Digital & Analog ConversionDigital & Analog Conversion

DigitalDigital--toto--Analog Analog Converters(DACsConverters(DACs) )

]222[ 22

11

nnRout bbbVV −−− +++= L

output voltageanalog=outV

voltagereference=RVdbinary worbit -...21 nbbb n =

Rnout VNV2

= input DAC of equivalentnumber whole10 base −=N

nRout VV −=∆ 2

changeoutput smallest =∆ outV

voltagereference=RV

wordin the bits ofnumber =n

RR VVV 9375.0]2222[ 4321max =+++= −−−−

RR VVV 9961.0]22222222[ 87654321max =+++++++= −−−−−−−−

4bit

8bit

Conversion ResolutionConversion Resolution

Generic DAC diagram Typical DAC Circuit

DAC CircuitDAC Circuit

Summing Inverting Amplifier

+−= 2

3

21

1

2 VRRV

RRVout

I1

I3 I2

Is

A

AnalogAnalog--toto--Digital Converters(ADCs)Digital Converters(ADCs)

R

innn V

Vbbb ≤+++ −−− 222 22

11 L

nRVV −=∆ 2

ageinput volt analog=inV voltagereference analog=RV

output digitalbit -...21 nbbb n =

= n

R

in

VVN 2INTRnin VNV

2=

Conversion Resolution

Generic ADC diagramData-acquisition timing diagram Read Operation at any time after the end-of-convert

ADC CharacteristicsADC Characteristics

1. Analog Voltage Input : Signal Input to be Converted2. Power Supply3. Reference Voltage4. Digital Output

N output Lines Connected to Memory Bus5. Control Lines

SC : Start of ConversionEOC : End of ConversionRD : Read

6. Conversion Time

Successive approximation using Internal DAC

Parallel Feedback ADCParallel Feedback ADC

DualDual--Slope ADCSlope ADC

Op amp integrator, comparator, counter. Commonly used in digital voltmeters.Typical timing diagram

∫= dtVRC

V x1

1 xVTRCV 11

1=

∫−= dtVRC

VV R1

12 Rx tVRC

VTRC

V 1112 −=

Rx

x VTtV

1

=

Basic Concept of a sample-and-hold circuit for use with the ADC.

Sampled signal is literally “held”during the ADC conversion

Sample and HoldSample and Hold

ADC interfaced to Computer bus with Tri-state bufferAddress decoding by computer software.

Microprocessor Compatible ADCMicroprocessor Compatible ADC

FrequencyFrequency--based Convertersbased Converters

General diagram of a frequency-based analog-to digital converter.

Common V-to-F Converteruseful in frequency-based ADCs.

Useful for generation of frequencyBy resistance or capacity.

LM331LM331 555 timer555 timer

DAS HardwareDAS Hardware

Figure 3.29Typical layout of a data-acquisition board for use in a personal computer expansion slot.

DATADATA--ACQUISITION SYSTEMSACQUISITION SYSTEMS

Multi-position switch for selecting particular inputs to ADC

Analog MultiplexerAnalog Multiplexer

DAS SoftwareDAS Software

Start ADC-Test EOC-Input

Temperaturehistory

No loading

Loading

No loading Loading

LabViewLabView as DAS Softwareas DAS Software

변태유기소성

t=0

t=t

L01

L02

dL

dl

∆L1 ∆L2

0102

12

LLLL

−∆−∆

=ε

● Power : 50 kW●Maximum temp. : 1500 oC●Maximum load : 90 kgf●Measure of disp. : LVDT &

Laser disp. Sensor● Cooling Method : Gas cooling (Ar)

변태소성 측정장치

FET as an electronic switch.FET as an electronic switch.