operational amplifiers david lomax azeem meruani gautam jadhav
TRANSCRIPT
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Operational Amplifiers
David Lomax
Azeem Meruani
Gautam Jadhav
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What is an Op-Amp
Low cost integrating circuit consisting of:TransistorsResistorsCapacitors
Able to amplify a signal due to an external power supply
Name derives from its use to perform operations on a signal.
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Applications of Op-Amps
Simple Amplifiers Summers Comparators Integrators Differentiators Active Filters Analog to Digital Converters
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Symbol for an Op-Amp
+V
-V
Inverting Input Terminal
Non-Inverting Input Terminal
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IC Circuit
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What do they really look like?
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Ideal Op-Amps
Infinite input impedance I+ = I- = 0
Infinite gain V+ = V-
Zero output impedanceOutput voltage is independent of output current
Vout
V+
V-
I+
I-
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Inverting Amplifier
R
RF
Vin
iin
iout
C
R
R
V
V F
in
out
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Non-Inverting Amplifier
R
RF
iin
iout
C
Vin
R
R1
V
V F
in
out
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Summing Circuits
• Used to add analog signals
• Voltage averaging function into summing function
Calculate closed loop gain for each input
11 R
RA fCL
21 R
RA
f
CL
31 R
RA
f
CL
CLnino AVV 3
32
21
1 R
RV
R
RV
R
RVV
fff
o
321 VVVVo If all resistors are equal in value:
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Difference Circuit• Used to subtract analog signals
• Output signal is proportional to difference between two inputs
12 VVVout If all resistors are equal:
1
31
124
4132
)( R
RV
RRR
RRRVVout
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Integrating Circuit• Replace feedback resistor of inverting op-amp with capacitor
• A constant input signal generates a certain rate of change in output voltage
• Smoothes signals over time
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Differentiating Circuit• Input resistor of inverting op-amp is replaced with a capacitor
• Signal processing method which accentuates noise over time
• Output signal is scaled derivative of input signal
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Filters
Low Pass Filters High Pass Filters Band Pass Filters
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Low Pass Filter• Used to filter out signals above a specified frequency
• Example: Noise
Frequency range is governed by:
CRf
2
1
Where
R = R2
C = C2
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High Pass Filter• Filters out frequencies below a specified frequency
• Reverse locations of resistors and capacitors in a low pass filter
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Band Pass Filter
• Created by combining a high and low pass filter
• Only allows signals within frequency ranges specified by the low and high pass filters to pass
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Comparator Circuit
• Determines if one signal is bigger than another
• No negative feedback, infinite gain and circuit saturates
• Saturation: output is most positive or most negative value
V1 is Vref
V2 is Vin
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OR Gate
If U1 or/and U2 = 5V,
U3 = 5V
If U2 and U1 = 0V,
U3 = 0V
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Offset Comparator
If
U3 = 0V
If
U3 = 5V
1
21
22
.URR
RU
21
2112
RR
.RU5.RU
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Real Vs Ideal Op Amp
Parameters Ideal Typical
Input Impedance
∞ 106Ω
Output Impedance
0Ω 100-1000Ω
Voltage Gain ∞ 105 - 109
Common Mode voltage
0 10-5
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Non-Ideal Op-Amps
Gain Bandwidth Falloff Frequency Slew Rate (ΔV/ΔT) Rise Time
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Gain Bandwidth
Gain Bandwidth Product (GBP)- is the product of the open-loop gain and the bandwidth at that gain.
For practical purposes the actual gain should only be 1/10 to 1/20 of the open loop gain at a given frequency to ensure that the op-amp will operate without distortion.
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Open and Closed Loop Response
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Important Parameters for Op-Amps
Input Parameters Voltage (Vicm) Offset voltage Bias current Input Impedance
Output Parameters Short circuit current Voltage Swing Open Loop Gain Slew Rate
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Where to buy Op-Amps
Newark Electronics Radio Shack DigiKey Jameco
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References
David G Alciatore & Michael B. Histand, Introduction to Mechatronics and Measurement Systems
http://www.elexp.com/t_gain.htm http://allaboutelectronics.com Electronics book
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Questions ?