Op Amp Applications Handbook Walt Jung, Editor

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141 Specialty Amplifi ers summed in a root-sum-squares (RSS) fashion. IN+ fl ows through one-half of RS, and IN– the other half. This generates two noise voltages, each having an amplitude, INRS/2. Each of these two noise sources is refl ected to the output by the in amp gain, G. The total output noise is calculated by combining all four noise sources in an RSS manner: 2 2 2 2 ⎛ 2 2 2 IN RS IN R ⎞ + − S NOISE( RTO) = BW VNO + G ⎜VNI + + ⎝ 4 4 ⎟ ⎠ If I N+ = I N− = I N, 2 2 ⎛ 2 2 2 IN R ⎞ S NOISE( RTO) = BW VNO + G ⎜VNI + ⎝ 2 ⎟ ⎠ Eq. 2-6 Eq. 2-7 The total noise, referred to the input (RTI) is simply the above expression divided by the in amp gain, G: 2 2 2 V ⎛ NO 2 INR ⎞ S NOISE( RTI) = BW + V 2 NI G ⎜ + ⎝ 2 ⎟ ⎠ Eq. 2-8 In amp data sheets often present the total voltage noise RTI as a function of gain. This noise spectral density includes both the input (VNI) and output (VNO) noise contributions. The input current noise spectral density is specifi ed separately. As in the case of op amps, the total in amp noise RTI must be integrated over the applicable in amp closedloop bandwidth to compute an RMS value. The bandwidth may be determined from data sheet curves that show frequency response as a function of gain. Regarding this bandwidth, some care must be taken in computing it, as it is often not constant bandwidth product relationship, as is true with VFB op amps. In the case of the AD620 in amp family for example, the gain-bandwidth pattern is more like that of a CFB op amp. In such cases, the safest way to predict the bandwidth at a given gain is to use the curves supplied within the data sheet.
Chapter Two In Amp Bridge Amplifi er Error Budget Analysis It is important to understand in amp error sources in a typical application. Figure 2-24 shows a 350 Ω load cell with a full-scale output of 100 mV when excited with a 10 V source. The AD620 is confi gured for a gain of 100 using the external 499 Ω gain-setting resistor. The table shows how each error source contributes to a total unadjusted error of 2145 ppm. Note, however, that the gain, offset, and CMR errors can all be removed with a system calibration. The remaining errors—gain nonlinearity and 0.1 Hz to 10 Hz noise— cannot be removed with calibration and ultimately limit the system resolution to 42.8 ppm (approximately 14-bit accuracy). This example is of course just an illustration, but should be useful towards the importance of addressing performance-limiting errors such as gain nonlinearity and LF noise. +10V V CM = 5V 350Ω, 100mV FS LOAD CELL AD620B SPECS @ 25°C, ±15V V OSI + V OSO /G = 55µV max I OS = 0.5nA max Gain Error = 0.15% Gain Nonlinearity = 40ppm 0.1Hz to 10Hz Noise = 280nVp-p CMR = 120dB @ 60Hz In Amp Performance Tables + – 499Ω R G AD620B G = 100 REF MAXIMUM ERROR CONTRIBUTION, +25°C FULLSCALE: V IN = 100mV, VOUT = 10V VOS 55µV ÷ 100mV 550ppm Figure 2-24: AD620B bridge amplifi er dc error budget I OS Gain Error Gain Nonlinearity CMR Error 0.1Hz to 10Hz 1/f Noise Total Unadjusted Error Resolution Error 142 350Ω × 0.5nA ÷ 100mV 0.15% 40ppm 120dB 1ppm × 5V ÷ 100mV 280nV ÷ 100mV ≈ 9 Bits Accurate ≈ 14 Bits Accurate 1.8ppm 1500ppm 40ppm 50ppm 2.8ppm 2145ppm 42.8ppm Figure 2-25 shows a selection of precision in amps designed primarily for operation on dual supplies. It should be noted that the AD620 is capable of single 5 V supply operation (see Figure 2-15), but neither its input nor its output are capable of rail-to-rail swings. These tables allow at-a-glance inspection of key errors, which can be critical in getting the most performance from a system. From Figure 2-25 for example, it can be noted that the use of an AD621 in lieu of the AD620B in the gain-of-100 bridge circuit of Figure 2-24 allows reduction of the gain nonlinearity component of error by a factor of four times. It is also important to separate out errors that can be calibrated out as mentioned above, and those that can only be minimized by device specifi cation improvements. Comparison of the AD620B and the AD622 specifi cations, for example, shows a higher VOS for the latter. But, since VOS can be calibrated out, the fact that it is higher for the AD622 isn’t material to this particular application. The gain nonlinearity between the AD620 and AD622 is the same, so in an auto-cal system, they would likely perform comparably. On the other hand, the AD621B would be preferable for its lower gain nonlinearity, as noted.
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Op Amp Applications Handbook
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Op Amp Applications Handbook Walt J
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v Contents Foreword ...............
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vii Foreword The signal-processing
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ix Preface Op Amp Applications Hand
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xi Preface and diversity of use. Th
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Signal Amplifi ers; Audio Amplifi e
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1928 Harold S. Black applies for pa
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CHAPTER 1 Op Amp Basics ■ Section
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CHAPTER 1 Op Amp Basics James Bryan
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As a precursor to more detailed sec
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INPUT 7 Op Amp Basics Note that wit
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Thus an ideal noninverting op amp s
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G2 V 2 V 1 R G ' OP AMP G = VOUT /V
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13 Op Amp Basics It is important to
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dB A VOL β G CL Figure 1-7: Op amp
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Input Dynamic Range 17 Op Amp Basic
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19 Op Amp Basics dual- supply devic
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References: Introduction 21 Op Amp
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The previous section examined op am
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25 Op Amp Basics The CFB topology i
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GAIN (R1) 1.04Ω - 37.4Ω FEEDBAC
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References: Op Amp Topologies 29 Op
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This section describes op amps in t
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Single Supply Offers: − Lower Pow
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+VS 7 (−) 2 INPUTS 3 (+) −VS 4
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37 Op Amp Basics has a maximum inpu
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Offset as Low as 50µV Offset TC ~
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+VS (+) INPUTS (−) −V S J1 I1 V
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(A) (B) (C) +VS +VS NPN NPN -V S V
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Figure 1-33: AD8531/AD8532/AD8534 C
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47 Op Amp Basics a device, even wit
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BIPOLAR (NPN-BASED): This is Where
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Most op amp specifi cations are lar
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Figure 1-39: Alternate input offset
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Figure 1-42: Noninverting op amp ex
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57 Op Amp Basics Extremely low inpu
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Input Impedance Figure 1-48: Input
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61 Op Amp Basics Some fast op amps
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±10V RAMP 10kΩ 10kΩ V OS -VREF
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65 Op Amp Basics This sine wave sig
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V 1 R1 − + Figure 1-56: Measuring
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GAIN dB OPEN LOOP GAIN, A(s) IF GAI
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GAIN dB G1 G2 Figure 1-62: Frequenc
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Figure 1-65: Johnson noise of resis
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100 10 795 743 NOISE n/√Hz or µV
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20nV/div. (RTI) + 100 90 .... ....
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Nominal Peak-to-Peak 2 × rms 3 ×
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B A V N,R1 ∼ 4kTR1 V N,R3 ∼ 4kT
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V s = Signal Amplitude (RMS Volts)
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85 Op Amp Basics Note inverting mod
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Power Supplies and Decoupling 87 Op
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This section examines in more detai
Page 108 and 109: 91 Op Amp Basics Note that the offs
Page 110 and 111: 93 Op Amp Basics the nulling amplif
Page 112 and 113: Noise Considerations for Chopper-St
Page 114 and 115: Introduction High speed analog sign
Page 116 and 117: 99 Op Amp Basics voltage, v, into a
Page 118 and 119: g 1 f = = = 153MHz u m 2 CP 2 520 1
Page 120 and 121: v in R1 + v − − gm + I T i = v
Page 122 and 123: +V S − −VS Q1 Q3 Q5 Q2 Q4 Q6 Fi
Page 124 and 125: 107 Op Amp Basics Note also that th
Page 126 and 127: Q1 + − Q2 I1 I2 Figure 1-110: Sim
Page 128 and 129: R1 C2 A − R2 B |A(s)| VFB OP AMP
Page 130 and 131: High Speed Current-to-Voltage Conve
Page 132 and 133: 4mA C1 20pF 500Ω − VFB 1 fp = =
Page 134 and 135: Voltage Feedback Op Amps: − Volta
Page 136 and 137: CHAPTER 2 Specialty Amplifi ers ■
Page 138 and 139: CHAPTER 2 Specialty Amplifi ers Wal
Page 140 and 141: Probably the most popular among all
Page 142 and 143: 125 Specialty Amplifi ers buffers i
Page 144 and 145: 127 Specialty Amplifi ers balanced
Page 146 and 147: 129 Specialty Amplifi ers When dual
Page 148 and 149: V1 (-) 100kΩ V REF + 25kΩ 25k
Page 150 and 151: -IN ~ 400Ω V CM + VSIG ~ 2 _ + VS
Page 152 and 153: 135 Specialty Amplifi ers The gener
Page 154 and 155: In Amp DC Error Sources 137 Special
Page 156 and 157: Figure 2-20: AD620 In amp common-mo
Page 160 and 161: AD524C AD620B AD621B 1 AD622 AD624C
Page 162 and 163: R+∆R R-∆R V B R-∆R R G R+∆R
Page 164 and 165: 147 Specialty Amplifi ers A factor
Page 166 and 167: 149 Specialty Amplifi ers Classic C
Page 168 and 169: Most data acquisition systems with
Page 170 and 171: 153 Specialty Amplifi ers To unders
Page 172 and 173: Low Noise PGA 155 Specialty Amplifi
Page 174 and 175: 157 Specialty Amplifi ers The OP113
Page 176 and 177: 159 Specialty Amplifi ers Since tra
Page 178 and 179: Analog Isolation Techniques There a
Page 180 and 181: 163 Specialty Amplifi ers An isolat
Page 182 and 183: Figure 2-51: AD215 120kHz low disto
Page 184 and 185: 167 Specialty Amplifi ers This prod
Page 186 and 187: References: Isolation Amplifi ers 1
Page 188 and 189: CHAPTER 3 Using Op Amps with Data C
Page 190 and 191: CHAPTER 3 Using Op Amps with Data C
Page 192 and 193: 175 Using Op Amps with Data Convert
Page 194 and 195: References: Introduction 177 Using
Page 196 and 197: ADC and DAC Static Transfer Functio
Page 200 and 201: ADC Input-Referred Noise 183 Using
Page 202 and 203: 75Ω 185 Using Op Amps with Data C
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191 Using Op Amps with Data Convert
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Introduction Op amps are often used
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Input Common-Mode Voltage Range Out
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~ R EXT V SOURCE R INT 7kΩ SWITCH
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~ R S V S REFOUT/ REFIN V INX R1 2k
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Driving CMOS ADCs with Switched Cap
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V IN + - Figure 3-35: Optimizing si
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INPUT ±1V 1kΩ + 10µF Drivers fo
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Op Amp Applications Handbook Walt Jung, Editor

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