor issue of interline devices was addressed. Today, frame-transfer is usually chosen when an interline architecture is not available, such as in a back-illuminated device.CCDs containing grids ofpixelsare used indigital cameras,optical scanners, and video cameras as light-sensing devices. They commonly respond to 70 percent of theincidentlight (meaning a quantum efficiency of about 70 percent) making them far more efficient thanphotographic film, which captures only about 2 percent of the incident light. CCD megapixelHewlett-Packarddigital cameraMost common types of CCDs are sensitive to near-infrared light, which allowsinfrared photography,night-visiondevices, and zerolux(or near zero lux) video-recording/photography. For normal silicon-based detectors, the sensitivity is limited to 1.1m. One other consequence of their sensitivity to infrared is that infrared fromremote controlsoften appears on CCD-based digital cameras or camcorders if they do not have infrared blockers.Cooling reduces the array'sdark current, improving the sensitivity of the CCD to low light intensities, even for ultraviolet and visible wavelengths. Professional observatories often cool their detectors withliquid nitrogento reduce the dark current, and therefore the thermal noise, to negligible levels.An intensified charge-coupled device (ICCD) is a CCD that is optically connected to an image intensifier that is mounted in front of the CCD.

4.4 INTENSIFIED CHARGE COUPLED DEVICESAn image intensifier includes three functional elements: aphotocathode, amicro-channel plate(MCP) and aphosphor screen. These three elements are mounted one close behind the other in the mentioned sequence. The photons which are coming from the light source fall onto the photocathode, thereby generating photoelectrons. The photoelectrons are accelerated towards the MCP by an electrical control voltage, applied between photocathode and MCP. The electrons are multiplied inside of the MCP and thereafter accelerated towards the phosphor screen. The phosphor screen finally converts the multiplied electrons back to photons which are guided to the CCD by a fiber optic or a lens.An image intensifier inherently includes ashutterfunctionality: If the control voltage between the photocathode and the MCP is reversed, the emitted photoelectrons are not accelerated towards the MCP but return to the photocathode. Thus, no electrons are multiplied and emitted by the MCP, no electrons are going to the phosphor screen and no light is emitted from the image intensifier. In this case no light falls onto the CCD, which means that the shutter is closed. The process of reversing the control voltage at the photocathode is calledgatingand therefore ICCDs are also called gateable CCD cameras.Besides the extremely high sensitivity of ICCD cameras, which enable single photon detection, the gateability is one of the major advantages of the ICCD over theEMCCD cameras. The highest performing ICCD cameras enable shutter times as short as 200picoseconds. ICCD cameras are in general somewhat higher in price than EMCCD cameras because they need the expensive image intensifier. On the other hand EMCCD cameras need a cooling system to cool the EMCCD chip down to temperatures around 170K. This cooling system adds additional costs to the EMCCD camera and often yields heavy condensation problems in the application.ICCDs are used innight vision devicesand in a large variety of scientific applications.

4.5 Defects in CCD ArraysSince the CCD is made from semiconductor material as the medium for photon detection~ there may be several types of localised defects present on the chip. If a localized defect is present in one element then it can prevent all the subsequent elements in the line from working. Furthermore a localised defect present inthe read-out register can prevent many complete lines from working. Theoretically it is unlikely that such defects will be introduced after device manufacture. In practicep there is always a possibility that defects will be introduced 9 because of the complicated fabrication process. At present it is generally difficult to obtain a chip which is 100 per cent free from defects. However 9 the problem of localised defects in the CCD arraydoes not pose any difficulty for our astronomical work because only the good part of the CCD need be used.

5.CCD5.1 SPECIFICATIONS OF CCD

Specifications for the ST-8300 CCD Kodak KAF-8300

Pixel Array 3326 x 2504 pixels

Total Pixels 8.3 Megapixels

Pixel Size 5.4 x 5.4 microns

Shutter Type Electromechanical

Exposure 0.1 to 3600 seconds

Dimensions 4 x 5 x 2 inches

MITS COLLEGE, MADANAPALLIWhen further image processing and data reduction is necessary, many other useful programs exist, one of which is IRAF. IRAF stands for Image Reduction and Analysis Facility, and is a general purpose software system for the reduction and analysis of astronomical data. IRAF is written and supported by the IRAF programming group at the National Optical Astronomy Observatories (NOAO) in Tucson, Arizona. NOAO is operated by the Association of Universities for Research in Astronomy (AURA), Inc. under cooperative agreement with the National Science Foundation.3 Basic IRAF operations will be explain in further detail later on in this report.

ECE, DEPARTMENT

5.2 Color Camers : Digital color cameras generally use aBayer maskover the CCD. Each square of four pixels has one filtered red, one blue, and two green (thehuman eyeis more sensitive to green than either red or blue). The result of this is thatluminanceinformation is collected at every pixel, but the color resolution is lower than the luminance resolution.Better color separation can be reached by three-CCD devices (3CCD) and adichroic beam splitter prism, that splits theimageintored,greenandbluecomponents. Each of the three CCDs is arranged to respond to a particular color. Manyprofessional videocamcorders, and some semi-professional camcorders, use this technique, although developments in competing CMOS technology have made CMOS sensors, both with beam-splitters and bayer filters, increasingly popular in high-end video and digital cinema cameras. Another advantage of 3CCD over a Bayer mask device is higherquantum efficiency(and therefore higher light sensitivity for a given aperture size). This is because in a 3CCD device most of the light entering the aperture is captured by a sensor, while a Bayer mask absorbs a high proportion (about 2/3) of the light falling on each CCD pixel.For still scenes, for instance in microscopy, the resolution of a Bayer mask device can be enhanced bymicro scanningtechnology. During the process ofcolor co-site sampling, several frames of the scene are produced. Between acquisitions, the sensor is moved in pixel dimensions, so that each point in the visual field is acquired consecutively by elements of the mask that are sensitive to the red, green and blue components of its color. Eventually every pixel in the image has been scanned at least once in each color and the resolution of the three channels become equivalent (the resolutions of red and blue channels are quadrupled while the green channel is doubled).5.3 Sensor sizesSensors (CCD / CMOS) come in various sizes, or image sensor formats. These sizes are often referred to with an inch fraction designation such as 1/1.8 or 2/3 called theoptical format. This measurement actually originates back in the 1950s and the time of Vidicon tubes.5.4 Electron Multiplying CCD : Anelectron-multiplying CCD(EMCCD, also known as an L3Vision CCD, a product commercialized by L2V Ltd., GB, L3CCD or Impactron CCD, a product offered by Texas Instruments) is a charge-coupled device in which a gain register is placed between the shift register and the output amplifier. The gain register is split up into a large number of stages. In each stage, the electrons are multiplied byimpact ionizationin a similar way to anavalanche diode. The gain probability at every stage of the register is small (P< 2%), but as the number of elements is large (N > 500), the overall gain can be very high (), with single input electrons giving many thousands of output electrons. Reading a signal from a CCD gives a noise background, typically a few electrons. In an EMCCD, this noise is superimposed on many thousands of electrons rather than a single electron; the devices' primary advantage is thus their negligible readout noise. It is to be noted that the use ofavalanche breakdownfor amplification of photo charges had already been described in the US patent US3761744[18]in 1973 by George E. Smith/Bell Telephone Laboratories.EMCCDs show a similar sensitivity toIntensified CCDs(ICCDs). However, as with ICCDs, the gain that is applied in the gain register is stochastic and theexactgain that has been applied to a pixel's charge is impossible to know. At high gains (> 30), this uncertainty has the same effect on thesignal-to-noise ratio(SNR) as halving thequantum efficiency(QE) with respect to operation with a gain of unity. However, at very low light levels (where the quantum efficiency is most important), it can be assumed that a pixel either contains an electron or not. This removes the noise associated with the stochastic multiplication at the risk of counting multiple electrons in the same pixel as a single electron. To avoid multiple counts in one pixel due to coincident photons in this mode of operation, high frame rates are essential. The dispersion in the gain is shown in the graph on the right. For multiplication registers with many elements and large gains it is well modelled by the equation:ifwhere Pis the probability of gettingnoutput electrons givenminput electrons and a total mean multiplication register gain ofg.Because of the lower costs and better resolution, EMCCDs are capable of replacing ICCDs in many applications. ICCDs still have the advantage that they can be gated very fast and thus are useful in applications likerange-gated imaging. EMCCD cameras indispensably need a cooling system using eitherthermoelectric coolingor liquid nitrogen to cool the chip down to temperatures in the range of 65 to 95C (85 to 139F). This cooling system unfortunately adds additional costs to the EMCCD imaging system and may yield condensation problems in the application. However, high-end EMCCD cameras are equipped with a permanent hermetic vacuum system confining the chip to avoid condensation issues. The low-light capabilities of EMCCDs primarily find use in astronomy and biomedical research, among other fields. In particular, their low noise at high readout speeds makes them very useful for a variety of astronomical applications involving low light sources and transient events such aslucky imagingof faint stars, high speedphoton countingphotometry,Fabry-Prot spectroscopyand high-resolution spectroscopy. More recently, these types of CCDs have broken into the field of biomedical research in low-light applications including small animal imaging,single-molecule imaging,Raman spectroscopy,super resolution microscopyas well as a wide variety of modern fluorescence microscopytechniques thanks to greater SNR in low-light conditions in comparison with traditional CCDs and ICCDs. In terms of noise, commercial EMCCD cameras typically have clock-induced charge (CIC) and dark current (dependent on the extent of cooling) that together lead to an effective readout noise ranging from 0.01 to 1 electrons per pixel read. However, recent improvements in EMCCD technology have led to a new generation of cameras capable of producing significantly less CIC, higher charge transfer efficiency and an EM gain 5 times higher than what was previously available. These advances in low-light detection lead to an effective total background noise of 0.001 electrons per pixel read, a noise floor unmatched by any other low-light imaging device.

5.5 Frame Transfer CCD The frame transfer CCD imager was the first imaging structure proposed for CCD Imaging by Michael Tompsett at Bell Laboratories. A frame transfer CCDis a specialized CCD, often used inastronomyand someprofessional video cameras, designed for high exposure efficiency and correctness. The normal functioning of a CCD, astronomical or otherwise, can be divided into two phases: exposure and readout. During the first phase, the CCD passively collects incomingphotons, storingelectronsin its cells. After the exposure time is passed, the cells are read out one line at a time. During the readout phase, cells are shifted down the entire area of the CCD. While they are shifted, they continue to collect light. Thus, if the shifting is not fast enough, errors can result from light that falls on a cell holding charge during the transfer. These errors are referred to as "vertical smear" and cause a strong light source to create a vertical line above and below its exact location. In addition, the CCD cannot be used to collect light while it is being read out. Unfortunately, a faster shifting requires a faster readout, and a faster readout can introduce errors in the cell charge measurement, leading to a higher noise level. A frame transfer CCD solves both problems: it has a shielded, not light sensitive, area containing as many cells as the area exposed to light. Typically, this area is covered by a reflective material such as aluminium. When the exposure time is up, the cells are transferred very rapidly to the hidden area. Here, safe from any incoming light, cells can be read out at any speed one deems necessary to correctly measure the cells' charge. At the same time, the exposed part of the CCD is collecting light again, so no delay occurs between successive exposures. The disadvantage of such a CCD is the higher cost: the cell area is basically doubled, and more complex control electronics are needed

6.Practical Applications of the CCD Camera : As stated, CCD cameras are useful in scientific imagery, especially in astronomy, where, with the help of a telescope, they allow for high resolution images of stars, galaxies, and other celestial bodies that human eye cannot detect. CCD cameras can also be used in a laboratory to image in finer detail than a regular camera. The fact that CCDs are extremely sensitive to light makes them useful in experimentation where faint light detection is needed. For example, the 8-inch shutter pictured below leaks about 1/10,000ths of incident light. Even in a dark room, the leaked light was imperceptible to experimenters. Though, a 10 second integration time CCD exposure can resolve all the details of the leaked light as shown in the picture. By applying IRAF image processing (to be described later), we removed extraneous lighting by subtracting a dark image from the signal image.

7. DEVELOPMENTSEvery conceivable scheme has been tried to improve the various performance parameters. Indeed, some that would be hard to conceive have been tried and in a few cases these unusual approaches have proved successful. I will point out a few state-of-the-art devices that excel in the more important areas ofperformance.

7.1 ResolutionThe term resolution is used to denote several different performance parameters. From photography, we get lines per millimeter or more generally the smallest feature that can be distinguished on the image plane. In computer speak, we have a count of the number of pixels in each of the horizontal and vertical directions. Also, the product of the two linear pixel counts would be a total pixel count. Final, there is the aerial density of pixels on a CCD. This is typically in units of pixels per square centimeter. More often, we see something like, one-third inch, 1.3 Mega -pixel. The one-third inch refers to the chips diagonal measurement. The professional still camera, Nikon D1x, with its 5.47 Mega -pixel CCD produces images in 3008x1960 resolution. The chip size (23.7 x 15.6mm) is somewhat smaller than the 36 x 24 mm format of the common (among serious photographers) F lenses that this camera in designed to use. Nikons amateur camera, D100, ups the resolution to 6.1 pixels (3008 x 2000).Soon the Hubble Space Telescope (HST) will utilize a new Wide Field Camera (WFC3) incorporating 16 Mega -pixel CCD. This is a single chip offering 4096x4096 resolution.

7.2 SensitivityHere we mean the amount of charge developed for a given amount of light. Practically speaking sensitivity would be output signal (millivolts) per integrated light value (lumen-seconds). Intensified CCD (ICCD) is the technique most often used in the maximum sensitivity cameras. Roper Scientific (brand name: Princeton Instruments) manufactures some of the most sensitive ICCD cameras. These cameras (512x 512 pixels, frame-transfer architecture) have very high quantum efficiency (QE) and are capable of seeing single-photon events.

7.3 Speed

By speed, we generally mean, frame rate. Of course, when thinking of useful speed, we must consider sensitivity. The speedy motion of a lot of empty cells would not be very useful! A frame rate of 30 frames per second fps would be adequate for most video cameras (high speed scientific cameras need more).Surprisingly, digital still cameras can benefit from much higher speed (up to100 fps).This demand for great speed comes, not from the desire to take a large quantity of pictures in a small time but rather speed is needed for the auto-exposure (AE) and auto-focus (AF) functions incorporated in virtually all CCD still cameras. Other things being equal, as the pixel count goes up the time required to read all of the pixels increases. A interesting trick to achieve a high resolution (large pixel count) and still quickly readout enough information to meet the needs of AE and AF is reported in one of my cited papers. Furumiya et al. report a dual frame rate high-resolution CCD that runs in high-frame-rate skip mode (75 fps) to meet the speed requirement of AE and AF. Using ten (10) phase lines per V-CCD, they merge the pixels 5-to-1 vertically. This allows the entire CCD to be analyzed in one-fifth the normal time! Of course the resulting image in only one-fifth normal height (in the pixel sense) but that does not matter much for the AE and AF functions. The V-CCD is then operated in normal mode (15 fps) to take the picture. Here we use the common three-phase transfer-mode to acquire the full 1308x1032 pixel image.In looking at A CCD diagram, it is clear that the H-CCD is the weak link in terms of speed. The H-CCD must transfer an entire row of pixels, one at a time, before the V-CCD can move in the next row. This forces the V-CCD to move about one thousand times slower than the H-CCD! The obvious answer is to build the H-CCD as a specialized, high transfer rate, unit. Furumiya et al. report a 30 fps progressive scan device where the relatively slow V-CCD is backup by a 49 MHz H-CCD. They achieve this performance by using a two-phase drive on the H-CCD and different doping for the H-CCD vs. V-CCD.

7.4 Cost

Generally, by cost, we mean the total cost to market.The least expensive devices, available today, use the CMOS technology. But,then again, CMOS is not CCD! CMOS imaging devices have found there way into cheap web cameras and toy digital still cameras. They may soon show up as safety sensors in such items a automatic garage door openers.

8.CCD PROPERTIES

Quantum Efficiency is the percentage of photons striking the CCD that are actually collected.

Scotopic vision is low light conditions (rod cells) , Photopic is daytime (cone cells)

CCD Quantum Efficiency is determined by CCD type (front/back side, resistivity of Si, and temperature of operation) and CCD coating

9.USES OF CCD9.1 USE IN ASTRONOMY :Due to the high quantum efficiencies of CCDs, linearity of their outputs (one count for one photon of light), ease of use compared to photographic plates, and a variety of other reasons, CCDs were very rapidly adopted by astronomers for nearly all UV-to-infrared applications.Thermal noise andcosmic raysmay alter the pixels in the CCD array. To counter such effects, astronomers take several exposures with the CCD shutter closed and opened. The average of images taken with the shutter closed is necessary to lower the random noise. Once developed, thedark frameaverage image is then subtractedfrom the open-shutter image to remove the dark current and other systematic defects (dead pixels, hot pixels, etc.) in the CCD.TheHubble Space Telescope, in particular, has a highly developed series of steps (data reduction pipeline) to convert the raw CCD data to useful images. CCD cameras used inastrophotographyoften require sturdy mounts to cope with vibrations from wind and other sources, along with the tremendous weight of most imaging platforms. To take long exposures of galaxies and nebulae, many astronomers use a technique known asauto-guiding. Most auto guiders use a second CCD chip to monitor deviations during imaging. This chip can rapidly detect errors in tracking and command the mount motors to correct for them.An interesting unusual astronomical application of CCDs, calleddrift-scanning, uses a CCD to make a fixed telescope behave like a tracking telescope and follow the motion of the sky. The charges in the CCD are transferred and read in a direction parallel to the motion of the sky, and at the same speed. In this way, the telescope can image a larger region of the sky than its normal field of view. TheSloan Digital Sky Surveyis the most famous example of this, using the technique to produce the largest uniform survey of the sky yet accomplished. In addition to astronomy, CCDs are also used in astronomical analytical instrumentation such asspectrometers

9.2 Use of a CCD in a Controlled Environment For the purposes of this essay and the description of CCD operation, functionality, test methods, and data reduction, it will be assumed that all CCD use is in a controlled environment such as an indoor laboratory or dark room. A procedure for operation in this type of environment will be described. Keep in mind that CCD usage in different situations call for other procedures than the ones described below, although many of the same principles still apply. The CCD that was used for the actual data that will be represented is a product of SBIG, Santa Barbara Instrumentation Group. The model used was the ST-8300M/C.

CONCLUSIONThe device that was first envisioned as a new-kind of computer memory has grown up to become the dominant process for image capture. Although other technologies are available, the charge-coupled device gives the best performance in terms of resolution, sensitivity and just about every other parameter (with the possible exception being cost).

REFERENCE1. Etchells, Dave: Imaging Resource, http://www.imaging-resource.com/2. Furumiya, M.; Hatano, K.; Murakami, I.; Kawasaki, T.; Ogawa, C.; Nakashiba, Y.: A 1/3-in 1.3 M-pixel single-layer electrode CCD with a high-frame-rate skip mode, IEEE Transactions on Electron Devices, Volume 48 Issue 9, pp 1915-1921, September 20013. Furumiya, M.; Suwazono, S.; Morimoto, M.; Nakashiba, Y.; Kawakami, Y.; Nakano, T.; Satoh, T.; Katoh, S.; Syohji, D.; Utsumi, H.; Taniji, Y.; Mutoh, N.; Orihara, K.; Teranishi, N.; Hokari, Y.: A 30 frames/s 2/3-in 1.3 M-pixel progressive scan IT-CCD image sensor, IEEE Transactions on Electron Devices, Volume 48 Issue 9 , pp 1922-1928, September. 20014. Kodak CCD Primer, #KCP-001, Charge-Coupled Device (CCD) Image Sensors, Eastman Kodak Co., Microelectronics Technology Div., Rochester, http://www.kodak.com/5. Lucent Technologies: Inventors of charge-coupled device receive prestigious C&C Prize, Murray Hill, http://www.lucent.com7. Roper Scientific, Princeton Instruments, http://www.photomet.com8. Scientific Imaging Technologies: An Introduction to Scientific Imaging Charge-Coupled Devices, Beaverton, http://www.site-inc.com/9.Streetman, Ben G.: Solid State Electronic Devices, 4th ed, Prentice Hall, Englewood Cliffs, 199511 Wide Field Camera 3, Hubble Space Telescope, NASA/Goddard, http://wfc3.gsfc.nasa.gov/index.html

MADANAPALLE INSTITUTE OF TECHNOLOGY AND SCIENCE(Approved by AICTE, New Delhi, Affiliated to JNTU, Ananthapur)Madanapalle-517325, Andhra Pradesh.

BONAFIDE CERTIFICATEThis is to certify that this technical seminar report CCD:DESIGN AND APPLICATIONS OF CHARGE COUPLED DEVICES submitted in partial fulfilment of the requirement for the award of the degree for bachelor technology in electronics and communication engineering is a result of the bonafide work carried out by D.DINESH (11691A0424). He is bonafide student of this college studying IV year B.Tech during academic year 2011-2015.

Prof. A R REDDY, M.Tech, Ph.DHead of the department,Dept. of ECE.

Acknowledgement

I extend my sincere gratitude towards Prof. Mr.A.R.REDDY, Head Of the Department,Dept. of E.C.E for giving me his valuable knowledge and wonderful technical guidance. I also thank all the other faculty members of ECE department and my friends for their help and support.