Operational Amplifiers - Georgia Institute of...
Transcript of Operational Amplifiers - Georgia Institute of...
Operational AmplifiersME 6405, Fall ‘04
Martin GudemNurudeen Olayiwola
Henry Won
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Operational Amplifiers
Goals:• Introduction• Characteristics• Types• Models VS. reality
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Introduction
Most transducers provide analog signals:
• Too small• Too noisy
•Wrong information•DC offset
Measurement system
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Amplifiers
• Ideally: Increase amplitude without affecting other properties of the signal
Av =VoutVin
Zin =VinIin
Zout =VoutIout
• Voltage gain:
• Impedances:
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Terminology
Closed loop → Stabilized signal
Open loop
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Ideal Model
• Aid in circuit analysis
1. I+ = I- = 02. V+ = V-
3. Zout = 0
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Configuration
• 741 General purpose amplifier
Pin-out
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Internal design
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The Ideal Op-Amp
• Infinite Input Resistance• Zero input current• Zero Output Resistance• Infinite Gain• Common Mode Voltage Gain Zero• Zero Noise / Zero Output Allowed• Unlimited Bandwith• Temperature Independent
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Ideal v. Real Op-Amps
100 – 1000 Ω0Output Resistance
10-50Common Mode Gain
Attenuates and phases at high frequencies (depends
on slew rate)
infinityBandwidth
10-12 – 10-8 A0Input Current
Bandwidth and gainindependentTemperature
105 - 109infinityOperational Gain
106 Ω (bipolar)109 Ω - 1012 Ω (FET)
infinityInput Resistance
Typical Op-AmpIdeal Op-Amp
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/opampcon.html#c1
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Op-Amps for Math
• Inverting• Non-Inverting• Summing• Differencing• Integrating• Differentiating
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Inverting
“An Application Guide for Op-Amps”, National Semi-Conductor, Application Note 20, February 1969.
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Non - Inverting
“An Application Guide for Op-Amps”, National Semi-Conductor, Application Note 20, February 1969.
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Summing Op-Amp
“An Application Guide for Op-Amps”, National Semi-Conductor, Application Note 20, February 1969.
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Differencing Op-Amp
“An Application Guide for Op-Amps”, National Semi-Conductor, Application Note 20, February 1969.
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Integrating Op-Amp
“An Application Guide for Op-Amps”, National Semi-Conductor, Application Note 20, February 1969.
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Differentiating Op-Amp
“An Application Guide for Op-Amps”, National Semi-Conductor, Application Note 20, February 1969.
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Use of an Op amp
• Filters:3 types 1. Low Pass Filter (LPF)
– Used to filter higher freq.
2. High Pass Filter (HPF)– used to filter low freq.
3. Band Pass Filter (BPF)-a combination of LPF and HPF
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Contd.
• Dual input (dual source – and + with respect to ground), – Used in audio equip. control circuits, medical equipment, etc.
• Single input
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Order of filters
• First order• Second orderOur examples show second order Filters.- What was the order of the filter we used in lab?
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LPF
This filter is used to remove noise signals that are above the specified frequency.The frequency range is given by the equation below
Where f=freq.R=R2C=C1
RCf
π21
=
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HPF
HPF is used to remove all freq.Below the specified freq. and it isCreated by reversing the positionof the capacitor and resistor In a LPF
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BPF
This is a combination of the LPF and HPF. It allows for freq. within the range for the LPF and HPF.
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Instrumentation OP Amp
This is used in Situations where output voltageneeds to varied.
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Analysis of instrumentation op amp
• Vo = Vo1 – Vo2• Vo1=V1+VR• Vo2 =V2 – VR• VR = (V1-V2)R/RA• Vo= V1-V2+2VR =(V1-V2)(1+2R/RA)
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The use of filters
• Communications• Removing noise from a power input
• Radio communications• Infrared/ LED signals transm.• Etc
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Conclusions
• One major disadvantage– Distortion when dealing with really low freq. ranges
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Conclusions contd.
• Advantages– Useable in different industries– Signal and power amplification– Simple– Cheap and easy to build– Makes life easier– Math operations
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References
• www.electronics-tutorials.com• www.play-hookey.com• Alcitore, Histand Introduction to Mechatronics and Measurement Systems