1. Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Chapter 14: Op-Amp Applications

2. Slide 1 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Op-Amp Applications A. Constant-Gain Multiplier B. Voltage Summing C. Voltage Buffer D. Controlled Sources E. Instrumentation Circuits F. Active Filters

3. Slide 2 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. A. Constant–Gain Amplifier [Formula 14.1] [Formula 14.2]

4. Slide 3 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Multiple-Stage Gains The Total Gain: A = A 1 * A 2 * A 3 More specifically:

5. Slide 4 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. B. Voltage Summing The output is the sum of individual signals times the gain: [Formula 14.3]

6. Slide 5 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. C. Voltage Buffer Realistically these circuits will be designed using resistors that are equal (R1 = Rf) to void out problems with offset voltages. Any amplifier with no gain (or loss) is called a unity gain amplifier. The advantages of using a unity gain amplifier: very high input impedance very low output impedance

7. Slide 6 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. D. Controlled Sources Voltage-Controlled Voltage Source Voltage-Controlled Current Source Current-Controlled Voltage Source Current-Controlled Current Source

8. Slide 7 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Voltage-Controlled Voltage Source The op-amp is functioning as it always has: the output voltage is the gain times the input voltage. What makes an op-amp different from other amplifiers is it’s impedance characteristics and gain calculations that depend solely on external resistors.

9. Slide 8 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Voltage-Controlled Current Source Again a familiar op-amp circuit, the only difference is the output is a current through the feedback resistor. The output current can be calculated: [Formula 14.9]

10. Slide 9 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Current-Controlled Voltage Source This is simply another way of applying the op-amp operation. Whether the input is a current determined by V in /R 1 or as I 1, it will still provide or -I1*RL.

11. Slide 10 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Current-Controlled Current Source This circuit appears more complicated than the others but it is really the same thing. [Formula 14.11]

12. Slide 11 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. E. Instrumentation Circuits Some examples of instrumentation circuits using op-amps: Display Driver Instrumentation Amplifier

13. Slide 12 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Display Driver

14. Slide 13 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Instrumentation Amplifier For all R’s at the same value (Except R p ) [Formula 14.12]

15. Slide 14 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. F. Active Filters Adding capacitors to op-amp circuits provides an external control for the cutoff frequencies. The op-amp active filter provides controllable cutoff frequencies and controllable gain. Low-Pass Filter High-Pass Filter Bandpass Filter

16. Slide 15 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Low-Pass Filter First-order low-pass filter. The upper cutoff frequency: The gain: [Formula 14.14] [Formula 14.13]

17. Slide 16 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Low-Pass Filter (Cont’d) Second-order low-pass filter: By adding more RC networks the roll-off can be made steeper.

18. Slide 17 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. High-Pass Filter The lower cutoff frequency: [Formula 14.15]

19. Slide 18 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Bandpass Filter There are two cutoff frequencies: upper and lower. They can be calculated using the same low-pass cutoff and high-pass cutoff frequency formulas in the appropriate sections. The frequency response plot: