Lect. 25: Data Converters

Data Converters ADC: Analog to Digital Converter- ADC: Analog to Digital Converter

- DAC: Digital to Analog Converter

Why data conversion?y

Digital Signal Processing is very powerful: DSP is much better if possible

R l ld i d f l i lReal world is made up of analog signals

Analog Digital Analog

/R l

Analog Digital Analog

R lA/D Converter

Digital Signal

ProcessorD/A

Converter

Real World

Real World

Electronic Circuits 2 (09/1) W.-Y. Choi

Lect. 25: Data Converters

Analog DigitalRF Signlas

DSP

SYN

LNA

PA

ADC

DACLCD, Speaker

SYNPA DAC

CCD, Microphone

LNA: Low Noise AmplifierLNA: Low Noise Amplifier

PA: Power Amplifier

SYN: Frequency Synthesizer

Electronic Circuits 2 (09/1) W.-Y. Choi

Lect. 25: Data Converters

A/D Process

Input analog signal

Sampled signal

Sample and Hold Circuit

Electronic Circuits 2 (09/1) W.-Y. Choi

Lect. 25: Data Converters

tquantization

digital coding

Output Code

digital coding

10

11

… 01011 ….

000

01

1/4 1/2 3/4 1Vin

Electronic Circuits 2 (09/1) W.-Y. Choi

Lect. 25: Data Converters

D/A Process

Digital input: …01011 ….

Key parameters: Resolution and bandwidth

Electronic Circuits 2 (09/1) W.-Y. Choi

Lect. 25: Data Converters

Hardware implementation of D/A Converter

Input: b1b2b3 … bN (bN: Least significant bit)

1 2 Nb b bD 1 2

1 2 2 2 2

NND = + + ⋅ ⋅ ⋅ +

1

Vout/Vref

1/2

3/4

=1

4= 1LSB

VLSB

Vref

0

00 01 10 11

1/4

Code

Electronic Circuits 2 (09/1) W.-Y. Choi

Lect. 25: Data Converters

N-bit D/A Converter 1 21 2

2 2 2NN

b b bD = + + ⋅ ⋅ ⋅ +

Binary weighted resistors

REF REF REF REF 1 21 2 1 1 2

V V V 2V

2 2 2 2 2N

O NN N

b b bi b b b

R R R R−

⎛ ⎞= + + ⋅ ⋅ ⋅ + = + + ⋅ ⋅ ⋅ +⎜ ⎟⎝ ⎠

⎛ ⎞1 21 2

2 2 2N

o REF REFN

b b bv V V D⎛ ⎞= − + + ⋅ ⋅ ⋅ + = −⎜ ⎟

⎝ ⎠

Electronic Circuits 2 (09/1) W.-Y. Choi

Lect. 25: Data Converters

N-bit D/A Converter

Accuracy of DAC: Precision of binary resistors, Switch performance

With binary weighted resistors, big differences in R

Electronic Circuits 2 (09/1) W.-Y. Choi

Lect. 25: Data Converters

D/A Converter: R-2R Ladder

12 4 2NI I I I−= = = =1 2 32 4 2 NI I I I= = = ⋅ ⋅ ⋅ =

1 2, ... 2 4 2REF REF REF

N N

V V VI I I

R R R= = = Many other techniques available.

Active research area:2 4 2

R R R

REF 1 2 REF2

V V( ... + )

2 2 2N

O N

b b bi D

R R= + + =

Active research area: Resolution, power, manufacturability

Electronic Circuits 2 (09/1) W.-Y. Choi

Lect. 25: Data Converters

Ex.) 3-bit Flash ADCFlash ADC

111

+Vref

1111111

Comparator Output

3-bitDigital Output(Binary Code)

+VrefVin

011100101110111

00001110001111001111101111111111111

VinN-bit Output

Decoder

000001010011

0000000000000100000110000111

p

2N-1

-Vref Output: 101-Vref comparator

Thermometer Code

Fast because of parallel processing

R matching problem Expensive, High-performance applications

Electronic Circuits 2 (09/1) W.-Y. Choi

Lect. 25: Data Converters

Feedback-Type ADC

Vout/Vref

Count up DAC Until DAC output matches analog input

1/2

3/4

1

=14

= 1LSBVLSB

Vref

000 01 10 11

1/4

1/2

Code

Very simple but not for high performance

Electronic Circuits 2 (09/1) W.-Y. Choi

Lect. 25: Data Converters

Dual-Slope ADC

Ch th i t t f T ithCharge up the integrator for T1 with vA

1A

PEAKv

V TRC

= ⋅RC

Simultaneously count up the counter to 2N

Electronic Circuits 2 (09/1) W.-Y. Choi

Lect. 25: Data Converters

Dual-Slope ADC

Discharge the integrator with VDischarge the integrator with VREF

Stop counting when vI reaches 0 at T2

REFVV T2

2 1 2

REFPEAK

NA A

REF REF

V TRC

v vT T n

V V

= ⋅

⎛ ⎞ ⎛ ⎞∴ = ==> =⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠

High accuracy: No direct dependence on R, C

But slow

Electronic Circuits 2 (09/1) W.-Y. Choi

REF REFV V⎝ ⎠ ⎝ ⎠But slow

Lect. 25: Data Converters

16Active research area:

Wireless infrastructurehighly integrated communication

phased array antenna systemimaging system

High energy physics Instrumentation

Low amplitude signal communication14

Resolution, power, manufacturability

ION

(bit) CCD imaging

IF and baseband digitizationfax machine

telecommunications and digital video

Cellular/PCSbase station

communicationreceiver

HDTVmedical imaging

digital communicationradar systems

12

RESO

LU

T and digital videoapplications

receiver

Set-top boxesIF and baseband communications

scanners

Test equipmentcable modem

radar systems

Digital oscilloscopeshigh speed modem, broadband wireless

communication subsystems

Radar/communicationCable reverse path

wireless point to point systems

10

R

LCD displaysystems

gigabit ethernet

Video digitizinghigh speed digital

communicationdisk-drive control

scannersCamcorder

communication subsystems wireless local loop

Gigabit ethernetcode conversion for

flat panel displayDigital read

-channel system

8

Digital receivers for high-bit-rate communications6

for DVD SOC

Electronic Circuits 2 (09/1) W.-Y. ChoiSPEED (MHz)

1 20 40 60 80 100 120 140 160 180 200 1600