pi0128wsn, pi0256wsn, pi0512wsn 50- m m-pitch wide aperture spectroscopic photodiode arrays engineering data sheet page 1 of 8 revised march 21, 2002 description peripheral imaging corporation's wsn series is family of self-scanning photodiode solid-state linear imaging arrays. these photodiode sensors employ pic?s proprietary cmos image sensing technology to integrate the sensors into a single monolithic chip. these sensors are optimally designed for applications in spectroscopy. accordingly, these sensors contain a linear array of photodiodes with an optimized geome t - rical aspect ratio (50- m m aperture pitch x 2500- m m aperture width) for helping to maintain mechanical stability in spectroscopic instruments and for providing a large light-capturing ability. the family of sensors consists of photodiode arrays of various lengths, 128, 256, and 512 pixels. the wsn photodiode arrays are mounted in 22-pin ceramic side-brazed dual-in-line packages that fit in standard dip sockets. a diagram of its pinout config u - ration is seen in figure 1. features 65-pc saturation capacity for wide dynamic range. wide spectral response (180 ? 1000 nm) for uv and ir response. np junction photodiodes with superior resistance to uv damage. low dark current. integration time up to 9 seconds at room temper a - ture. integration time extended to hours by cooling. high linearity. low power dissipation (less than 1 mw). geometrical structure for enhanced stability and registration. standard 22-lead dual-in-line ic package. figure 1 . pinout configuration. sensor characteristics the peripheral imaging corporation's self-scanned wsn photodiodes are spaced on a 50- m m pitch. the line density is 20 diodes/mm and accordingly the overall die lengths of the different arrays vary with the number of photodiodes. for example, the 128-pixel array is 6.4-mm long, the 256-pixel array is 12.8-mm long, and the 512-pixel array is 25.6-mm long. each array has four additional dummy photodiodes. on each side, there are one dark (non-imaging) dummy phot o - diode and one imaging dummy photodiode. the height of the sensors is 2500 m m. the tall, narrow apertures make these sensors desirable for use in monochr o - mators and spectr o graphs. peripheral imaging corporation ?
pi0128wsn, pi0256wsn, pi0512wsn engineering data sheet page 2 of 8 revised march 21, 2002 figure 2 . geometry and layout of photodiode pixels. during normal operation, the photons incident in or near the np photodiode junction generate free charges that are collected and stored on the junction's depletion capacitance. the number of collected charges is proportional to the light exposure. figure 3 shows the stored signal charge as function of light exposure at a wavelength of 575 nm. the exposure is the product of the light intensity in nw/cm 2 and integration time in seconds. the charge accumulates linearly until reac h - ing the saturation charge, and the corresponding exposure is the saturation exposure. the responsivity may be calculated as the saturation charge divided by saturation exposure. the predicted typical responsivity of a photodiode is 3.5 10 -4 c/j/cm 2 at 575 nm. figure 4 shows the predicted responsivity of the photodiodes as a function of wavelength. 0 10 20 30 40 50 60 70 80 0 50 100 150 200 250 e xpo sure (nj/cm 2 ) output charge (pc) saturation charge saturation exposure figure 3 . stored signal charge as function of exposure at a wavelength of 575 nm.
pi0128wsn, pi0256wsn, pi0512wsn engineering data sheet page 3 of 8 revised march 21, 2002 0.0 e+00 5.0 e -05 1.0 e -04 1.5 e -04 2.0 e -04 2.5 e -04 3.0 e -04 3.5 e -04 4.0 e -04 4.5 e -04 5.0 e -04 100 300 500 700 900 wavelength (nm) r e sponsivity (c/j/cm 2 ) qe=20% qe=40% qe=60% qe=80% figure 4 . predicted spectral response. note: quantum efficiency (qe) can be calculated by dividing the responsivity by the area of the sensor's element and multiplying the resulting ratio by the energy per photon in electron volts ( ev). the dark current is typically 0.2 pa at 25 o c and varies as function of temperature. the dark current will co n - tribute dark-signal charges and these charges will increase linearly with integration time. the dark signal and the photogenerated signal combined result in the total signal charge. self-scanning circuit figure 5 shows a simplified electrically equivalent circuit diagram of the photodiode array. an mos read switch connects every photodiode in the array to a common output video line. incident photons generate electron charge that is collected on each imaging photodiode while the switch is open. the shift register is activated by the start pulse. a pulse propagates through each shift register stage and activates the mos read switches sequentially. as the shift register sequentially closes each read switch, the negative stored charge, which is proportional in amount to the light exposure, from the corresponding photodiode is readout onto the video line, qout. typically, an external charge-integrating amplifier senses the neg a - tive output charge on the video line from each photod i - ode pixel. the shift register continues scanning the photodiodes in sequence, until the last shift register stage is reach, at which time the fourth and last dummy pixel is read out and end-of-scan (eos) output is held high for one clock cycle. the next start pulse can then restart the shift register. i/o pins although the wsn package has 22 pins, as shown in figure 1, there are only 6 functionally active i/o pins in addition to the supply pins, as shown in figure 5. in essence, only two clocks, clk and start, are r e - quired for controlling the timing of the sensor's video readout. the remaining i/o descriptions are for the figure 5 . simplified circuit diagram of a wsn photodiode array. shift register
pi0128wsn, pi0256wsn, pi0512wsn engineering data sheet page 4 of 8 revised march 21, 2002 video signal output, the end-of-scan signal, the two temperature diodes, and the supply biases. qout must be biased externally to vbias (see reco m - mended operating conditions section below). each temperature diode is operated with a small constant current that forward-biases its pn junction. by mea s - uring the forward-bias voltage, one can track the silicon die temperature. the temperature diodes may be disabled by connecting their anodes to vss. these i/os are listed with their acronym designators and functional descriptions in the following table 1. table 1 . symbols and functions and i/o pins. symbol function and description vss ground. vdd +5.0 volts. start start pulse: input to start the line scan. clk clock pulse: input to clock the shift register. eos end of scan: output from the shift register to indicate the completion of one line scan. qout video charge output: output from the photodiodes pixels. td1 temperature diode 1: anode of temperature diode 1. td2 temperature diode 2: anode of temperature diode 2. nc no connection
pi0128wsn, pi0256wsn, pi0512wsn engineering data sheet page 5 of 8 revised march 21, 2002 clock and voltage requirements the clocking requirements are relatively simple. as it was indicated in figure 5 and table 1, there are only two input signals that require clocked inputs. they are clk, the clock for the shift register, and start, the shift register start pulse. the timing specifications and the symbol definition for figure 6 are listed in table 2. the control clock amplitudes for i/os are compatible with the 5-volt cmos devices. figure 6 . timing diagram. table 2 . symbol definitions and timing specifications for timing diagram. item symbol min typical max units clock cycle time to 666 (128wsn) 666 (256wsn) 1000 (512wsn) 10000 ns clock high pulse width twh 566 (128wsn) 566 (256wsn) 900 (512wsn) ns clock low pulse width twl 100 ns clock duty cycle 1 50 99 % data setup time tds 100 ns data hold time tdh 100 ns eos low-to-high delay telh 400 ns eos high-to-low delay tehl 400 ns signal delay time tsd 50 ns signal settling time tsh 566 (128wsn) 566 (256wsn) 900 (512wsn) ns signal settle to clock edge tsch 0 ns
pi0128wsn, pi0256wsn, pi0512wsn engineering data sheet page 6 of 8 revised march 21, 2002 recommended operating conditions the following table lists the recommended operating conditions. table 3. recommended operating conditions at 25 o c. parameters symbol min typical max units power supply vdd 4.5 5.0 5.5 volts input clock pulses high level 1 vih vdd ? 0.8 vdd vdd volts input clock pulse low level 1 vil 0.0 0.0 0.8 volts video charge output external bias vbias vdd ? 0.5 vdd ? 0.5 vdd volts clock frequency fclk 0.1 1.5 (128wsn) 1.5 (256wsn) 1.0 (512wsn) mhz integration time 2 tint 0.09 (128wsn) 0.18 (256wsn) 0.52 (512wsn) 9000 ms notes: 1. applies to all control-clock inputs. 2. integration time is specified at room temperature such that the maximum dark current charge build up in each pixel is less than 10% of the minimum saturation charge. accordingly, it may be as long as 9 seconds at room temperature. longer integration times may be achieved by cooling the device. an appropriate clock frequency must be chosen so that the shift register completes its operation within the desired integration time.
pi0128wsn, pi0256wsn, pi0512wsn engineering data sheet page 7 of 8 revised march 21, 2002 electro-optical characteristics the following table lists the electro-optical characteristics. table 4. electro-optical characteristics at 25 o c. parameters symbol min typical max units center-to-center spacing 50 m aperture width 2500 m pixel area a 1.25x10 -3 cm 2 fill factor 1 ff 86 % quantum efficiency 1,2 qe 70 % responsivity 1,2 r 3.5 10 -4 c/j/cm 2 nonuniformity of response 3 2 5 +/-% saturation exposure 2 esat 160 185 nj/cm 2 saturation charge 4 qsat 55 65 pc average dark current 5 0.2 0.6 pa spectral response peak l 600 nm spectral response range 6 180 ? 1000 nm notes: 1. fill factor, quantum efficiency, and responsivity are related by the equation r = ( q e l / hc) . qe . ff . a, where q e is the charge of an electron and hc/ l is the energy of a photon at a given wavelength. responsivity is therefore given per pixel. 2. at wavelength of 575 nm (yellow-green) and with no window. 3. measured at 50% vsat with an incandescent tungsten lamp filtered with an schott kg -1 heat-absorbing filter. 4. saturation charge specified for a video output bias of 4.5 volts. 5. max dark leakage 1.5 x average dark leakage measured with an integration period of 500 ms at 25 o c. 6. from 250-1000 nm, responsivity 3 20% of its peak value.
pi0128wsn, pi0256wsn, pi0512wsn engineering data sheet page 8 of 8 revised march 21, 2002 package dimensions the following figure provides the package dimensions. device a b pi0128wsn 1.0800.010 6.4 mm pi0256wsn 1.0800.010 12.8 mm pi0512wsn 1.6000.010 25.6 mm figure 7 . package dimensions. note: dimensions are in inches except where millimeters (mm) are indicated. ? ? 2001-2002 ami semiconductor. printed in usa. all rights reserved. specifications are subject to change without notice. contents may not be reproduced in whole or in part without the express prior written permission of amis. information furnished herein is believed to be accurate and reliable. however, no responsibility is assumed by amis for its use nor for any infringement of patents or other rights granted by impl ication or otherwise under any patent or patent rights of amis.
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