1. Operational Amplifiers
Chapter

2. The Summing Amplifier Circuit
Lecture Example 1: Solve of vo in terms of va, vb, vc, Ra, Rb, Rc and Rf.
5.4 – 5.6

3. Lecture Example 2 (The Summing Amplifier Circuit): a
Lecture Example 2 (The Summing Amplifier Circuit): a. Find v0 in the circuit shown if va=0.1V and vb=0.25V.
b. If vb=0.25V, how large can va be before the op amp saturates?
c. If va=0.10V, how large can vb be before the op amp saturates?
d. Repeat (a), (b), and (c) with the polarity of vb reversed.
5.4 – 5.6

4. The Noninverting Amplifier Circuit
Lecture Example 3: Solve of vo in terms of vg, Rs , Rf, and Rg.
5.4 – 5.6

5. ‘Pedagogical’ Design Challenge
Design Challenge: build an audio mixer with four tracks for your garage band:
Requirements:
Track 1: Singer (gain 2)
Track 2: Drummer (gain ¼)
Track 3: Flute (gain 5)
Track 4: Guitar (gain 1)
Your cat is very sensitive to inverted signals, so make sure your final signal is not inverted. Ignore frequency behavior. All feedback loops have 100kW. All feedback resistors: Rf=100kW.
5.4 – 5.6

6. The Difference Amplifier Circuit
Lecture Example 4: Solve of vo in terms of va, vb, Ra, Rb, Rc and Rd.
5.4 – 5.6

7. Lecture Example 5: Assume that the op amp in the circuit is ideal.
Find the output voltage when the variable resistor is set to 60 kW.
How large can RX be before the amplifier saturates?
5.4 – 5.6

8. Operational Amplifiers A More Realistic Model
Chapter 5.7

9. Equivalent Circuit for an Op Amp
What assumptions are different than the ideal Op Amp assumptions?
Ri →∞
A →∞
R0 →0
5.7

10. Equivalent Circuit for an Op Amp
For a μA741 op amp, the typical values are;
Ri = 2 MΩ, R0 = 75 Ω, and A = 105.
5.7

11. An inverting-amplifier circuit
5.7

12. An inverting-amplifier circuit
5.7

13. A noninverting-amplifier circuit
5.7

14. A noninverting-amplifier circuit
5.7

15. Lecture Example 6 (non-ideal op amp): The inverting amp shown has an input resistance of 500kW, an output resistance of 5kW, and an open-loop gain of 300,000. Assume that the amplifier is operating in its linear region.
Calculate the voltage gain (v0/vg) of the amp.
Find the value of vn in mV when vg=1V.
Find the resistance seen by the signal source (vg).
Repeat (a)-(c) using the ideal model for the op amp.
5.4 – 5.6