1. Electronic Circuit-II
Chapter 3

2. Topics in the Chapter 3 Feed Back of OPAMP. Importance of feedback.
Inverting feedback.
formula for gain, calculation of gain & problems
Noninverting feedback, problems.
How gain can be controlled using Feedback.
Effect of Feedback on OPAMP in terms of input and output impedances.

3. Negative Feedback
Negative feedback is the process of returning a portion of the output signal to the input with a phase angle that opposes the input signal.

5. The advantage of negative feedback is that precise values of amplifier gain can be set. In addition, bandwidth and input and output impedances can be controlled.

6. Noninverting Amplifier
A noninverting amplifier is a configuration in which the signal is on the noninverting input and a portion of the output is returned to the inverting input.

7. Circuit diagram for Noninverting OP-AMP

8. Noninverting Amplifier
Example:
Determine the gain of the noninverting amplifier shown.
Solution:
= 25.8

9. Inverting Amplifier
An inverting amplifier is a configuration in which the noninverting input is grounded and the signal is applied through a resistor to the inverting input.

10. 0 V (virtual ground)

11. Determine the gain of the inverting amplifier shown.
Example:
Determine the gain of the inverting amplifier shown.
Solution:
= -24.8
The minus sign indicates inversion.

12. Noninverting amplifier:
Impedances
Noninverting amplifier:
Generally, assumed to be ∞
Generally, assumed to be 0
Inverting amplifier:
Generally, assumed to be Ri
Generally, assumed to be 0
Note that the output impedance has the same form for both amplifiers.

13. Quiz 6. The input impedance of a noninverting amplifier is
a. nearly 0 ohms
b. approximately equal to Ri
c. approximately equal to Rf
d. extremely large

14. Quiz
7. The noninverting amplifier has a gain of 11. Assume that Vin = 1.0 V. The approximate value of Vf is
a. 0 V
b. 100 mV
c. 1.0 V
d. 11 V

15. Quiz
8. The inverting amplifier has a gain of -10. Assume that Vin = 1.0 V. The approximate value of the voltage at the inverting terminal of the op-amp is
a. 0 V
b. 100 mV
c. 1.0 V
d. 10 V

16. Quiz
9. To compensate for bias current, the value of Rc should be equal to
a. Ri
b. Rf
c. Ri||Rf
d. Ri + Rf

17. Quiz
10. Given a noninverting amplifier with a gain of 10 and a gain-bandwidth product of 1.0 MHz, the expected high critical frequency is
a. 100 Hz
b. 1.0 kHz
c. 10 kHz
d. 100 kHz

18. Quiz
10. Given a noninverting amplifier with a gain of 10 and a gain-bandwidth product of 1.0 MHz, the expected high critical frequency is
a. 100 Hz
b. 1.0 kHz
c. 10 kHz
d. 100 kHz

19. Quiz
Answers:
6. d
7. c
8. a
9. c
10. d