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EE 310 Electronic Circuit Design I
Spring 2014
Experiment 8
Op Amp Design ProjectRocket Probe Signal Conditioning and Interfacing Circuits
Tianyu L
Section 00
Introduction:
The Object of this lab is to design an op amp circuit which can measure the current of charge that is collected
buy a rocket probe. The major voltage is 20Vpp, 10Hz frequency , and with the triangle wave. The current
will move through 4 block of op amp so that the final signal can read by an encoder. Also we need to measure
the polarity of current of input signal through a non-linear op amp circuit.
The power supply of the experiment is from +15V to -15V . The probe current of collected charge, I, will need to
be simulated. We will consider its magnitude to be 10 A.The nature of vP
is as follows: it is a 20-V p-p triangular
waveform having a mean (DC) value equal to zero volts and a frequency of 10 Hz.
Diagram of Probe Signal Conditioning and Interfacing Circuits
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Circuit Design and Supporting Analysis
Block 1. Transresistance Amplifier
Schematic:
Used to get 10A current and convert it to voltage signal.
Circuit Description and Design Reasoning:
The purpose of the transresistance amplifier is to convert the input current of the circuit into a voltage
source. Its a non-inverting amplifier circuit using op amp. The resistor value is 1M and 100K .
Op amp had very big input impedance. So we can assume V-= V+and I-= I+=0.
So we apply KCL @ V-:
( )
So Vo1 = (1+106/10
5) 20Vpp= 22Vpp = -11V~11V
I = Vo1/ (R1+ Rf1) = (-11V~11V) / (106+10
5) = -9.09A ~ 9.09A
In this stage, we get 10A input current and convert it to a voltage signal of 22Vpp.
Block 2 Difference Amplifier
Schematic:
Used to get Vo2= VpVo1
U1
LM7 CN
3
2
4
7
6
51
R1
1.0M
Rf1
100k
VCC
15V
VEE
-15V
XFG1
Vo1
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Circuit Description and Design Reasoning:
The purpose of the difference amplifier is to remove the bias voltage from the output voltage of the
last block. The resistor value are same in this case which is 100K .
V- = V+ Apply KCL @ V-
( )
Plug in R2= R3= R4= Rf2= 100k
Vo2= VpVo1= 2Vpp
In this stage, we use a difference amplifier and get output voltage equals to difference of
Vp and Vo1.
U2
LM7 CN
3
2
4
7
6
51
R4
100k
R2
100k
R3
100k
Rf2
100k
XFG2
VCC
15V
VEE
-15V
VO2
Vo1
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Block 3. Signal Conditioner
Schematic:
Used to get output range in 0~5V
Circuit Description and Design Reasoning:
The purpose of this circuit is to take the Vo2 through the signal conditioner to make the output
voltage from 0 to 5V.
Use superposition:
V-= V+ Apply KCL @ V-
For this problem, let Rf3/ R7= R6/ R5= 2.5
Choose Rf3= R6= 75k, R5= R7= 30k
Then Vo3 = 2.5 Vo2+ 2.5 V, which met the requirement
U3
LM7 CN
3
2
4
7
6
51
R6
75k
R5
30kR7
30k
Rf3
75k
VCC
15V
VDD
2.5V
VEE
-15V
Vo2
VO3
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Block 4. Polarity Monitor subsystem.
Schematic:
Circuit Description and Design Reasoning:
The purpose of the block is to determine the polarity of the input voltage using a
comparator circuit using voltage divider and op amp.
Apply KCL @ Vo
Let R9= R8
In this problem, when Vo= 15V, Vo2= 5V.
So R9= 4R10
Choose R9= 10k, R10= 2.5k
Then we convert -15V~15V to -5V~5V.
U4
LM7 CN
3
2
4
7
6
51
XFG3
VEE
-15V
VCC
15V
R9
10k
R8
10k
R10
2.5k
VCC
15V
Vo2
Vo
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Data
Measurements for each stage:
Block 1. Transresistance Amplifier
: Channel 1: Vo1; Channel 2: Vp
Block 2 Difference Amplifier
: Channel 1: Vo1; Channel 2: Vo2
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Block 3. Signal Conditioner
: Vo2; Channel 2: Vo3
Block 4. Polarity Monitor subsystem.
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: Channel 1: Vp; Channel 2: Vo2
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Multisim simulation:
Block 1: Vo1 p-p= 22V
Block 2: Vo2 p-p = 2V
Block 3 Vo3: -5.36mV~4.99V
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Block 4: Vo= 0.179V~4.83V
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Final output
Bonus:
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Result and their Significance
Our results very close to our theoretical calculations. The output voltage of block 1 is 22.8Vpp, which is
near to 22Vpp. The output of block 2 is 1.94Vpp, which is close to theoretical value of 2Vpp. The block
3 and block 4 the output range is from 0 to 5V. The block 3 minimum voltage is 100mV and maximum
voltage is 5.4V. The block 4 minimum voltage is 200mV and maximum voltage 4.9V. We can see the
Multisim simulations also close to our results.
Error analysis
For the block 1 the %error is 3.63%. The block 2 the %error is 3%. The block 3 and block4 the %error
are 6%. Depend on those percent errors, which is on accept range. The major reason of errors is the
resistor value we used not exactly same as the theoretical value. Also the oscilloscope has large internal
resistance. These reasons will influence our accurate of measurement.
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Summary and Conclusion
We designed the function of a rocket probe by using op amps. To achieve our goal to measure the
voltage output of each block and make the voltage to what we want. To compare our results and
theoretical calculation results, there are only a little percent error which means we made a successful
design and experiment.