The document presents information on digital to analog conversion (DAC). It discusses the basic concept of DAC, where a digital input is converted to a proportional analog output. It then describes two common types of DAC - the weighted resistor DAC and R-2R ladder DAC. Applications of DACs are also highlighted, such as in digital audio, function generators, and motor controllers. The document provides details on the circuit design and output calculation for both weighted resistor and R-2R ladder DACs. It concludes that the R-2R ladder DAC only requires two resistor values but has slower conversion than the weighted resistor DAC.

1. A Presentation on
Digital to Analog
Conversion (DAC)

2. Digital to Analog Conversion (DAC)
Submitted To:
Shakila Naznin
Lecturer
Electronics & Communication Engineering Discipline
Khulna University.
Khulna.
08.09.2014 2

3. Digital to Analog Conversion (DAC)
Submitted By:
Shazid Reaj
Student Id: 120914
Dabashis Ray
Student Id: 120905
Abu Jubair Obhi
Student Id: 120901
2nd Year, Term II
Electronics & Communication Engineering Discipline,
Khulna University.
Khulna. 08.09.2014 3

4. Digital to Analog Conversion (DAC)
Outline’s
 Basic concept about DAC
 Application
 Operation of Weighted Resistor DAC
 Operation of R-2R Ladder DAC
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5. Digital to Analog Conversion (DAC)
Terminology
Analog: continuously valued signal, such as
temperature or speed, with infinite possible values in
between.
Digital: discretely valued signal, such as integers,
encoded in binary.
digital-to-analog converter: DAC, D/A, D2A
Real world (lab) is analog
V
Computer (binary) is digital
t
V
08.09.2014 5

6. Digital to Analog Conversion (DAC)
What is a DAC?
A digital-to-analog converter (DAC) takes a digital code
as its input and produces an analog voltage or current as
its output. This analog output is proportional to the digital
input.
DAC 100101…
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7. Digital to Analog Conversion (DAC)
 Digital to Analog conversion involves
transforming the computer’s binary output in 0’s
and 1’s (1’s typically = 5.0 volts) into an analog
representation of the binary data
 DAC:
Vmax
 n digital inputs for digital encoding
x0
x1
 analog input for Vmax
…
DAC
Xn-1
 analog output a
a
 General Concept:
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8. Digital to Analog Conversion (DAC)
Block Diagram
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9. Digital to Analog Conversion (DAC)
Resolution:
Resolution is the amount of variance in
output voltage for every change of the LSB in
the digital input.
 Just as with ADCs, there are several
common ways of specifying a DAC’s resolution:
 Number of bits, n
 Number of output codes = 2n, or number of
steps in the output = 2n − 1
08.09.2014 9

10. Digital to Analog Conversion (DAC)
 Percentage resolution = 1 / (2n − 1),
expressed as a percentage
 Step size, = V/ (2n − 1)
ref Example:
Find out the percentage resolution of a DAC of n bits, and
hence determine the value for n = 12.
Solution:
Percentage resolution =
1 ´
100%
2 n -
1
For n = 12,
Percentage resolution =
1
12 ´ = =
-
100% 0.0244% 244ppm (part per million)
2 1
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11. Digital to Analog Conversion (DAC)
Resolution: Examples
Formula 4-bit DAC 10-bit DAC
Number of bits n 4 ?
Number of output
2n 16 ?
codes Number of steps in
2n−1 15 ?
the output Percentage
1 / (2n−1) 1/15 ?
resolution Step size (assuming
V/ 2n-1 V/ 15 ?
5 V reference
ref ref voltage)
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12. Digital to Analog Conversion (DAC)
 Applications for Digital to Analog
Converters:
CCiirrccuuiitt CCoommppoonneennttss
 Voltage controlled Amplifier
 digital input, External Reference Voltage as control
 Digitally operated attenuator
 External Reference Voltage as input, digital control
 Programmable Filters
 Digitally controlled cutoff frequencies
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13. Digital to Analog Conversion (DAC)
 Applications for Digital to Analog
Converters:
DDiiggiittaall AAuuddiioo
 CD Players  MP3 Players  Telephone
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14. Digital to Analog Conversion (DAC)
 Applications for Digital to Analog
Converters:
FFuunnccttiioonn GGeenneerraattoorrss
 Digital Oscilloscopes
Digital Input
Analog Output
 Signal Generators
 Sine wave generation
 Square wave generation
 Triangle wave generation
 Random noise generation
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15. Digital to Analog Conversion (DAC)
 Applications for Digital to Analog
Converters:
MMoottoorr CCoonnttrroolllleerrss
 Cruise
Control
 Valve Control  Motor Control
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16. Digital to Analog Conversion (DAC)
 Many types of DACs available
– Binary Weighted Resistor
– R-2R Ladder
– Multiplier DAC
– Non-Multiplier DAC
• Among them Weighted & R-2R are
commonly used.
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17. Digital to Analog Converter(DAC)
Binary Weighted Resistor
General Concept:
 Utilizes A Inverting
Weighted Op-amp
Circuit.
 Weighted Resistors
Are Used To
Distinguish Each Bit
From The Most
Significant To The
Least Significant
Rf
R 2R
V
o
-VREF
å i I
LSB
4R 8R
MSB
08.09.2014 17

18. Digital to Analog Converter(DAC)
Binary Weighted Resistor
Binary Representation
VREF
Least
Significant Bit
Most
Significant Bit
SET CLEARED
( 1 1 1 1 )2 = ( 15 )10
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19. Digital to Analog Converter(DAC)
Output Voltage Analysis
MSB LSB
V
V
V
MSB
V IR R V
ö çè
÷ø
= - = - æ + + +
1 2 3 4
R
R
R
R
2 4 8
out f f
LSB
V K 1 13
V
K
= -æ ´ + ´ + ´ + ´
ö çè
= - ÷ø
out K
K
1 10
K
K
K
K
0 10
10
5
1 10
2.5
10
1.25
08.09.2014 19

20. Digital to Analog Converter(DAC)
Binary Weighted Resistor
FinalV Vout.Resolution OUT =
More Generally:
= Vref
Resolution n -
2 1
If, Vref
= 13
Then resolution for 4 bit =
V
13 =
-
Then binary 1111(15V) is
0.867
16 1
V 10
K
ö çè
out
= -
V V
K
K
K
1 10
K
K
K
K
13
1 .867
1 10
10
5
1 10
2.5
1.25
out
´ ÷ø
= -æ ´ + ´ + ´ + ´
08.09.2014 20

21. Digital to Analog Converter(DAC)
Binary Weighted Resistor
 Advantages
 Simple Analysis
 Fast Conversion
 Disadvantages
 This setup requires a wide range of accurate values of
resistors
 A 10 bit DAC needs resistors ranging from R to
R/1024.
 Requires low switch resistances in transistors
 Usually limited to 8-bit resolution.
08.09.2014 21

22. R-2R Ladder DAC
 Introduction:
 Problem With The
Weighted Resistor DAC
Is Solved.
 Only R & 2R Value Of
Resistor Are Required.
Vout
Digital to Analog Converter(DAC)
08.09.2014 22

23. Digital to Analog Converter(DAC)
R-2R Ladder DAC
General Concept:
Bit: 0 0
0 0
Each Bit Corresponds
To A Switch:
Cases:
Bit Is High
Bit Is Low
4-Bit Converter
Vref
08.09.2014 23

24. Digital to Analog Conversion (DAC)
R-2R Ladder DAC
 Current Dependent On Bits Position
 The Current Is Divided By A Factor Of 2 At Each Node
08.09.2014 24

25. Digital to Analog Conversion (DAC)
R-2R Ladder DAC
 Analysis For Current From (001) Shown Below
0 I
VREF
R
0 I
0 I
0 I
R R R 2R 2R 2R 2R
Op-Amp input
“Ground”
B0
2
4
8
B1 B2
0 I
2
08.09.2014 25

26. R-2R Ladder DAC
Output Analog Voltage
 Using Thevenin’s Equivalent
C
D
B
A
E V R V th A =
2 ´
V
0 0 R +
R
2 2 2
= =
R R th =
 Equivalent Circuit :
C
B
D
Digital to Analog Conversion (DAC)
08.09.2014 26

27. Digital to Analog Conversion (DAC)
 Similarly:
R-2R Ladder DAC
R
´
2 0 V
4 0
R R
D
´
2 0 V
2 0
R R
2 2 4
D
C
R
E V
V
th B =
+
= =
R
´
2 2 0
D
R R th =
2 2 8
E V
V
th C =
+
= =
0 V
R R
2 2 4
E V
V
th B =
+
= =
R R th =
R R th =
OUT V
ù
úû
0 1 2 3 V D D D D
R
= · é + + +
êë
16 8 4 2
f
TotalV ref
R
OUT
D is the binary input
08.09.2014 27

28. Digital to Analog Conversion (DAC)
R-2R Ladder DAC
FinalV Vout.Resolution OUT =
 Practically:
= V
Resolution n
If, = 5V
Then resolution for 4 bit =
Then binary 13V is
0
-
2 1
0 V
0.334
V
5 =
-
16 1
V 10
K
out
=
ö çè
V V
K
K
K
1 10
K
K
K
K
4.342
1 .334
0 10
10
5
1 10
2.5
1.25
out
´ ÷ø
= æ ´ + ´ + ´ + ´
08.09.2014 28

29. Digital to Analog Conversion (DAC)
R-2R Ladder DAC
 Advantages
 Only Two Resistor Values(R & 2R)
 Does Not Require High Precision Resistors.
 Disadvantages
 Lower Conversion Speed Than Binary Weighted
DAC
08.09.2014 29

30. Thanks
08.09.2014 30

31. QQuueessttiioonnss ??
08.09.2014 31