Sigma Delta ADC Report - B.Tech final year project

8/10/2019 Sigma Delta ADC Report - B.Tech final year project

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MAJOR PROJECT REPORT

Analog to Digital converter using CMOS technology

SUBMITTED IN PARTIA !U!IMENT O! T"E RE#UIREMENTS

!OR T"E A$ARD O! DE%REE O! BAC"EOR O! TEC"NOO%&

IN

EECTRONICS AND COMMUNICATION EN%INEERIN%

%ui'e( Mr. Amit Saxena Su)*itte' By(

Mukul Nigam (00796402810)

Paras Sanoria (00296402810) Mukul oel (01096402810)

MA"ARAJA A%RASEN INSTITUTE O! TEC"NOO%&

SECTOR+,,- RO"INI- DE"I+..//012

A!!IIATED TO

%URU %OBIND SIN%" INDRAPRAST"A UNI3ERSIT&- NE$ DE"I+..//40

5,/./+,/.67


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Certifcate

This is to certify that the Major Project Report entitled Analog to Digital

converter using CMOS technology done by Muul !iga" #$$%&'($)*+$,-

Paras Sanoria #$$)&'($)*+$, . Muul /oel #$+$&'($)*+$, is an authentic

0or carried out by the" at Maharaja Agrasen 1nstitute of Technology

under "y guidance2 The "atter e"bodied in this "ajor project 0or has

not been sub"itted earlier for the a0ard of any degree or diplo"a to the

best of "y no0ledge and belief2

Date3 )&thApril )$+(

#Signature of the guide,

Mr2 A"itSa4ena


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AC8NO$ED%EMENT

!e "oul# like to arti$ulate our %ro&oun# gratitu#e an# in#e'te#ness to our %roe$t gui#e

Mr. Amit Saxena "*o *as al"a+s 'een a $onstant moti,ation an# gui#ing &a$tor

t*roug*out t*e %roe$t time in an# out as "ell. -t *as 'een a great %leasure &or us to get an

o%%ortunit+ to "ork un#er *im an# $om%lete t*e %roe$t su$$ess&ull+. !e "is* to exten#

our sin$ere t*anks to Pro&. S u%ta /ea# o& e%artment &or a%%ro,ing our %roe$t "ork

"it* great interest. An un#ertaking o& t*is nature $oul# ne,er *a,e 'een attem%te# "it* our

re&eren$e to an# ins%iration &rom t*e "orks o& ot*ers "*ose #etails are mentione# in

re&eren$es se$tion. !e a$kno"le#ge our in#e'te#ness to all o& t*em.

Mukul Nigam Paras Sanoria Mukul goel(00796402810) (00296402810) (01096402810)


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ABSTRACT

Analogto#igital $on,erters %la+ an essential role in mo#ern re$ei,er

#esign.3on,entional N+uist $on,erters reuire analog $om%onents t*at are %re$ise an#/ig*l+

immune to noise an# inter&eren$e. -n $ontrast o,ersam%ling $on,erters $an 'e im%lemente#

using sim%le an# *ig*toleran$e analog $om%onents. Moreo,erSam%ling at *ig* &reuen$+

eliminates t*e nee# &or a'ru%t $uto&&s in t*e analog antialiasing &ilters. A te$*niue o& noise

s*a%ing is use# in 567 $on,erters in a##ition to o,ersam%ling to a$*ie,e a *ig*

resolution $on,ersion. A signi&i$ant a#,antage o& t*e met*o# is t*at analog signals are $on,erte#

using sim%le an# *ig*toleran$e analog $ir$uits usuall+ a 1'it $om%arator an# analog signal

%ro$essing $ir$uits *a,ing a %re$ision t*at is usuall+ mu$* less t*an t*e resolution o& t*e o,erall

$on,erter.

-n t*is %a%er t*e #esign te$*niue &or a lo"$ost &irst or#er narro" 'an# sigma#elta

mo#ulator in a stan#ar# 0.9m CMOS te$*nolog+ is #es$ri'e# .5*is $ir$uitr+ %er&orms t*e

&un$tion o& an analogto#igital $on,erter. A &irstor#er 1'it sigma#elta () analogto#igital

$on,erter is #esigne# an# simulate# using 5s%i$e -. 5*e anal+sis o& sigma#elta

mo#ulator stru$tures an# t*e #esign &lo" "ere gi,en. 5*e mo#ulator is %ro,e# to 'e ro'ustness

t*e *ig* %er&orman$e in sta'ilit+ .5*e simulation are $om%are# "it* t*ose &rom a tra#itional

analogto#igital $on,erter to %ro,e t*at sigma#elta is %er&orming 'etter in t*e $ase o& "eak

signals a$uisition. 5*e #esign &lo" $onsist o& a o%am% one o& t*e ke+ $om%onent o& sigma

#elta a#$ "*i$* is use# &or #esigning o& integrator an# summing $ir$uit &ollo"e# '+ a *ig*

s%ee# $om%arator an# a #igital toanalog $on,ertor in t*e &ee#'a$k %at*.


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Ta)le o9 content

A3:N;!


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)2+? ;nd6point 1!


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(2 Conclusion and @uture 0or222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222 (?

(2+2 Conclusion2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222('

(2)2 @uture or2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222 ('


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ist o9 9igures

igure 2.1 Ar$*ite$ture o& las* A3............................................................................................ 7

igure 2.2 Ar$*ite$ture o& Pi%e ine A3 ..................................................................................... 9

igure 2.> Su$$essi,eA%%roximation A3.................................................................................. 10

2.4 ual Slo%e A3 ..................................................................................................................... 12

2.? =lo$k #iagram o& a sigma#elta analog to #igital $on,erter ................................................... 14

2.6 (a)@n#er sam%le# signal ......................................................................................................... 1?

2.7 ig2.6(') ;,ersam%le# signal................................................................................................. 16

2.8 Putting noise s*a%ing an# igital &ilter toget*er .................................................................... 16

2.9 e%resentation o& N in an A3 trans&er $ur,e.................................................................. 18

2.10 =est &it -N ........................................................................................................................... 19

2.11 .1 S$*emati$ o& ;%am% ............................................................................................................. >?

>.2 reuen$+ res%onse o& ;%am% .............................................................................................. >?

>.> S$*emati$ esign o& lat$*3om%arator .................................................................................. >7

>.4 Simulate# "a,e&orm o& 3om%arator....................................................................................... >8

>.? S$*emati$ o& summing am%li&ier. ........................................................................................... >9

>.6 Simulation result o& summing am%li&ier. ................................................................................ >9

>.7 s$*emati$ o& -ntegrator ........................................................................................................... 40

>.8 Simulation esult o& integrator ............................................................................................... 41

>.9 S$*emati$ o& A3 .................................................................................................................. 42

>.10 simulation result o& A3 ...................................................................................................... 42

>.11 s$*emati$ o& a sigma#elta A3 .......................................................................................... 44

>.12 simulation result o& Sigma elta A3 ................................................................................. 44


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.2 INTRODUCTION

+


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INTRODUCTION

.2. MOTI3ATION

e$ent resear$* on a#io reuen$+ () $ommuni$ation em%*asies 'ot* *ig*er

integration to meet $ustomer #eman# &or lo"$ost lo"%o"er small&orm &a$tor %ersonal

$ommuni$ation #e,i$e .5*is re#u$tion in %o"er $an 'e a$*ie,e# '+ mo,ing to"ar#s smaller

&eature sie ./o"e,er as "e mo,e to"ar#s smaller &eature sie t*e %ro$ess ,ariations an# ot*er

noni#ealities "ill greatl+ a&&e$t t*e %er&orman$e o& t*e #e,i$e. ;ne o& t*ea%%li$ations "*ere lo"

%o"er #issi%ation lo" noise *ig* s%ee# less ;&&set ,oltage are reuire# is Analog to igital

3on,erters (A3) &or mo'ile an# %orta'le #e,i$es. 5*e %er&orman$e limiting &a$tor o& su$*

A3 is gain am%li&iers an# $om%arators. -n "ireless a%%li$ation o,ersam%ling analogto#igital

$on,ersion *as 'e$ome %o%ular 'e$ause o& its in$rease# %er&orman$e an# &lexi'ilit+.

;,ersam%ling uses a sam%ling rate t*at is mu$* greater t*an t*e 'an#"i#t* o& t*e signal o&

interest. igital signal %ro$essing is t*en &urt*er use# &or &iltering an# #o"n sam%ling. Sigma

#elta A3 is a lo"$ost lo"'an#"i#t* lo"%o"er *ig*resolution A3 an# *as ,arie#

a%%li$ations in #ata a$uisition $ommuni$ations signal %ro$essing an# instrumentation. -t *a#

its origins in t*e earl+ #e,elo%ment %*ases o& %ulse $o#e mo#ulation (P3M) s+stems t*is

te$*niue *as 'een in existen$e &or man+ +ears 'ut re$ent a#,an$e in te$*nolog+ *as ma#e t*is

#e,i$e %ra$ti$al an# t*ere use is 'e$oming "i#es%rea# it *as 'e$ome a $*oi$e &or mo#ern ,oi$e

'an# au#io an# *ig* resolution in#ustrial measurement a%%li$ation. 5*e Sigma elta A3 is

no" use# &or mu$* lo" $ost lo" %o"er *ig* resolution a%%li$ations.


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,2 Sig*a Delta Overvie 'its. A&ter last stage t*e am%li&ie# remain#er signal is

&ee#into 4 =it &las* A3 t*at "ill generate 4 least signi&i$ant 'its. As e,er+ stage generates 'its

at #i&&erent instant in time t*ere&ore it is reuire# to align all t*e 'its '+ s*i&t register %rior to

a%%l+ing 12'it #igital out%ut to t*e #igitalerror$orre$tion logi$. uring t*e inter,al "*en one


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stage $om%letes t*e %ro$essing o& one sam%le an# %asses t*e magni&ie# remain#er to t*e ot*er

stage. 5*e next stages are also %er&orming t*e same o%eration 'e$ause sam%le an# *ol# $ir$uit is

Successive A==ro?i*ation ADC

Su$$essi,ea%%roximationregister (SA) analogto#igital $on,erters (A3s) are mostl+ use in

me#ium to *ig*resolution an# lo" sam%ling rate a%%li$ations. 5*ese are mostl+ in t*e

range'et"een 8 to 16 'its. -t also %ro,i#es small &orm &a$tor an# lo" %o"er $onsum%tion. As its

%o"er $onsum%tion is lo" t*ere&ore it is t*e goo# $*oi$e &or lo" %o"er a%%li$ation su$* as

Porta'leC'atter+%o"ere# instruments %en #igitiers in#ustrial $ontrols an# #ataCsignal

a$uisition. SA A3 a$tuall+ im%lements 'inar+ sear$* algorit*m t*ere&ore its internal

$ir$uitr+ mig*t "ork at se,eral mega*ert 'ut #ue to t*e su$$essi,e a%%roximation algorit*m t*e

sam%ling rate o& A3 is uite small. 5*ere are man+ "a+s to im%lement SA A3 'ut its 'asi$

stru$ture is s*o"n in igure ,.:

igure 2.> Su$$essi,eA%%roximation A3


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-n t*is stru$ture tra$kC*ol# $ir$uit is use# to *ol# t*e analog in%ut ,oltage ( -N). 5*e

'inar+sear$* algorit*m is im%lemente# '+ N'its register. -nitiall+ t*e ,alue o& register is set to

mi#s$alier. MS= set to I1J an# all t*e ot*er 'its are set to I0J. 5*e out%ut o& A3 (A3)

'e$omes *al& t*e re&eren$e ,oltage


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2.4 ual Slo%e A3

5*e 'e*a,ior o& t*is stru$ture is similar to #igital ram% A3 ex$e%t t*at sa"toot*"a,e&orm is

use# as re&eren$e signal. I-ntegrating A3s %ro,i#es *ig* resolution an# $an %ro,i#e goo# noise

ree$tion an# line &reuen$+J. As #ual slo%e stru$ture integrates in%ut signal &or &ixe# time

instant t*ere&ore in%ut signal 'e$omes a,erage an# t*is "ill %ro#u$e out%ut "it* greater noise

immunit+. ue to t*is &a$t it is ,er+ use&ul &or *ig* a$$ura$+ a%%li$ations. 5*e ot*er a#,antage

o& t*is stru$ture is t*at it a,oi#s A3 in t*e stru$ture t*at #e$reases t*e #esign $om%lexit+. 5*e

main limitation o& t*is stru$ture is t*at it onl+ suita'le &or lo" 'an#"i#t* in%ut signals.

,24ADC co*=arison

-t s*o"s t*e range o& resolutions $on,ersion met*o# en$o#ing met*o# $on,ersion time sie

a#,antages an# #isa#,antages a,aila'le &or &las* sigma#elta su$$essi,e a%%roximation #ual

slo%e an# %i%eline $on,erters. As one $an o'ser,e t*at &las* A3 %ro,i#e t*e *ig*est s%ee#

amongst all t*e ot*er t+%es o& A3. 5*e s%ee# o& sigma #elta $on,erter is $om%ara'le "it* SA

A3 'ut e,en it is mu$* slo"er t*an &las* A3. rom t*e resolution %oint o& ,ie" su$$essi,e

a%%roximation resolution t*at is &rom 8 to 16 'its is $om%ara'le "it* %i%eline# stru$ture 'ut t*e

&astest &las* *as maximum resolution o& 6 to 8 'its. 5*ere&ore "e $an $on$lu#e t*at it is al"a+s

t*e tra#eo&& 'et"een s%ee# a$$ura$+ an# %o"er. 5*e sele$tion o& ar$*ite$ture is #e%en#e# u%on


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t*e a%%li$ation.All &amilies o& $on,erters are s%ee# u% "it* t*e 3M;S %ro$ess im%ro,ements

e.g. su$$essi,e a%%roximation $on,ersion time *as 'een in$rease# to tens o& mi$rose$on#s. 5*is

also e&&e$ts t*e %o"er $onsum%tion o& #ata $on,erters. ;n t*e ot*er *an# im%ro,ement in SP

&un$tionalit+ also im%a$ts on t*e A3 #esign e.g. im%ro,ement in sigma#elta $on,erter '+

a##ing &ast an# more $om%lex #igital &ilter.

,20Sig*a Delta ADC

Sigma #elta A3 $omes un#er t*e $ategor+ o& o,ersam%ling A3 "*i$* sam%les t*e signal at

an o,er sam%le# &reuen$+ o& &NDk2 "*ere k is t*e o,ersam%ling ratio an# is gi,en '+ t*e

&ollo"ing euation.

:D&nC 2.1

,.>s*o"s t*e 'lo$k #iagram an# #es$ri%tion o& sigma #elta A3. 5*e mo#ulator %art sam%les

t*e in%ut signal at a mu$* *ig*er &reuen$+ set '+ t*e o,er sam%ling $on,ert "*i$* $on,erts t*e

analog in%ut signal to %ulse #ensit+ mo#ulate# signal &ollo"e# '+ a #e$imation &ilter "*i$*

$ontains t*e original in%ut signal an# out o& 'an# noise.Eoth the mo#ulator an# t*e #e$imator

are o%erate# "it* t*e same o,er sam%ling $lo$k. 5*e mo#ulator is o& &irst or#er "it* a 1'it

uantie an# it generates a 1'it out%ut. 5*e out%ut o& t*e #e$imator is N'it #igital #ata "*ere

N is t*e out%ut resolution o& t*e A3 an# is #e%en#ent on t*e o,er sam%ling ratio o& t*e

$on,erter.


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2.? =lo$k #iagram o& a sigma#elta analog to #igital $on,erter

5*e &ollo"ing su'se$tions 'elo" gi,es ano,er,ie" o& t*e terms uantiation noise signal

sam%ling an# noise s*a%ing "*i$* are relate# to sigma#elta $on,erters.

,2@#uantiation Noise

5*e analog signal $an take an+ $ontinuous ,alue. =ut a #igital n'it signal onl+ settles to 2n

#is$rete ,alues. uantiation noise is t*e #i&&eren$e 'et"een t*e analog ,alue an# its #igital

re%resentation "*i$* $auses t*e #istortion .uantiation error $an 'e #e&ine# as a measure o& an

n'it $on,erterEs &ailure to re%resent a$$uratel+ an analog signal in t*e #igital #omain.

,2./ Signal Sa*=ling

-n t*e %ro$ess o& o,ersam%ling t*e in%ut analog signal is sam%le# at a mu$* *ig*er &reuen$+

t*en t*e N+uist&reuen$+ "*i$* re#u$es t*e uantiation noise to a great extent in t*e reuire#

'an# o& interest. -n or#er to $onstru$t t*e sam%le# signal "it*out #istortion t*e sam%ling

&reuen$+ must 'e t"i$e o& t*e signal &reuen$+ as state# '+ t*e sam%ling t*eorem. )2's*o"s

t*e s%e$trum o& an un#er sam%le# signal2O /ere t*e sam%ling &reuen$+ &s is less t*an t"i$e

t*e in%ut signal &reuen$+ 2&. 5*e s*a#e# %ortion o& t*e &igure s*o"s t*e aliasing "*i$* o$$urs


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"*en


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t*e sam%ling &reuen$+ is not t"i$e t*e signal &reuen$+. !e get a #istorte# signal at t*e out%ut

,.4s*o"s t*e s%e$trum o& an o,ersam%le# signal 2O/ere t*e sam%le# signal in t*e &reuen$+

#omain a%%ears as a series o& 'an#limite# signals.5*is %uts t*e entire in%ut signal 'an#"i#t* at

less t*an &SC2 "*i$* re#u$es t*e aliasing.

,2.. Noise Sha=ing

-t is one o& t*e %ro%erties o& sigma#elta A3s "*i$* results #ue to t*e a%%li$ation o& &ee#'a$k

"*i$* exten#s #+nami$ range. 5*e $lose# loo% mo#ulator "orks as a *ig*%ass &ilter &or

uantiationnoise an# as a lo"%ass &ilter &or t*e in%ut signal. !*en t*e signal is o,ersam%le#

t*e uantiation noise %o"er in t*e N+uist 'an#"i#t* s%rea#s o,er t*e "i#er 'an#"i#t* "*i$*

is s*o"n in 2.8. 5*e total uantiation noise is still t*e same 'ut t*e uantiation noise in t*e

'an#"i#t* o& interest is re#u$e# signi&i$antl+. 5*e &igure illustrates t*e noise s*a%ing "*i$* is

a$*ie,e# '+ using t*e o,ersam%le# sigma#elta mo#ulator.

2.6 (a)@n#er sam%le# signal


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2.7ig2.6(') ;,ersam%le# signal

-n a sigma#elta A3 t*e analog mo#ulator sam%les t*e in%ut at o,ersam%ling ratio an# a&ter

t*e in%ut signal %asses t*roug* t*e mo#ulator it is &e# into t*e #igital &ilter or a #e$imator. 5*e

#igital &ilter %ro,i#e a s*ar% $uto&& at t*e 'an#"i#t* o& interest "*i$* essentiall+ remo,es out o&

'an# uantiation noise an# signals

2.8 Putting noise s*a%ing an# igital &ilter toget*er


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,2., S=ur+ !ree Dyna*ic Range 5S!DR7

S is t*e ratio o& t*e strengt* o& t*e &un#amental &reuen$+ to t*e strongest s%urious signal in

t*e out%ut o& A3s. S is an in#i$ator o& &i#elit+ o& an A3. Nonlinearit+ in t*e A3

generates s%urious signals t*at a&&e$t t*e a$*ie,a'le S.S $an 'e $al$ulate# using t*e

'elo" &ormula

SDSignal (#=) largest s%ur (#=)

,2.: Di99erential non+ linearity 5DN7

N is a measure o& se%aration 'et"een a#a$ent le,els measure# at ,erti$al

um%.Nmeasures an+ #e,iation &rom one S=. -n ot*er "or#s &or an i#eal A3 t*e out%ut is

#i,i#e# into 2N uni&orm ,oltage le,els ea$* "it* "i#t*. An+ #e,iation &rom t*e i#eal ste% "i#t*

is $alle##i&&erential non linearit+ (N) an# is measure# in num'er o& $ounts (S=s). 5*e N

is 0S=or i#eal A3s. -n a %ra$ti$al A3 N error $omes &rom its ar$*ite$ture. or

exam%le in a SA A3 N error ma+ 'e $ause# near t*e mi#range #ue to mismat$*ing o&

its A3. et us $onsi#er an exam%le o& a >'it A3 "it* trans&er $*ara$teristi$s as s*o"n in

ig. -n t*is A3 ea$* in%ut ste% s*oul# 'e exa$tl+ 1C8 o& t*e &ulls$ale in%ut range (1 S= o&

t*is A3). i,en t*at t*is A3 *as an in%ut range o& 8 t*e &irst out%ut$o#e transition is

$ause# '+ an in%ut $*ange o& 0.? (ulls$ale in%ut rangeC16 D S=) "*i$* is as ex%e$te#.

/o"e,er t*e se$on# transition &rom 001 to 010 takes %la$e a&ter an in%ut $*ange o& 1.2?

(1.2? S=) an# so is too large '+ 0.2? S=. Similarl+ t*ere is a ,ariation in ste% sie at ea$* o&

t*e &ollo"ing ste%s. 5*e N o& t*is %arti$ular A3 $an 'e s%e$i&ie# as 0.7? S= "*i$* is t*e

maximum #e,iation &rom t*e i#eal ste% sie o& t*is A3 t*roug*out its trans&er.


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2.9 e%resentation o& N in an A3 trans&er $ur,e

,2.6 Integral non+linearity 5IN7

-ntegral non linearit+ (-N) is t*e maximum #i&&eren$e 'et"een a$tual &inite

resolution$*ara$teristi$ an# i#eal &inite resolution $*ara$teristi$s. -n t*e ot*er "or#s -N is a

measure o&*o" $losel+ t*e A3 out%ut mat$*es its i#eal res%onse. -N $an 'e #e&ine# as t*e

#e,iation inS= o& t*e a$tual trans&er &un$tion o& t*e A3 &rom t*e i#eal trans&er $ur,e. -N

$an 'e estimate# using N at ea$* ste% '+ $al$ulating t*e $umulati,e sum o& N errors u% to

t*at %oint. -n realit+ -N is measure# '+ %lotting t*e A3 trans&er $*ara$teristi$s as ex%laine#

'elo". 5*ere are t"o met*o#s to &in# t*e -N error

1. =est &it ('est straig*t line) met*o#

2.


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5*e i#eal trans&er $ur,e *ere is #ra"n su$* t*at it #e%i$ts t*e nearest &irstor#er a%%roximation to

t*e a$tual trans&er $ur,e o& t*e A3. 5*e inter$e%t an# slo%e o& t*is i#eal $ur,e $an len# us t*e

,alues o& t*e o&&set an# gain error o& t*e A3. uite intuiti,el+ t*e 'est &it met*o# +iel#s 'etter

results &or -N.

2.10 =est &it -N

5*e onl+ real use o& t*e 'est &it -N num'er is to %re#i$t #istortion in A3 a%%li$ations. 5*is

num'er "oul# 'e eui,alent to t*e maximum #e,iation &or an A3 a%%li$ation.

,2.> En'+=oint IN(

5*e


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2.11


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#e$rea$e#.5*e #ensit+ o& Q1sE an# Q0sE &orming a %ulse stream at t*e out%ut is t*e #igital

re%resentation o& t*e in%ut analog signal. A $on,erter nee#s a sam%ling &reuen$+ more t*en

t"i$e t*e signal &reuen$+ to re%ro#u$e t*e signal "it*out #istortion. 5*e #ensit+ o& t*e %ulses

re%resents t*e a,erage ,alue o& t*e in%ut most o& t*e %ulses are *ig* &or t*e %ositi,e %eak o&

analog signal an# t*e #ensit+ o& negati,e %ulses re%resents t*e negati,e %eak o& t*e signal.

=+ 'alan$ing t*ree maor #esign as%e$ts t*e resolution o& t*e sigma #elta A3 $an 'e

in$rease# t*e+ are t*e o,er sam%ling ratio uantier resolution an# or#er o& mo#ulator. 5*e use

o& a *ig*er or#er mo#ulator re#u$es t*e su%erim%ose# noise in t*e 'it stream. 5*e in 'an#

uantiation noise $an 'e re#u$e# '+ #ou'ling t*ere sam%ling &reuen$+. 5*e in%ut analog signal

$an #ire$tl+ 'e sam%le# using an in%ut o,er sam%le $lo$k as it uses t*e %ro$ess o& o,ersam%ling

t*is also eliminates t*e use o& antialiasing &ilter #ue to o,ersam%ling %ro$ess.

,2., Bloc 'iagra* o9 *o'ulator

5*e mo#ulator $onsists o& an -ntegrator i&&eren$e Am%li&ier 1'it lat$*e# 3om%arator

(A3) an# a 1'it A3.,2.,s*o"s t*e 'asi$ stru$ture o& a mo#ulator. 5*e mo#ulator %us*es t*e

out%ut o& t*e mo#ulator to a *ig*er &reuen$+ range "*i$* $an 'e &iltere# using a #igital

#e$imation &ilter.


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,2.4 DECIMATOR

e$imation is t*e %ro$ess o& $on,erting t*e sam%ling rate o& a signal &rom a gi,en *ig*er

rate &s tolo"er rate &n.e$imation means re#u$ing '+ a &a$tor 10.'ut in $ommuni$ation it is t*e

re#u$tion in t*e sam%ling rate o& t*e signal. -t is a #igital lo" %ass &ilter "*i$* %er&orms t*e

sam%les rate re#u$tion o%eration. 5*e sigma#elta mo#ulator %er&orms t*e o%eration o& noise

s*a%ing an# *en$e t*e noise is %us*e# to *ig*er &reuen$ies so t*at t*e #e$imation stage

&ollo"ing t*e mo#ulator $an &ilter out t*is noise a'o,e t*e $uto&& &reuen$+. 5*e 'an# limite#

signal $an t*en 'e resam%le '+ #is$ar#ing : F 1 sam%les out o& e,er+ : sam%les "*ere : 'eing

t*e o,ersam%ling ratio. =+ a,eraging : sam%les out o& t*e uantie# sigma#elta out%ut t*e

#e$imation &ilter a$*ie,es a *ig* out%ut resolution an# also t*e &reuen$+ o& t*e out%ut #ata is at

t"i$e t*e in%ut signal 'an#"i#t* "*i$* is t*e n+uist rate.


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)


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:2 Syste* level Design o9 Sig*a Delta ADC

)=


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)

Design o9 Sig*a Delta ADC

Sigma #elta A3 as s*o"n in &igure2.1 $onsist o& a Mo#ulator an# a e$imation &ilter. -n t*is

re%ort #esigning o& sigma #elta A3 is im%lemente# in 90um 3M;S te$*nolog+. 5*e mo#ulator

runs on a su%%l+ ,oltage o& 1.8, an# a$*ie,es a SN o& 8?#= &or a signal 'an# "i#t* o& 20

:/. -t o%erates at an o,ersam%ling ratio o& 64 an# a sam%ling &reuen$+ o& 2.?6 M/.

:2.2 Designing o9 Sig*a Delta Mo'ulator

5*e Mo#ulator as s*o"n in igure 2.> $onsists o& a single stage integrator a summing am%li&ier

a uantier($om%arator) an# a 1'it A3.5*e 'asi$ 'uil#ing 'lo$k o& t*is mo#ulator is a sim%le

t"o stage #i&&erential ;%am%.

:2,2 Designing o9 Co*=arator

3om%arator or uantier is one o& t*e $ore $om%onents o& an+ analogto#igital $on,erter (A3)

as "e kno" N+uist $on,erters nee# %re$ise analog $om%onents in t*eir $on,ersion $ir$uits.

5+%i$all+ auantier #esign in$lu#es a ,er+ %re$ise sam%lean# *ol# $ir$uit an# a *ig*a$$ura$+

$om%arator "orking at N+uist sam%ling &reuen$+. 5*e a$$ura$+ reuirement o& t*e $om%arator

#e%en#s on t*e a$$ura$+ reuirement o& t*e $on,erter in mo#ulators t*e $om%arator is

reuire# to "ork at a *ig* o,ersam%ling &reuen$+ 'ut its resolution $an 'e as small as 1 'it.

5*ere&ore t*e $om%arator #esigning mo#ulators &o$uses more on a *ig*s%ee# o%eration

instea# o& a$$ura$+an# uses a $om%lementar+ $om%arator "it* lat$* or lat$*e# $om%arator

&ollo"e# '+ a 'u&&er "*i$* *el%s in 'u&&ering t*e out%ut o& t*e $om%arator


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)

:2:2 Designing o9 Su**ing A*=li9ier

5*e summing am%li&ier is one o& t*e &lexi'le $ir$uits o& Sigma #elta A3. -t is gi,en "it* t*e

analog in%ut signal in one o& its terminal an# t*e ot*er is gi,en t*e &ee# 'a$ke# loo% &rom t*e

out%ut o& A3. -t is 'asi$all+ a summing am%li&ier "it* one resistor in t*e in%ut si#e an# a

$om'ination o& resistor &or t*e &ee#'a$k %at* also. 5*is $ir$uit is #esigne# using 90um 5s%i$e

- te$*nolog+. /ere a in%ut ,oltage o& 2.?, is gi,n as an in%ut to t*e summing am%li&ier an#

t*e

$orres%on#ing out%ut "ill 'e t*e sum o& t*e in%ut an# t*e &ee# 'a$k ,oltage 4.?s*o"s t*e

s$*emati$ o& summing am%li&ier an# 4.6s*o"s t*e transient anal+sis o& t*e a'o,e $ir$uit.

>.? S$*emati$ o& summing am%li&ier.


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)

:2>2 Designing o9 Integrator

5*e integrator is #esigne# using a t"o stage ;%Am% in 5s%i$e - 90um 3M;S te$*nolog+

an# is $onne$te# "it* a &ee# 'a$k $a%a$itor "*i$* *el%s in $*arging o& t*e in%ut ,oltage to gi,e

a integrate# out%ut. -t is gi,en a sinusoi#al in%ut signal &rom t*e summing am%li&ier "*ose

out%ut is t*e sum o& t*e in%ut an# t*e &ee# 'a$k signal an# gi,es ram% out%ut $orres%on#ing to a

gi,en sinusoi#al in%ut. 5*e 'elo" >.7s*o"s t*e stru$ture o& a integrator $ir$uit an#

4.8gi,es t*e simulation result o& t*e integrator.

>.7 s$*emati$ o& -ntegrator


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)

>.8 Simulation esult o& integrator

:212 Designing o9 Digital+to+Analog Converter

A sigma #elta $on,ertor uses multi'it uantier an# multi'it #igitaltoanalog (A3) to

re$onstru$t t*e analog signal&or su$* A3 t*e linearit+ o& t*e $on,ertor is im%ortant. or a *ig*

resolution A3 a$$ura$+ is one o& t*e maor %ro'lems t*at it en$ounters &or t*is a single 'it

s+stem is use# to o,er$ome t*e a$$ura$+ %ro'lem. -n one 'it A3 linearit+ is #etermine# '+ t*e

a$$ura$+ o& s"it$*ing 'et"een t*e re&eren$e signal &or *ig* s"it$*ing a$$ura$+ t*e s+stem "ill

'e ,er+ linear.


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=

igure >.6 3ir$uit o& A3

igure >.7 !a,e&orm o& A3


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=

:242 Sche*atic o9 9irst Or'er Mo'ulator(

5*e sigma#elta AC $on,erter stan#s out to 'e t*e most a#,an$e# among all t*e ata

$on,erters #is$usse# so &ar. A 'lo$k le,el s$*emati$ o& a &irst or#er AC $on,erter is as #e%i$te#

'elo" in ig4.11.5*e &igure s*o"s t*e 'lo$k #iagram o& a &irst or#er eltasigma 3on,erter (

A3). -t $onsists o& -ntegrator a $om%arator (1 'it A3) 1'it A3. -n a'o,e $ir$uitr+ a 1'it

A3 (generall+ kno"n as a 3om%arator) #ri,e it "it* t*e out%ut o& an integrator an# &ee# t*e

integrator "it* an in%ut #i&&eren$e# "it* t*e out%ut a 1'it A3. 5*e t+%e o& AC $on,erters

#is$usse# so &ar are N+uist $on,erters "*ere '+ sam%ling rate is t"i$e t*e in%ut signal

&reuen$+ &or error &ree signal a%%roximation. ;nl+ "a+ to #e$rease t*e uantiation noise or

'etter signal re%resentation is sam%ling t*e signal man+ more times. 5*is is t*e &un#amental

t*eor+ in sigma #elta #ata $on,erters.4.11s*o"s t*e s$*emati$ o& asigma#elta A3 t*e $ir$uit

is &e# "it* a sinusoi#al signal o& 2.?, an# &reuen$+ o& 100M/ to t*e summing $ir$uit "*ose

ot*er terminal is $onne$te# to t*e &ee#'a$k out%ut signal o& one 'it A3 .5*e out%ut o& t*is

$ir$uit is gi,en to t*e integrator an# t*e ot*er terminal o& integrator is $onne$te# to a groun#. t*e

out%ut o& t*e integrator is gi,en to t*e lat$*e#$om%arator "*ose ot*er to terminals are

$onne$te# to $lo$k signals "*i$* *el%s t*e $om%arator to in$rease t*e s%ee# an# also t*e

sensiti,it+ o& t*e $ir$uit. 5*e $om%arator $om%ares t*e in%ut signal &rom t*e integrator "it* t*e

re&eren$e signal an# gi,es t*e $orres%on#ing out%ut as s*o"n a'o,e. -t "ill gi,e a %ositi,e signal

"*en e,er t*e in%ut signal $rosses t*e re&eren$e signal a'o,e its ,alue an# a negati,e "*en it

$rosses t*e re&eren$e signal. 5*e %ulse o& 'it generate# &rom t*e $om%arator is gi,en as a in%ut to

t*e A3 "*i$* is $onne$te# as a &ee#'a$k to t*e AS3 $ir$uit. 5*is %ro$ess is iterate# se,eral

times to get a series o& #igital 'it stream. 5*e simulation result o& t*e a'o,e $ir$uit is s*o"n in

4.12'elo".


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=

>.11 s$*emati$ o& a sigma#elta A3

>.12 simulation result o& Sigma elta A3

5*e a'o,e s$*emati$ $ir$uit simulates an in%ut analog signal an# t*ere '+ gi,es a $orres%on#ing

#igital stream o& %ulses at t*e out%ut o& t*e mo#ulator $ir$uits. 5*is is a$*ie,e# #ue to t*e


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=

$ontinuous iteration o& t*e in%ut signal to t*e mo#ulator.


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62 Conclusion an' !uture


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?

62.2 Conclusion

A Sigma #elta Analog to #igital 3on,ertor is #esigne# '+ integrating t*e $om%onents o& t*e

s+stem.. 5*is is use# as a summing $ir$uit "*i$* *el%s in %ro,i#ing t*e #i&&erential &ee# 'a$k

in%ut to t*e integrator. ollo"e# '+ a *ig* s%ee# $om%arator is #esigne# &or t*is a lat$*e# t+%e

$om%arator is use# "*i$* $om%ares t*e in%ut signal "it* a re&eren$e signal an# gi,es t*e

$orres%on#ing result "*i$* is t*en &e# to 1 'it igital to Analog (A3) $ir$uit at t*e &ee#'a$k

%at* o& t*e s+stem. 5*is %ro$ess is iterate# an# a %ulse o& #igital signal is a$*ie,e# at t*e out%ut

o& t*e s+stem. 5*e sigma #elta A3 "as simulate# using a stan#ar# 5s%i$e - .+nami$ lat$*

$om%arator *as 'een #esigne# in or#er to re#u$e stati$ %o"er #issi%ation. 5*e #i&&erent %arts

o& t*e #+nami$ lat$* $om%arator likeR %ream%li&ier #+nami$ lat$* an# out%ut 'u&&er are

im%lemente# on 5s%i$e - "it* 1.2 %o"er su%%l+. 5*e simulation results s*o"n &or a

sam%ling &reuen$+ o& 2.? / an# t*e a,erage %o"er #issi%ation o& t*e %ro%ose# $om%arator is

68 !.

62,2 !uture $or

5*e &uture "ork o& Sigma #elta A3 is

1. esign o& a *ig* s%ee# *ig* %re$ision re#u$e# sie 3M;S $om%arator.

2. 3om%arison "it* existing $om%arator.

>. esigning o& a *ig* s%ee# an# lo" %o"er Sigma #elta A3

4. esigning o& a multi'it Sigma #elta A3.


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RE!ERENCES

1O 2 Facob Eaer #)$$&,2 CMOS M ix e d- Signa l Circ u it D e s ig n #)nd ;d2,2 iley6

1;;;21S E !&% * 6$ 6

(%$6)&$)'6)2http3GGCMOSedu2co"G.

2ONa"s*a# Amin o* $*it uan an# -'ra*im A*ma#.IAn O Ma i Ta S*ero :*an AnisNuras*ikinNor#in A/M Ua*irulAlam.IA lo" 3ost irst ;r#er

Sigma elta 3on,erter esign An# Anal+sisJ.

4O 5*e esign o& Sigma elta Mo#ulation A3 3on,ertersJ -


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9O.#in*heol +oo, Daegyu ee, "yusun Choi, and Ali Tangel Iutureea#+ @ltra&ast 6 =it

3M;S A3 &or S+stemon3*i% A%%li$ationsJ Pro$ee#ings o& 14t* Annual -O. +.-T. 'ang and %. &aavi IAn 6'it 1?0M/ 3M;S AC 3on,erterJ -)R>08>17 Mar$* 2000.

14O.D. ee, #. +oo, ". Choi, and #. hanavi Iattree en$o#er #esign &or ultra*ig* s%ee# &las*

analogto#igital $on,ertersJ in Pro$. -


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%arallel A3s &eaturing re#u$e# $on,ersion noise in t*e $ase o& single 'u''les in t*e

t*ermometer $o#eJ. -

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Sigma Delta ADC Report - B.Tech final year project

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