The ADC is often from a competitor Answering this question is a challenging taskand there is no absolute answer only a list of gray areas and tradeoffs It would be handy to have a table with ADCs on one side and recommended op amps on the other But ID: 22192
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5Analog Applications JournalInterfacing op amps and analog-to-digital convertersIntroductionOne of the most common questions asked of the TI High-Speed Amplifiers Applications team is what op amp to use 4Q 2002www.ti.com/sc/analogapps AmplifierADCAnalogInput PowerSupply Figure 1. Focusing on power supplycharacteristics Texas Instruments Incorporated 6Analog Applications Journal www.ti.com/sc/analogapps4Q 2002What is used for the signal source to the amplifier blockin front of the ADC? Is it another amplifier, a sensor, etc.?Describe the input signal. For example, is it continuousAre there any unusual characteristics of the signalWhat is the output amplitude range of the source?Does the source produce a voltage or a current output?Is the signal source output single-ended or differential?What is the output impedance of the signal source?Is the input signal dc-referenced? If so, to what dc volt-What are the frequency characteristics of the input sig-frequency isn’t important, this opens the possibility ofWhat level of rejection is required out-of-band? SomeIs there a known interfering frequency (system clock,tional circuitry to produce a high Q notch filter.Is there a requirement for gain or phase flatness orIs there a matching requirement on the input impedanceance(e.g., 50 Has the ADC been selected, or can it be changed toWhat is the desired sampling rate? Designers oftenmaximum level of performance, but this typically isn’tthe case. For example, an 80-megasample-per-secondWhat is the desired resolution and effective number ofbits? A 14-bit converter won’t effectively yield 14 bits.What is the full-scale input range of the data converter?Will the data converter be used with single-ended or dif-ferential inputs? Typically, most high-performance dataAre there any other options on the data converter thatAre there any compensation requirements for the inputof the data converter? Normally, a small RC filter isinterface circuit may exhibit instability. AmplifierADCAnalogInput PowerSupply Figure 2. Focusing on the input signal AmplifierADCAnalogInput PowerSupply Figure 3. Focusing on the ADC Texas Instruments Incorporated 7Analog Applications Journal 4Q 2002www.ti.com/sc/analogappsthe correct operational amplifier, it is possible that theHas the operational amplifier already been selected, orAre there specific requirements for the package of theDoes the cost of the operational amplifier interface orshould be complete. The wise designer, however, shouldwork to be thrown on the trash heap. Yet a wise designeramplifier.ti.comis wasting money on the data converter.In addition to the “Related Web sites” below, TI has aamplifier.ti.comdataconverter.ti.com AmplifierADCAnalogInput PowerSupply Figure 4. Focusing on the operational amplifiers IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reservestandard warranty. Testing and other quality control techniques areused to the extent TI deems necessary to support this warranty.applications using TI components. To minimize the risksunder the patents or other intellectual property of the third party, or aTexas Instruments products and application solutions: TIWorldwide Technical Support InternetTI Semiconductor Product Information Center Home Pagesupport.ti.comTI Semiconductor KnowledgeBase Home Pagesupport.ti.com/sc/knowledgebase Phone+1(972) 644-5580Fax+1(972) 927-6377 Internet/Emailsupport.ti.com/sc/pic/americas.htmBelgium (English)+32 (0) 27 45 5 32Netherlands (English)+31 (0) 546 87 95 45Finland (English)+358 (0) 9 25173948Russia+7 (0) 95 7850415France+33 (0) 1 30 70 11 64Spain+34 902 35 40 28Germany+49 (0) 8161 80 33 11Sweden (English)+46 (0) 8587 555 22Israel (English)1800 949 0107United Kingdom+44 (0) 1604 66 33 99Italy800 79 11 37Fax+(49) (0) 8161 80 2045 Internetsupport.ti.com/sc/pic/euro.htmInternational+81-3-3344-5317Domestic0120-81-0036Internationalsupport.ti.com/sc/pic/japan.htm Domesticwww.tij.co.jp/picInternational+886-2-23786800DomesticToll-Free NumberToll-Free NumberAustralia1-800-999-084New Zealand0800-446-934China800-820-8682Philippines1-800-765-7404Hong Kong800-96-5941Singapore800-886-1028Indonesia001-803-8861-1006Taiwan0800-006800Korea080-551-2804Thailand001-800-886-0010Malaysia1-800-80-3973Fax886-2-2378-6808Emailtiasia@ti.comInternetsupport.ti.com/sc/pic/asia.htmti-china@ti.com of similar import. Similarly, such statements herein that describethe company's products, business strategy, outlook, objectives,of operations. We disclaim any intention or obligation to updateTrademarks: Mailing Address: Texas InstrumentsDallas, Texas 75265 © 2005 Texas Instruments Incorporated amplifier.ti.comdataconverter.ti.compower.ti.com microcontroller.ti.comwww.ti.com/audiowww.ti.com/automotivewww.ti.com/broadbandwww.ti.com/digitalcontrolwww.ti.com/militarywww.ti.com/opticalnetworkwww.ti.com/securityTelephony www.ti.com/telephony Video & Imaging www.ti.com/videowww.ti.com/wireless S