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Operational Amplifiers Brandon Borm Shelley Nation Chloe Milion.

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Presentation on theme: "Operational Amplifiers Brandon Borm Shelley Nation Chloe Milion."— Presentation transcript:

1 Operational Amplifiers Brandon Borm Shelley Nation Chloe Milion

2 Outline Introduction Background Fundamentals of Op-Amps Real vs. Ideal Applications

3 What is an Op-Amp Low cost integrating circuit consisting of  transistors  resistors  capacitors Op-amps amplify an input signal using an external power supply

4 Uses for Op-Amps Op-Amps are commonly used for both linear and nonlinear applications Linear  Amplifiers  Summers  Integrators  Differentiators  Filters (High, Low, and Band Pass) Non-linear  Comparators  A/D converters

5 Vacuum Tube Op-Amps First op amps built in 1930’s- 1940’s  Technically feedback amplifiers due to only having one useable input Used in WWII to help how to strike military targets  Buffers, summers, differentiators, inverters Took ±300V to ± 100V to power

6 Solid State Discrete Op-Amps Solid state op amps invented in 1960’s  Possible due to invention of silicon transistors and the IC  Chip and discrete parts Reduced power input to ±15V to ±10V Packaging in small black boxes allowed for integration with a circuit

7 Monolithic Integrated Circuit Op-Amp First created in 1963  μA702 by Fairchild Semiconductor μA741 created in 1968  Became widely used due to its ease of use  8 pin, dual in-line package (DIP) Further advancements include use of field effects transistors (FET), greater precision, faster response, and smaller packaging

8 Features of Op-Amps +V in : non-inverting input -V in : inverting input +V s : positive source -V s : negative source V out : output voltage ON: Offset Null NC: Not Connected V out +V s -V s +V in -V in + - ON -V in +V in -V s ON V out +V s NC

9 Characteristics of Op-Amps Ideal Op-Amp Infinite open loop gain (G OL ):  Zero common mode gain Infinite bandwidth:  Range of frequencies with non-zero gain Real Op-Amp Limited open loop gain:  Decreases with increase in frequency  Non-zero common mode gain Limited Bandwidth:  Gain becomes zero at high frequencies

10 Characteristics of Op-Amps Ideal Op-Amp Infinite slew rate Infinite input impedance  No input current Zero output impedance  Infinite output current Real Op-Amp Finite slew rate Large input impedance  Small input current Non-zero output impedance  Limited output current

11 Summary of Characteristics ParameterIdeal Op-AmpTypical Op-Amp G OL ∞10 5 - 10 9 Common Mode Gain 010 -5 Bandwidth∞1-20 MHz Input Impedance ∞10 6 Ω (bipolar) 10 9 -10 12 Ω (FET) Output Impedance 0100-1000 Ω

12 Ideal Op-Amp Active device Infinite open loop gain Infinite input impedance Zero output impedance + - +V s -V s V diff i in = 0A V out = V diff x G openloop

13 Negative Feedback V out is a linear function of the input voltage Z in = infinity I in =0A V diff =0V Modelisation of basic mathematical operation

14 Non Inverting Circuit + - R1R2 +V s -V s i in = 0A V diff = 0V V in V out 0A V-V- V - - V out i (1) V - - V out = R2 x i (2) V - = - R1 x i V - = V + = V in (2) i = -V in /R1 (1) V in – V out = -V in x R1/R2 V out = (1 + R1/R2) x V in

15 Inverting Circuit + - R1R2 +V s -V s V diff = 0V V in V out i in = 0A i V - - V out V in – V - (1) V - - V out = R2 x i (2) V in - V - = R1 x i V - = V + = 0 (1) i = V in / R1 V out = - R2/R1 x V in

16 Follower Circuit V in V out + V s - V s

17 Summing Op-Amp Adds analog signals Solving for V out : Ohm’s Law:

18 Summing Op-Amp

19 Difference Op-Amps Subtracts analog signals Output voltage is proportional to difference between input voltages:

20 Difference Op-Amp

21 Integrator Op-Amps Similar layout to inverting op-amp, but replace feedback resistor with a capacitor A constant input signal generates a certain rate of change in output voltage Smoothes signals over time Output voltage is proportional to the integral of the input voltage:

22 Integrator Op-Amp

23 Differentiating Op-Amp Similar to inverting op-amp, but input resistor is replaced with a capacitor Accentuates noise over time Output signal is scaled derivative of input signal:

24 Differentiating Op-Amp

25 Active Filters Different types of active filters:  Low Pass Filters out frequencies above a cutoff frequency  High Pass Filters out frequencies below a cutoff frequency  Band Pass Passes a range of frequencies between two cutoff frequencies

26 Active Low-Pass Filter Cutoff frequency:

27 Active High-Pass Filter Switch positioning of capacitors and resistors from low- pass filter locations to create high-pass filter.

28 Active Band-Pass Filter Created by connecting output of a high- pass filter to the input of a low-pass filter or vice versa. Also can create using only 1 op-amp with feedback and input capacitors

29 No negative feedback V out is a non-linear function of the differential input voltage V + - V - V + - V - = V diff V out = sign(V diff ) x V s Binary logic and oscillator

30 Comparator + - +V s -V s i in = 0A V diff V+ V- V out 0V + V s V out ( volts ) V diff - V s

31 Comparator

32 Questions?

33 References “Operational Amplifiers.” “Real vs. Ideal Op Amp.” http://hyperphysics.phy- http://hyperphysics.phy- “741 Op Amp Tutorial.” 1.html 1.html “Op Amp History.” Analog Devices. chives/39-05/Web_ChH_final.pdf chives/39-05/Web_ChH_final.pdf

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