lab8 opamp dssign amp

5/24/2018 Lab8 Opamp Dssign Amp

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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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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


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:


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.

lab8 opamp dssign amp

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