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operational amplifiers

Operational Amplifiers

Brandon Borm

Shelley Nation

Chloe Milion

outline
Outline
  • Introduction
  • Background
  • Fundamentals of Op-Amps
  • Real vs. Ideal
  • Applications
what is an op amp
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
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
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 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
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

+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
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
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
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
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
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
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
Follower Circuit

+ Vs

Vin

Vout

- Vs

summing op amp
Summing Op-Amp
  • Adds analog signals

Ohm’s Law:

Solving for Vout:

difference op amps
Difference Op-Amps
  • Subtracts analog signals
  • Output voltage is proportional to difference between input voltages:
integrator op amps
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
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
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
Active Low-Pass Filter
  • Cutoff frequency:
active high pass filter
Active High-Pass Filter
  • Switch positioning of capacitors and resistors from low-pass filter locations to create high-pass filter.
active band 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
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
Comparator

Vout ( volts )

+Vs

iin = 0A

+

+ Vs

Vout

Vdiff

-

V+

Vdiff

0V

V-

-Vs

- Vs

references
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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