Itroduction to operational amplifiers

1. DEPARTMENT OF PHYSICS
M.SC. 1ST SEMESTER (2015-2016)
SUB: ELECTRONICS
PRESENTED BY: CHITRA JAIN
SUBMITTED TO : DR. R. J. SENGWA

2. OPERATIONAL AMPLIFIERS
(OP-AMPs)

3.  History
1. First developed by “JOHN R.RAGAZZINE”
in 1947 with vacuum tube.
2. In 1960 “ROBERT J. WIDLAR” fabricated
OP-AMP with the help of IC fabrication
technology.
• μA741 created in 1968
• Became widely used due to its ease of use
• 8 pin, dual in-line package (DIP)

4.  Features of Op-Amps
1. +Vin: non-inverting input
2. -Vin: inverting input
3. +Vs: positive source
4. -Vs: negative source
5. Vout: output voltage
6. ON: Offset Null
7. NC: Not Connected
6 Vout
+Vcc
-Vcc
+Vin
-Vin
3 + 7
2 - 4

6. Equivalent circuit of an op-amp:

7. What is an OP-AMP?
• Op-Amp get their name from their ability to
perform mathematical operations such as
summation, integration etc. etc.…
•“An Op-Amp is a Direct coupled, High gain
amplifier usually consisting of one or more
Differential amplifiers, that can be used to amplify
dc as well as ac input signals”.

8. 1. Differential amplifier:
which can accept two signals and amplifies
the difference between these two input
signals.
2. The internal stages are direct coupled i.e.
no coupling capacitors are used.the direct
coupling allows the Op-Amp to amplify dc as
well as ac.
3. An Op-Amp has very High Open Loop
Voltage gain ( ideally ∞).

9. Block diagram of Op-Amp

10. Differential Amplifier stage
• Provides differential input for the op amp
• Provides dc gain
• has very high input impedance
- draws negligible input current

11. High Gain Voltage amplifier
• Provides the “gain” of the amplifier
• Gains up the differential signal from input
and conveys it to the output stage

12. Low Impedance output stage
• Delivers current to the load
• Very low impedance

13. Characteristics of Op-Amp
IDEAL Op-Amp
1. Input Impedance
Infinite (∞) ; No input current
2. Output Impedance
Zero ; Infinite output current
3. Voltage Gain (Vo/Vi )
Infinite (∞)
4. Band width
Infinite (∞)
5. Slew Rate
Infinite (∞)
6. Noise
Zero
REAL Op-Amp
1. Input Impedance
More than 100 MΩ ; small input current
2. Output Impedance
Less than 100 Ω ; Limited output current
3. Voltage Gain (Vo/Vi )
Very high and adjustable
4. Band width
Very large and adjustable
5. Slew Rate
Very high
6. Noise
Small

14. Parameters of an Op-Amp
OUTPUT OFFSET VOLTAGE:(𝑉𝑜𝑜)
In DC biasing if both the inputs are grounded then DC
voltage at output terminal w.r.t. ground is called “output
offset voltage” ranges from zero to few mV.
INPUT OFFSET VOLTAGE: (𝑉𝑖𝑜)
voltage difference between two input terminal to
make the output offset voltage zero is called “ input
offset voltage”.

15. INPUT COMMON MODE RANGE:
It is the maximum differential signal that can be
applied safely to OP-Amp input terminals.
Common mode rejection ratio(CMMR):
Ability of an Op-Amp to reject a signal applied to both
inputs simultaneously.
 Slew Rate:
Slew rate of an op amp describes how fast the output
voltage can change in response to an immediate change in
voltage at the input(dvo/dt)
It should be high.(volts/microseconds).

16. Output voltage swing:
It is the maximum peak to peak output voltage which can
be obtained without waveform distortion.
Full Power bandwidth:
It is the maximum Frequency over which the full output
voltage swing can be obtained.
Input Bias Current:
Average value of current flowing into inverting and non
inverting terminals while output voltage is zero.

17. Ideal Voltage transfer Curve
• Transfer curve shows how output
follows the input.
• for small value of input voltage the
relationship b/w i/p and o/p voltage is
linear.
• The o/p voltage never exceed the DC
supply voltage.
• When o/p voltage is equal to or greater
than supply voltage referred to as
saturation of amplifier which results in
distortion due to non linear behavior.

18. Open Loop Configuration

19.  Application of Op-Amps
1. As an Amplifier
2. As an oscillatory circuit
3. As log and antilog Amplifier
4. Voltage Comparator
5. Adder, Subtractor, Integrator and
many more.