Operational Amplifier has been used in several years. It is known due to its high gain amplifier with a high input impedance and low output impedance.

1. Engr. Jesus Rangcasajo
ECE 321 Instructor
jesusrangcasajo@gmail.com

2.  Electronic devices capable of amplification or
increasing the amplitude of power, current or voltage
at its output.
 Circuits designed to increase the amplitude of level of
an electronic signal.
 Used as boosters.
AMPLIFIER
input output

3. 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 W)
Note:
The op-amp has two inputs and one output

4. Basic Op-Amp
One of the input terminals (1) is
called an inverting input terminal
denoted by ‘-’
The other input terminal (2) is
called a non-inverting input
terminal denoted by ‘+’

5. Op-Amp Gain
Op-Amps have a very high gain. They can be connected open-
loop or closed-loop.
1. 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.
2. 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

7. Virtual Ground Principles
A very important principle in Op-amps circuit analysis.
It states that the differential input voltage is ZERO,
meaning V+ = V-.
It seems that the two inputs are short circuited but,
actually not.
There is even no current flow from V+ to V-.

8. 𝑉𝐷 = 𝑉+ − 𝑉−
𝑉+
𝑉−
+ −
+
−
𝑉𝑜0 = 𝑉+ − 𝑉−
𝑉+ = 𝑉−
Virtual Ground Principles

9. Op-Amps
Configuration

10. Inverting Amplifier
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.

11. 𝐼1
𝐼𝑓
𝑉𝑎
𝑉+ = 𝑉− = 𝑉𝑎=0
By virtual ground:
Finding a relation between Vo and V1, considering the op-amp is
IDEAL, so there is NO CURRENT that flows into the device and 𝐈 𝟏 =
𝐈 𝐟
𝐈 𝟏
𝐼1 =
𝑉1 − 𝑉𝑎
𝑅1
𝐈 𝒇
𝐼𝑓 =
𝑉𝑎 − 𝑉𝑜
𝑅𝑓

12. 𝐈 𝟏 = 𝐈 𝐟
𝑉1 − 𝑉𝑎
𝑅1
=
𝑉𝑎 − 𝑉𝑜
𝑅𝑓
𝑉1 − 0
𝑅1
=
0 − 𝑉𝑜
𝑅𝑓
𝑉𝑜 = −
𝑅𝑓
𝑅1
𝑉1
The negative sign denotes a 180 phase shift between input and output

13. Noninverting Amplifier

14. Unity Follower

15. Summing Amplifier

16. Integrator
 The output is the integral of the input.
 This circuit is useful in low-pass filter circuits

17. Differentiator
 The differentiator takes the derivative of the input.
 This circuit is useful in high-pass filter circuits.

18. Example:
What is the output voltage and Gain?

19. What output voltage results in the circuit above for an
input of Vi =-0.3 V?

20. Thank you!