Group1 141018102550-conversion-gate01

A Presentation on
Digital to Analog
Conversion (DAC)

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

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

Outline’s
 Basic concept about DAC
 Application
 Operation of Weighted Resistor DAC
 Operation of R-2R Ladder DAC
08.09.2014 4

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
t
Computer (binary) is digital
V
08.09.2014 5

What is a DAC?
DAC
100101…
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.
08.09.2014 6

 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:
 n digital inputs for digital encoding
 analog input for Vmax
 analog output a
DAC
Vmax
x0
x1
Xn-1
…
a
 General Concept:
08.09.2014 7

Block Diagram
08.09.2014 8

 Just as with ADCs, there are several
common ways of specifying a DAC’s resolution:
 Number of bits, n
 Number of output codes = 2
n
, or number of
steps in the output = 2
n
− 1
Resolution:
Resolution is the amount of variance in
output voltage for every change of the LSB in
the digital input.
08.09.2014 9

 Percentage resolution = 1 / (2
n
− 1),
expressed as a percentage
 Step size, = Vref / (2
n
− 1)
Example:
Find out the percentage resolution of a DAC of n bits, and
hence determine the value for n = 12.
Solution:
Percentage resolution =
For n = 12,
Percentage resolution =
%100
12
1
×
−n
million)per(partppm244%0244.0%100
12
1
12
==×
−
08.09.2014 10

Resolution: Examples
Formula 4-bit DAC 10-bit DAC
Number of bits n 4 ?
Number of output
codes
2
n
16 ?
Number of steps in
the output
2
n
−1 15 ?
Percentage
resolution
1 / (2
n
−1) 1/15 ?
Step size (assuming
5 V reference
voltage)
Vref / 2
n
-1 Vref / 15 ?
08.09.2014 11

 Applications for Digital to Analog
Converters:
 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
Circuit ComponentsCircuit Components
08.09.2014 12

Converters:
Digital AudioDigital Audio
 CD Players  MP3 Players  Telephone
08.09.2014 13

 Digital Oscilloscopes
Digital Input
Analog Output
 Signal Generators
 Sine wave generation
 Square wave generation
 Triangle wave generation
 Random noise generation
Converters:
Function GeneratorsFunction Generators
08.09.2014 14

Converters:
Motor ControllersMotor Controllers
 Cruise
Control
 Valve Control  Motor Control
08.09.2014 15

 Many types of DACs available
– Binary Weighted Resistor
– R-2R Ladder
– Multiplier DAC
– Non-Multiplier DAC
• Among them Weighted & R-2R are
commonly used.
08.09.2014 16

Digital to Analog Converter(DAC)
Binary Weighted Resistor
 Utilizes A Inverting
Weighted Op-amp
Circuit.
 Weighted Resistors
Are Used To
Distinguish Each Bit
From The Most
Significant To The
Least Significant
Rf
2RR
V
o
-VREF
∑ iI
LSB
4R 8R
MSB
General Concept:
08.09.2014 17

Binary Representation
VREF
Least
Significant Bit
Most
Significant Bit
CLEAREDSET
( 1 1 1 1 )2 = ( 15 )10
08.09.2014 18







+++−=−=
R
V
R
V
R
V
R
V
RIRV
842
4321
ffout
MSB LSB
LSB
MSB
V
K
K
K
K
K
K
K
K
V 131
10
10
0
5
10
1
5.2
10
1
25.1
10
out −=





×+×+×+×−=
Output Voltage Analysis
08.09.2014 19

Resolution.VoutFinalVOUT =
More Generally:
If, = 13
Then resolution for 4 bit =
Then binary 1111(15V) is
12
Resolution n
−
=
Vref
Vref
867.0
116
13
=
−
V
VV
K
K
K
K
K
K
K
K
V
13
867.1
10
10
1
5
10
1
5.2
10
1
25.1
10
out
out
−=
×





×+×+×+×−=
08.09.2014 20

 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

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

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

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

R-2R Ladder DAC
0I
 Analysis For Current From (001) Shown Below
VREF
R
R R R 2R
2R2R2R
Op-Amp input
“Ground”
B0
2
0I
4
0I
8
0I
B1
B2
2
0I
08.09.2014 25

R-2R Ladder DAC
 Output Analog Voltage
 Using Thevenin’s Equivalent
A
B
C
D
222
2 00 V
RR
VR
VE Ath =
+
×
==
RRth =
 Equivalent Circuit :
B
C
D
08.09.2014 26

 Similarly:
D
C
D
422
2 02
0
V
RR
R
VE
V
Bth =
+
×
==
D
RRth =
822
2 04
0
V
RR
R
VE
V
Cth =
+
×
==
422
2 02
0
V
RR
R
VE
V
Bth =
+
×
==
RRth =
RRth =
OUTV






+++•=
24816
3210 DDDD
V
R
R
TotalV ref
f
OUT
R-2R Ladder DAC
D is the binary input
08.09.2014 27

R-2R Ladder DAC
Resolution.VoutFinalVOUT =
 Practically:
If, = 5V
Then resolution for 4 bit =
Then binary 13V is
12
Resolution n
0
−
=
V
0V
334.0
116
5
=
−
V
VV
K
K
K
K
K
K
K
K
V
342.4
334.1
10
10
0
5
10
1
5.2
10
1
25.1
10
out
out
=
×





×+×+×+×=
08.09.2014 28

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

Questions ?Questions ?
08.09.2014 31

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