Operational Amplifiers C H A P T E R 02 Operational Amplifiers  Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.1 Circuit symbol for the op amp. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.2 The op amp shown connected to dc power supplies. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.3 Equivalent circuit of the ideal op amp. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure E2.3 Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.5 The inverting closed-loop configuration. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2. 6 Analysis of the inverting configuration Figure 2.6 Analysis of the inverting configuration. The circled numbers indicate the order of the analysis steps. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.7 Analysis of the inverting configuration taking into account the finite open-loop gain of the op amp. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2. 8 Circuit for Example 2. 2 Figure 2.8 Circuit for Example 2.2. The circled numbers indicate the sequence of the steps in the analysis. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2. 9 A current amplifier based on the circuit of Fig. 2. 8 Figure 2.9 A current amplifier based on the circuit of Fig. 2.8. The amplifier delivers its output current to R4. It has a current gain of (1 + R2 /R3), a zero input resistance, and an infinite output resistance. The load (R4), however, must be floating (i.e., neither of its two terminals can be connected to ground). Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure E2.5 Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure E2.6 Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.10 A weighted summer. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.11 A weighted summer capable of implementing summing coefficients of both signs. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.12 The noninverting configuration. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2. 13 Analysis of the noninverting circuit Figure 2.13 Analysis of the noninverting circuit. The sequence of the steps in the analysis is indicated by the circled numbers. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2. 14 (a) The unity-gain buffer or follower amplifier Figure 2.14 (a) The unity-gain buffer or follower amplifier. (b) Its equivalent circuit model. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure E2.9 Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure E2.13 Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.15 Representing the input signals to a differential amplifier in terms of their differential and common-mode components. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.16 A difference amplifier. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.17 Application of superposition to the analysis of the circuit of Fig. 2.16. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.19 Finding the input resistance of the difference amplifier for the case R3 = R1 and R4 = R2. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2. 20 A popular circuit for an instrumentation amplifier Figure 2.20 A popular circuit for an instrumentation amplifier. (a) Initial approach to the circuit (b) The circuit in (a) with the connection between node X and ground removed and the two resistors R1 and R1 lumped together. This simple wiring change dramatically improves performance. (c) Analysis of the circuit in (b) assuming ideal op amps. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.22 The inverting configuration with general impedances in the feedback and the feed-in paths. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.23 Circuit for Example 2.4. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2. 24 (a) The Miller or inverting integrator Figure 2.24 (a) The Miller or inverting integrator. (b) Frequency response of the integrator. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.25 The Miller integrator with a large resistance RF connected in parallel with C in order to provide negative feedback and hence finite gain at dc. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2. 26 Waveforms for Example 2. 5: (a) Input pulse Figure 2.26 Waveforms for Example 2.5: (a) Input pulse. (b) Output linear ramp of ideal integrator with time constant of 0.1 ms. (c) Output exponential ramp with resistor RF connected across integrator capacitor. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2. 27 (a) A differentiator Figure 2.27 (a) A differentiator. (b) Frequency response of a differentiator with a time-constant CR. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.28 Circuit model for an op amp with input offset voltage VOS. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure E2.21 Transfer characteristic of an op amp with VOS = 5 mV. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.29 Evaluating the output dc offset voltage due to VOS in a closed-loop amplifier. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.30 The output dc offset voltage of an op amp can be trimmed to zero by connecting a potentiometer to the two offset-nulling terminals. The wiper of the potentiometer is connected to the negative supply of the op amp. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2. 31 (a) A capacitively coupled inverting amplifier Figure 2.31 (a) A capacitively coupled inverting amplifier. (b) The equivalent circuit for determining its dc output offset voltage VO. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.32 The op-amp input bias currents represented by two current sources IB1 and IB2. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.33 Analysis of the closed-loop amplifier, taking into account the input bias currents. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.34 Reducing the effect of the input bias currents by introducing a resistor R3. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.35 In an ac-coupled amplifier the dc resistance seen by the inverting terminal is R2; hence R3 is chosen equal to R2. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.36 Illustrating the need for a continuous dc path for each of the op-amp input terminals. Specifically, note that the amplifier will not work without resistor R3. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.37 Determining the effect of the op-amp input offset voltage VOS on the Miller integrator circuit. Note that since the output rises with time, the op amp eventually saturates. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.38 Effect of the op-amp input bias and offset currents on the performance of the Miller integrator circuit. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.39 Open-loop gain of a typical general-purpose internally compensated op amp. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.40 Frequency response of an amplifier with a nominal gain of +10 V/V. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.41 Frequency response of an amplifier with a nominal gain of 10 V/V. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.42 (a) A noninverting amplifier with a nominal gain of 10 V/V designed using an op amp that saturates at ±13-V output voltage and has ±20-mA output current limits. (b) When the input sine wave has a peak of 1.5 V, the output is clipped off at ±13 V. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.

Figure 2.44 Effect of slew-rate limiting on output sinusoidal waveforms. Microelectronic Circuits, International Sixth Edition Sedra/Smith Copyright © 2011 by Oxford University Press, Inc.