operational amplifier

1. Presented By
Amrita Singh

2. Introduction
 Operational Amplifiers are represented both schematically
and realistically below:
 Active component!

3. Basic Details
 Differential Amplifier
 Amplifies difference between inputs
 Output gain high
 A ~= 106
 Tiny difference in the input voltages result in a very large
output voltage
 Output limited by supply voltages
 Comparator
 If V+>V-, Vout = HVS
 If V+<V-, Vout = LVS
 If V+=V-, Vout = 0V

4. 3-stage Op-Amp

5. Ideal Op Amp
 Zin is infinite
 Zout is zero
 Amplification (Gain) Vout / Vin = ∞
 Unlimited bandwidth
 Vout = 0 when Voltage inputs = 0

6. Ideal Op Amp
Parameters Ideal Op-Amp Typical Op-Amp
Input Resistance infinity 106  (bipolar)
109  - 1012  (FET)
Input Current 0 10-12 – 10-8 A
Output Resistance 0 100 – 1000 
Operational Gain infinity 105 - 109
Common Mode Gain 0 10-5
Bandwidth infinity Attenuates and phases at
high frequencies
(depends on slew rate)
Temperature independent Bandwidth and gain

7. Applications
 Comparator
 Voltage follower
 Signal Modulation
 Mathematical Operations
 Filters

8. Non-inverting Op-Amp
Application: Amplifier

9. Inverting Op-Amp
Application: Analog inverter

10. Comparator
Application: Low-voltage alarms, night light
controller

11. Pulse Width Modulator
Output changes when
Vin ~= Vpot
Potentiometer used to vary duty
cycle
Application: Motor controllers

12. Summation
Application: Add multiple sensors inputs until
a threshold is reached.

13. Difference
 
1
31
124
4132
)( R
RV
RRR
RRRV
Vout 



If all resistors are equal:
12 VVVout 
Application: Subtractor

14. Integrator
Application: PID Controller

15. Differentiator
(where Vin and Vout are functions of time)

16. Filters
• Decouple the low-pass RC filter from the
load.
Application: Simple audio. Remove
frequencies over 20kHz (audible)

17. Low-pass Filter (active)
Cutoff frequency
This works because the capacitor needs time
to charge.

18. High pass filter (active)
Band-pass filter cascades both high-pass and
low-pass!