Instrumentation: Liquid and Gas Sensing (Design Conference 2013)

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This session focuses on liquid and gas sensing in instrumentation applications.

Liquid Sensing:
Visible light absorption spectroscopy and colorimetry are two fundamental tools used in chemical analysis. Most of these light-based systems use photodiodes as the light sensor, and require similar high input impedance signal chains. This session examines the different components of a photodiode amplifier signal chain, including a programmable gain transimpedance amplifier, a hardware lock-in amplifier, and a Σ-Δ ADC that can measure a sample and reference channel to greatly reduce any measurement error due to variations in intensity of the light source.

Gas Sensing:
Many industrial processes involve toxic compounds, and it is important to know when dangerous concentrations exist. Electrochemical sensors offer several advantages for instruments that detect or measure the concentration of toxic gases. This session will describe a portable toxic gas detector using an electrochemical sensor. The system presented here includes a potentiostat circuit to drive the sensor, as well as a transimpedance amplifier to take the very small output current from the sensor and translate it to a voltage that can take advantage of the full-scale input of an ADC.

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Instrumentation: Liquid and Gas Sensing (Design Conference 2013)

  1. 1. Instrumentation: Liquid and GasSensingReference Designs and System Applications
  2. 2. Legal Disclaimer Notice of proprietary information, Disclaimers and Exclusions Of WarrantiesThe ADI Presentation is the property of ADI. All copyright, trademark, and other intellectual property andproprietary rights in the ADI Presentation and in the software, text, graphics, design elements, audio and all othermaterials originated or used by ADI herein (the "ADI Information") are reserved to ADI and its licensors. The ADIInformation may not be reproduced, published, adapted, modified, displayed, distributed or sold in any manner, inany form or media, without the prior written permission of ADI.THE ADI INFORMATION AND THE ADI PRESENTATION ARE PROVIDED "AS IS". WHILE ADI INTENDS THE ADIINFORMATION AND THE ADI PRESENTATION TO BE ACCURATE, NO WARRANTIES OF ANY KIND ARE MADEWITH RESPECT TO THE ADI PRESENTATION AND THE ADI INFORMATION, INCLUDING WITHOUT LIMITATIONANY WARRANTIES OF ACCURACY OR COMPLETENESS. TYPOGRAPHICAL ERRORS AND OTHERINACCURACIES OR MISTAKES ARE POSSIBLE. ADI DOES NOT WARRANT THAT THE ADI INFORMATION ANDTHE ADI PRESENTATION WILL MEET YOUR REQUIREMENTS, WILL BE ACCURATE, OR WILL BEUNINTERRUPTED OR ERROR FREE. ADI EXPRESSLY EXCLUDES AND DISCLAIMS ALL EXPRESS AND IMPLIEDWARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT OFANY THIRD PARTY INTELLECTUAL PROPERTY RIGHTS. ADI SHALL NOT BE RESPONSIBLE FOR ANY DAMAGEOR LOSS OF ANY KIND ARISING OUT OF OR RELATED TO YOUR USE OF THE ADI INFORMATION AND THE ADIPRESENTATION, INCLUDING WITHOUT LIMITATION DATA LOSS OR CORRUPTION, COMPUTER VIRUSES,ERRORS, OMISSIONS, INTERRUPTIONS, DEFECTS OR OTHER FAILURES, REGARDLESS OF WHETHER SUCHLIABILITY IS BASED IN TORT, CONTRACT OR OTHERWISE. USE OF ANY THIRD-PARTY SOFTWAREREFERENCED WILL BE GOVERNED BY THE APPLICABLE LICENSE AGREEMENT, IF ANY, WITH SUCH THIRDPARTY.©2013 Analog Devices, Inc. All rights reserved.2
  3. 3. Todays AgendaUnderstand challenges of precision high impedance sensingapplicationsElectrochemical gas detection (CN0234)Spectroscopy application using transimpedance amplifiers forphotodiode preamplifiers (CN0312) Design problems Low current measurement Noise Maintaining required bandwidthApplications selected to illustrate important design principlesapplicable to a variety of high impedance sensor conditioningcircuitsSee tested and verified Circuits from the Lab® signal chain solutionschosen to illustrate design principles Low cost evaluation hardware and software available Complete documentation packages: Schematics, BOM, layout, Gerber files, assemblies3
  4. 4. Circuits from the LabCircuits from the Lab® reference circuits are engineered and testedfor quick and easy system integration to help solve today‟s analog,mixed-signal, and RF design challenges.4 Complete Design Files onCD and Downloadable■ Windows Evaluation Software■ Schematic■ Bill of Material■ PADs Layout■ Gerber Files■ Assembly Drawing■ Product Device Drivers Evaluation Board Hardware
  5. 5. System Demonstration Platform (SDP-B, SDP-S) The SDP (System Demonstration Platform) boards provides intelligent USBcommunications between many Analog Devices Evaluation Boards andCircuits from the Lab boards and PCs running the evaluation software.5EVALUATIONBOARDSDP-BUSBPOWERUSBSDP-SEVALUATIONBOARDPOWER SDP-S (USB to serial engine based) One 120-pin small footprint connector. Supported peripherals: I2C SPI GPIO SDP-B (ADSP-BF527 Blackfin® based) Two 120-pin small footprint connectors Supported peripherals: I2C SPI SPORT Asynchronous Parallel Port PPI (Parallel Pixel Interface) Timers
  6. 6. Gas DetectorsCommonly used for industrial safety Area monitors permanently mounted near potentialgas sources Portable detectors worn on worker’s clothingCapable of detecting sub-ppm levels of toxic gasesUse infrared light, electrochemical sensors, heat, or a combination Multiple-gas detectors will typically have one sensor per target gas6
  7. 7. Gas Detection Using Electrochemical SensorsTypically used as toxic gas detectors Carbon monoxide, chlorine, hydrogen sulfide and other nasty industrialchemicals Can detect down to sub-ppm levels of gas concentration Could have VERY long settling times (10s or minutes)A potentiostat circuit is used to keep the reference electrode andworking electrode at the same voltage by controlling the voltage atthe counter electrodeA transimpedance amplifier converts the current in/out of theworking electrode into a voltage7+−…To make thevoltage betweenRE and WE 0V…...and this current isproportional to gasconcentration…Inject currenthere…
  8. 8. CN0234: Single Supply, Micropower Toxic GasDetector Using an Electrochemical SensorCircuit Features Low power gas detection 110 µA total current Buck-boost regulator for highefficiencyCircuit Benefits Detects dangerous levels of gas Low power, battery operated8Target Applications Key Parts Used Interface/ConnectivityIndustrialMedicalConsumerADA4505-2ADR291ADP2503AD7798SPI (AD7798)SDP(EVAL-CN0234-SDPZ)USB (EVAL-SDP-CB1Z)EVAL-CN0234-SDPZADAPTER BOARDTO EVAL-SDP-CB1ZIndustry-StandardFootprint
  9. 9. 5V, AVCC 3.3VAIN1(+)AIN1(−)AVDDVIN VOUTREFIN(+) DVDDREFIN(−)GNDDOUT/RDYDINSCLKCSAD7798TOSDP2.5V465C610µFC110.1µFC132.2µFC120.1µFC1022µFR5100kΩR811.5kΩR7330kΩR636.5kΩR433ΩAVCCR31MΩR211kΩR111kΩR61kΩGDQ1MMBFJ177SGDQ2NTR2101PT1GOSCTSC50.02µFC922µF4587SW1PVINVINEN AGNDSYNC/MODESW2VOUTFBPGND211036 9C40.02µFC30.02µFC20.1µFC10.1µF2.5VGNDVREFL11.5µHADP2503ACPZ11CEREWE23U3CO-AX2AGNDU2-BADA4505-2U2-AADA4505-2U1ADR291GR AVCC832 64J2-1J2-2DGND 12B212B121AVCC2.5V TO 5.5VEXTERNALINPUTL21k AT 100MHz++5VVCC5VAVCCCN0234: Single Supply, Micropower Toxic GasDetector Using an Electrochemical Sensor9Total current consumption is 110 μAfor normal operation (not includingADC).P-Channel JFET keepsRE and WE shorted whencircuit is powered off.ADP2503 buck-boostregulates battery inputor external power to 5 VADR291 generates 2.5 Vto offset circuit for singlesupply operationEfficient reversevoltage protectionADA4505-2 has 2 pA maxInput bias current and 10 μAquiescent current per ampAD7798 providesdifferential input, andallows full evaluation offront end circuit.Can be in power downmode most of time @ 1 µA0.16Hz BW
  10. 10. Gas Detection Using Electrochemical SensorsMost instruments are portable, battery powered.Low power consumption is absolute highest priority. Impractical to power down analog circuitry due to long sensor settling times. Bandwidth is less than 1 Hz, so micropower op amps are a good fit.Typical accuracy of 1% to 5% is required.10
  11. 11. CN0234 Features and HintsProvides a convenient platform to experiment with electrochemicalsensorsSensor can measure up to 2000 ppm of carbon monoxide 2000 ppm of carbon monoxide will kill you, so test with less than 100 ppmunless using a fume hood.Electrochemical sensors‟ offset is very sensitive to temperature andhumidity Best practice is to calibrate with a known gas concentration periodically.On-board 16-bit ADC allows evaluation of entire sensor circuit Using a 16-bit ADC results in high dynamic range without the need forprogrammable gains.10-pin header allows easy access to ADC‟s serial port Easy to interface to your own microcontroller or Analog Devices SDP boardusing adapter board.11
  12. 12. CN0234 Circuit Evaluation BoardEVAL-CN0234-SDPZ12SDP CONNECTOR10-PIN FEMALECONNECTOR10-PIN MALE CONNECTOR ON BOTTOM OF PCBSOFTWARE DISPLAY Complete Design Files■ Schematic■ Bill of Material■ PADs Layout■ Gerber Files■ Assembly DrawingEVAL-CN0234-SDPZADAPTER BOARDTO EVAL-SDP-CB1ZIndustry-StandardFootprint
  13. 13. Spectroscopy and Colorimetry13 Fundamentals of Spectroscopy Signal Conditioning Synchronous Detection Photodiode Fundamentals Photodiode Preamp Design Challenges and Solutions■ Bias Current■ Stability■ Noise Programmable Gain Transimpedance Amplifiers (PGTIA) CN0312 Dual Channel Spectroscopy/Colorimetry DemoBoard Illustrates a System Solution
  14. 14. Quick Intro to SpectroscopySpectroscopy is the study of the interaction of matter and radiatedenergy. Matter = liquids and gases Radiated energy = light14We can use spectroscopy techniques toanswer two questions about an unknownsample:■ What is it?■ How much is there?Light after passingthrough a prism
  15. 15. What Is It? (Absorption Spectra)All atoms and molecules have unique and well known spectra By measuring a material’s spectra, we can determine the chemical composition,concentration, etc. No need to look at the entire spectrum—measuring a subset of wavelengthsmay be sufficientAbsorption spectrum A sample absorbs light at specific wavelengths according to the compounds ormolecules present in it After obtaining the absorption spectrum of a sample, we can refer to librariescontaining thousands of spectrums for known substances15Absorption Spectra for Hydrogen
  16. 16. How Much Is There? (Beer-Lambert Law)Measure the Concentration“ The [light] absorbed is directly proportional to the path lengththrough the medium and the concentration of the absorbingspecies.” This works for gases or liquids. c = Concentration l = Path length ε = Molar absorptivity (Known constant for a givencompound)16
  17. 17. Beer-Lambert Law in the Real World …In real life, whatever we are measuring needs to be in a container ofsome sort. The container walls will cause reflections, extra absorption, and light scattering,making it impossible to apply the simple Beer-Lambert Equation.To compensate for the effects of the container, we can compare theabsorption between two containers. One container holds the sample, while the other container holds a knownsubstance (such as water, air, or whatever solvent was used to prepare thesample)Instead of looking at the difference between transmitted andreceived light, we look at the ratio of light received through thesample cell, and light received through the reference cell.17
  18. 18. So Where Is This Stuff Used Anyway?18Chromatography Gas LiquidSpectroscopy Ultraviolet (UV) Visible (VIS) Near infrared (IR) Fourier Transform IR (FT-IR) Raman Fluorescence Atomic AbsorptionParticle AnalysisNondispersive Infrared (NDIR)Gas DetectionColorimetryWater QualityFlame Detection
  19. 19. UV-VIS Spectroscope Sensor Signal Chain19Programmable gaintransimpedance ampAC couplingbufferingSynchronousdetector (full-wave rectifier)24-bitsigma-deltaADCSignal bandwidths tend to be < 5 kHz, butfront-end op amp may have very high gain.Liquid
  20. 20. Synchronous Detection in the FrequencyDomain (Similar to RF Demodulation or Full-Wave Rectification)It is equivalent to having a band-pass filter around the modulationfrequency Unlike a discrete component band-pass filter, it can easily be made very narrowat the expense of response time.Using a square wave makes modulation very simple Noise at harmonics of the fundamental does not get rejected, so selectmodulation frequency carefully!20
  21. 21. Ultraviolet-Visible (UV-VIS) Sensor: “Large Area”Silicon PhotodiodeModeled as a light-dependent current sourceCj can be 50 pF to 5000pF depending on the size of the diodeRsh can be from 500 MΩ to 5 GΩ at 25°C for different diodesRs is typically a few ohms and can be ignored for most calculationsDark current is the amount of current generated when no light hitsthe photodiode Should ideally be zero, but increases with reverse bias voltage21CjRshIdRs
  22. 22. Photodiode Transfer FunctionOperating the photodiode with zero reverse bias results in thelowest dark current (photovoltaic mode) Manufacturers typically spec dark current at Vr = 10 mV22(a) (b)PHOTODIODECURRENTDARKCURRENTPHOTODIODEVOLTAGESHORT CIRCUITCURRENTSHORTCIRCUITVOLTAGELIGHTINTENSITYidark10mV
  23. 23. Measuring Photodiode OutputPhotodiode voltage is very nonlinear with light inputPhotodiode current is linear with light input Need to convert photodiode current to an output voltageTransimpedance amplifier Current-to-voltage converter Transimpedance "gain" = Rf In dB: 20log(Rf/1Ω)23
  24. 24. Transimpedance AmplifierLooks like a short to the photodiodePhotodiode current flows through thefeedback resistor and is convertedto a voltageIdeally, ALL of the photodiode current goes through Rf In reality, all op amps have input bias current that introduces error to the outputOp amp offset voltage causes offset due to itself and to increaseddark currentOp amps with pA-class Ib and low input offset voltages are typicallypreferred (usually FET inputs) AD8605 (1 pA Ib, 300 μV Vos), AD8615 (1 pA, 60 μV Vos),ADA4817 (20 pA Ib, 2 mV Vos) AD549 (0.06 pA Ib, 500 μV Vos)24
  25. 25. Transimpedance Amplifier StabilityExample Photodiode: Cs = 150 pF, Rsh = 600 MΩOp Amp: AD8615 Ib = 1 pA max (200 fA typical!), Cin = 9.2 pF, 24 MHz unity gain frequencyAssume Rf = 1 MΩ so 5 V out when Id = 5 μARf and Cin form a pole in the open-loop transfer function25Don’t forget op amp’sdifferential andcommon-mode inputcapacitance!Ci = CDIFF + CCM1MΩ150pF9.2pF
  26. 26. Transimpedance Amplifier StabilityThe amplifier has no phase margin It’s an oscillator, not an amplifierThe phase must be „a healthydistance‟ away from 180° whenthe unity gain crosses 0 dBTo guarantee stability, design for45° of phase margin Unless you KNOW you need lessphase margin, consider this a minimum 60° or more makes it easier to sleepat night.26120dB80dB60dB40dB20dB0dB100dB100Hz 1kHz 10kHz 100kHz0°180°90°p1f p2fcf
  27. 27. Transimpedance Amplifier StabilityAdding a capacitor in parallel with Rf introduces a zero to the open-loop transfer function and stabilizes the amplifier We want to guarantee at least 45°of phase margin Using a larger Cf results in morephase margin But also lowers the signal bandwidth. For now, select Cf = 4.7 pF• Could go as low as 1 pF, but parasiticcapacitances start to dominate27
  28. 28. Compensated Open-Loop Gain28Phase Margin ≈ 85°Zero
  29. 29. Closed-Loop Bandwidth and Gain29f3db signal ≈ 34kHz
  30. 30. Transimpedance Amplifier Noise SourcesMajor Contributors: Resistor Johnson Noise Current Noise Voltage Noise301MΩ4.7pF
  31. 31. Transimpedance Amplifier Resistor NoiseFeedback Resistor Johnson Noise Appears on the output unamplified314.7pF1MΩ
  32. 32. Transimpedance Amplifier Op Amp CurrentNoiseOp Amp Current Noise Appears on the output as a voltage Multiplied by Rf331MΩ4.7pFAD861550fA/√Hz
  33. 33. Transimpedance Amplifier Voltage Noise-1Op Amp Voltage Noise Modeled as a voltage source on the + input Vout = Input Noise × Noise Gain In a ‘DC’ circuit, the noise gain is equal to thenoninverting gain.341MΩ4.7pFAD8615
  34. 34. Transimpedance Amplifier Voltage Noise-2Op Amp Voltage Noise Modeled as a voltage source on the + input Vout = Input Noise × Noise Gain In a ‘DC’ circuit, the noise gain is equal to thenoninverting gain. …actually, the noise gain is still simplythe noninverting gain, it’s just thatthe noninverting gain is a function offrequency!351MΩ4.7pFAD8615
  35. 35. Noise Gain vs. Signal GainUnlike other amplifier configurations, the noise gain is very differentfrom the signal gain.The op amp‟s noise appearsat the output multiplied bythis gain (~35× at the peak)361MΩ4.7pF150pF+9.2pFAD86157nV/√Hz,24MHz GBW24MHz
  36. 36. Op Amp Output NoiseTo get the output noise in V rms, integrate the square of the noisedensity over frequency and take the square root. Or take a shortcut!Approximation: 254 µV rmsUsing Integration: 266 µV rms (I dare you to do it by hand!)3738MHz
  37. 37. By the Way… Are FET Input Op Amps Alwaysthe Best Choice?AD8615FETAD8671Bipolar38In=50fA/√HzIn=300fA/√HzLESS DRIFTLOWER 1/F NOISELOWER VOLTAGE NOISEHIGHER CURRENT NOISE7nV/√Hz2.5nV/√hzINPUT VOLTAGE NOISE INPUT BIAS CURRENTINPUTBIASCURRENT(pA)INPUTBIASCURRENT(nA)
  38. 38. TIA Output NoiseThe three main noise contributors are all Gaussian and independentof each other, so we can RSS them togetherThis is just transimpedance amplifier noise Johnson noise of photodiode shunt resistor, Rsh, is integrated over the signalnoise bandwidth: 1.57 × (1/2πRfCf). Negligible if Rsh >> Rf Shot noise of photodiode is negligible39Contributor Output NoiseFeedback Resistor 30 µV rmsOp amp Current Noise 12 µV rmsOp amp Voltage Noise 254 µV rms
  39. 39. Add Filter after Amplifier to Reduce NoiseOp Amp noise over large noise gainbandwidth dominates…But the signal bandwidth is much lower Signal Bandwidth = 34 kHzWhat if we simply add an RC low passfilter after the amplifier? Cut-off frequency similar to the signalbandwidthReduce RMS noise from 256 µV rms to49 µV rms with simple 34 kHz RC filter For the cost of about US$0.03 (assuming youuse expensive C0G caps!) If the output is going to an ADC, you mayalso need to buffer it.4034kHz BW1MΩ4.7pF
  40. 40. The Need for Programmable GainThe same equipment may need totest samples with very differentlight absorption. Almost-clear liquids like water oralcohol-based solutions Very opaque liquids like petroleum-based compounds Sometimes simultaneously Concentration ratiosProgrammable gain amplifiers helpincrease the system‟s dynamicrange41VS.
  41. 41. System Output NoiseA good PGA will contribute very little noise when G = 1When G = 10, the TIA noise is also amplified 10×Limit the PGA bandwidth to reduce noise42
  42. 42. Two Alternatives: TIA + PGA vs. PGTIATIA + PGA Traditional Photodiode Amplifier Programmable Gain Amp Possibly Followed by ADC DriverPGTIA Programmable Gain TransimpedanceAmplifier Lower Noise43
  43. 43. An Alternative Architecture: PGTIAFor G = 1 MΩ and the same bandwidth, the noise remains the sameFor G = 10 MΩ and the same bandwidth, the noise goes up about 3×(not 10×) Cf = 0.47 pFFurther noise reduction by adding a low-pass filter at the output Attenuate everything beyond the signal bandwidthDo not have to consider additional errors due to a second amplifier44
  44. 44. So, How Do You Build a PGTIA?The basic idea:Gain and frequency response depends on switch on and offimpedance Changes with temperature, supply voltage, and signal voltage45ClpRlpRfCfRfCf−+
  45. 45. Improved PGTIAKelvin switching Twice as many switches, but switch resistance does not matter very much. Looks like an op amp output with slightly higher output resistance46Rf2Cf2Rf1Cf1-+CpCp
  46. 46. PGTIA: Frequency Domain Effects-1Cp is typically less than 1 pF In our G = 10 MΩ example, Cf is only 0.47 pF Even Cp = 0.5 pF can make a big difference!47Rf2Cf2Rf1Cf1-+CpCp
  47. 47. PGTIA: Frequency Domain Effects-2Cp is typically less than 1 pF In our G = 10 MΩ example, Cf is only 0.47 pF Even Cp = 0.5 pF can make a big difference!48Rf2Cf2Rf1Cf1-+2*CpTotal FeedbackCapacitance2*CpCf12*Cp+ Cf1Cf2 +=
  48. 48. PGTIA: Adding More Switches-1Adding a set of switches in series reduces Cp by halfBetter, but what if you need more?49
  49. 49. PGTIA: Adding More Switches-2Even more switches to keep Cp away from the feedback path50
  50. 50. PGTIA: Adding More Switches-3Even more switches to keep Cp away from the feedback pathThere is no free lunch! One switch in series with feedback path will affect the DC gain But less than ~5 ppm for a typical 50 Ω switch and Rf = 10 MΩ.512 pF here won’t domuch of anything.0.5 pF in series with Cf1 =<0.5 pF from In– to ground.This is negligible whencompared with thephotodiode’s 150 pFcapacitance!
  51. 51. CN-0312 PGTIA Switch Configuration52ADG633 Ron ~ 50Ω
  52. 52. CN0312: Dual-Channel Colorimeter withProgrammable Gain TransimpedanceAmplifiers and Synchronous DetectorsCircuit Features Three modulated LED drivers Two photodiode receive channels Programmable gainCircuit Benefits Ease of use Self contained solution Dual channel, 16-bit ADC for dataanalysis53Target Applications Key Parts Used Interface/ConnectivityIndustrialMedicalConsumerAD8615/AD8618AD8271ADG633, ADG733ADR4525AD7798SPI (AD7798)SDP (EVAL-CN0312-SDPZ)USB (EVAL-SDP-CB1Z)EVAL-SDP-CB1ZEVAL-CN0312-SDPZ
  53. 53. CN0312 Dual Channel Spectroscopy/Colorimetry Demo Board54AD8615AD8615AD8615AD8615ADG733ADG733AD8271AD8271AD7798ADR4525
  54. 54. CN0312 Addresses Challenges of PrecisionPhotometryConvenient platform for exploring programmable gain TIAsFeatures Three square-wave modulated LEDs Two photodiode channels with selectable gain Hardware lock-in amplifiers AD7798 16-bit sigma-delta ADCs55J2 -J2 +120PINSDPLEDsBeam-splitterReferenceContainerSampleContainerD2D3Photodiodes(Notice correctorientation ofanode tab)External6-12VDC120PINSDPEVAL-SDP-CB1ZCON AORCONBEVAL-CN0312-SDPZUSBPCUSBEVAL-SDP-CB1ZEVAL-CN0312-SDPZ
  55. 55. SummaryMany chemical analyzer applications are based on light andphotodiodes.Designing with photodiodes presents unique challenges: Photodiode’s large shunt capacitance makes the amplifier unstable, requiringcompensation Compensation reduces the signal bandwidth Reduced signal bandwidth may not be so bad (if you don’t need it!), since italso implies lower noise gain Signal bandwidth is dominated by Rf and Cf Noise gain bandwidth can be much higher than the signal bandwidth, andits magnitude is mainly determined by the ratio of the diode’s shunt capacitanceto Cf.ADI‟s amplifier portfolio allows you to customize a solution for verylow input bias currents, low noise, and/or low drift, depending oneach specific application!56
  56. 56. Tweet it out! @ADI_News #ADIDC13What We CoveredGas Detection Using Electrochemical Sensors (CN0234) Gas detection fundamentals Electrical equivalent circuit Conditioning circuitsSpectroscopy and Colorimetry (CN0312) Fundamentals of spectroscopy Modulated laser light sources Photodiode receivers Synchronous demodulation Transimpedance amplifiers Gain Stability Noise Programmable gain transimpedance amplifiers57
  57. 57. Tweet it out! @ADI_News #ADIDC13Visit the Single Supply, Micropower GasDetector Demo in the Exhibition Room58SDP CONNECTOR10-PIN FEMALECONNECTOR10-PIN MALE CONNECTOR ON BOTTOM OF PCBSOFTWARE DISPLAY Complete Design Files■ Schematic■ Bill of Material■ PADs Layout■ Gerber Files■ Assembly DrawingEVAL-CN0234-SDPZADAPTER BOARD TOEVAL-SDP-CB1ZIndustry-StandardFootprintThis demo board is available for purchase:www.analog.com/DC13-hardware
  58. 58. Tweet it out! @ADI_News #ADIDC13Visit the Dual Channel Spectroscopy/ColorimetryDemo Board in the Exhibition Room59Circuit Features Three modulated LED drivers Two photodiode receive channels Programmable gainCircuit Benefits Ease of use Self contained solution Dual channel 16-bit ADC for dataanalysis Complete Design Files■ Schematic■ Bill of Material■ PADs Layout■ Gerber Files■ Assembly DrawingEVAL-SDP-CB1ZEVAL-CN0312-SDPZThis demo board is available for purchase:www.analog.com/DC13-hardware
  59. 59. Tweet it out! @ADI_News #ADIDC13Design Resources Covered in This Session60Design Tools and Resources:Name Description URLPhotodiode Wizard Complete design tool for photodiodepreamplifiershttp://www.analog.com/photodiode_wizardSystem DemonstrationPlatform (SDP)SDP provides easy data transfer andanalysis of product and reference circuitboardshttp://www.analog.com/sdpSignal Chain Designer™ Complete engineering designenvironmenthttp://www.analog.com/scdAD7798 Tools Tools, software, and simulation models http://www.analog.com/en/analog-to-digital-converters/ad-converters/ad7798/products/product.html#product-designtoolsAsk technical questions and exchange ideas onlinein our EngineerZone™ Support Community ez.analog.com
  60. 60. Tweet it out! @ADI_News #ADIDC13Part Number DescriptionADA4505-2 Micropower Rail-to-Rail I/O Dual Op AmpADR291 Micropower 2.5 V Voltage ReferenceADP2503 2.5 MHz Buck-Boost DC-to-DC ConverterAD7798 3-Channel 16-Bit Low Power Sigma-Delta ADCAD8615/AD8618 Precision Single/Quad Rail-to-Rail Input/Output Op AmpADG633 CMOS, ±5 V/+5 V/+3 V, Triple SPDT SwitchADG733 CMOS, 2.5 Ω Low Voltage, Triple SPDT SwitchesAD8271 Programmable Gain Precision Difference AmplifierADR4525 Ultralow Noise, High Accuracy 2.5 V ReferenceSelection Table of Products Covered Today61
  61. 61. Tweet it out! @ADI_News #ADIDC13References-1Circuit Notes CN0234, Micropower Toxic Gas Detector Using an Electrochemical Sensor www.analog.com/CN0234 CN0312, Dual Channel Colorimeter with Synchronous Detection andProgrammable Gain Transimpedance Amplifier www.analog.com/CN0312 CN0272, 2 MHz Bandwidth PIN Photodiode Preamp with Dark CurrentCompensation www.analog.com/CN027262
  62. 62. Tweet it out! @ADI_News #ADIDC13References-2Mini-Tutorials MT-047, Op Amp Noise www.analog.com/MT-047 MT-048, Op Amp Noise Relationships: 1/f Noise, RMS Noise, and EquivalentNoise Bandwidth www.analog.com/MT-048 MT-049, Op Amp Total Output Noise Calculations for Single-Pole System www.analog.com/MT-049 MT-050, Op Amp Total Output Noise Calculations for Second-Order System www.analog.com/MT-050 MT-059, Compensating for the Effects of Input Capacitance on VFB and CFBOp Amps Used in Current-to-Voltage Converters www.analog.com/MT-059 MT-088, Analog Switches and Multiplexers Basics www.analog.com/MT-08863
  63. 63. Tweet it out! @ADI_News #ADIDC13References-3Textbooks Sensor Signal Conditioning, Analog Devices, 1999, Chapter 5 www.analog.com/high_impedance_sensors Hamamatsu Opto-Semiconductor Handbook http://jp.hamamatsu.com/sp/ssd/tech_handbook_en.html Greame, Jerald. Photodiode Amplifiers: Op Amp Solutions. McGraw-Hill, NewYork, 1995.64

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