Electronics and Communications Dept.
Experiment No:(1)
Fourth Year
DAC
Digital to analog convertor
(DAC)
Object:To study and implement two digital to analog circuits.
Equipment:AVO meter.
DC Power supply.
741 Op-Amp
Resistors
Theory:In order to interface digital systems with analog world, special components are
necessary which can convert information from analog to digital (ADC) and also from
digital to analog (DAC). A DAC is a device, which produce analog voltage, or current
proportional to the digital signal at its input.
Multiplying (DAC)
If the reference voltage used for a (DAC) can be varied during its operation, the
analog output is directly proportional to the product of the reference voltage and the
digital input.
Types of DAC's
1. R-2R ladder DAC.
2. Weighted – Resistor DAC.
3. Multiplying DAC.
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Electronics and Communications Dept.
Experiment No:(1)
Fourth Year
DAC
Procedure:1. Four-bit binary R-2R ladder (DAC)
Connect the circuit of figure (1) and verify its operation by changing bits (where
GND represent 0 input and 𝑉𝑟𝑒𝑓 = 5𝑉 represent 1 input)
Note: The MSB is the one closest to the op-amp.
The analog output voltage is given by:
𝐷
𝑉𝑜 = 𝑉𝑟𝑒𝑓 [ 16𝑜 +
where 𝐷𝑖 = 1 if switch is connected to 𝑉𝑟𝑒𝑓
i.e. 𝐷𝑜 , 𝐷1 , 𝐷2 , 𝐷3 = {
𝐷1
+
𝐷2
+
𝐷3
8
4
2
and 𝐷𝑖 = 0 if switch is grounded.
1
𝑤ℎ𝑒𝑛 𝑐𝑜𝑛𝑛𝑒𝑐𝑡𝑒𝑑 𝑡𝑜 𝑉𝑟𝑒𝑓
0 𝑤ℎ𝑒𝑛 𝑐𝑜𝑛𝑛𝑒𝑐𝑡𝑒𝑑 𝑡𝑜 𝑔𝑟𝑜𝑢𝑛𝑑
2. Weighted-Resistor (DAC)
Connect the circuit of figure (2) and verify its operation by changing bits.
Fig. (2) Weighted Resistor DAC
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]
Electronics and Communications Dept.
Experiment No:(1)
Fourth Year
DAC
The analog output voltage is given by
𝐷3
𝐷2
𝐷1
𝐷0
𝑉𝑂 = −𝑅𝑓 ∙ 𝑉𝑟𝑒𝑓 [
+
+
+ ]
𝑅⁄8 𝑅/4 𝑅⁄2 𝑅
where 𝐷𝑖 = 1 if switch is connected to 𝑉𝑟𝑒𝑓 and 𝐷𝑖 = 0 if switch is grounded.
Report:-
1. Define a DAC and list its main parts.
2. What is the function of the Op-amp in a DAC system? What happens if the
Op-Amp input terminals are exchanged?
3. Discuss the results obtained and compare them to the theoretical ones.
Explain the difference between the measured and calculated results.
4. For Binary-weighted resistor DAC of more than 4-bits, Binary Weighted
Quads are used. Explain the operation of 8-bit binary quads DAC.
5. How could a binary-weighted DAC operate with BCD input? Explain.
6. Compare between the R-2R ladder DAC and Weighted resistor DAC. Which
one is better in your opinion and why?
References:1.
“Microelectronics” by Jacob Millman, 2nd edition, 1987.
2.
“Microelectronic Circuits: analysis and design” by M. H. Rashid,
2nd edition, 2011.
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