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Analog to Digital Converters Analog to Digital Converters

Analog to Digital Converters - PowerPoint Presentation

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Analog to Digital Converters - PPT Presentation

Stu Godlasky Nikita Pak James Potter Introduction What is an analog to digital converter ADC Going from analog to digital Types and properties of ADC What is an Analog to Digital Converter Converts an analog signal to discrete time digital ID: 151994

analog digital registers converter digital analog converter registers atd successive control adc voltage result bit register signal approximation channel

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Slide1

Analog to Digital Converters

Stu Godlasky

Nikita Pak

James PotterSlide2

Introduction

What is an analog to digital converter (ADC)

Going from analog to digital

Types and properties of ADCSlide3

What is an Analog to Digital Converter

Converts an analog signal to discrete time digital

Computers need digital. (On / Off , High / Low , 1/0)Slide4

Going from Analog to Digital

Two step process

Sampling – Measuring analog signal at uniform time intervals

Quantization – Assigning discrete measurements a binary code (each sample will have a binary number associated with it)

T

1

T2 T3 T4Example of digital signal from 3 bit ADC010 010 011Slide5

Aliasing

Every analog signal has a frequency

Nyquist Frequency (half sampling frequency)

Aliasing occurs when signal above Nyquist frequencySlide6

Quantization Error

Analog (infinite values) – Digital (finite values)

Upon reconstruction of analog signal

Increases as resolution decreases

Resolution - Q

EFSR - full scale voltage rangeN = Number of discrete voltage intervalsN = 2k where k is the number of bitsSlide7

Quantization Error

Quantized signal only has values at midpoint of voltage bandSlide8

Types of Analog to Digital Converters

Dual Slope A/D Converter

Successive Approximation A/D Converter

Flash A/D Converter

Delta – Sigma A/D ConverterSlide9

Dual Slope Analog to Digital Converter

Also referred to as an Integrating ADC

IntegratorSlide10

Dual Slope Analog to Digital Converter

Converts in two phases (ramp up / ramp down )

Input voltage measurement not dependant on integrator components Slide11

Dual Slope Analog to Digital Converter

Pros

Conversion result is insensitive to errors in the component values

Fewer adverse affects from noise

High accuracy

Cons Slow Accuracy is dependant on the use of precision external components CostSlide12

Successive Approximation Analog To Digital Converter

DAC = Digital to Analog Converter

EOC = End of Conversion

SAR = Successive Approximation Register

S/H = Sample and Hold Circuit

Vin = Input Voltage Vref = Reference VoltageSlide13

Successive Approximation Analog to Digital Converter

Uses an n-bit DAC and original analog results

Performs a bit by bit comparison of V

DAC

and V

in If Vin > VREF / 2 MSB set to 1 otherwise 0 If Vin > VDAC Successive Bits set to 1 otherwise 0Slide14

Successive Approximation ADC Example

10 bit ADC

V

in

= 0.6 V

Vref = 1VN = 2n (n = number of bits)N = 210 = 1024Vref = 1V/ 1024 = 0.0009765625V (resolution)Slide15

Successive Approximation Digital to Analog Converter

Pros

Capable of high speed and reliable

Medium accuracy compared to other ADC types

Good tradeoff between speed and cost

Capable of outputting the binary number in serial (one bit at a time) format.Cons Higher resolution successive approximation ADCs will be slowerSlide16

Flash Analog to Digital Converter

Also called a parallel ADC

2

N

– 1 Comparators

2N ResistorsControl Logic (encoder) Slide17

Flash Analog to Digital Converter

Uses the resistors to divide reference voltage into intervals

Uses comparators to compare V

in

and the reference voltages

Encoder takes the output of comparators and uses control logic to generate binary digital outputSlide18

Flash Analog to Digital Converter

Pros

Very Fast (Fastest)

Very simple operational theory

Speed is only limited by gate and comparator propagation delay

Cons Expensive Prone to produce glitches in the output Each additional bit of resolution requires twice the comparators and resistorsSlide19

Sigma-Delta Analog to Digital Converter

Input over sampled, goes to integrator

Integration compared with ground

Iteration drives integration of error to zero

Output is a stream of serial bitsSlide20

Sigma-Delta Analog to Digital Converter

Pros

High resolution

No need for precision components

Cons

Slow due to over sampling Only good for low bandwidthSlide21

Comparison of ADCs

Type

Speed (relative)

Cost (relative)

Resolution

Dual Slope

SlowMed12-16FlashVery FastHigh4-12Successive ApproxMedium – FastLow8-16Sigma – DeltaSlowLow12-24Slide22

Analog to Digital Converter Applications

Nikita PakSlide23

Analog to Digital Converter Applications

Music recording

Data acquisition/measurement devices

thermocouples

digital

multimetersstrain gaugesConsumer Productscell phonesdigital camerasSlide24

Music Recording

A to D used

to convert sound pressure waves into discrete digital signal (later,

D to A

used to convert back to an electrical signal for a

speaker)Saves a tremendous amount of spaceEx. CD samples at 44.1 kHz (Nyquist frequency = 22.05 kHz is higher than human ear can detect)CD recording often done with flash A to DSlide25

Data Acquisition

D

ata acquisition: the

process of obtaining signals from sensors that measure physical

conditions

Sensors give analog voltage that must be converted to work on a computerMost National Instruments DAQ’s use successive approximation A to DSlide26

Measurement Devices

T

hermocouple: a

junction of dissimilar metals creates a voltage difference that is temperature

dependent

Digital multimeter: converts signal to a voltage and amplifies it for measurementMore accurate than analog counterpartsSlide27

Measurement Devices

S

train gauge: most common type measures the change in resistance as a metal pattern is deforme

dSlide28

Consumer Products

C

ell phones: convert

your voice into a digital signal so it can be more efficiently transmitted by compressing the

signal

Digital camera ccd: absorbed photons create charges that are converted into a sequence of voltagesThese voltages are converted to a digital signalBoth often use flash A to DSlide29

ADC on Your Microcontroller

Input Pins

ADC Built-into

MC9S12C32Slide30

ADC in Block Diagram

ATD 10B8C

Port ADSlide31

Details of ATD 10B8C

Analog-To-Digital

Resolution: 8 or 10 Bits (manually chosen)

8-Channel multiplexed inputs

Conversion time: 7 µs (for 10 bit mode)

Optional external trigger“Successive approximation” type ADCSlide32

ATD 10B8C Block DiagramSlide33

ATD 10B8C Block Diagram

Reference Voltages

Source

V

source

Results of Successive Approximation

“Holds” Source VoltageSlide34

Registersand

Setting Up Your ATD10B8C

James PotterSlide35

ADC Registers

All information about registers found in

Chapter 8 of

MC9S12C Family Reference Manual

8 Result Registers

6 Control Registers2 Status Registers2 Test Registers1 Digital Input Enable Register1 Digital Port Data RegisterSlide36

Result RegistersSlide37

Result Registers

8 registers

,

Each with

High and low byteSlide38

Result Registers:Left-Justified (Default)

High Byte

Low ByteSlide39

Result Registers:Right-Justified

High Byte

Low ByteSlide40

Control RegistersSlide41

Control Registers:ATDCTL2 Slide42

Control Registers:ATDCTL2 Slide43

Control Registers:ATDCTL3Slide44

Control Registers:ATDCTL3Slide45

Control Registers:ATDCTL4Slide46

Control Registers:ATDCTL4Slide47

Control Registers:ATDCTL5Slide48

Control Registers:ATDCTL5Slide49

Control Registers:ATDCTL5Slide50

Single Channel (MULT = 0)Single Conversion (SCAN = 0)

7

6

5

4

3

210

Port ADATD ConverterResultRegister

InterfaceATDDR0ATDDR1ATDDR2ATDDR3ATDDR4ATDDR5

ATDDR6

ATDDR7Slide51

Single Channel (MULT = 0)Continuous Conversion (SCAN = 1)

7

6

5

4

3

210

Port ADATD ConverterResult

RegisterInterfaceATDDR0ATDDR1ATDDR2ATDDR3ATDDR4ATDDR5

ATDDR6

ATDDR7Slide52

Multiple Channel (MULT = 1)Single Conversion (SCAN = 0)

7

6

5

4

3

210

Port ADATD ConverterResultRegister

InterfaceATDDR0ATDDR1ATDDR2ATDDR3ATDDR4ATDDR5

ATDDR6

ATDDR7Slide53

Single Channel (MULT = 1)Continuous Conversion (SCAN = 1)

7

6

5

4

3

210

Port ADATD ConverterResult

RegisterInterfaceATDDR0ATDDR1ATDDR2ATDDR3ATDDR4ATDDR5

ATDDR6

ATDDR7Slide54

Status RegistersSlide55

Status Register 0:ATDSTAT0Slide56

Status Register 0:ATDSTAT0Slide57

Status Register 1:ATDSTAT1Slide58

Setting Up Your ATD10B8CSlide59

Setting Up the ATD

Step 1: Power-up the ATD and define settings in

ATDCTL2

ADPU

= 1 powers up the ATDASCIE = 1 enables interruptStep 2: Wait for ATD recovery time (~ 20μs) before proceedingStep 3: Set number of successive conversions in ATDCTL3S1C,

S2C, S4C, S8C determine number of conversions (see Table 8-4) Slide60

Setting Up the ATD

Step 4: Configure resolution, sampling time, and ATD clock speed in

ATDCTL4

PRS0

,

PRS1, PRS2, PRS3, PRS4 set sampling rate (see Table 8-6) SRES8 sets resolution to 8-bit (= 1) or 10-bit (= 0)Step 5: Configure starting channel, single/multiple channel, SCAN and result data signed or unsigned in ATDCTL5CC

, CB, CA determine input channel (see Table 8-12)MULT sets single (= 0) or multiple (= 1) inputsSCAN sets single (= 0) or continuous (= 1) samplingDJM sets output format as left-justified (=0) or right-justified (=1)DSGN sets output data as unsigned (=0) or signed (=1)Slide61

Thank You