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Operational Amplifiers Brandon Borm Shelley Nation Chloe Milion

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

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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

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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

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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

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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

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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

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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

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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

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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

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

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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

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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

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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

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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

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

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

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Summing Op-Amp

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

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Difference Op-Amp

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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:

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Integrator Op-Amp

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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:

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Differentiating Op-Amp

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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

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Active Low-Pass Filter Cutoff frequency:

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

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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

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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

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

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Comparator

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Questions?

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References “Operational Amplifiers.” “Real vs. Ideal Op Amp.” astr.gsu.edu/hbase/electronic/opamp.html#c4 astr.gsu.edu/hbase/electronic/opamp.html#c4 “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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