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Operational Amplifiers. Brandon Borm Shelley Nation Chloe Milion. Outline. Introduction Background Fundamentals of Op-Amps Real vs. Ideal Applications. What is an Op-Amp. Low cost integrating circuit consisting of transistors resistors capacitors

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## Operational Amplifiers

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**Operational Amplifiers**Brandon Borm Shelley Nation Chloe Milion**Outline**• Introduction • Background • Fundamentals of Op-Amps • Real vs. Ideal • Applications**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**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**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 http://en.wikipedia.org/wiki/Image:K2-w_vaccuum_tube_op-amp.jpg1**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**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**+Vs**+Vin + Vout -Vin - -Vs Features of Op-Amps • +Vin: non-inverting input • -Vin: inverting input • +Vs: positive source • -Vs: negative source • Vout: output voltage • ON: Offset Null • NC: Not Connected ON NC +Vs -Vin +Vin Vout -Vs ON**Ideal Op-Amp**Infinite open loop gain (GOL): 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 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 Characteristics of Op-Amps**Ideal Op-Amp**• Active device • Infinite open loop gain • Infinite input impedance • Zero output impedance +Vs iin = 0A + Vdiff Vout = Vdiff x Gopenloop - -Vs**Negative Feedback**• Vout is a linear function of the input voltage • Zin = infinity Iin=0A Vdiff=0V • Modelisation of basic mathematical operation**Non Inverting Circuit**+Vs (1) V- - Vout = R2 x i iin = 0A + Vout (2) V- = - R1 x i Vdiff = 0V Vin - V- = V+ = Vin (2) i = -Vin/R1 0A -Vs R1 R2 i (1) Vin – Vout = -Vin x R1/R2 V- V- - Vout Vout = (1 + R1/R2) x Vin**Inverting Circuit**+Vs (1) V- - Vout = R2 x i iin = 0A + Vout (2) Vin - V- = R1 x i Vdiff = 0V - -Vs V- = V+ = 0 (1) i = Vin / R1 Vin R1 R2 i Vin – V- V- - Vout Vout = - R2/R1 x Vin**Follower Circuit**+ Vs Vin Vout - Vs**Summing Op-Amp**• Adds analog signals Ohm’s Law: Solving for Vout:**Difference Op-Amps**• Subtracts analog signals • Output voltage is proportional to difference between input voltages:**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:**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:**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**Active Low-Pass Filter**• Cutoff frequency:**Active High-Pass Filter**• Switch positioning of capacitors and resistors from low-pass filter locations to create high-pass filter.**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**No negative feedback**• Vout is a non-linear function of the differential input voltage V+ - V- • V+ - V- = Vdiff • Vout = sign(Vdiff) x Vs • Binary logic and oscillator**Comparator**Vout ( volts ) +Vs iin = 0A + + Vs Vout Vdiff - V+ Vdiff 0V V- -Vs - Vs**References**• “Operational Amplifiers.” http://en.wikipedia.org/wiki/Op_amp • “Real vs. Ideal Op Amp.” http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/opamp.html#c4 • “741 Op Amp Tutorial.” http://www.uoguelph.ca/~antoon/gadgets/741/741.html • “Op Amp History.” Analog Devices. http://www.analog.com/library/analogDialogue/archives/39-05/Web_ChH_final.pdf

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