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low noise, high sensitivity optical sensor data sheet adpd2214 rev. 0 document feedback information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. specifications subject to change without notice. no license is granted by implication or otherwi se under any patent or patent rights of analog devices. trademarks and registered trademarks are the property of their respective owners. one technology way, p.o. box 9106, norwood, ma 02062 - 9106, u.s.a. tel: 781.329.4700 ? 2016 analog devices, inc. all rights reserved. technical support www.analog.com features ultra h igh detectivity photodetector 9 0 fa/hz (typical) u ltralow noise f loor signal - to - noise ratio ( snr ) near s hot n oise limit 137 a (typical) of supply current when active (e e = 0 w/cm 2 ) 1 a (typical) of supply current in standby high speed, deep junction photodiode nominal linear output current : 240 a (typical) flexible output configuration excellent pulse response high ambient light rejection space - saving , 4 mm 4 mm lfcsp package applications heart rate , pulse oximetry monitoring (p hotoplethysmography ) battery - powered medical sensors chemical a nalysis functional block d iagram figure 1 . general description the adpd2214 is an optical sensor optimized for biomedical applications. very low power consumption and near theoretical s ignal - to - n oise r atio (snr) are achieved by packaging an ultralow capacitance deep junction silicon photodiode operated in zero bias photoconductiv e mode with a low noise current amplifier. the adpd2214 offers a typical 7 5 khz bandwidth performance , which is well suited for use with pulsed excitation. the adpd2214 uses very little power during operation and incorporates a power - down pin , enabling power cycling to optimize battery life in portable applications. the adpd2214 provides shot noise limited performance , making it an excellent choice for measuring signals with the highest possible fidelity in low light conditions. this combination of low power, very high snr , and electromagnetic interference (emi) immunity enables low - power system solutions not possible w ith traditional photodiode (pd) and transimped ance amplifier ( tia ) systems. 13722-001 gnd pwdn out adpd2214 vcc current amplifier + ?
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adpd2214 data sheet rev. 0 | page 2 of 13 table of contents features .............................................................................................. 1 applications ....................................................................................... 1 functional block diagram .............................................................. 1 general description ......................................................................... 1 revision history ............................................................................... 2 specifications ..................................................................................... 3 absolute maximum ratings ............................................................ 4 thermal resistance ...................................................................... 4 soldering profile ........................................................................... 4 esd caution .................................................................................. 4 pin configuration and function descriptions ............................. 5 typical performance characteristics ............................................. 6 terminology ...................................................................................... 8 theory of operation ........................................................................ 9 overview ........................................................................................ 9 shot noise limited performance ............................................... 9 sensitivity and snr .......................................................................9 linearity ..........................................................................................9 package considerations ................................................................9 epad connection .........................................................................9 applications information .............................................................. 10 powering the device .................................................................. 10 power-down ............................................................................... 10 pulse mode operation ............................................................... 10 output configuration ................................................................ 10 3-wire cable voltage configuration ....................................... 10 3-wire current mode configuration ...................................... 10 evaluation board schematic and layout .................................... 12 outline dimensions ....................................................................... 13 ordering guide .......................................................................... 13 revision history 4/16revision 0: initial version
data sheet adpd2214 rev. 0 | page 3 of 13 specifications v cc = 3.3 v , t a = 25 c, = 528 nm, unless otherwise noted . i pd is the photodiode current, i mod is the modulation current, e e is irradiance, i out is output current, v bias is the bias voltage, r feedback is the tia feedback resistor, and r load is the load resistance. table 1. parameter symbol test conditions/comments min typ max unit gain gain (current amplifier) tla 24 dynamic performance frequency response peaking <6 db rise time t r 10% to 90% full scale ( fs ) ( i out = 24 a ) 6 s fall time t f 90% to 10% fs ( i out = 24 a) 6 s bandwidth bw i pd = 10 na, i mod = 1 na 75 khz optical performance diode active area 4.5 mm 2 saturation irradiance 890 w/cm 2 noise performance current noise , output referred 1 e e = 0 w/cm 2 1920 fa/hz i pd = 10 na to 300 na 1.4 n shot fa/hz i pd > 300 na 1.15 n shot fa/hz current noise floor, input referred e e = 0 w/cm 2 , at 1 khz 9 0 150 fa/hz noise equivalent power nep at 1 khz 100 fw/hz e e required for snr = 10000:1 a t 1 khz 80 nw/cm 2 power and supply supply voltage v cc 1.8 3.3 5.0 v power supply rejection ratio psrr v cc = 1.8 v to 5.0 v, e e = 890 w/cm 2 120 na/v current standby i standby pwdn > v ih 1 a supply at e e = 0 w/cm 2 i floor 137 a supply 2 i supply i out = 10 a 166 a i out = 240 a 950 a output characteristics amplifier static bias current input referred e e = 0 w/cm 2 10 na output referred e e = 0 w/cm 2 240 na maximum output voltage v out_max v cc ? 0.75 v nominal linear output current i out_fs v 240 a linearity into tia v bias = 1.3 v, r feedback = 25 k 60 db linearity into resistive load i out < 100 a , r load = 5 k 60 db peak output current 3 300 a output capacitance c out from out to gnd 5 pf output resistance r out from out to gnd 1000 m power - down logic input voltage high level v ih v cc ? 0.2 v low level v il 0.2 v leakage current high i ih pwdn = 3.3 v 0.2 n a low i il pwdn = 0 v ? 8.5 a operating ambient temperature range ? 40 + 85 c 1 n shot refers to photon shot noise. photon shot noise is the fundamental noise floor for all photodetectors in photoconductive mode. 2 i supply = i floor + (3.3 i out ). 3 outputs greater than i out_fs may have degraded performance.
adpd2214 data sheet rev. 0 | page 4 of 13 absolute maximum rat ings table 2. parameter rating supply voltage ( vcc ) 6.0 v storage temperature range ? 40 c to + 1 05 c junction temperature 110 c solder reflow temperature (< 1 0 sec) 260 c stresses at or above those listed under absolute maximum ratings may cause permanent damage to the product. this is a stress rating only; functional operation of the product at these or any other conditions above those indicated in the operational section of this specification is not implied. operation beyond the maximum op erating conditions for extended periods may affect product reliability. thermal resistance ja is specified for the worst case conditions, that is, a device soldered in a circuit board for surface - mount packages. table 3. thermal resistance package type ja jc unit 4 mm 4 mm lfcsp 52.45 11.55 c/w soldering profile figure 2 and table 4 provide information about the recommended soldering profile. figure 2 . recommended soldering profile table 4 . recommended soldering profile limits 1 profile feature condition ( pb free ) average ramp rate (t l to t p ) 2 c/sec maximum preheat minimum temperature (t smin ) 150c maximum temperature (t smax ) 200c time from t smin to t smax (t s ) 60 sec to 1 2 0 sec ramp - up rate (t smax to t l ) 2 c/sec maximum liquidus temperature (t l ) 217c time maintained above t l (t l ) 60 sec to 150 sec peak temperature (t p ) 260c + ( 0c/?5c ) time within 5c of actual t p (t p ) 2 0 sec to 3 0 sec ramp - down rate 3 c/sec maximum time from 25c (t25c) to peak temperature 8 minutes maximum 1 based on jedec standard j - std - 020d.1. esd caution t p t l t 25c t o peak t s prehe a t critica l zone t l t o t p temper a ture time ramp-down ramp-u p t smin t smax t p t l 13720-022
data sheet adpd2214 rev. 0 | page 5 of 13 pin configuration an d function descripti ons figure 3 . pin configuration table 5 . pin function descriptions pin no. mnemonic description 1 nic not internally connected . this pin c an be grounded. 2 nic not internally connected . this pin c an be grounded. 3 nic not internally connected . this pin c an be grounded. 4 vcc supply voltage. 5 pwdn power - down input. must be connected. pull this pin high to disable the device. 6 gnd ground. 7 out output terminal. 8 nic not internally connected . this pin c an be grounded. 9 nic not internally connected . this pin c an be grounded. 10 nic not internally connected . this pin c an be grounded. 11 epad exposed pad. the exposed pad must be left floating. the printed circuit board (pcb) area under the exposed pad can be left blank to facilitate this requirement. adpd2214 t op view (not to scale) notes 1. nic = not internal l y connected. 2. the exposed p ad must be left flo a ting. the pcb are a under the exposed p ad can be left blank t o f acili ta te this requiremen t . 13722-003 1 nic 2 nic 3 nic 4 vcc 5 pwdn 10 nic 9 nic 8 nic 7 out 6 gnd + ?
adpd2214 data sheet rev. 0 | page 6 of 13 typical performance characteristics figure 4. relative radiant sensitivity vs. angular displacement figure 5. responsivity vs. wavelength figure 6. power-down recovery time, 1% figure 7. supply current vs. output current (i out ) over supply voltage (v cc ) figure 8. small signal pulse response figure 9. bandwidth/peaking 13722-004 ?80 ?70 ?60 ?50 ?40 ? 30 ? 20 ? 10 0 0.2 0 0.2 0.4 0.4 0.6 0.6 0.8 s rel relative radiant sensitivity 1.0 horizontal vertical 0 1 2 3 4 5 6 7 responsivity (a/w) wavelength ( ) 300 331 362 393 424 455 486 517 548 579 610 641 672 703 734 765 796 827 858 889 920 951 982 1013 1044 1075 13722-005 ?10?10 10 30 50 time (s) output w a veform 1s 10s pwdn 13722-007 0 50 100 150 200 250 300 350 400 450 i out (a) v cc = 1.8v v cc = 2.5v v cc = 3.3v v cc = 5v 13722-009 supply current (a) 0 200 400 600 800 1.0m 1.2m 1.4m 1.6m 1.8m 0 20406080100 normalized output time (s) 1a 100na 13722-010 100 1k 10k frequency (hz) 100k 1m normalized response (db) ?25 ?20 ?15 ?10 ?5 0 5 13722-011
data sheet adpd2214 rev. 0 | page 7 of 13 figure 10 . noise bandwidth/peaking 10f 100f 1p 10p 100 1k 10k 100k frequenc y (hz) rms noise current referred t o input (a) 13722-014
adpd2214 data sheet rev. 0 | page 8 of 13 terminology optical power optical power is defined as the photon energy per unit of time measured as radiant flux () or radiant power, which is radiant energy (q) per unit of time. responsivity photodiode responsivity, , is a constant that correlates incident optical power (p opt ) with photodiode current (i pd ) and is typically expressed in units of amperes per watt ( a/w ). responsivity is essentially the quantum efficiency of the ability of the sensor to convert light into electron/hole pairs and is highly dependent upon the wavelength of the incident light as well as sensor material and temperature. photodiode area photodiode area is a measure of the photosensitive area of the diode . in pin diodes , this is the photosensiti ve area of intrinsic silicon between the positive and negative doped diffusion areas. in general, larger photodiodes demonstrate greater sensitivity as the output signal increases linearly with photosensitive area while noise increases at the sum of the sq uare of the photosensitive area. a larger photodiode area has a higher capacitance and longer carrier diffusion paths adversely affecting bandwidth. photo conductive mode photoconductive operation of a photodiode occurs when photons entering the silicon gen erate electron/hole pairs that are swept by the electric field to the opposite terminal. these carriers are presented at the terminals of the photodiode as a current proportional to the luminous flux incident on the junction of the photodiode. shot noise shot noise is a statistical fluctuation in any quantized signal such as photons of light and electrons in current. the magnitude of the shot noise is expressed as a root mean square (rms) noise current . shot n oise is a fundamental limitation in photodetect ors and takes the form of shot noise = (2 qi pd ) where : q is the charge of an electron (1.602 10 ? 19 coulomb). i pd is the photodiode current. photoplethysmography (ppg) photoplethysmography uses light to measure biological functions by sensing changes in the absorption spectra of soft tissue due to changes in hemoglobin volume and composition. linearity linearity is a measure of the deviation from an ideal change in output current relative to a change in optical power falling on the sensor. linearity is specified as the deviation from a best straight line fit of the current output of the sensor over a speci - fied range of optical power. linearity is a critical specification in ppg measurement s due to the requirement of sensing small ac signals impressed upon large dc offsets. static bias the adpd2214 has an internal 10 na bias that linearize s the input current mirror at low input levels and prevents transient reverse bias of the amplifier input stage. this bias is fixed and appears on the output as a 240 na typical offset. noise equivalent power (nep) noise e quivalent p ower is the amount of incident light power on a photo detector, which generates a photocurrent equal to the total noise current of the sensor . the n oise level is proportional to the square root of the frequency bandwidth ; therefore, nep is specified with a 1 hz bandwidth. nep is the fundamental baseline of the detectivity of the sensor .
data sheet adpd2214 rev. 0 | page 9 of 13 theory of operation overview the adpd2214 is an integrated , low power , optical sensor composed of a deep junction silicon photodiode coupled to a low noise current amplifier in an optically transparent chip scale package. the adpd2214 is optimized for battery - powered, wearable , medical, and industrial optical sensing applications requiring low power and high snr . shot noise limited p erformance the on - board photodiode of the adpd2214 is operated in photoconductive mode with a zero bias voltage. this mode of operation allows the diode to operate with no dc dark current caused by leakage across the depletion area of the diode , providing a fundamental limit of shot noise. the n oise level is proportional to the square root of the frequency bandwidth . sensitivity and snr snr is a measure of the ability of th e sensor to separate the signal of interest from spurious signals that occur from the surrounding environment of the device , such as ambient light, non linearity , and noise within the device itself. the adpd2214 operates its integrated photodiode in a zero biased photoconductive mode to provide near zero dark current and , therefore , no dark shot noise component contribution from th e photodiode. the integrated current amplifier requires an internal bias current of 10 na to im prove bandwidth and linearize response at low light levels. this bias generates a shot noise component of 9 0 fa/hz at the output of the current amplifier and es tablishes the noise floor of the adpd2214 . to optimize the sensitivity of the adpd2214 , it is important to en sure that the optical signal is concentrated on the photoactive area of the integrated photodiode . the on - board precision current amplifier is shielded and is not significantly affected by light hitting its surface , but device sensitivity is based solely on the opti cal power incident to the photo detector. linearity linearity is critical to ppg due to the need to accurately extract a small amplitude , pul satile ac signal modulated onto the large dc component , which is caused by nonpulsatile tissue absorption and ambient light. in pulsed light applications, bandwidth is a critical component of the linear ity because fast recovery of the device from dark and/or power - down condition s can have a profound effect on the ability of the sensor to extract the signal of interest. the adpd2214 is production trimmed to ensure 60 db linearity at an irradiance of up to e e = 890 w/cm 2 , = 528 nm, at a supply voltage of 3.3 v. package consideratio ns the adpd2214 is packaged with a transparent epoxy molding compound. to maintain optimum sensitivity , take care in handling the device to prevent scratches or chemicals that may affect the surface finish above the photo diode. due to the lack of stabilizing fillers ( typically up to 70% silica ) used in opaque molding compounds , the maximum storage temperature of the adpd2214 is 105 c. the temperature profile for soldering is shown in figure 2 . epad connection the epad on the adpd2214 acts as a common electrical, thermal, and mechanical platform for the photodiode and amplifier and must not be connected externally. external cooling is not required due to the extremely low power consumption of the adpd2214 . analog devices, inc., recommends removal of traces beneath the device to eliminate potential coupling of external signals into the sensitive internal nodes of the adpd2214 .
adpd2214 data sheet rev. 0 | page 10 of 13 application s information the current output of the adpd2214 provides flexibility in interfacing to external circuitry. powering the device the adpd2214 is powered f r o m a single positive 1.8 v to 5 .0 v supply. the adpd2214 features high psrr, but proper circuit layout and bypassing is recommended to provide maximum sensitivity, especially in situations where the adpd2214 may share reference nodes with transmitters in pulse mode applications. above the quiescent current of the integrated current amplifier, there is a linear relatio nship to incident light as the current amplifier amplifies the photodiode output by a factor of 24. in typical battery - powered operation, the output of the source leds is dynamically reduced to save power based on the received signal strength of the photos ensor. the extremely low noise floor of the adpd2214 provides very high snr, allowing accurate signal extraction with minimal so urce power and at low incident optical power. power - down the adpd2214 is optimized for battery - powered operation by the inclusio n of an extremely low power standby mode that can be quickly switched to provide ultra low power consumption during dark periods in pulsed or mode locked applications , where the light source is cycled to improve ambient light rejection and reduce transmitte r power consumption. the power - down pin is not internal ly p ulled up or down, a nd must be connected to an external logic level for proper operation of the adpd2214 . pulse mode operation th e adpd2214 is optimized for b attery - powered operat ion by the inclusion of a power - down pin (pwdn). when sensing is inactive, the adpd2214 can be quickly swit ched into standby mode , reducing the supply current to 1 a during dark periods for pulsed or mode locked applications , where the light source is cycled to improve ambient light rejection and reduce transmit ter power consumption. for multiple wavelength systems, sequentially pulsing the optical emitters removes the need for multiple narrow bandwidth sensors. for both multiple wavelength (spo2) and single wavelength ( heart rate monitoring ) systems, pulsed operation can pro vide significant power savings fo r battery - powered systems. pulsed mode operation provides a calibration signal that is necessary to compensate for ambient light diffused throughout the tissue, which can be extracted by measuring the sensor output while the system emitters are off. advanc ed algorithms can then extract the signal of interest from dc offsets, noise, and interferer signals such as motion artifacts. output configuration the output of the adpd2214 allows different configurations depending on the application. the current gain of the adpd2214 reduces the effect of surrounding interferers but, for best perfor - mance, careful design and lay out is still necessary to achieve the best performance. the effect of capacitance on the output must be considered carefully regardless of configuration as bandwidth and response time of the system can be limited simply by the time required to charge and d ischarge parasitics. because the adpd2214 is effectively a current source, the adpd2214 output voltage drifts up to its complianc e voltage, approximately 1.2 v below vcc, when connected to an inter face that presents a high impedance. the rate of this drift is dependent on the adpd2214 output current, parasitic capaci t ance, and the impedance of the load. this drift can require additional settling time in circuits following the adpd2214 if they are actively multiplexing the output of the adpd2214 or presenting a high impedance due to power cycling. for multi plexed systems, a current steering architecture may offer a performance advantage over a break - before - make switch matrix. 3 - wire cable volta ge configuration the adpd2214 can be used in a minimal 3 - wire voltage configuration, offering a compact solution with very few components ( see figure 11 ). a shunt resistor (r s ) sets the transimpedance gain in front of the analog - to - digital converter (adc). this configuration allows flexibility in matching the adc converter full - scale input to the full - scale output of the adpd2214 . the dynamic range of the interface is limited to the compliance voltage of the adpd2214 . no additional amplification is needed prior to the adc. response time at the lower end of the range is limited by the ability of the output current to charge the parasitic capacitance presented to the output of the adpd2214 . 3 - wire current mode co nfiguration when used in the 3 - wire current mode configuration with a photodiode (se e figure 12), the adpd2214 is insensitive to load resistance and can be used when the signal processing is further from the sensor. emi noise and shielding requirements are minimized; however, cable capacitance has a direct effect on bandwidth, making the 3 - wire current mode configuration a better choice for unshielded interfaces. the feedback capacitance ( c f ) value must be chosen carefully to eliminate stability and bandwidth degrada tion of the adpd2214 . large capacitance around the feedbac k loop of the tia has a direct effect on the bandwidth of the system.
data sheet adpd2214 rev. 0 | page 11 of 13 figure 11. adpd2214 used in 3-wire cable voltage configuration figure 12. adpd2214 used in 3-wire current mode configuration adpd2214 current amplifier + ? adc and microprocessor 3.3v 3.3v r s gnd out vcc 13722-023 vcc out gnd 3.3v c f r f tia 3.3v adpd2214 adc and microprocessor 0v to v cc ?0.75 current amplifier + ? 13722-024
adpd2214 data sheet rev. 0 | page 12 of 13 evaluation board schematic and layout figure 15 shows the evaluation board schematic. figure 13 and figure 14 show the evaluation board layout for the top and bottom layers, respectively. figure 13. adpd2214 evaluation board top layer figure 14. adpd2214 evaluation board bottom layer figure 15. adpd2214 evaluation board schematic (do not install c3c) 13722-027 13722-028 e v a lz-adpd2214 u1c 1 3 5 4 7 10 pwdn nic nic vcc gnd nic 2 8 9 nic v cc pwdn gnd out nic nic out epad r1c 100k ? r2c 100k ? c2c 1f c3c 0.01f dni dni c1c 0.01f 6 13722-026
data sheet adpd2214 rev. 0 | page 13 of 13 outline dimensions figure 16. 10-lead lead frame chip scale package [lfcsp] 4 mm 4 mm body and 0.65 mm package height (cp-10-14) dimensions shown in millimeters ordering guide model 1 temperature range package description package option ordering quantity ADPD2214ACPZ-R7 ?40c to +85c 10-lead lead frame chip scale package [lfcsp] cp-10-14 1500 adpd2214acpz-rl ?40c to +85c 10-lead lead frame chip scale package [lfcsp] cp-10-14 5000 evalz-adpd2214 evaluation board 1 z = rohs compliant part. top view 10 1 6 5 bottom view seating plane 0.70 0.65 0.60 2.80 2.70 2.60 3.50 3.40 3.30 0.203 ref 0.20 min 0.050 max 0.035 nom 0.65 bsc exposed pad 4.10 4.00 sq 3.90 for proper connection of the exposed pad, refer to the pin configuration and function descriptions section of this data sheet. coplanarity 0.08 0.45 0.40 0.35 09-20-2013-a pin 1 index area pkg-004307 0.35 0.30 0.25 0.225 0.175 0.125 ?2016 analog devices, inc. all rights reserved. trademarks and registered trademarks are the prop erty of their respective owners. d13722-0-4/16(0)

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