Department of Mechanical Engineering Chapter 6-3 Operational amplifier
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Department of Mechanical Engineering
Chapter 6-3 Operational amplifier
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Department of Mechanical Engineering
Some Op-amps
Current to Voltage Amplifier
Voltage-to-Current Amp
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Department of Mechanical Engineering
Some Op-amps
Precision Diode Putting a diode in the feedback path produces a diode which gives virtually zero output for half a cycle and a gain of unity for the other half cycle. It can therefore rectify signals which are smaller than a diode drop. This device would usually be followed by a voltage follower.
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Department of Mechanical Engineering
Summing Amplifier Apply Kirchoff’s current law to the V- node:
0...21 =++++ RFRNRR IIII
0...2
2
1
1 =++++⇒F
OUT
N
N
RV
RV
RV
RV
Like the inverting amp, V- = 0
+++−=⇒
N
NFOUT R
VRV
RVRV ...
2
2
1
1
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Input Impedances
Input impedance seen by: – Input 1 = R1 – Input 2 = R2 – Input N = RN
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Department of Mechanical Engineering
Example
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Department of Mechanical Engineering
Summing amplifier applications
If the input resistances of a summing amplifier are connected to potentiometers the individual input signals can be mixed together by varying amounts. For example, you could produce an audio mixer for adding or mixing together individual waveforms (sounds) from different source channels (vocals, instruments, etc) before sending them combined to an audio amplifier.
Summing Amplifier Audio Mixer
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Department of Mechanical Engineering
Non-inverting summing amplifier
14vKVout ′=
At node 1
At node 2 ( )[ ] 01 321
2
3
32
2
22
1
12 =++−
′+
−′+
−′+
−′KKKR
vKRvv
KRvv
KRvv
aaaa
3322112 vKvKvKv ++=′
( )3322114 vKvKvKKvout ++=
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Department of Mechanical Engineering
Non-Inverting Summing Amplifier
1
21RR
VVOUT +=
+
2
0
21
21
VVV
RVV
RVV
+=⇒
=−
+−
+
++
21 21
1
2 VVRRVOUT
+
+=∴
21 VVVOUT +=∴If R1=R2
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Department of Mechanical Engineering
Non-Inverting Summing Amplifier
1
21RR
VVOUT +=
+
3
0
21
21
VVV
RV
RVV
RVV
+=⇒
=−
+−
+−
+
+++
31 21
1
2 VVRRVOUT
+
+=∴
21 VVVOUT +=∴If R2=2R1
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Department of Mechanical Engineering
Design Example A customer want to automate a pressure measurement, which requires
converting the output of the pressure transducer to a computer input. The conversion can be done using a standard integrated circuit called an analog-to-digital converter (ADC). The ADC requires an input voltage between 0V to 10V, while the pressure transducer output varies between -250mV and 250mV. Design a circuit to interface the pressure transducer with the ADC.
VvVmVvmV
100250250
2
1
≤≤≤≤−
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Department of Mechanical Engineering
Design Example bavv += 12 ( )( ) bmVaV
bmVa+=
+−=25010
2500
VbVVa
520
==
520 12 += vv
A Design plan
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Design Example
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Department of Mechanical Engineering
Example Design a circuit having three inputs, v1, v2, v3, and
two output va and vb, that are related by the equation, assuming a 5-V source available
−
+
−
−=
4
20682312
3
2
1
vvv
vv
b
a
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Department of Mechanical Engineering
Example
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Department of Mechanical Engineering
Example A microphone has an unloaded voltage vs=20mV. An op amp is
available as shown. It is desired to provide an output voltage of 4V. Design an inverting circuit and a noninverting circuit and contrast the input resistance at terminal x-y seen by the microphone. Which configuration would you recommend in order to achieve good performance in spite of changes in the microphone resistance.
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Department of Mechanical Engineering
Example
For example, Let R1=0, and R2=2MΩ
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Department of Mechanical Engineering
Example
MEMS1082Some Op-ampsSome Op-ampsSumming AmplifierInput ImpedancesExampleSumming amplifier applicationsNon-inverting summing amplifierNon-Inverting Summing AmplifierNon-Inverting Summing AmplifierDesign ExampleDesign ExampleDesign ExampleExampleExampleExampleExampleExample
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