TI，Analysis and Measurement of Intrinsic Noise in Op Amp CircuitsPart X: Instrumentation Amplifier Noise2R2difVinVinVa1A150kRa2Split Input Stage50kVcMRtA2Va2+2Input StageMVaM+Differential Gain Stage2VatR3150kR5150kVa1 R3 150kR5150k日A3Inverting AmpyoutGain =-1A3youtVin difR3150kR5150kNon-inverting AmpGain =2A3a2R4150kR6150kVoutVoltage DividerVa2Gain =1/2Va2+ VrefOutput StageDif AmpVa? R4150kR6150ka222vFind out Through SuperpositionVout = Va2-Va1 VrefcIm 21+2[1] Input StageTop Half[2 Input Stage1+2CIn2Bottom Half矿。1+ut -va2 al[3 Output StageRFSubstitute1+CILL1+2-+vnef[1and [2]into [3]outref [4] SimplifydifVin2Va1A1150k150kWCM50kA3Vout50k150k150kA2Va22Vin+Input StageOutput StageInputRTOgain =GganVn RtoTotalIin=G[5] Noise referredn RTon out/+to the outputn outn in 2 [6]Noise referredto the inputtOutputNoiseCurrent nois日nput NoiseOutput Noise)Tetal Input-Referred Ncise 1(npart Noise)+0.11001k10kFrequency(Hz)G=1VN100G=10V/10排G=100.1000V/日Current noise10010k命Frequency(hz)+V=5￥Vin-15k15k2.49gVNA333A350kVin dif 2mv150k150kVin+2.501y100kV= GNDOPA333Vref pin象1001AOPA33355nvTET pin230nwOPA343≥100k50k128.10otzmann's constant+25 Temperature in keli inR=如kInput resistanceParallel combination of v ot age divider)r=23了I n neqF Thermal Noise from input resistorn=100fA Current noise from OPA333in i=n regB Voltage Noise from current noise中喧∨ tage noise tron0PA33H9] Total rms noise frrefn1=627、QVHz reference dr iwer circuten_r R/2RRUse superposition to combineRnoise sources an the negativeRand positive inputnpRRVoltage noise from current noise[10]ResistoNoisese superp osition to add the noise frthe input resistance and both current noise sourcesR+thAssumNote that these sources are un correlated+2en th2 [11 Total Nois e from inpuresistors and current sourceFor this example(r=5k, in=100fA/)6.4Resistor no iseR=0.2n Voltage noise from current no iseHY2(09-+2(9D=9Total Noise from nputre sisters and current source