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MEMS$and$Sensors$
Whitepaper$Series$
$
$
Introduction$to $the$MIPI$I3C$$
Standardized$Sensor$Interface$
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August$2016$
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Whitepaper! Topics:! sensors,!digital! commu n i ca t io n ! (MIPI!I3C,! I²C,!SPI),! standardized! sensor!interface,!
unified!sensor!link,!high-speed!data!rate,!sensor!data!batching,!sensor!hubs,!mobile,!wearab le s !a n d !Io T !
!
About! Us:! MIPI!Alliance! (MIPI)! develops! interface! specifications! for! mobile! and! mobile-influ e n ce d !
industrie s. !There! is! at! least!on e! M IPI!specification!in!every!sm artphone! manufactured! today.!Founded! in!
2003,!the!organization! has!more!than!270!member! companies!worldwide! and! 14!active!working!groups!
delivering! specifications! within! the! mobile!ecosystem.!Members! of! the! organization! include! handset!
manufacturers,! device! OEMs,! software! providers,! semiconductor! companies,! application! processor!
developers,!IP!tool!providers,!test!and!test!equipment!companies,!as!well!as!cam era,!tablet!and!laptop!
manufacturers.!For!more!information,!please!visit! www.mipi.org.!
!
Contact!Information:!!!
Melanie!Cole!(melanie.cole@mipi.org)!
Manager,!Integrated!Marketing!&!Membership!!
MIPI!Alliance!(www.mipi.org)! !
Introduction!to!the!MIPI!I3C!!
Standardized!Sensor!Interface
! !
!
Copyright!2016!MIPI!Alliance,!Inc.!!All!rights!reserved.! ! 2!
!
Introdu c tio n!
The!total!global!sen sor!market!is!expe cte d !to!re ac h!$154 .4B !by!2020
1
.!!$10.4 6B !of!this!will! be!made! up!
by!in te g ra te d !sensors!that!include!decision!m ak ing,!logic! functions!and!digital!comm unication.!!Sensors!
are! experiencing! an! unprecedented! growth,! from! $65 0M! in! 2012! and! with! an! expected! compound!
annual!growth!rate!of!36.25%!through !2020
2
.!!A!major!driver!has!been!the!adoption!of!low-cost,!sm all!
form! factor! sen sors! in! smartpho nes,! tablets! and! a! growing! num ber! of! wearables! applications.! ! The!
original! iPhone! was! introduced! in! 2007! w ith! advanced! sensing! capabilities! (i.e.! ambient! light,!
accelerometer!an d!proximity)!that!provided!an!inno vative !and!imp rov ed !user!interface.!!Since!then,!th e!
adoption!of!sensors!has!rapidly!escalated!and!the!larges t! se n so r! manufa ct u rer s! n o w ! sh ip ! billions!of!units!
per! year! for! mobile! and!consumer! applications.!!This! trend! is!continuing.! ! Smartphone! providers! are!
trying!to!gain!a !comp etitive!adva nta ge!by!adopting!new!sensors! and!sensing! technologies!fo r!impro ved !
user!experiences.!!Increased ! s e n so r ! c o n te n t!allows ! more!com plex!features!thro ugh ! sen so r! fusion , !where!
sensor! data! from ! m ultiple! sen sors! is! aggregated! and! analyzed! to! provide ! functions! that! cannot! be!
achieved! with! a! single! sensor.! ! Advanced! functionality! such! as! dead-reck on ing,! augmented/virtu al!
reality! and ! others! require! better! performing,! faster! and! som etime s! d uplicate! sets! of! senso rs.!!New!
sensing!techno logy!is!also!being!developed.!!A!possible!next!frontier!co uld! be!the!addition!of!gas!and!
chemical!sensors!to!mo nitor!a ir!qua lity!and!to xicity!leve ls!in!the!world!around!us.!!!
The!proliferation!of!sensors!in!mobile!devices!req uire s!app lication !proce sso rs!and/ or!sens or!hub s!with!
an!increased!numb er!of!logic!pins!used!for!sensor!communication! and!control.!!In!a!typical!app lica tio n,!
multiple! digital! communication! interfaces! are! used! along! with! supporting! logic! lines! for! de dica ted !
interrupt ! and! sleep!signals.!!Top!tier!smartphones! include!10!or!more!sensors! and!a!critical!point!has!
been!reached!where! 20! or! more! logic!signals!are!required.!!There!are!other! complicating!factors!as!well.!!
The! de! facto! com munication! standard! for! sensors! in! mobile! and! consum e r! applicatio ns ! is! I ²C.! ! I²C!
requires!only!two !signal!lines!(clock!and!data),!but!has!several!shortcomings,!including!the!inability!for!
sensor! slaves! to! in itia te ! communicat ion ,! an! overhead! protocol! that! reduces! throughput! and! pull-up!
resistors! that! limit! clock! speed! and! incre ase s! power! dissipation.!! Another!comm only! u s ed ! standard! is!
the! serial! peripheral! interface! or! SPI.! ! SP I! req uire s! four! com m u nic ation ! lines! and! is! used! whe re! large!
amounts! of! data! needs! to! b e! transferred,! such! as! clearing! data! batches! from! first! in,! first! out! (FIFO)!
buffers.! ! To!its! disadvantage,! SPI! lack s! a! clearly! defined! standard! that! has! resulted!in! m any! different!
implementatio n s.!!!
There! is! no! consistent! method ! fo r! in terfac ing ! to ! senso rs,! which! causes! considerable! integr at io n !
challenges.!! Device!and!platform!designers!are!faced!with!digital! in t erf ac e! f ra gmentat ion ! a n d ! h av e ! to !
deal! with! I²C,! SPI,! UART! and ! others.! ! What! if! there! was! a! single,! scalable,! cost-effective! and! clearly!
defined!standard!communication! interface! for!sensors?!!A nd!w hat!if!this!standard!could!unite!the!be st !
of! I²C! and! SPI! w hile! adding! new! functionality! that! the! current! standards! are! lacking?! ! In! 20 1 3 ,! MIPI!
Alliance!formed !a! Se nso r!Wo rking !Group!w ith!a! goal!to! develop!an! I²C! compatible!interface!with!sensor-
focused,!differentiated ! features.! !An!extensive!industry!survey!was!performed!in!conjunction!w ith!the!
MEMS! &! Sensors! Ind u s tr y! Group ! (MSIG)! to! collect! in form a tion ! a bo ut! what! a! ne w ! sta nd ard ! sh ou ld!
include.!!The!culmin at io n !of!this!survey!along !with !the!ongoing!efforts!of!the!Sensor!Working!Group!is!
the!brand! new!MIPI®! Alliance! Specification!for!I3C
SM
!Improved!Inter! In te g ra te d !Circu it!(MIPI!I3C)!senso r!
interface !st an d a rd .!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
1
!“Global!Market!for!Sensors!to!Reach!Nearly!$154.4!Billion!in!2020;!Image!Sensors!Moving!at!11.7%”,!BCC!Research,!July!2014!
2
!“Smart!/!Intelligent!Sensor!Market!by!Type,!Application!&!by!Geography,!!2013!–!2020”,!MarketsAndMarkets,!March!2014!
Introduction!to!the!MIPI!I3C!!
Standardized!Sensor!Interface
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Copyright!2016!MIPI!Alliance,!Inc.!!All!rights!reserved.! ! 3!
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MIPI!I3C!Scope!and!Purpose!
The! MIPI! I3C! inte rfa c e! is! an ! evo lut io n ary ! stan d a rd ! that ! imp ro v es ! upon! the! features! of! I²C,! while!
maintaining!backward!compatibility.! ! This! standard! offers!a! flexible! multi-drop! interface! between! the !
host!processor!and!peripheral!sensors!to!support!the!growing!usage!of!sensors!in!embe d d ed !system s. !!
The! m ain! purpose! of! MIPI! I3C! is! thre ef o ld:! 1) ! to! sta n d ard iz e ! sen so r! co mmun ica tio n ,! 2)! red u ce ! th e!
number!of!physical!pins!used!in!sensor!system!integration!and! 3)!support!low-power,!high-spee d! and!
other!critical!features!that!are!currently!covered!by!I²C!and!SPI.!!Developing!the!MIPI! I3 C !inter f ace!has!
been! a! com munal! effort! to! identify! the! real! market! needs,! define! a ! standard! and! merge! technology!
contributions!from!leading!SoC,!sensor!hub!and!sen sor!vendors.!!During!the!initial!phases!of!the!MIPI!I3C!
development,!multiple!proposals!were!considered! and! technically!graded ! to! com e ! up! with!a!standard!
that! satisfies! a! broad! ran ge ! of! app lication s! th at! extends! beyond! the! smartphon e.! ! The! subsequent!
development!work!has!been!a!broad!effort! from!many!MIPI!Alliance!members
3
.!!The!MIPI! I3C!stan dard!
is!current ly!b e in g!f ina liz ed !a n d !will!be!released!later!in!2016,!exclusively!to!MIPI!Alliance!memb ers .!
MIPI!I3C!Fact!Sheet!
MIPI!I3C!Standardized!Sensor!Interface!
I3C$MAIN$
MASTER
I3C$
SLAVE
I3C$
SECONDARY$
MASTER
SDA
SCL
I2C$
SLAVE
!
Two-wire!communication!interface,!clock!(SCL )!a nd!data!(SDA)!
Number!of!gates!
<!2,000!
Bandwidth!
>!33!Mbps!
Features!
In-band!interrupts!
In-band!command!codes!
Dynamic!addressing!
Multi-master!/!multi-drop!
Hot-join!support!
Backward!compatible!with!I²C!
Table&1:!MIPI!I3C!standardized!sensor!interface!at!a!glance.!
MIPI! I3 C ! was! initially! intended! for! mobile! applications! as! a! single! interface! that! can! be! used! for! any!
sensor.!!Modern!smartphones!that!include!a!multitude!of!sensors!and !a!slew!of!sup porting! logic!lines!
are!pushing!the!boundaries!of!both!I²C!and!SPI.!!MIPI! I3C!will! accommodate!many!sensors!on!the!sam e!
communication! bus,! wh ile! e liminating! additional! logic! signa ls! needed! to! supp ort! interrupt! o r! sleep!
mode!functionality.!!The!MIPI!I3C!stand ard!is!useful!fo r!other!applications!than!smartphon es .!!It!offers!
high!speed!data!transfer!at!very!low!power!levels,!which!is!hig h ly!des irab le !for!any!emb ed d e d !system.!!
Wearables!is!a!g re at !examp le !where!multiple! sensors!are! used! in! a!very! limited!physical!space!and! with!
stringent! power! restrictions.!!Over! time,! the! MIPI! I3C! could! conceivably! become! much! more! than! a!
standardized! sensor! interface! and! develop! into! a! de! facto! bus! communication! standa rd! for! t ouch!
sensing,!alway s-on!and!low !resolution!cameras,!acoustics,!environmental!sensors!and!transducers!that!
currently!use!I²C,!SPI,!UART!a n d !o t h e rs .!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
3
!AMD,!Broadcom,!Cadence,!Intel,!InvenSense,!Knowles,!Lattice!Semiconductor,!MediaTek,!Mentor!Graphics,!Nvidia,!NXP,!Qualcomm,!QuickLogic,!Sony,!
STMicroelectronics,!Synopsys,!VLSI!Plus,!ZMDI!(now!IDT)!and!others.!
Introduction!to!the!MIPI!I3C!!
Standardized!Sensor!Interface
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Copyright!2016!MIPI!Alliance,!Inc.!!All!rights!reserved.! ! 4!
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MIPI!I3C!Fundamentals!!
The!MIPI!I3C!inte rfa c e!uses!an!I²C -like!interfa c e!with!an! open!drain!data!line!(SDA)!and!a! push-pull! clock!
line!(SCL).!!The!open!drain! (i.e.!open!collector)! SDA !line! allows!for!slaves!to!take! control!of! the!data! bus!
and!initiate! interrupts.!!The! pu sh-pull!SCL!line!is !used!by!the!master!to!clock!the!comm u nica tion !bus!u p!
to!1 2.5 ! MHz.!!MIPI!I3C!supports!multiple!classes!of!devices!including!main!master,!se cond ary! master,!
MIPI!I3C!slave!and!I²C!slave.!!The!master!can!dynam ically!assign!7-bit!addresses!to!all!MIPI!I3C!devices!
while!supporting!the!static!addresses!of! legacy!I² C!devices.!!This! ensures! full!comp atibility!betw een!MIPI!
I3C!and!I²C.!!The!MIPI!I3C!interface!repre s en t s! a! sh ift !in ! p ower!per fo rmance!while!pr ov id in g! g re at er! th a n !
an! order! of! m agnitude! im p ro v e m e n t! in ! sp ee d ! ov e r! I²C.! ! I3C! offe r s! fo u r! d a ta ! tra n sf er ! m o d e s! th a t ,! on !
maximum!base!clock!of!12.5MHz,! provide!a! raw! bitrate!of!12.5! M bps!in!the!baseline!SDR!d ef au lt !mode,!
and!25,!27.5!and!39.5!Mbps,!respectively!in!the!HDR!modes.!After!excluding!transaction!control!bytes,!
the! effective! data! bitrates! achieved! in! each! mo de! are! 11.1,! 2 0,! 23.5! and! 33.3! M b ps,! respectively,!
protected! by! I3C's! basic! error! detection! mechanisms.! The! bar! charts! in! Figure! 1! comp are! the! energy!
consumption!(per!bit)!of!the!various!MIPI!I3C!modes!with!I²C!(left)!and!the !correspo nd ing!raw!bitrates!
(right).!!Based! on! these! results,! the! MIPI! I3C! is! a! more! power! efficient! interface! even! in! the! I²C-
compatible!mode.!!The!MIPI!I3C!ternary!HDR-TSP!mode!is!the!fastest!and!most!power!efficient!mode,!
supporting!effective!data!bitrates!over!33!Mbps.!
!!
I3C I3C
0
5
10
15
20
25
30
35
40
45
SDR HDR-DDR HDR-TSL HDR-TSP
I2C
Raw Bitrate
Mbps for I3C Data Modes (@12.5MHz)
vs I2C (@400KHz)
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
SDR HDR-DDR HDR-TSL HDR-TSP
I2C
Energy Consumption
milliJoules per Megabit for I3C Data Modes (100pF)
vs I2C (100pF, 3.54KOhm)
mJ per Mega-bit, VDD=1.8V
mJ per Mega-bit, VDD=3.3V
Assumptions:
1) All symbols in each mode have equal probability for use.
2) Energy consumption is the energy delivered by pull-up
devices to the bus (which includes drivers and resistors).
!
Figure&1:!Energy!consumption!for!MIPI!I3C!modes!in!comparison!to!I²C!(left)!and!raw!bitrates!for!MIPI!I3C!
modes!compared!to!I²C!(right).!!Image!from!MIPI!Alliance.!
A! very! useful! feature! allows! MIPI!I3C! slaves! to ! initiate! in-band! interrupts,! which! currently! requires! a !
dedicated!signal!line!for!both!I²C!and!SPI!devices.!!The!in-band!interrupt!feature!enables!slaves!to!issue!a!
“start”!whe n!the!bus!is!available!(i.e.!idle).! !The! master!provides! an !inte rf ac e!clock!fo r!the!slave!to!drive!
its!maste r- assigned! address!o nto!the!bus! to ! initiate! an! interrup t.! ! If!there! is! a! conflict!where!multiple!
slaves!are!trying! to !initiate!an !interrupt!simultaneo usly,!the !lo west!assig n e d !a d d re s s !w in s !by! arbitration.!!
The!master!can!acknowledge! (ACK)!the!interrupt!and!restart!the!bus! or!continue!to!clock!out!d ata !from!
the!slave.!!A!not-acknowledge!(NACK)!ca n!be !sent! to!end! the!communication.! !For!example,!an!am bient!
light!sensor!is!co mmon ly!used!to!control!the!backlight!brightness!of!a!display!in!mob ile !device s.!!If!the!
light!co n d itio n s!change,!the!sen so r!will!send !an!inte rru p t!to!the!system!and!re quests!that!senso r!d ata !is!
Introduction!to!the!MIPI!I3C!!
Standardized!Sensor!Interface
! !
!
Copyright!2016!MIPI!Alliance,!Inc.!!All!rights!reserved.! ! 5!
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sent!to!the!master.!!When! light! conditions! are! stable,! there! is! no! need! to! inqu ire! the! sensor!and!use!
power!for!unnecessary!sensor!data!transmissions.!
MIPI!I3C!slaves!are!allowed!to!join!the!bus!after!it !has!a lre ad y !been!configur ed.!!This!is!called!hot-join.!!
Sensors! that! are! connected! on! the! same! bus! can! be! pow ered! off! until! they! are! needed.! ! Hot-join in g!
should! adhere! to!specific!electrical!limits!and! not!disturb!the! MIPI!I3C!lin e s.!!A!set!of! common!command!
codes! (CCCs)! has! been! defined! for! standard! operations! like! enabling! and! disabling! events,! managing !
MIPI! I3C! specific! features! (dynamic! addressing,! timing! co ntrol! etc.)! and ! others.! ! T hese! C CCs! can! be!
broadcasted! (sent! to! all! devices)! or! directed! at! a! specific! device! on! the! bus.! Power! efficiency! and!
performance! are! crucial! in! sensor! applications.! ! Always-on! sensors! and! sensor! hubs! are! constantly!
accumulating! sensor! data! even! while! the! main! application! processor! is! idle! (i.e.! low-power! m ode! or!
deep!sleep).!!Accumulated!sensor!data!is!commonly!organ ize d ! in!batche s !that! need ! to!be! periodically!
and! quickly! transmitted! between! sensors,! sensor! hub s! and! application! processor! to! m inimize! power!
consumption.!!The!industry! has!fa vo red !SPI!for!high-speed!tran sm ission !of!batched!sensor!data,!but!SPI!
is!more!c o mplex!an d !h as !h igh e r!p in !co u n t!t h an !I ²C.!!!
MIPI!I3C!Sensor!Interface!Standardization!
I²C! and!SPI!have! become!synonymous!w ith!digital!com m un ication! fo r! se ns ors.! !I²C!or!inter-inte gr at ed !
circuit!was!originally!developed!by!Philips!Sem iconductor!(no w !NXP!Semiconductors)!back!in!1982!as!a!
simple!commu nication! b us! for! b uilding! con trol! electronics.!! The! initial!version!of! I²C! ran!at!a! 100! kHz!
bitrate!an d!faster!bitrate!versions!were!adder!later.!!To!this! day,!the!400! kHz!version! is!the!most!widely!
used!and!the!primary! communication!protocol!for!sensors.!!I²C!uses!two!bidirectional!open- drain!signal!
lines,!o n e !data!line!(S D A )!and!one!clock!lin e !(SCL). !!The!I²C!bus!is!designed!for!one!or!multiple!masters!
and! one! or! m ore! slaves! (see! Figure! 2).! ! Slave! device s! can! be! individually! a d dr es se d ! by! a! 7 -bit! (most!
common)! or!10-bit!addressing!scheme.!!Th e!master!generates!the!clock!and!initiates!the!communication!
with!the!slave(s).! !However,!an!I²C!slave! cannot!initiate!communication!and!this!is !a!majo r!sho rtc om ing !
that!the!MIPI!I3C!standard!has!resolved!with!in-band!interrupts.!!!
I2C$MAIN$
MASTER
INE RTI AL$
SENSOR
SLAVE
HUMIDITY$
SENSO R
SLAVE
SDA
SCL
ALTIMETER
SLAVE
!!! !
Figure&2:!I²C!sample!schematic!with!one!master!and!three!slaves,!inertial!sensor,!hu midity!sen s o r,!
pressure!sensor!and!a!microcontroller!(µC)!(left)!and!sam p le!tim ing !dia gra m !(righ t).!!!
S!=!Start,!B1!to!Bn!are!bits!and!P!=!Stop.!!Image!(right)!from!Wikipedia.!!
(https://en.wikipedia.org/wiki/I%C2%B2C)!
SPI! or! serial!peripheral!interface! is! a! synchronous! digital! commun ication! interface! for! sho rt! distances!
and!primarily!used!in!embedded!system s.!!The!standard!was!invented!by!Motorola! and!first!introduced!
as!an!external!microcontroller!bus!in!1979.!!The!SPI!bus!includes!four!logic!signals,!serial!clock!(SCLK),!
master! out/slave! in! (MOSI),! master! in/slave! out! (MISO)!and! slave! select! (SS).!!The! clock! polarity! and!
phase! can! be! programmatically! configured! to! fo u r! different! SPI! m o d es ! (i.e.! 0,! 1,! 2! an d! 3).! ! Figu re ! 3!
displays!an!SPI!implementation!with! three ! sla ves!(left),!the!four! SP I! m od es ! (m idd le)! and! a! corresponding!
sample!timing!plot!for!the!respective !four!SPI!m o de s!(right).!!Alternative!naming!conventions!is!widely!
Introduction!to!the!MIPI!I3C!!
Standardized!Sensor!Interface
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Copyright!2016!MIPI!Alliance,!Inc.!!All!rights!reserved.! ! 6!
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used!for!these! signals,!but!the! functionality!is !the!sam e .!!Contrary!to! the!addressing!schemes!for! the!I²C!
and!MIPI!I3C!stand ards,!the!S PI!master!uses!the! dedicated! slave!select!(SS)!line!to!address!each!slave!
individua lly .! ! The! two! extra!lines!required!for! SPI!puts!it!at!a! disadvantage! com p are d! to ! the! tw o-wire!
I²C/MIPI!I3C!interf ac es ! in! app lica tio n s ! wh er e! rea l-estate!is!precious!and!wh ere!the! master!has!limited!
digital!output!channels!for!multiple!SS!signals.!!The!SPI!interface!is!push-pull!(as!opposed!to!I2C!being!
open!drain)!and!supports!high-speed!bitrates!up!to !1 00!MHz.!!There!is!no!limitation!for!the!num ber!of!
bits! per! transfer! (as! opposed! to! I ²C! that! transmits! 8! bits! per! cycle)! and! it! allows! streaming! of! larger!
amounts!of!data.!!SPI!is!con sidered!lower!power!than!I²C!since!it!requires!less!supporting!circuitry!an d!
eliminates!the!pull-up!resistors!used!for!I²C.!!!!!!!!!!!!
!!!! !!!!! &&
Figure&3:!SPI!bus!single!master!and!three!slaves!(left),!SPI!modes!(middle)!and!sample!timing/mode!
diagram!(right).!!Image s !fro m!Wikip e dia .!
(https://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus)!
Both!SPI!and!I²C!are!legacy!interfaces!that!have!failed!to!evolve! along!with!the! m arket!need s!for! low er-
power,!increased!flexibility!and!interfac e!standard iza tio n !for!sensor!ap p lication s .!!Th ey!are!widely!u sed!
and! accepted! across! many! applications! in! m any! industrie s.! ! While ! it! would ! be! tem p tin g ! to! develo p ! a!
completely! new,! revolutionary! digital! commun ication! interface,! the! evolutionary! MIPI! I3C! interf ac e!
allows! co-existence!between!I²C!and!MIPI!I3C!devices.!!This! enables! a!gradua l!migration!to!MIPI!I3C!and!
does!not!require!an!immediate!upgrade!of!existing!products!(i.e.!sensors)!from!I²C!to!MIPI!I3C.!!The!MIPI!
I3C!inter fa ce !strives!to! re-use,!build!upon!and! im prove! I²C!fo r!easy!system! integration! while!maintaining!
backward!compatibility.!!!
The!main!focus!for! th e! M IPI! I3C !s tan da rd! has!been!to!unify!a!fragmented!interface!industry!by!defining!a!
standard!that!is!low!cost!(i.e.!takes!up!very!little!circuit!real-estate!on!the!sensor!side),!high-speed!and!
that! use s! as! little! powe r! as! p oss ible.! ! The! MIPI! I3C! standard! provides! immediate ! bene fit s! for! existing!
sensor! system s! and! there! are! a lso! provisions! in! anticipation! for! future! mobile! and! other! system!
architectures.!!The! first! MIPI! I3C! compliant! IP! blocks! were! announced! in! April! 2016! with! immediate!
availability.! ! These!IP! blocks! can! be! dropped! directly! into! new! IC! designs! to! add! th e! MIPI! I3C! sensor!
interface .!!This!solution!supports!all!MIPI!I3C!data!rates!up!to!33.3!Mbps,!dynamic!address!allocation!and!
multi-master!operations.!!It!is!also !co mp liant!with!the!M IPI!Camera!Control!Interface!(CCI)!and!backward!
compatible!with!I²C.!!Th e ! ide a !is!m ea nt!for!developers!to!future!proo f!th eir!d esign s!fo r!le g ac y! I²C!devices!
while!utilizing!the!new!functionalities!that!the!MIPI!I3C!standard!offers.!!Table!2!com pares! and ! con trasts!
MIPI!I3C,!I²C!and!SPI.!
Introduction!to!the!MIPI!I3C!!
Standardized!Sensor!Interface
! !
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Copyright!2016!MIPI!Alliance,!Inc.!!All!rights!reserved.! ! 7!
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Parameter!
MIPI!I3C!
(Improved!Inte r!Int eg ra te d! Circuits)!!
I²C!!
(Inter!Integrated!C irc uits )!
SPI!!
(Serial!Periphera l!Inte rfa ce )!
Overview!
I3C$MAIN$
MASTER
I3C$
SLAVE
I3C$
SECONDARY$
MASTER
SDA
SCL
I2C$
SLAVE
!
I2C$MAIN$
MASTER
I2C$
SLAVE
I2C$
SLAVE
SDA
SCL
I2C$
SLAVE
SLAVE_INT
SLAVE_INT
!
!
SPI
MASTER
SCLK
MOSI
MISO
SS1
SS2
SPI/
SLAVE
SPI/
SLAVE
SLAVE_INT
SLAVE_INT
!
Number!!
of!Lines!
2-wire!
2-wire!(plus!separate!wires!for!each!
required!interrupt!signal )!
4-wire!(plus!separate!wires!for!each!
required!interrupt!signal )!
Effective! Data!
Bitrate!
33.3!Mbps!max!at!12.5!MHz!
(Typically:!10.6!Mbps!at!12!MHz!!
SDR)!
3!Mbps!max!at!3.4!MHz!(Hs)!
0.8!Mbps!max!at!1!MHz!(Fm+)!
0.35!Mbps!max!at!400!KHz!(Fm)!
Approx.!60!Mbps!max!at!60!MHz!for!
conventional!implementations!
(Typically:!10!Mbps!at!10!MHz)!
Advantages!
• Only!two!signal!lines!!
• Legacy!I²C!devices!co-exist!on!the!
same!bus!(with!some!limitations)!
• Dynamic!addressing!and!supports!
static!addressing!for!legacy!I²C!
devices!
• I²C-like!d ata!rate!messaging!(SDR)!
• Optional!high!data!rate!messaging!
modes!(HDR)!
• Multi-drop!capab ility!and!dynamic!
addressing!avoids!collisions!
• Multi-master!capability!
• In-band!Interrupt!support!
• Hot-join!support!
• A!clear!master!ownership!and!
handover!mechanism!is!defined!
• In-band!integrated!commands!
(CCC)!Support!
• Only!two!signal!lines!
• Flexible!data!transmission!rates!
• Each!device!on!the!bus!is!
independe n tly!a d dr es sa b le!
• Devices!have!a!simple!master/slave!
relationship!
• Simple!implementation!
• Widely!adopted!in!sensor!
applications!and!beyond!
• Supports!multi-master!and!multi-
drop!capability!features!
• Full!duplex!communication!
• Push-pull!drivers!
• Good!signal!integrity!and!high!speed!
below!20MHz!(higher!speed!are!
challenging)!
• Higher!throughput!than!I²C!and!
SMBus!
• Not!limited!to!8-bit!words!
• Arbitrary!choice!of!message!size,!
content!and!purpose!
• Simple!hardware!interfacing!
• Lower!power!than!I²C!
• No!arbitration!or!associated!failure!
modes!
• Slaves!use!the!master's!clock!
• Slaves!do!not!need!a!unique!address!
• Not!limited!by!a!standard!to!any!
maximum!clock!speed!(can!vary!
between!SPI!devices)!
Disadvantages!
• Only!7-bits!are!available!for!device!
addressing!
• Slower!than!SPI!(i.e.!20Mbps)!
• New!standard,!adoption!needs!to!
be!proven!
• Limited!number!of!devices!on!a!
bus!to!around!a!dozen!devices!!
!
• Only!7-bits!(or!10-bits)!are!available!
for!static!device!addressing!
• Limited!communication!speed!rates!
and!many!devices!do!not!support!the!
higher!speeds!
• Slaves!can!hang!the!bus;!will!require!
system!restart!
• Slower!devices!can!delay!the!
operation!of!faster!speed!devices!
• Uses!more!power!than!SPI!
• Limited!number!of!devices!on!a!bus!
to!around!a!dozen!d evice s!
• No!clear!master!ownership!and!
handover!mechanism.!
• Requires!separate!support!signals!for!
interrupts!
• Need!more!pins!than!I²C/MIPI!I3C!
• Need!dedicated!pin!per!slave!for!
slave!select!(SS)!
• No!in-band!addressing!
• No!slave!hardware!flow!control!!
• No!hardware!slave!acknowledgment!
• Supports!only!one!master!device!
• No!error-checking!protocol!is!
defined!
• No!formal!standard,!validatin g!
conformance!is!not!possible!
• SPI!does!not!support!hot!swapping!
• Requires!separate!support!signals!
for!interrupts!
Table&2:!Comparison!between!digital!communication!interfaces:!MIPI!I3C,!I²C!and!SPI.! !
Introduction!to!the!MIPI!I3C!!
Standardized!Sensor!Interface
! !
!
Copyright!2016!MIPI!Alliance,!Inc.!!All!rights!reserved.! ! 8!
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MIPI!I3C!Protocol!and!System!Integration!
The!MIPI!I3C!interface ! provides!several!comm un ication! protocols!including!an!I²C!like!single!data!rate!
(SDR)!messaging!mode!run n ing!up!to!1 2.5!MHz! and! several!high!data!rate!(HD R )!messaging!modes!that!
are!not!I² C!compatible.!!Both!the!SDR!and!HDR!form at s!share!a!two-wire!interface!with!a!bidirectional!
data!pin!(traditionally!SD A)!and!one!pin!either!used! as!a!clock!pin!(SCL!on!SDR!and!HDR-DDR!protocols)!
or! as! a! bidirectional! data! pin! (on! HDR-TSL! and! HDR- TSP! protocols).! ! The! I²C! compatible! SDR! format!
supports!a!mix!of!various!message!types!like!standard!I²C!messages,!broadcast!and!CCC!m essages!that!
allow! the! master! to! communicate! to! all! devices! on! the! bus! and ! slave! initiated! requests! (e.g.! in-band!
interrupt s!or!re q u e st s!to!assume! the! master! role).!!The! SDR!mode!is!more! flexible!than! I²C! and!allows!a!
secondary!master!a nd!a!mix!of!I²C!and!MIPI! I3C!slaves.!!I²C!slaves!m ust!be !a cco m m od ate d!by!standard !
I²C! data! rate! speeds! and! comm unication! protocol! initiated! by! a! start-bit! followed! by! a! 7-bit! slave!
address.!!In!other!words,!the!MIPI!I3C!SDR!mode!cou ld!be!operated!exactly!like!an!I²C!bus.!!All!devices!
on! th e!bus! must!be! upgraded!to!MIPI!I3C!to!be !able!to!take! full!advantage!of!the!MIPI!I3C!interface !like!
the!HDR!m od es,!t h o u g h .!
The!high!speed!MIPI! I3C!modes!support!speeds!beyond!the!12.5!Mbps!base!SDR!mode.!!There!are!two!
main!HDR!modes,!HDR-DDR!(double!data!rate)!and!HDR-TSL/TSP!(ternary!symbol).!!These!modes!offer!
bitrates! over! 33! Mbps! at! a! fraction! of! the! per! bit! power! of! I²C! (400! kHz,! fast! mode).! ! Slave-side!
implementatio n !is!sim p le !an d !th is!m ode!can!coexist!with!legacy!I²C! devices.!! In! practice,!this!means! that!
HDR-DDR!can!be!used!to!communicate!with!MIPI!I3C!slaves!while!allowing!I²C!devices!to!be!on!the!same!
bus! and! communicate! w ith! these! using! legacy! I²C! in te rfa ce .! ! The! I²C! devices! are! expected! to! simp ly!
ignore!the!high!speed!MIPI!I3C!HDR!transmissions.!!The!HDR-DDR!mode!uses!the!SCL!signal!as!a!clock!
with!data!bits!being!clo ck ed !on!bot h !SCL!edg es !(I²C! and!MIPI!I3C!SD R!m odes!cha nge!SDA! on ly!when!SCL!
is!low).!! HDR-DDR!moves!data!by!“words”,!w hich!contain!tw o ! pream ble !bits,!1 6 ! pa yl o a d ! bits! an d ! two!
parity! bits.! ! There! are! four! word! types! defined:! command! word,! user! data! word,! cyclic-redun da ncy -
check! (CRC)! word! and! reserved! word.!!The! different! word! types! have! specific! functions,! like! the!
command!word!tha t!indic at es!the!direction!of!data!m ove m en t!either!as!write!(m aste r!to!slave)!or!read!
(slave!to!master).!!Th e!HDR-TSL/TSP!enab les!ternary!(i.e.!base!three! numerals!codes)! sym b ol!coding!for!
pure!MIPI!I3C!implem e nt a tio n ! (TSP )!and!I²C-legacy! inclus ive ! (TSL )! syste ms.!! HDR-TSL!is!using!both!SCL!
and!SDA!as!data!lines,!where!at!leas t!one!line!m u st !transition !each!period.!!Trans itio n !indices!are!u se d !
for!encoding !binary!into!ternary!symbols!transfer!to!enab le!high !spe ed !transm issio n!at!ve ry!low !po w er.!
A!major!challenge!for!sm artp ho ne s,!wea ra b le s !and!other!systems!is!to !integra te !multiple !senso rs!that!
are! using! different! comm unication! protocols.!!Similar! sensors! from ! various! vendors! have! been!
notoriously!inconsistent!in!specifying!sensor!performance!and!com munication!inte rfa c e.!!Back!in!2013,!
Intel,! Q u a lc o mm! a n d ! MS IG! pio n e e re d ! a! sensor! performance! standard! for! mobile! devices! called! the!
“Standardized!sensor!pe rformance!parameter!definitions”
4
.!!Th is!later!became!the!IEEE!2700!standard.!!
Similarly!there!is!a!need!to!standardize!how!microcontrollers!and!application!processors!communicate!
with!sensors!in!a!system.!!!Currently,!each!sensor!has!its!own!set!of!functions!and !co mman d !st ru ct ur e .!!It!
would!be!highly!beneficial!to!have!a!unified!“sensor!link”!th at!would!use!a!con sistent!implementatio n!
for!all!types!of!sensors.!!As!an!example,!a!“Read!Pressure”!command!for!a!barometric!pressure!sensor!
would! return! a! 16-bit! pressure! result! independent! of! its! vendor.! ! This! sensor! link! could! allow! pre-
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
4
!“Standardized!sensor!performance!parameter!definitions”,!MEMS!Industry!Group,!May!2014!http://www.memsindustrygroup.org/default.asp?page=SPD!!
Introduction!to!the!MIPI!I3C!!
Standardized!Sensor!Interface
! !
!
Copyright!2016!MIPI!Alliance,!Inc.!!All!rights!reserved.! ! 9!
!
compiled!libraries!that!would! greatly!simplify!software!development!for!th e!tran sfer!layer!be tw ee n!the!
master!and!slaves!on!the!MIPI!I3C!bus.!
Case!Study!|!MIPI!I3C!for!smartphones!
The! many! sensors! packed! into! modern! smartphones! are! enabling! advanced! features! like! activity!
recognition ,!pe d e st rian !navigation,! health! and!fitness!tracking!capabilities!and! others.!!Sm artphones!are!
employing!sensor!fusion!and!algorithms!to!recognize!the!difference !be tw een !w alkin g!an d !driving ,!or!to!
make!clever!power!saving!schemes! like !sw it ch in g !off !the !Wi-Fi! if! the!phone!has! been!idle !fo r!a !pe rio d !of !
time.! ! As! the! trend! for! adding! more! sensors! continues,! the! implementa tion ! is! quickly! becoming!
unmanageable.!!High-end!smartphones!already!have!10!sensors!or!more,!and!can!require!up!to!20 !signal!
lines.!!Add itio n a l!sensors !will!requ ire!additional!logic!lines!and!increase!the!overall!power!consumption.!!
Then!there!are! the! always-on! features!that!enable!constant!monitoring!of!sen so r!function s!even!whe n!a!
device! is! in! idle! mode.! ! A! smartphone! located! in! the! u ser’s! pocke t! or! p urse! will!continue!to! run! the !
pedometer!mode!for!step!counting,!along!with!other!activity!recognition!features.!!The!fact!that!some!
sensors!are!alw ays!active!and!that!sensor!data!is!always!being!transferred!between!devices,!require s!a!
very! low! power! communication! interface.!!Both! I²C! and! SPI! are! typically! used! to! support! multiple!
sensors,!but!they!bo th!have!d rawb acks!for!sensor!interconnections.!!Neither!o f!them!hav e!a!metho d!to!
notify!the!m aster!about!a!change!in!state!or!to!initiate!a!sensor!data!transfer.!!These!notifications!are!
currently!being!p erformed! by!external!general!purpose!input!and!output!(GPIO)!signals.!!MIPI!I3C!can!
replace! b oth ! I²C! and! SPI! with! a! more! power! efficient! two-wire! in te rfa c e.!!The! MIPI!I3C! standa rdized!
sensor!interface!will!eliminate!or!reduce!the!need!for!external!GPIOs!and!substitute!these !with!in-band!
interrupt s.!!The!resu lt!is!a!simp ler !and !mo re !flexib le !imp le m e n ta tio n .!!Table!3!lists! a!number!of!sensors!
and!other!devices!that!are!being!targeted!by!the!MIPI!I3C!interface .!
!
Table&3:!Partial!list!of!sen so rs !and!other!functions!ta rgete d!b y!the!MIPI!I3C!interface.!
Case!Study!|!MIPI!I3C!for!wearables!
Wearables!are!characteristically!small!and!have!severe!power!limitations.!!It!would!be!hig h ly !d e sira b le !to!
replace! the! commonly! used! I²C! bus! with! a! more! pow er! efficient! and! flexible! interface.! ! Similar! to!
smartphones,!the! MIPI!I3C!could!replace! digital!con trol!signals!for! senso rs!w ith!in-band!interrupts.!!This!
would!save!space!on!densely!populated! printed!circuit!boards!(PCBs).!!The!images!in!Figure!4!display!a!
Introduction!to!the!MIPI!I3C!!
Standardized!Sensor!Interface
! !
!
Copyright!2016!MIPI!Alliance,!Inc.!!All!rights!reserved.! ! 10!
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simple!wearable!that!on ly!con tains !one !sen sor,!an !acc elero m ete r.!!The!w earable’s!electronic!module!is!
shown!to!scale!(middle)!along!with!the!P CB !that!is!moun ted !inside!the!electro nic!modu le!(right).!!There!
is!not !a!lot!of!room!on !this!PC B!for!componen ts!and!traces ,!nor!is !there!much !space!for!a!battery !inside!
the!housing.!!Needless!to! say,!the! ability!to!both! save! real!estate!and!reduce!pow er! are!two! very! critical!
aspects!for!developing!new!and!better!performing!wearables.!!
! ! !
Figure&4:!Simple!activity!tracker!Fitbit!Flex,!product!(left),!electronic!module!(middle)!and!PCB!assembly!
with!the!accelerometer!marked!with!a!yellow!square!(right).!!Images!fr o m !UserLib!
(http://www.userlib.com/fitbit-flex-manual-tutorial/)!and!iFixit!
(https://www.ifixit.com/Teardown/Fitbit+Flex+Teardown/16050).!
Case!Study!|!MIPI!I3C!for!IoT!devices!
Internet!of!Things!(IoT)!devices!are!making!everyday!items!like!h omes!and!cars!smarter!to!improve!o u r!
daily!lives.!!This!would!not!be!possible!without!the!use!of!sensors!to!gather!and!analyze!data!from!the!
world! around!us.!!Figure!5!shows!a!typical!system!w ith!tw o !typ es!o f!sen sor!h ub s!tha t!interfa ce!d irectly!
to!a!ran ge! o f!se ns ors.!!The!sensor!hubs! act!as!the!master!and!control!the!commun ication!at!all!times,!for!
both! I2C! and! SPI.!!In! this! system,! MIPI! I3C! can ! replace! all! other! communication! inte rfa ce s! with! two!
wires.!!It!will!allow!slave!devices!to!initiate!commun ication !w ith!sim ple!in - band!interrupt!requests.!!!
!!!!!! !
Figure&5:!Two!common!types!of!sensor!hub!architectures!for!mobile,!wearables!and!IoT!devices;!
application!processor!with!sensor!hub!(left)!and!externa l!sen so r!hub !(righ t).!! !
Introduction!to!the!MIPI!I3C!!
Standardized!Sensor!Interface
! !
!
Copyright!2016!MIPI!Alliance,!Inc.!!All!rights!reserved.! ! 11!
!
Summary!
The!MIPI!I3C!standardized!sensor!interface! is!a!game!changer!for!integrated!sensor!systems.!! It!has! built!
a! superset! of! features! on! top! of! the! existing! I²C! (t w o -wire)! interface! with! additional! high! data! rate!
modes! th at! can! satisfy! sensor! use! cases! that! currently! require! an! SPI! bus! (four-wire).! ! MIPI!I3C! is! an!
evolutionary!standard! th at!c om b ine s!the !adv an tage !of!I²C!and! SPI!while!adding!new!features!such!as!in-
band! interrupts,! dyn am ic! addressing! and! advanced! power! management.!!It! is! de fin e d ! to! main t ain !
backward!compatibility!with!I²C!and!offers!drastically!lower!cost,!lower!p ow e r!and !better!scalability!than!
I²C,!SPI,!U A R T !a n d! o t h e r!d i git a l!in t e rfa c e s.!!Sensor!usage!in !m o d er n!s m a rt ph o n e s!th a t!cu rrently!requires!
up! to! 20! signal! lines! includin g ! int er ru pt s ,! ca n! now! be! replaced! by! two.! ! This! is! a! major! shift! in!
streamlining!sensor!integration ,!which!we!expect!to!drive!cost!efficiencies!and!standardize!a!fragmented!
industry .! !MIPI!I3C!has!clear!advantages!in!mobile!and!consumer!electronics!like!smartphones,!tablets!
and! w earables.! ! It! is! also! practical! for! other! use! cases! that! em ploy! sensors,! like! IoT! devices! and!
applications!for!medical,!industrial,!automotive!and!others.!!With!a!widespread! adoption,!MIPI!I3C!has!
great!potential!and!could!extend!to!other!non-sensor!devices!such!as!touch!sensing,!always-on,!and!low-
resolution! c ameras! (higher! res o lu tio n ! cameras! and! displa y s! are! cover ed ! by! other! MIPI! Alliance!
interface s).!!If!th is!h a pp e n s,!MIPI!I3C!could!truly!be!a!standard!for!the!futu re.!!!!!
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Contact!Information:!
Melanie!Cole!(melanie.cole@mipi.org)!
Manager,!Integrated!Marketin g !& !Memb e rs h ip !!
MIPI!Alliance!(www.mipi.org)!
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MIPI!is!a!registered!service!mark!of!MIPI!Alliance.!All!other!MIPI!specification!names!are!service!marks!of!
MIPI!Alliance.!!Third!party!marks!are!the!property!of!their!respective!owners.!
