The purpose of this lab is to allow students to gain experience constructing Digital to Analog Converters in Multisim. Students will extend the concepts learned in the module and homework to build an 8-Bit DAC. Several binary inputs and the associated analog output values measured with a virtual digital multimeter will be captured in screenshots.
1. Watch the video
2. Determine the values of all the remaining seven resistors and fill in the table 1.
Table1:
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Resistors
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Values
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R1
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1K ?
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R2
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R3
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R4
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R5
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R6
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R7
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R8
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3. Recall the binary to decimal conversion and fill the table below:
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Bits
|
Binary Input
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Decimal conversion
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MSB
(S1)
|
1000 0000
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S2
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S3
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S4
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S5
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S6
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S7
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LSB
(S8)
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0000 0001
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4. Construct an 8-bit binary weighted DAC in Multisim and measure the output voltage Vout using the multimeter and record the computed gain below.
Table2:
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Bits
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Binary Input
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Vin
|
Rn
(n = 1,2,3,4,5,6,7,8)
|
RF
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Output Voltage (Vout)
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Voltage Gain (Av)
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MSB
(S1)
|
1000 0000
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S2
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S3
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S4
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S5
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S6
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S7
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LSB
(S8)
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0000 0001
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5. Take the screenshots of Vout measurements for the input/output combination for each of the above 8-bits.
6. Answer the following questions:
a. Determine the approximate value of RF which results in accurate digital to analog conversion.
b. Write the expression for Vout in terms of Vin, RF and R for each bit. Also, express Vout in terms of all 8 input voltages.
c. Starting from the least significant bit to the most significant bit, what is the effect of feedback resistance on the output voltage?
d. From your measurements, does increase in the digital value result in increase in analog value? Please explain.
e. Is the voltage gain of the op Amp different for each bit? Please explain why?