OPERATIONAL AMPLIFIER Module 3 OPERATIONAL AMPLIFIER

Brainstorming Session…. What does an AMPLIFIER do?

What is an IC?

Integrated Circuits

Inside an IC

OP-Amp is an amplifier 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

Operational Amplifier 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)

The 741 Op-amp The most common op-amp is the 741 IC.

Figure : Op Amp packages 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

What are these pins? http://www.quia.com/pp/200743.html 7. +VCC 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 http://www.quia.com/pp/200743.html

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 -VIN +VIN VOUT +VS -VS (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?

Operational Amplifier Single-Ended Input + terminal : Source – terminal : Ground 0o phase change + terminal : Ground – terminal : Source 180o phase change Ref:080114HKN Operational Amplifier

Operational Amplifier Double-Ended Input Differential input 0o phase shift change between Vo and Vd Qu: What Vo should be if, Ans: (A or B) ? (A) (B) Ref:080114HKN Operational Amplifier

Common-Mode Operation Same voltage source is applied at both terminals Ideally, two input are equally amplified Output voltage is ideally zero due to differential voltage is zero Practically, a small output signal can still be measured Note for differential circuits: Opposite inputs : highly amplified Common inputs : slightly amplified  Common-Mode Rejection Ref:080114HKN Operational Amplifier

Common-Mode Rejection Ratio (CMRR) Differential voltage input : Common voltage input : Common-mode rejection ratio: Output voltage : Note: When Gd >> Gc or CMRR  Vo = GdVd Gd : Differential gain Gc : Common mode gain Ref:080114HKN Operational Amplifier

Operational Amplifier Op-Amp Properties Infinite Open Loop gain The gain without feedback Equal to differential gain Zero common-mode gain Pratically, Gd = 20,000 to 200,000 (2) Infinite Input impedance Input current ii ~0A T- in high-grade op-amp m-A input current in low-grade op-amp (3) Zero Output Impedance act as perfect internal voltage source No internal resistance Output impedance in series with load Reducing output voltage to the load Practically, Rout ~ 20-100  Ref:080114HKN Operational Amplifier

Ideal Vs Practical Op-Amp Open Loop gain A  105 Bandwidth BW 10-100Hz Input Impedance Zin >1M Output Impedance Zout 0  10-100  Output Voltage Vout Depends only on Vd = (V+V) Differential mode signal Depends slightly on average input Vc = (V++V)/2 Common-Mode signal CMRR 10-100dB Ref:080114HKN Operational Amplifier

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(

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)

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

Ideal Op-Amp Applications Analysis Method : Two ideal Op-Amp Properties: The voltage between V+ and V is zero V+ = V The current into both V+ and V termainals is zero For ideal Op-Amp circuit: Write the kirchhoff node equation at the noninverting terminal V+ Write the kirchhoff node eqaution at the inverting terminal V Set V+ = V and solve for the desired closed-loop gain Ref:080114HKN Operational Amplifier

Operational Amplifier Inverting Amplifier Kirchhoff node equation at V+ yields, Kirchhoff node equation at V yields, Setting V+ = V– yields Notice: The closed-loop gain Vo/Vin is dependent upon the ratio of two resistors, and is independent of the open-loop gain. This is caused by the use of feedback output voltage to subtract from the input voltage. Ref:080114HKN Operational Amplifier

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

Noninverting Amplifier Kirchhoff node equation at V+ yields, Kirchhoff node equation at V yields, Setting V+ = V– yields or Ref:080114HKN Operational Amplifier

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 ANI = Noninverting Gain

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

Operational Amplifier Multiple Inputs Kirchhoff node equation at V+ yields, Kirchhoff node equation at V yields, Setting V+ = V– yields Ref:080114HKN Operational 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

Operational Amplifier Inverting Integrator Now replace resistors Ra and Rf by complex components Za and Zf, respectively, therefore Supposing The feedback component is a capacitor C, i.e., The input component is a resistor R, Za = R Therefore, the closed-loop gain (Vo/Vin) become: where What happens if Za = 1/jC whereas, Zf = R? Inverting differentiator Ref:080114HKN Operational Amplifier

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

Operational Amplifier Op-Amp Integrator Example: Determine the rate of change of the output voltage. Draw the output waveform. Solution: (a) Rate of change of the output voltage (b) In 100 s, the voltage decrease Ref:080114HKN Operational Amplifier

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

Op-Amp Differentiator Ref:080114HKN Operational Amplifier

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 Astable Multivibrator

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.

Practical-Summing Amplifier

Results Table Vo = - (V1 + V2 )