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Operational amplifiers l.jpg

Operational Amplifiers

Brandon Borm

Shelley Nation

Chloe Milion


Outline l.jpg
Outline

  • Introduction

  • Background

  • Fundamentals of Op-Amps

  • Real vs. Ideal

  • Applications


What is an op amp l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
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


Features of op amps l.jpg

+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


Characteristics of op amps l.jpg

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


Characteristics of op amps10 l.jpg

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 l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
Follower Circuit

+ Vs

Vin

Vout

- Vs


Summing op amp l.jpg
Summing Op-Amp

  • Adds analog signals

Ohm’s Law:

Solving for Vout:



Difference op amps l.jpg
Difference Op-Amps

  • Subtracts analog signals

  • Output voltage is proportional to difference between input voltages:



Integrator op amps l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
Active Low-Pass Filter

  • Cutoff frequency:


Active high pass filter l.jpg
Active High-Pass Filter

  • Switch positioning of capacitors and resistors from low-pass filter locations to create high-pass filter.


Active band pass filter l.jpg
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 l.jpg
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 l.jpg
Comparator

Vout ( volts )

+Vs

iin = 0A

+

+ Vs

Vout

Vdiff

-

V+

Vdiff

0V

V-

-Vs

- Vs




References l.jpg
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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