THE USE OF CCD IMAGE LINE SENSORS IN VIDEO AND COMPUTER SYSTEMS. Luděk Bartoněk 1,JiříKeprt 2

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1 acta univ. palacki. olomuc., fac. rer. nat. ( ), physica 40 41, THE USE OF CCD IMAGE LINE SENSORS IN VIDEO AND COMPUTER SYSTEMS Luděk Bartoněk 1,JiříKeprt 2 1) Department of Experimental Physics, Natural Science Faculty of Palacký University, Svobody 26, Olomouc, Czech Republic 2) Joint Laboratory of Optics of Palacký University and Physical Institute of Academy of Sciences of Czech Republic, 17. listopadu 50, Olomouc, Czech Republic (Received February 13, 2002; accepted March 4, 2002) KEY WORDS: CCD line sensor, PSD sensor, parallel interface EPP able (IEEE1284), hybrid A/D converter WSH 570. ABSTRACT: This paper presents a way for practical use of the CCD linear image sensor (B/W) for scanning of light in some optical applications (spectroscopy). Communication of the equipment (detector CCD) with computer is realized by the help of parallel interface of personal computer (PC) without additive interface card. In final part of this contribution is presented a design of measuring circuit (interface) for sensor ILX511 with A/D converter, the type WSH570. The use of the line detector is demonstrated on detection of optical spectrum of mercury lamp. 1 Introduction Measurement of luminosity is a question all the time very actual. Trend of concurrently time is to take measurements in co-operation with computing system. The wiring diagram of measuring circuit is based on the use of suitable detector which signal is proportional to luminous intensity. The signal is further digitized and by the help of interface is stored in the memory for the next processing. Whole equipment may be engineered in the form of suitable board (card), which is placed into computer. In our case we created the interface of CCD detector ILX511 (Sony) connected with personal computer (PC) by the help of standard parallel port (the part of their equipment), so that no additional interface cards are needed. The control is made by direct port accesses and without any special drives or libraries. 87

2 2 Position Sensing Detectors For determination of objects position it is most advantageous to use positional 1D or 2D detectors. Position Sensing Detectors PSD (Fig. 1) are silicon photodiodes that provide an analog output directly proportional to the position of a light spot on the detector active area. The PSD allows you to monitor simultaneously the position and light intensity. The position resolution of a PSD is the minimum detectable displacement of a spot of light on the detector surface. The position resolution of ON-TRAK PSD s have been proven better than one part in a million [1]. 2.1 Theory of Operation Figure 1: The block diagram of Position Sensing Detector The Position Sensing Detector consists of n-type silicon substrate with two resistive layers separated by a p-n junction. The front side has an ion implanted p-type resistive layer with two contacts at opposite ends. The back side has an ion implanted n-type resistive layer with two contacts at opposite ends placed orthogonally to the contacts on the front side. On a single axis PSD the electrodes are placed at opposite ends of the p-type resistive layer. A light spot within the spectral range of silicon will generate a photocurrent which flows from the incident point through the resistive layers to the electrodes. The resistivity of the ion implanted layer is extremely uniform so the photogenerated current at each electrode is inversely proportional to the distance between the incident spot of light and electrodes. The one-dimension PSD detector (1D), his equivalent circuit and spectral range, they are displayed in Fig. 2 and Fig. 3. The photoelectric current generated by the incident light flows through the device and can be seen as an input bias current divided into two output currents, Y1 and Y2. The relationship between these two output currents gives the light spot position through the formula P osition = Y 1 Y 2 : L (1) Y 1 + Y 2 2 where L is equal to the length of the PSD. With this equation the intensity of the incident light spot does not affect the calculation of the light spot position. 88

3 Figure 2: One-dim. PSD equivalent circuit, Ip = Photocurrent generated by incident light, D = Ideal diode, PN junction of PSD, C = Junction capacitance, Rsh = Shunt resistance, Rp = Position resistance Figure 3: Spectral range of PSD 3 Charge Couple Devices (CCD) At present for measuring of luminosity are very widespread sensors in solid state on basis CCD (Charge Couple Devices). CCD structure was discovered in the year 1969 and in comparison with vacuum pick-up tube they have first of all small mass, high lifetime and reliability, small input power and also simple technology of production [2]. Charge coupled device (CCD) is created by rows of simple structure MIS (metal insulator semiconductor) created on common semiconductor substrate so that tapes of metal electrode of sensor are formed into lines (at 1D) or into regular matrix (2D). 3.1 Study of CCD Transmission of a charge in CCD structure we can introduce for instance by onedimensional shift of the electrical charge. At circuit we consider 8 electrodes where every third is accessible to relevant point of source clock how is illustration et pictures 4, 5, 6. 89

4 Figure 4: Storage of the information in points 1, 4, 7 In starting position are connected electrodes 1, 4, 7 with voltage, which storage of the charge R2 U stor = U 2 : (2) On all the others electrodes it is voltage U 1,where U 1 <U stor : (3) The silicon tablet is grounded. We suppose, that in spatially defined depletion region 1 and 7 are the charge clusters and in spatially defined depletion region 4 there are not (Fig. 4). At following time we will connect voltage to electrodes 2, 5 and 8 for record of information U rec = U 3 ;(U 3 >U 2 ) (4) so that the clusters of charge begin walk up from structure 1 to structure 2 and from structure 7 into structure 8. At structure 4 there is not any shift (Fig. 5). Figure 5: Transfer the information by means of CCD structure In further time there will be on electrodes 2, 5, 8 the voltage U stor and on others electrodes occurs storage cycle of information (Fig. 6). The information (charge clusters) are preserved and shifted about one position. Thereby the charge is transferred. Figure 6: Storage of the information in point 2, 5, 8 If we place charge detector on CCD element below electrode 8, in first time we can shift the charge on this detector and read charge from CCD element 7. For further 90

5 displacement it is possible to read the charge from element 6 etc. till there will be read the charges from the whole structure. 4 Description of CCD linear Sensor ILX511 The ILX511 is a rectangular reduction type of CCD linear image sensor designed for bar code POS hand scanner and optical measuring equipment use (Fig. 7a, b). Figure 7: CCD linear sensor ILX511 from Sony a) plastic cases ILX511 package outline, b)frontview It has a build-in timing generator, clock-drives and sample-and-hold circuit, ensure single 5 V power supply for easy use. Number of effective pixels is Pixel size is 14μm x 200μm ultra-high sensitivity. The plastic cases of microchip circuit have 22 pins DIP, maximum clock frequency is 2MHz. Course of driving signal of ILX511 is on the Fig. 8. Figure 8: Clock timing diagram of ILX511 Price of this type is Euro/unit. Perspective, up March 2003, firm SONY intend to replace the type ILX511 by the new sensor ILX554A with pixel sizes 14μm x56μm[3]. The new price should be 19,75 Euro/unit. Circuit of ILX511 contains: Output amplifier, S/H circuit, CCD analog shift register, clock-drivers, clock pulse generator (Fig. 9). 91

6 4.1 Interface Figure 9: Inside circuit block diagram of sensor ILX511 For right function of sensor it is necessary to ensure its right timing pulse. Figure 10: Block diagram of interface In Fig. 10 it is a block diagram of controller for sensor ILX511. Signal from the sensor is modified (low-pass filter) and is feed into 8-bit A/D converter. Output of converter is connected with EPP port. Programmatic logic manages the activity of the whole controller. 92

7 5 Design of ILX511 interface PC with hybrid converter type of WS570 In Fig. 11a there is demonstrated the application circuit of the sensor ILX511 without S/H mode. Schema of A/D converter of the type VSH570 is describe in Fig. 11b. Figure 11a: Application circuit (without S/H mode) Figure 11b: Inside circuit block diagram of hybrid A/D converter type of WSH570 The WSH570 (Fig. 11b) is anagogic numerical 8-bit approximation converter for instrument application with unipolar or bipolar input and parallel or serial exit. Converter contains source of referential voltage, D/A converter, comparator, register of approximation and clock register. Supply voltage is in interval < 18V; U;+18V >, conversion time is 5μs [4]. 5.1 Standard parallel port PC Difference in the port modes according to standards SPP, EPP or ECP is in extensive possibility of two-way communication by the help of data bit D0 D7. That is reached by the help of change hardware structure of terminal parts of these connections. 93

8 Figure 12: Data pin SPP Figure 13: Data pin EPP and ECP In Fig. 12 and Fig. 13 there is a circuit of end parts data bit of parallel port according to specifications EPP and ECP. The diagram shows entrance data into input register [5], [6]. By this way it can be possible to set the port in mode reading so that there is can be written the value of logical A s. That transistor stapling logical level 0 stay unbuttoned and over terminator resistance it is possible to read logical level of transmission from outside. Data can be recorded and read on data port after the operation of data setting into enter mode (log.1) by addition of 5. bit location on address 378H+2. 6 The use of CCD linear sensor in spectroscopy As an example of the use of linear CCD sensor is its application in spectroscopy. If we put a transparent holographic grating (HG)in convergent beam of light (Fig. 14) we can see on the scale (in a focus plane F of the convergent beam) spectra of the light (rainbows) in visible range from violet and blue across green and yellow to orange and red. Figure 14: Diffraction of a convergent beam of light on a holographic grating (HG) 94

9 Figure 15: Spectral sensitivity of the line sensor ILX511 If we replace in our visible spectrum (as the source of light we used a metal filament lamp) the shade by our CCD linear sensor, we can see the sensitivity of the elements (pixels) of the sensor on different compounds (colors) of the white light (Fig. 15). As it is well known and it is clear from Fig. 15, the elements of CCD sensors are more sensitive on the red part of the spectrum. In Fig. 15 there is shown an example of a continuous spectrum. More important in the praxis is the case of a line pattern spectrum. If we use as the source of light a quicksilver (mercury) lamp then linear CCD sensor can detect the line pattern spectrum. The most important lines of this spectrum are visible from the spectrograph demonstrated in Fig. 16. Figure 16: The measured spectrum of a mercury lamp 95

10 7 Conclusion From the record of spectrum of a metal filament lamp it is clear that linear sensor ILX511 is very sensitive especially in the area of reds colors. That s why for the recored linearity of the whole spectrum it is necessary to smooth the sensitivity of the sensor by suitable software. Whole arrangement interface over concurrently port PC computer enables communication of the detector and computer in very short time (> 10ms/ row). SOUHRN POUŽITÍ CCD OBRAZOVÝCH ŘÁDKOVÝCH SNÍMAČŮ VE VIDEO A POČÍTAČOVÝCH SYSTÉMECH Tento článek představuje čtenáři CCD lineární snímač (B/W) pro skenování světelného signálu s ohledem na použití ve vybraných optických aplikacích (spektroskopie). Komunikace zařízení (detektor CCD) s počítačem je realizována pomocí paralelního rozhraní osobního počítače (PC) bez přídavné karty rozhraní. V konečné části tohoto příspěvku je uveden návrh měřicího zapojení (interface) pro sensor ILX511 s A/D převodníkem typu WSH570. Použití řádkového detektoru je demonstrováno na příkladu záznamu čarového optického spektra rtuťové výbojky. 8 References [1] SiTek PSD (Position Sensing Detectors) 2001, [2] Cenkl, B.: Užití CCD prvků při snímání a digitalizaci obrazové informace počítačem, DP, PřF UP [3] EURECA Messtechnik GmbH, Am Feldgarten 3D Köln, GERMANY [4] Tesla ELTOS, katalog I., TISK Brno [5] Řehák, J.: HW server. Ruská 106 Praha , [6] Kainka, B.: Využití rozhraní PC, měření, řízení a regulace pomocí standardních portů PC, HEL Ostrava