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’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
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 in -V in ON -V in +V in -V s + +V s -V s NC +V s V out ON V out
Characteristics of Op-Amps Ideal Op-Amp Real Op-Amp Infinite open loop gain (G OL ): Zero common mode gain Limited open loop gain: Decreases with increase in frequency Non-zero common mode gain Infinite bandwidth: Range of frequencies with non-zero 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 No input current Large input impedance Small input current Zero output impedance Infinite output current Non-zero output impedance Limited output current
Summary of Characteristics Parameter G OL Common Mode Gain Bandwidth Input Impedance Output Impedance Ideal Op-Amp Typical Op-Amp ∞ 10 5 - 10 9 0 ∞ ∞ 0 10 -5 1-20 MHz 10 6 Ω (bipolar) 10 9 -10 12 Ω (FET) 100-1000 Ω
Ideal Op-Amp Active device Infinite open loop gain Infinite input impedance Zero output impedance i in = 0A + V diff +V s -V s V out = V diff x G openloop
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
Non Inverting Circuit +V s i in = 0A + V out V diff = 0V V in 0A -V s R2 R1 i (1) (1) V - V out = R2 x i (2) V =
-
R1 x i V = V + = V in (2) i = -V in /R1 V in – V out = -V in x R1/R2 V V - V out
V out = (1 + R1/R2) x V in
Inverting Circuit
V in
i in = 0A + V diff = 0V +V s R1 i -V s R2
V out
(1) V - V out = R2 x i (2) V in - V = R1 x i V (1) = V + = 0 i = V in / R1 V in – V V - V out
V out = - R2/R1 x V in
Follower Circuit + V s V in V out - V s
Summing Op-Amp • Adds analog signals Ohm’s Law: Solving for V out :
V
1
V
R
1
V
2
R
2
V
V
3
R
3
V
V
R f V out V out
R f
V
1
R
1
V
2
R
2
V
3
R
3
Summing Op-Amp
Difference Op-Amps • Subtracts analog signals • Output voltage is proportional to difference between input voltages:
V out
R
3 (
R
4
R
1
R
4
R
2 )
R
1
V
2
R R
1 3
V
1
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:
V out
,
final
V out
,
initial
1
RC
0
t V in dt
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:
V out
RC dV in dt
Differentiating Op-Amp
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:
c
1
R
2
C
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 V out is a
non-linear
input voltage V + - V function of the differential V + - V = V diff V out = sign(V diff ) x V s Binary logic and oscillator
V+ Comparator +V s V i in = 0A +
V diff
-V s
V out V out ( volts ) + V s
0V
V diff - V s
Comparator
Questions?
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/741/74 1.html
“Op Amp History.” Analog Devices. http://www.analog.com/library/analogDialogue/ar chives/39-05/Web_ChH_final.pdf