dac-digital to analog converter
TRANSCRIPT
A Presentation on
Digital to Analog Conversion (DAC)
Digital to Analog Conversion (DAC)
Submitted To:
Shakila NazninLecturer
Electronics & Communication Engineering Discipline
Khulna University.
Khulna.
08.09.2014 2
Digital to Analog Conversion (DAC)
Submitted By:
Shazid ReajStudent Id: 120914
Dabashis Ray Student Id: 120905
Abu Jubair ObhiStudent Id: 120901
2nd Year, Term IIElectronics & Communication Engineering Discipline, Khulna University.Khulna.
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Outline’s
Basic concept about DAC Application Operation of Weighted Resistor DAC Operation of R-2R Ladder DAC
Digital to Analog Conversion (DAC)
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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
t
Computer (binary) is digital
V
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What is a DAC?
DAC100101…
Digital to Analog Conversion (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.
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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: n digital inputs for digital encoding
analog input for Vmax
analog output a
DAC
Vmax
x0x1
Xn-1
…a
General Concept:
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Block DiagramDigital to Analog Conversion (DAC)
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Digital to Analog Conversion (DAC)
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
Resolution:Resolution is the amount of variance in output voltage for every change of the LSB in the digital input.
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Digital to Analog Conversion (DAC)
Percentage resolution = 1 / (2n − 1), expressed as a percentage
Step size, = Vref / (2n − 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 =
%10012
1 ×−n
million)per (part ppm244%0244.0%10012
112
==×−
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Digital to Analog Conversion (DAC)
Resolution: Examples
Formula 4-bit DAC 10-bit DAC
Number of bits n 4 ?
Number of output codes
2n 16 ?
Number of steps in the output
2n−1 15 ?
Percentage resolution
1 / (2n−1) 1/15 ?
Step size (assuming 5 V reference voltage)
Vref / 2n-1 Vref / 15 ?
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Digital to Analog Conversion (DAC)
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
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Digital to Analog Conversion (DAC)
Applications for Digital to Analog Converters:
Digital AudioDigital Audio
CD Players MP3 Players Telephone
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Digital to Analog Conversion (DAC)
Digital OscilloscopesDigital InputAnalog Output
Signal Generators Sine wave generation Square wave generation Triangle wave generation Random noise generation
Applications for Digital to Analog Converters:
Function GeneratorsFunction Generators
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Digital to Analog Conversion (DAC)
Applications for Digital to Analog Converters:
Motor ControllersMotor Controllers
Cruise Control
Valve Control Motor Control
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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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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
2RRV
o
-VREF
∑ iI
LSB
4R 8R
MSB
General Concept:
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Digital to Analog Converter(DAC)
Binary Representation
VREF
Least Significant Bit
Most Significant Bit
CLEAREDSET
( 1 1 1 1 )2 = ( 15 )10
Binary Weighted Resistor
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Digital to Analog Converter(DAC)
+++−=−=
R
V
R
V
R
V
R
VRIRV
8424321
ffout
MSB LSB
LSB
MSB
VK
K
K
K
K
K
K
KV 131
10
100
5
101
5.2
101
25.1
10out −=
×+×+×+×−=
Output Voltage Analysis
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Digital to Analog Converter(DAC)
Binary Weighted Resistor
Resolution.VoutFinalVOUT =
More Generally:
If, = 13
Then resolution for 4 bit =
Then binary 1111(15V) is
12Resolution
n −= Vref
Vref867.0
116
13 =−V
VV
K
K
K
K
K
K
K
KV
13
867.110
101
5
101
5.2
101
25.1
10
out
out
−=
×
×+×+×+×−=
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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.
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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)
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Digital to Analog Converter(DAC)
R-2R Ladder DAC
Bit: 0 0 0 0
Each Bit Corresponds To A Switch:
Cases:Bit Is HighBit Is Low
4-Bit Converter
Vref
General Concept:
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R-2R Ladder DAC Current Dependent On Bits Position
The Current Is Divided By A Factor Of 2 At Each Node
Digital to Analog Conversion (DAC)
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R-2R Ladder DAC
0I
Analysis For Current From (001) Shown Below
VREF
RR R R 2R
2R2R2R
Op-Amp input“Ground”
B0
20I
40I
80I
B1B2
20I
Digital to Analog Conversion (DAC)
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R-2R Ladder DAC Output Analog Voltage Using Thevenin’s Equivalent
A
B
C
D
222
2 00 V
RR
VRVE Ath =
+×
==
RRth =
Equivalent Circuit :
B
C
D
Digital to Analog Conversion (DAC)
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Similarly:
D
C
D
422
2 020 V
RR
RVE
V
Bth =+×
==
DRRth =
822
2 040 V
RR
RVE
V
Cth =+×
==
422
2 020 V
RR
RVE
V
Bth =+×
==
RRth =
RRth =
OUTV
+++•=
248163210 DDDD
VR
RTotalV ref
fOUT
R-2R Ladder DAC
D is the binary input
Digital to Analog Conversion (DAC)
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R-2R Ladder DAC
Resolution.VoutFinalVOUT =
Practically:
If, = 5V
Then resolution for 4 bit =
Then binary 13V is
12Resolution
n0
−=V
0V334.0
116
5 =−V
VV
K
K
K
K
K
K
K
KV
342.4
334.110
100
5
101
5.2
101
25.1
10
out
out
=
×
×+×+×+×=
Digital to Analog Conversion (DAC)
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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
Digital to Analog Conversion (DAC)
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Thanks
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Questions ?Questions ?
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