Operational amplifier

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.