dac-digital to analog converter

A Presentation on

Digital to Analog Conversion (DAC)


Submitted To:

Shakila NazninLecturer

Electronics & Communication Engineering Discipline

Khulna University.

Khulna.

08.09.2014 2


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


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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…


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 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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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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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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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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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 AudioDigital Audio

CD Players MP3 Players Telephone

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http://configure.us.dell.com/dellstore/config.aspx?c=us&cs=19&l=en&oc=DDJ20M&s=dhs


Digital OscilloscopesDigital InputAnalog Output

Signal Generators Sine wave generation Square wave generation Triangle wave generation Random noise generation


Function GeneratorsFunction Generators

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http://www.electrorent.com/products/search/detail.aspx?Mfr=Lecroy+Corporation&MfrMod=LEC-LC584AL&Desc=1GHz+4CH+Digital+Scope



Motor ControllersMotor Controllers

Cruise Control

Valve Control Motor Control

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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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Binary Representation

VREF

Least Significant Bit

Most Significant Bit

CLEAREDSET

( 1 1 1 1 )2 = ( 15 )10


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+++−=−=

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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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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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


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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


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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


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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


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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


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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

=

×

×+×+×+×=


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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


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Thanks

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Questions ?Questions ?

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