An operational amplifier (op-amp) is an integrated circuit that can amplify or compare signals. It consists of transistors, resistors, and capacitors. Op-amps are used to build amplifiers, summers, integrators, differentiators, and comparators. They obey golden rules to make the difference between their input pins zero. Op-amps are also used in analog to digital converters, which sample analog signals and convert them to digital signals for processing.

1. Operational
Amplifiers
By Unsa Shakir

2. What is an Op-Amp
 Low cost integrating circuit consisting of:
• Transistors
• Resistors
• Capacitors
 Able to amplify a signal due to an external
power supply
 Name derives from its use to perform
operations on a signal.

3. Applications of Op-Amps
 Simple Amplifiers
 Summers
 Comparators
 Integrators
 Differentiators
 Analog to Digital Converters

4. Circuit Symbol and Pin Identification
 2 Inverting Input
 3 Non-Inverting Input
 6 Output
 7 + Voltage Supply
VCC
 4 – Voltage Supply
VEE
 1 and 5 -- Offset Null
U1
741
3
2
4
7
6
51

5. What do they really look like?

6. IC Circuit

7. Op-Amp “Golden Rules”
• When an op-amp is configured in any negative-
feedback arrangement, it will obey the following two
rules:
– The inputs to the op-amp draw or source no
current (true whether negative feedback or not)
– The op-amp output will do whatever it can (within
its limitations) to make the voltage difference
between the two inputs zero

8. Inverting Amplifier
R
RF
Vin
iin
iout
C
R
R
V
V F
in
out


9. Non-Inverting Amplifier
R
RF
iin
iout
C
Vin
R
R
1
V
V F
in
out


10. Summing Circuits
• Used to add analog signals
• Voltage averaging function
into summing function
Calculate closed loop gain for
each input
1
1
R
R
A
f
CL


2
1
R
R
A
f
CL


3
1
R
R
A
f
CL


CLnino AVV 
3
3
2
2
1
1
R
R
V
R
R
V
R
R
VV
fff
o 
 321 VVVVo If all resistors are equal in value:

11. Difference Circuit
• Used to subtract analog
signals
• Output signal is
proportional to difference
between two inputs
12 VVVout If all resistors are equal:
 
1
31
124
4132
)( R
RV
RRR
RRRV
Vout 




12. Integrating Circuit
• Replace feedback resistor of
inverting op-amp with capacitor
• A constant input signal
generates a certain rate of
change in output voltage
• Smoothes signals over time

13. Differentiating Circuit
• Input resistor of inverting op-
amp is replaced with a capacitor
• Signal processing method
which accentuates noise over
time
• Output signal is scaled
derivative of input signal

14. Comparator Circuit
• Determines if one signal is bigger than another
• No negative feedback, infinite gain and circuit saturates
• Saturation: output is most positive or most negative value
V1 is Vref
V2 is Vin

15. Analog to Digital Converters
 An electronic integrated circuit which transforms a signal from
analog (continuous) to digital (discrete) form.
 Microprocessors can only perform complex processing on digitized
signals.
 When signals are in digital form they are less susceptible to the
deleterious effects of additive noise.
 ADC Provides a link between the analog world of transducers and
the digital world of signal processing and data handling.
 Some examples of ADC usage are digital volt meters, cell phone,
thermocouples, and digital oscilloscope.

16. How ADC works ?
Mainly there are two steps for the analog to digital conversion:
S/H: Sampling and holding
Q/E: Quantizing and Encoding
The ADC process is shown in figure below:

17. Sampling & Holding
• It is used to sample the given input signal and to hold the
sampled value. Once a signal is sampled, it is called a
discrete signal.
• Sample and hold circuit is used to sample an analog signal
for a short interval of time in the range of 1 to 10µS and to
hold on its last sampled value until the input signal is
sampled again.
• The holding period may be from a few milliseconds to
several seconds.

18. Quantization and Encoding
 The output of a sampler is still continuous in amplitude. To
transmit as a digital signal we must restrict the number of
possible values.
 Quantization is the process of “rounding off” a sampled value
according to some rule.
– E.g. suppose we must round to the nearest tenth, then:
3.752 --> 3.8 0.001 --> 0
 Encoding: After identifying the closest value, a numerical
value is assigned to it and it is encoded in the form of a binary
number.