# Lecture 19 - Operational Amplifier

```CHAPTER 8
IDEAL OPERATIONAL AMPLIFIER AND
OP-AMP CIRCUITS
inverting
output
non-inverting
Op-amp circuit symbol
• Open loop mode
• Vo = Aod ( V2 – V1)
– Aod is referred to as the
open loop gain.
– Notice that is V2 = V1, the
open loop gain equals to

Final Exam SEM II 2012/2013
An ideal op-amp, was measured in a lab experiment in open-loop
mode. Determine the open loop gain (Aod) and complete the table
below which shows the results of the experiment.
V1 (1)
-1mV
-0.5V
0.99 V
V2 (2)
+1mV
-0.506 V
1V
Vo (3)
1V
-3V
5V
• Op amp can be configured to be used for
different type of circuit applications:
– Inverting Amplifier
– Non – inverting Amplifier
– Summing Amplifier
– Integrator
– Differentiator
Inverting Amplifier
Op-amp as an inverting amplifier
Voltage at node 1 (inverting) = voltage at node 2 (non-inverting )
KCL at node 1:
(Vi – 0) / R1 = (0 – Vo) / R2
Vi / R1 = - Vo / R2
Vo = - R2
Vi
R1
Exercise 8.3
Gain = - (R2 / R1) = -(150/12) = -12.5
Can the voltage gain be calculated the using the same formula?
Try and use the same method in deriving Vo/Vi
Non - Inverting Amplifier
Voltage at node 1 (inverting) = voltage at node 2 (non-inverting )
KCL at node 1:
(0– Vi) / R1 = (Vi – Vo) / R2
-(Vi / R1) = (Vi / R2) – (Vo / R2)
Vo / R2 = (Vi / R2) + (Vi / R1) = Vi 1 + 1
R2
Vo / Vi = R2 1 + 1
R2 R1
R1
Noninverting amplifier
Voltage Follower / Buffer Amplifier
Vo = Vi
Hence, gain = 1
Summing Amplifier
Summing
Similarly,Amplifier
i1 + i2 + i3 – i4 – 0 = 0
Output voltage
Solution: output voltage
Other Op-Amp Applications
Integrator
Integrator circuit
Differentiator
EXAMPLE 8.4
Differentiator circuit
Calculating Gain and Design Questions
NON - INVERTING
INVERTING
Calculating Output and Design Questions
SUMMING AMPLIFIER
INTEGRATOR AMPLIFIER
DIFFERENTIATOR AMPLIFIER
Calculate the input voltage if the final output, VO is 10.08 V.
What is the value of Vin1 from the figure above?
Calculate the output voltage, VO if V1 = V2 = 700 mV
IDQ
• Please write down the questions you attempted on the
cover page
• Organize your thoughts. When it is organized, so will your
workflow.
– Messy work will make the lecturers feel annoyed as they have to
look for your answers – bear in mind that lecturer handling one
section = 50-60 students – each paper has 5 questions
– TOTAL – 250 to 300 questions to mark
• Don’t leave a question blank – just write down anything
you know that might be related
• Be tactical.
• Study smart, pray and tawakal.
```