Op Amps for Everyone - The Repeater Builder's Technical ...

More documents

Recommendations

Info

External Compensation, Stability, and Performance At V CC = 5 V, the phase margin at the 0-dB crossover point is 60°, while it is 30° at V CC = 2.7 V. This translates into an expected overshoot of 18% at V CC = 5 V, and 28% at V CC = 2.7 V. Unfortunately the time response plots are done with 100-pF loading capacitance, hence we can not check our figures very well. The V CC = 2.7 V overshoot is approximately 2%, and it is almost impossible to figure out what the overshoot would have been with a 600 pF loading capacitor. The small-signal pulse response is done with mV-signals, and that is a more realistic measurement than using the full signal swing. Internally compensated op amps are very desirable because they are easy to use, and they do not require external compensation components. Their drawback is that the bandwidth is limited by the internal compensation scheme. The op amp open-loop gain eventually (when it shows up in the loop gain) determines the error in an op amp circuit. In a noninverting buffer configuration, the TL277X is limited to 1% error at 50 kHz (V CC = 2.7 V) because the op amp gain is 40 dB at that point. Circuit designers can play tricks such as bypassing the op amp with a capacitor to emphasize the high-frequency gain, but the error is still 1%. Keep Equation 7–1 in mind because it defines the error. If the TLV277X were not internally compensated, it could be externally compensated for a lower error at 50 kHz because the gain would be much higher. E V IN 1 A (7–1) 7.3 External Compensation, Stability, and Performance Nobody compensates an op amp just because it is there; they have a reason to compensate the op amp, and that reason is usually stability. They want the op amp to perform a function in a circuit where it is potentially unstable. Internally and noninternally compensated op amps are compensated externally because certain circuit configurations do cause oscillations. Several potentially unstable circuit configurations are analyzed in this section, and the reader can extend the external compensation techniques as required. Other reasons for externally compensating op amps are noise reduction, flat amplitude response, and obtaining the highest bandwidth possible from an op amp. An op amp generates noise, and noise is generated by the system. The noise contains many frequency components, and when a high-pass filter is incorporated in the signal path, it reduces high frequency noise. Compensation can be employed to roll off the op amp’s high frequency, closed-loop response, thus causing the op amp to act as a noise filter. Internally compensated op amps are modeled with a second order equation, and this means that the output voltage can overshoot in response to a step input. When this overshoot (or peaking) is undesirable, external compensation can increase the phase margin to 90° where there is no peaking. An uncompensated op amp has the highest bandwidth possible. External compensation is required to stabilize uncompensated op amps, but the compensation can be tailored to the specific circuit, thus yielding the highest possible bandwidth consistent with the pulse response requirements. 7-8
Dominant-Pole Compensation 7.4 Dominant-Pole Compensation We saw that capacitive loading caused potential instabilities, thus an op amp loaded with an output capacitor is a circuit configuration that must be analyzed. This circuit is called dominant pole compensation because if the pole formed by the op amp output impedance and the loading capacitor is located close to the zero frequency axis, it becomes dominant. The op amp circuit is shown in Figure 7–8, and the open loop circuit used to calculate the loop gain (Aβ) is shown in Figure 7–9. V IN + ∆V Z O V OUT – ∆V A C L Z F POINT X Z G Figure 7–8. Capacitively-Loaded Op Amp V OUT v (Test) = ∆V A Z O V (Return) Z F C L Z G Figure 7–9. Capacitively-Loaded Op Amp With Loop Broken for Loop Gain (Aβ) Calculation The analysis starts by looking into the capacitor and taking the Thevenin equivalent circuit. V TH Va Z O C L s 1 (7–2) Z TH Z O Z O C L s 1 (7–3) Then the output equation is written. Voltage-Feedback Op Amp Compensation 7-9
Page 1 and 2:
Design Reference August 2002 Advanc
Page 3 and 4:
Forward Everyone interested in anal
Page 5 and 6:
Contents Contents 1 The Op Amp’s
Page 7 and 8:
Contents 10 Op Amp Noise Theory and
Page 9 and 10:
Contents 14.4.3 AC Application Erro
Page 11 and 12:
Contents 17.7.1 Through-Hole Consid
Page 13 and 14:
Figures Figures 2-1 Ohm’s Law App
Page 15 and 16:
Figures 7-5 TL08X Frequency and Tim
Page 17 and 18:
Figures 13-12 Differential Amplifie
Page 19 and 20:
Figures 16-41 Comparison of Q Betwe
Page 21 and 22:
Figures A-37 Basic Wien Bridge Osci
Page 23 and 24:
Examples Examples 16-1 First-Order
Page 25 and 26:
Chapter 1 The Op Amp’s Place In T
Page 27 and 28:
The first signal conditioning op am
Page 29 and 30:
Chapter 2 Review of Circuit Theory
Page 31 and 32:
Voltage Divider Rule source, throug
Page 33 and 34:
Thevenin’s Theorem 2.5 Thevenin
Page 35 and 36:
Thevenin’s Theorem V OUT V TH R
Page 37 and 38:
Calculation of a Saturated Transist
Page 39 and 40:
Transistor Amplifier 2 V (from 8 V
Page 41 and 42:
Chapter 3 Development of the Ideal
Page 43 and 44:
The Noninverting Op Amp 3.2 The Non
Page 45 and 46:
The Adder 3-5, and if R F = 100 k a
Page 47 and 48:
Complex Feedback Networks portion o
Page 49 and 50:
Video Amplifiers 3.7 Video Amplifie
Page 51 and 52:
Summary 3.9 Summary When the proper
Page 53 and 54:
Chapter 4 Single-Supply Op Amp Desi
Page 55 and 56:
Circuit Analysis R G R F +V V IN _
Page 57 and 58: Circuit Analysis V OUT VCC -V IN
Page 59 and 60: Circuit Analysis R G R F V CC V REF
Page 61 and 62: Simultaneous Equations m 2 1 0.1
Page 63 and 64: Simultaneous Equations R F R G R G
Page 65 and 66: Simultaneous Equations measured 4.5
Page 67 and 68: Simultaneous Equations +5V R 2 820
Page 69 and 70: Simultaneous Equations |m| 5.56 R
Page 71 and 72: Simultaneous Equations 4.3.4 Case 4
Page 73 and 74: Simultaneous Equations -0.10 -0.15
Page 75 and 76: Chapter 5 Feedback and Stability Th
Page 77 and 78: Block Diagram Math and Manipulation
Page 79 and 80: Block Diagram Math and Manipulation
Page 81 and 82: Bode Analysis of Feedback Circuits
Page 87 and 88: Loop Gain Plots are the Key to Unde
Page 89 and 90: The Second Order Equation and Ringi
Page 91 and 92: Chapter 6 Development of the Non Id
Page 93 and 94: Review of the Canonical Equations T
Page 95 and 96: Noninverting Op Amps 6.3 Noninverti
Page 97 and 98: Inverting Op Amps The transfer equa
Page 99 and 100: Differential Op Amps A aZ G Z G Z
Page 101 and 102: Chapter 7 Voltage-Feedback Op Amp C
Page 103 and 104: Internal Compensation Figure 7-2 sh
Page 105 and 106: Internal Compensation AVD - Large-S
Page 107: Internal Compensation - Large-Signa
Page 111 and 112: Dominant-Pole Compensation 100 dB D
Page 113 and 114: Lead Compensation Gain compensation
Page 115 and 116: Lead Compensation slopes down at -2
Page 117 and 118: Compensated Attenuator Applied to O
Page 119 and 120: Lead-Lag Compensation C R + _ V OUT
Page 121 and 122: Conclusions Dominant pole compensat
Page 123 and 124: Chapter 8 Current-Feedback Op Amp A
Page 125 and 126: The Noninverting CFA output impedan
Page 127 and 128: The Inverting CFA V OUT V IN Z1 Z
Page 129 and 130: Stability Analysis 8.6 Stability An
Page 131 and 132: Selection of the Feedback Resistor
Page 133 and 134: Stability and Input Capacitance Tab
Page 135 and 136: Compensation of CF and CG Z F A R
Page 137 and 138: Chapter 9 Voltage- and Current-Feed
Page 139 and 140: Bandwidth The noninverting input of
Page 141 and 142: Bandwidth The CFA is a current oper
Page 143 and 144: Impedance The CFA stability is not
Page 145 and 146: Equation Comparison Table 9-1. Tabu
Page 147 and 148: Chapter 10 Op Amp Noise Theory and
Page 149 and 150: Characterization 10.2.2 Noise Floor
Page 151 and 152: Types of Noise 10.3.1 Shot Noise Th
Page 153 and 154: Types of Noise as average dc curren
Page 155 and 156: Types of Noise Some characteristics
Page 157 and 158: Noise Colors There are an infinite
Page 159 and 160:
Op Amp Noise 1000 Hz V n - Input No
Page 161 and 162:
Op Amp Noise can be represented bet
Page 163 and 164:
Op Amp Noise This simplifies the ga
Page 165 and 166:
Putting It All Together 10.6 Puttin
Page 167 and 168:
Putting It All Together When it is
Page 169 and 170:
References +5 V 100 k +5 V 100 k V
Page 171 and 172:
Chapter 11 Understanding Op Amp Par
Page 173 and 174:
Operational Amplifier Parameter Glo
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Additional Parameter Information 10
Page 181 and 182:
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
Additional Parameter Information +V
Page 189 and 190:
Additional Parameter Information of
Page 191 and 192:
Page 193 and 194:
Chapter 12 Instrumentation: Sensors
Page 195 and 196:
The system definition specifies the
Page 197 and 198:
pends heavily on test conditions su
Page 199 and 200:
the bias resistor, R 1 , is selecte
Page 201 and 202:
V OUT I D R F (12-6) The phototran
Page 203 and 204:
the semiconductor in a direction pe
Page 205 and 206:
eference has a temperature drift of
Page 207 and 208:
impedance of the transducer. The te
Page 209 and 210:
Y mX b (12-14) Two pairs of data
Page 211 and 212:
Table 12-5. Offset and Gain Error B
Page 213 and 214:
R G 23.7 kΩ R FB 280 kΩ R FA 200
Page 215 and 216:
12.10 Test The final circuit is rea
Page 217 and 218:
Chapter 13 Wireless Communication:
Page 219 and 220:
Wireless Systems ality. Image rejec
Page 221 and 222:
Wireless Systems of the DAC, is usu
Page 223 and 224:
Selection of ADCs/DACs The mean squ
Page 225 and 226:
Selection of ADCs/DACs fication. Wi
Page 227 and 228:
Anti-Aliasing Filters The op amp dy
Page 229 and 230:
Communication D/A Converter Reconst
Page 231 and 232:
External Vref Circuits for ADCs/DAC
Page 233 and 234:
External Vref Circuits for ADCs/DAC
Page 235 and 236:
High-Speed Analog Input Drive Circu
Page 237 and 238:
High-Speed Analog Input Drive Circu
Page 239 and 240:
Chapter 14 Interfacing D/A Converte
Page 241 and 242:
Understanding the D/A Converter and
Page 243 and 244:
Understanding the D/A Converter and
Page 245 and 246:
D/A Converter Error Budget 14.4.1 A
Page 247 and 248:
D/A Converter Error Budget 20 Ampli
Page 249 and 250:
D/A Converter Errors and Parameters
Page 251 and 252:
Page 253 and 254:
Page 255 and 256:
Page 257 and 258:
Increasing Op Amp Buffer Amplifier
Page 259 and 260:
Page 261 and 262:
Page 263 and 264:
Chapter 15 Sine Wave Oscillators Ro
Page 265 and 266:
Phase Shift in the Oscillator 15.3
Page 267 and 268:
Active Element (Op Amp) Impact on t
Page 269 and 270:
Analysis of the Oscillator Operatio
Page 271 and 272:
Sine Wave Oscillator Circuits Phase
Page 273 and 274:
Sine Wave Oscillator Circuits large
Page 275 and 276:
Sine Wave Oscillator Circuits The i
Page 277 and 278:
Sine Wave Oscillator Circuits R F 1
Page 279 and 280:
Sine Wave Oscillator Circuits V OUT
Page 281 and 282:
Sine Wave Oscillator Circuits resis
Page 283 and 284:
Sine Wave Oscillator Circuits 15.7.
Page 285 and 286:
Chapter 16 Active Filter Design Tec
Page 287 and 288:
Fundamentals of Low-Pass Filters V
Page 289 and 290:
Fundamentals of Low-Pass Filters A(
Page 291 and 292:
Fundamentals of Low-Pass Filters 16
Page 293 and 294:
Fundamentals of Low-Pass Filters 10
Page 295 and 296:
Low-Pass Filter Design The multipli
Page 297 and 298:
Low-Pass Filter Design C 1 R 1 R 2
Page 299 and 300:
Low-Pass Filter Design V IN R 1 R 2
Page 301 and 302:
Low-Pass Filter Design The general
Page 303 and 304:
Low-Pass Filter Design In order to
Page 305 and 306:
High-Pass Filter Design With C 1 =
Page 307 and 308:
High-Pass Filter Design 16.4.1 Firs
Page 309 and 310:
High-Pass Filter Design To simplify
Page 311 and 312:
Band-Pass Filter Design R 1 1 1 2
Page 313 and 314:
Band-Pass Filter Design 16.5.1 Seco
Page 315 and 316:
Band-Pass Filter Design Because of
Page 317 and 318:
Band-Pass Filter Design A mi is
Page 319 and 320:
Band-Pass Filter Design In accordan
Page 321 and 322:
Band-Rejection Filter Design |A| [d
Page 323 and 324:
Band-Rejection Filter Design or to
Page 325 and 326:
All-Pass Filter Design 0 |A| — Ga
Page 327 and 328:
All-Pass Filter Design Inserting th
Page 329 and 330:
All-Pass Filter Design The transfer
Page 331 and 332:
Practical Design Hints 16.8 Practic
Page 333 and 334:
Practical Design Hints +V CC +V CC
Page 335 and 336:
Practical Design Hints The differen
Page 337 and 338:
Practical Design Hints 16.8.4 Op Am
Page 339 and 340:
Filter Coefficient Tables 16.9 Filt
Page 341 and 342:
Filter Coefficient Tables Table 16-
Page 343 and 344:
Page 345 and 346:
Page 347 and 348:
References 16.10 References D.Johns
Page 349 and 350:
Chapter 17 Circuit Board Layout Tec
Page 351 and 352:
PCB Mechanical Construction 17.2 PC
Page 353 and 354:
PCB Mechanical Construction V+ IN -
Page 355 and 356:
Grounding ponents and feed-throughs
Page 357 and 358:
Grounding components carefully if t
Page 359 and 360:
The Frequency Characteristics of Pa
Page 361 and 362:
Page 363 and 364:
Page 365 and 366:
Page 367 and 368:
Page 369 and 370:
Decoupling + Figure 17-15. Logic Ga
Page 371 and 372:
Input and Output Isolation A decoup
Page 373 and 374:
Packages SINGLE DUAL SHORT TRACES L
Page 375 and 376:
Packages and other passive componen
Page 377 and 378:
References 17.8.4 Routing 17.
Page 379 and 380:
Chapter 18 Designing Low-Voltage Op
Page 381 and 382:
Dynamic Range The trick to designin
Page 383 and 384:
Signal-to-Noise Ratio Table 18-1. C
Page 385 and 386:
Input Common-Mode Range Many low vo
Page 387 and 388:
Input Common-Mode Range The input s
Page 389 and 390:
Output Voltage Swing Op amps always
Page 391 and 392:
Single-Supply Circuit Design every
Page 393 and 394:
Transducer to ADC Analog Interface
Page 395 and 396:
DAC to Actuator Analog Interface is
Page 397 and 398:
DAC to Actuator Analog Interface Th
Page 399 and 400:
Comparison of Op Amps Table 18-2. O
Page 401 and 402:
Summary mon-mode range of the op am
Page 403 and 404:
Appendix A Single-Supply Circuit Co
Page 405 and 406:
Introduction + 5 V R G R F +V CC _
Page 407 and 408:
Amplifiers A.3 Amplifiers Many type
Page 409 and 410:
Amplifiers A.3.3 Inverting Op Amp w
Page 411 and 412:
Amplifiers A.3.5 Noninverting Op Am
Page 413 and 414:
Amplifiers A.3.7 Noninverting Op Am
Page 415 and 416:
Amplifiers A.3.9 Differential Ampli
Page 417 and 418:
Amplifiers A.3.11 High Input Impeda
Page 419 and 420:
Amplifiers A.3.13 High-Precision Di
Page 421 and 422:
Amplifiers A.3.15 Variable Gain Dif
Page 423 and 424:
Amplifiers A.3.17 Buffer The buffer
Page 425 and 426:
Amplifiers A.3.19 Noninverting AC A
Page 427 and 428:
Computing Circuits A.4.2 Noninverti
Page 429 and 430:
Computing Circuits A.4.4 Inverting
Page 431 and 432:
Page 433 and 434:
Page 435 and 436:
Computing Circuits A.4.10 Noninvert
Page 437 and 438:
Page 439 and 440:
Oscillators A.5 Oscillators This se
Page 441 and 442:
Oscillators A.5.3 Wien Bridge Oscil
Page 443 and 444:
Oscillators A.5.5 Classical Phase S
Page 445 and 446:
Oscillators A.5.7 Bubba Oscillator
Page 447 and 448:
Appendix BA Single-Supply Op Amp Se
Page 449 and 450:
Table B-1. Single-Supply Operationa
Page 451 and 452:
A AC loads, DAC, 14-2 AC parameters
Page 453 and 454:
low pass filter, 16-1 low-pass filt
Page 455 and 456:
esistor ladder, 14-2 to 14-4 resist
Page 457 and 458:
phase shift for TL07x, 7-5 phase sh
Page 459 and 460:
N Noise, 10-8 to 10-10 avalanche, 1
Page 461 and 462:
packages, 17-24 to 17-27 parallel s
Page 463 and 464:
Theorem Norton’s, 2-5 Superpositi
show all

Op Amps for Everyone - The Repeater Builder's Technical ...

Create successful ePaper yourself

Delete template?

Save as template?