Lecture 12.pptx
- 1. EE 2105: Electronics Lecture 11 Operational Amplifier (Op-Amp) Arefin Ahamed Lecturer, EEE, KUET
- 2. Basic Op-Amp Dept. of Electrical and Electronic Engineering, KUET 2 Operational amplifier or op-amp, is a very high gain differential amplifier with a high input impedance (typically a few meg-Ohms) and low output impedance (less than 100 ). Note the op-amp has two inputs and one output. X Voltage or Current X 1. Very High Gain (A = 𝟏𝟎𝟓 to 𝟏𝟎𝟔) 2. Differential Input 𝑉+ 𝑉− 𝐕𝟎 = 𝐀(𝐕+- 𝐕−)
- 3. Basic Op-Amp Dept. of Electrical and Electronic Engineering, KUET 3 For ideal Op-Amp: 1. Current i = 0 2. 𝐕𝟎 = 𝐀(𝐕+- 𝐕−) i = 0
- 4. Op-Amp Gain Dept. of Electrical and Electronic Engineering, KUET 4 Op-Amps have a very high gain. They can be connected open-loopor closed-loop. • Open-loop refers to a configuration where there is no feedback from output back to the input. In the open-loop configuration the gain can exceed 10,000. • Closed-loop configuration reduces the gain. In order to control the gain of an op- amp it must have feedback. This feedback is a negative feedback. A negative feedback reduces the gain and improves many characteristics of the op-amp.
- 5. Inverting Op-Amp Dept. of Electrical and Electronic Engineering, KUET 5 • The signal input is applied to the inverting (–) input • The non-inverting input (+) is grounded • The resistor Rf is the feedback resistor. It is connected from the output to the negative (inverting) input. This is negative feedback.
- 6. Virtual Ground Dept. of Electrical and Electronic Engineering, KUET 6
- 7. Virtual Ground Dept. of Electrical and Electronic Engineering, KUET 7 An understanding of the concept of virtual ground provides a better understanding of how an op- amp operates. The non-inverting input pin is at ground. The inverting input pin is also at 0 V for an AC signal. The op-amp has such high input impedance that even with a high gain there is no current from inverting input pin, therefore there is no voltage from inverting pin to ground—all of the current is through Rf.
- 8. Inverting Op-Amp Gain Dept. of Electrical and Electronic Engineering, KUET 8
- 9. Practical Op-Amp Circuits Dept. of Electrical and Electronic Engineering, KUET 9 Inverting amplifier Noninverting amplifier Unity follower Summing amplifier Integrator Differentiator
- 10. Inverting/Noninverting Op-Amps R1 Vo Rf V1 InvertingAmplifier NoninvertingAmplifier o 1 Dept. of Electrical and Electronic Engineering, KUET 10 R1 V (1 Rf )V
- 11. Noninverting Op-Amps Dept. of Electrical and Electronic Engineering, KUET 11 𝑉− = 𝑅1 𝑅1 + 𝑅𝑓 𝑉0 𝑉0 = 𝐴(𝑉1 − 𝑅1 𝑅1+𝑅𝑓 𝑉0) 𝑉0 1 + 𝐴𝑅1 𝑅1+𝑅𝑓 = 𝐴𝑉1 𝑉0 = 𝐴𝑉1 1+ 𝐴𝑅1 𝑅1+𝑅𝑓 = 𝐴𝑉1 𝐴𝑅1 𝑅1+𝑅𝑓 ∴ 𝑉0 = 𝐴𝑉1( 𝑅1+𝑅𝑓 𝑅1 )
- 12. Math Problems Dept. of Electrical and Electronic Engineering, KUET 12
- 13. Unity Follower Dept. of Electrical and Electronic Engineering, KUET 13 Vo V1
- 14. Summing Amplifier Because the op-amp has a high input impedance, the multiple inputs are treated as separate inputs. Dept. of Electrical and Electronic Engineering, KUET 14 V3 3 2 1 o Rf V1 R V2 R R Rf Rf V
- 15. Math Problems Dept. of Electrical and Electronic Engineering, KUET 15
- 16. Math Problems Dept. of Electrical and Electronic Engineering, KUET 16
- 17. Integrator Dept. of Electrical and Electronic Engineering, KUET 17 RC The output is the integral of the input. Integration is the operation of summing the area under a waveform or curve over a period of time. This circuit is useful in low- pass filter circuits and sensor conditioning circuits. vo (t) 1 v1 (t)dt
- 18. Differentiator The differentiator takes the derivative of the input. This circuit is useful in high-pass filter circuits. dt Dept. of Electrical and Electronic Engineering, KUET 18 vo (t) RC dv1(t)
- 19. Op-Amp Applications Dept. of Electrical and Electronic Engineering, KUET 19 Constant-gain multiplier Voltage summing Voltage buffer Controlled sources Instrumentation circuits Active filters
- 20. Constant-Gain Amplifier Inverting Version Dept. of Electrical and Electronic Engineering, KUET 20 more…
- 21. Math Problems Dept. of Electrical and Electronic Engineering, KUET 21
- 22. Constant-Gain Amplifier Noninverting Version Dept. of Electrical and Electronic Engineering, KUET 22
- 23. Math Problems Dept. of Electrical and Electronic Engineering, KUET 23
- 24. Multiple-Stage Gains Dept. of Electrical and Electronic Engineering, KUET 24
- 25. Multiple-Stage Gains Dept. of Electrical and Electronic Engineering, KUET 25
- 26. Voltage Buffer Dept. of Electrical and Electronic Engineering, KUET 26 Any amplifier with no gain or loss is called a unitygain amplifier. The advantages of using a unity gain amplifier: • Very high input impedance • Very low output impedance Realistically these circuits are designed using equal resistors (R1 = Rf) to avoid problems with offset voltages.