 Operational Amplifiers

Presentation on theme: "Operational Amplifiers"— Presentation transcript:

Operational Amplifiers
Lecture (11) Operational Amplifiers

What does an AMPLIFIER do?
Integrated Circuits What does an AMPLIFIER do? What is an IC? OP-Amp is an amplifier IC Inside an IC

What can you do with Op amps?
You can make music louder when they are used in stereo equipment. You can amplify the heartbeat by using them in medical cardiographs. You can use them as comparators in heating systems. You can use them for Math operations like summing, integration etc.

OP-AMP (operational amplifier)
An OP-AMP is an integrated circuit (IC) used for amplification of signals. It is the most widely used analog IC. It is used in control systems, instrumentation, signal processing etc. The Operational Amplifier or "op-amp" is an amplifier with two inputs and one output. One input is the inverting input and the other is a non inverting input.

OP-AMP BLOCK DIAGRAM - V + V Output Differential Amplifier
Figure 1 Op Amp Block Diagram Inverting Input (- VIN) + V - V Output Noninverting Input (+ VIN) Differential Amplifier Voltage Amplifier Output Amplifier

OP-AMP HAS 3 –STAGE AMPLIFIER CIRCUITS
First Stage : Differential Amplifier -it gives the OP-AMP high input impedance (resistance) Second Stage: Voltage Amplifier – it gives high gain Third Stage : Output Amplifier (Emitter Follower) – gives low output impedance (resistance)

OP-AMP CHARACTERISTICS
Very high input impedance Very high gain Very low output impedance OP-AMP is a differential, voltage amplifier with high gain.

OP-AMP is a differential, voltage amplifier with high gain. Why????
Differential Amplifier: Because it amplifies the difference between 2 voltages Voltage Amplifier: Because input and output are voltages High Gain Amplifier: Because the voltage gain is very high (> 100,000)

Figure : Op Amp packages
The 741 Op-amp The most common op-amp is the 741 IC. Packaging Types Figure : Op Amp packages (b) OPA547FKTWT DIP SMT package (a) Op Amp 741 8-pins DIP package (c) TO-5 metal can 8-Leads package

OP-AMP pins identification
Figure 3 Op Amp pins Identification 1 2 3 4 5 6 7 8 +VCC -VEE - + 741 b) Notched Package a) Dot marked Package

Figure 4 Op Amp pins Description
What are these pins? Figure 4 Op Amp pins Description 1 2 3 4 5 6 7 8 1. Offset Null -VEE 8. N / C 6.Output 741 7. +VCC 3. Noninverting Input +VIN 2. Inverting Input –VIN 5.Offset Null

What are these pins? Pin 1 and Pin 5 : Offset null input, are used to remove the Offset voltage. Pin 2: Inverting input (-VIN), signals at this pin will be inverted at output Pin 6. Pin 3: Non-inverting input (+VIN), signals at pin 3 will be processed without inversion. Pin 4: Negative power supply terminal (-VEE). Pin 6: Output (VOUT) of the Op-Amp Pin 7: Positive power supply terminal (+VCC) Pin 8: No connection (N\C), it is just there to make it a standard 8-pin

Symbol of OP-AMP Figure 5 Op Amp Schematic Symbols +VS -VIN VOUT +VIN
(a) Without power connection (b) With power connection

Most Op Amps require dual power supply with common ground
Positive Supply (+15V) to pin7 Negative Supply (-15V) to pin4 Figure 6 Dual Supply Voltages connection -VIN + - +VIN VOUT +VS -VS 7 4 Common Ground

Some Op Amps work on single supply also
Figure 7 Single Supply Voltages connection -VIN + - +VIN VOUT -VS 7 4 +VS (a) Single Positive Voltage (b) Single Negative Voltage

Advantage of dual power supply
Using dual power supply will let the op amp to output true AC voltage. 0V +15V -15V Output Figure 8a Op Amp powered from Dual supply +30V Figure 8b Op Amp powered from Single supply 30 V

What is dual power supply?
Single Power Supply Figure 18 Dual Power Supply Common +15V –15V

How can you make a dual power supply using two 9V batteries?
What is the voltage between + of first battery and – of second battery?

OP-AMP CONFIGURATIONS
Figure Types of Feedback (a) No Feedback (open loop comparator circuit) (b) Negative Feedback (c) Positive Feedback

Feedback No feedback : Open loop (used in comparators)
Negative feedback : Feedback to the inverting input (Used in amplifiers) Positive feedback : Feedback to the non inverting input (Used in oscillators(

(a) Comparator Circuit
OP AMP as a Comparator (compares 2 voltages and produces a signal to indicate which is greater) +VS VO +VIN = –VIN –VS +VIN  –VIN +VIN  –VIN +VIN –VIN (a) Comparator Circuit (b) Comparator Output

Applications of Comparators
Analog to digital converters (ADC) Counters (e.g. count pulses that exceed a certain voltage level). Cross Over Detectors

OP-AMPS WITH NEGATIVE FEEDBACK
The two basic amplifier circuits with negative feedback are: The non-inverting Amplifier. The inverting Amplifier (Note: Negative feedback is used to limit the gain)

NON-INVERTING AMPLIFIER
The input signal is applied to the non-inverting input (+VIN). The output is fed back to the inverting input through resistor RF. VO VIN RF R1 Figure 11 Closed-Loop Noninverting Amplifier Circuit Where; VO = Output voltage Vin= Input voltage= Vf Ain = Non inverting Gain

Problem: Calculate the gain of a non inverting amplifier if Rin=3K and Rf=30K. If Vin=4mV, calculate the output voltage.

INVERTING AMPLIFIER The input signal is applied through a series input resistor RI to the inverting input. Also, the output is fed back through RF to the same input. The noninverting input is grounded. Where; VO = Output voltage VIN = Input voltage AI = Inverting Gain VO VIN RF RIN

Examples of Negative Feedback Applications:
A) Inverting Amplifiers 1.Summing Amplifier 2.Differentiator 3.Integrator B) Non Inverting Amplifiers 1. Voltage Follower

Figure 14 Summing Amplifier
Summing Amplifier (Adder) : the inputs are added and the sum is inverted . If all resistors are of equal value, then Vo = -(V1 + V2+ V3) Figure 14 Summing Amplifier V1 VO V2 V3 0V R1 R2 R3 RF

Differentiator (the input is differentiated with respect to time)
Figure 16 Inverting Op-Amp as Differentiator C R VIN VO

Integrator (the input is integrated with respect to time)
Figure 15 Inverting Op-Amp as Integrator R C VIN VO

Voltage Follower (Non Inverting)
It is a non inverting amplifier with gain=1 So the output is the same as input. VIN VO Figure 17 Voltage Follower

Positive Feedback is used in oscillators
Astable Multivibrator (Relaxation Oscillator) VO R2 R3 R1 C1 Figure 13 A stable Multi-vibrator

Offset Null Adjustment (practical)
Figure 22 Offset Null adjustment -VS N/C VO +VS VIN = 0 A741 1 2 3 4 5 6 7 8 V

offset voltage can be defined as the slight amount of voltage that appears at the output when the voltage differential (ΔVIN) between the input pins is 0 V. For more reading on op. Amplifiers