Op Amp History
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Transcript Op Amp History
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’s1940’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
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
+Vin
+Vs
+
Vout
-Vin
-
-Vs
ON
-Vin
NC
+Vs
+Vin
Vout
-Vs
ON
Characteristics of Op-Amps
Ideal Op-Amp
Infinite open loop gain
(GOL):
Zero
Real Op-Amp
Decreases
with increase
in frequency
Non-zero common mode
gain
common mode gain
Infinite bandwidth:
Range
of frequencies
with non-zero gain
Limited open loop gain:
Limited Bandwidth:
Gain
becomes zero at
high frequencies
Characteristics of Op-Amps
Ideal Op-Amp
Real Op-Amp
Infinite slew rate
Finite slew rate
Infinite input impedance
Large input impedance
No
Small
input current
Zero output impedance
Infinite
output current
input current
Non-zero output
impedance
Limited
output current
Summary of Characteristics
Parameter
Ideal Op-Amp Typical Op-Amp
GOL
∞
105 - 109
Common Mode
Gain
0
10-5
Bandwidth
∞
1-20 MHz
Input
Impedance
∞
Output
Impedance
0
106 Ω (bipolar)
109-1012 Ω (FET)
100-1000 Ω
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
Modelisation of basic mathematical
operation
Iin=0A
Vdiff=0V
Non Inverting Circuit
iin = 0A
Vin
+Vs
(1) V- - Vout = R2 x i
+
Vout
Vdiff = 0V
0A
R1
V- = V+ = Vin
-Vs
i
(2)
i = -Vin/R1
R2
(1)
V-
(2) V- = - R1 x i
Vin – Vout = -Vin x R1/R2
V- - Vout
Vout = (1 + R1/R2) x Vin
Inverting Circuit
+Vs
iin = 0A
(1) V- - Vout = R2 x i
+
Vout
Vdiff = 0V
(2) Vin - V- = R1 x i
-Vs
Vin
R1
Vin – V-
i
R2
V- - Vout
V- = V+ = 0
(1)
i = Vin / R1
Vout = - R2/R1 x Vin
Follower Circuit
+ Vs
Vin
Vout
- Vs
Summing Op-Amp
• Adds analog signals
Ohm’s Law:
Solving for Vout:
V1 V V2 V V3 V V Vout
R1
R2
R3
Rf
Vout
V1 V2 V3
R f
R1 R2 R3
Summing Op-Amp
Difference Op-Amps
• Subtracts analog signals
• Output voltage is proportional to
difference between input voltages:
Vout
R3 R1 R4
V
R3
V1
2
( R4 R2 ) R1
R1
Difference Op-Amp
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:
t
1
Vout , final Vout ,initial
Vindt
RC 0
Integrator 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:
Vout
dVin
RC
dt
Differentiating Op-Amp
Active Filters
Different types of active filters:
Low
Pass
Filters out frequencies above a cutoff frequency
High
Filters out frequencies below a cutoff frequency
Band
Pass
Pass
Passes a range of frequencies between two cutoff
frequencies
Active Low-Pass Filter
Cutoff frequency:
1
c
R2C
Active High-Pass Filter
Switch positioning of capacitors and resistors from lowpass filter locations to create high-pass filter.
Active Band-Pass Filter
Created by connecting output of a highpass 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
+
Vout
Vdiff
+ Vs
-
V+
Vdiff
0V
V-
-Vs
- Vs
Comparator
Questions?
References
“Operational Amplifiers.”
http://en.wikipedia.org/wiki/Op_amp
“Real vs. Ideal Op Amp.”
http://hyperphysics.phyastr.gsu.edu/hbase/electronic/opamp.html#c4
“741 Op Amp Tutorial.”
http://www.uoguelph.ca/~antoon/gadgets/741/74
1.html
“Op Amp History.” Analog Devices.
http://www.analog.com/library/analogDialogue/ar
chives/39-05/Web_ChH_final.pdf