gervasi timing
TRANSCRIPT
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8/21/2019 Gervasi Timing
1/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
Charge Transfer Model for
Input Signaling & Referencing
!ill "ervasi
#echnology Analystw$gervasi%att&i'co$
(w$gervasi%co$cast'net)
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8/21/2019 Gervasi Timing
2/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
Agenda
* Review traditional set+p hold ti$e
* -.a$ine i$pact o/ signal slew rate
* Co$pare single ended to di//erential
* hat a&o+t non1$onotonic signals
* 3ooking to the /+t+re* Call to action
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8/21/2019 Gervasi Timing
3/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
Why a New Model?
* 4aria&le 5re6+ency syste$s e.panding 7 5i.ed /re6+ency syste$s 8+st needed a
yes9no answer on signal integrity 7 4aria&le /re6+ency syste$s need $ore:
calc+lated &ased on availa&le data eye
Availa&le operating /re6+ency ;
< (re6+ired data eye = crap)
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8/21/2019 Gervasi Timing
4/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
Traditional Input Timing Model
>N?U#
Set+p @old
C3CB
C3CB
#i$ing derating &y inp+t signal slew rate:
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8/21/2019 Gervasi Timing
5/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
!ro"lems with Traditional Model
* Hoes not acco+nt /or di//erences &etween
single ended and di//erential
* Ass+$es set+p hold re$ain &alanced* No analytical way to pro8ect derating
* No g+idance to package developers
* No $echanis$ to handle non1$onotonicsignal transitions
* 3eaves i$portant picoseconds wasted
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8/21/2019 Gervasi Timing
6/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
Charge Transfer Model #CTM$
>N?U#
Charge #rans/er #i$ing Model 7 All inp+ts have a slew rate dependent aspect t-I# and
an independent aspect t>N# 7 S+$$ing t-I# = t>N# gives inp+t transition ti$e t#
7 #ransition ti$e t# has $in and $a. val+es
7 Hi//erential inp+t transitions inherently di//erent
t>N#t-I#
t#
T h e N e w
W a y
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8/21/2019 Gervasi Timing
7/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
%actors Affecting Transition
* -.ternal /actors that are edge ratedependent 7 ?ackage parasitics 7 >np+t stage < characteristics incl+ding
inp+t type sat+ration
* >nternal /actors that are edge rate
independent 7 >nternal loading $is$atch 7 n1chip ro+ting 7 ?rocess, voltage, te$perat+re
t & ' T
t I N T
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8/21/2019 Gervasi Timing
8/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
Standards (ersus !roprietary
* C#M was developed inside J-H-C /or HHR2
* Standards re6+ire an envelope within which $+ltiple
s+ppliers specs operate, there/ore:
7 > +se 4R-5 as an acc+$+lation start threshold
7 > +se 4>3AC and 4>@AC as sat+ration thresholds
7 #hese do not represent all inp+t types, but
7 #hey do de/ine a standard way to de/ine the envelope
* ?roprietary syste$s analyses co+ld +se real
thresholds /or increased application speci/ic acc+racy
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8/21/2019 Gervasi Timing
9/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
t'T for Slow Slew Rate) Single nded) simple model
VREF
VIHAC
=
VREF
+ VSAT
VIHDC
VILDC
VILAC
=
VREF
- VSAT
t'T
slew
At
T
EXT
*2=
tINT
tT
AT * Charge
to Transition
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8/21/2019 Gervasi Timing
10/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
t'T for %ast Slew Rate) Single nded) simple model
VREF
VIHAC
=
VREF
+ VSAT
VIHDC
VILDC
VILAC
=
VREF
- VSAT
t'TtSAT
ASAT * Charge
to Saturation
AA++ * Charge
after Saturation
AT * ASAT , AA++
SAT
SAT T
SAT EXT
V
A At t
)( −+=
(SAT * Saturation
(oltage ffset
tINT
Internal factorstT
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8/21/2019 Gervasi Timing
11/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
t'T for Slow Slew Rate) +ifferential) simple model
VREF
VIHAC
=
VREF
+ VSAT
VIHDC
VILDC
VILAC
=
VREF
- VSAT
AT * Charge
to Transition
t'T tINT
tT
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8/21/2019 Gervasi Timing
12/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
t'T for %ast Slew Rate) +ifferential) simple model
VREF
VIHAC
=
VREF
+ VSAT
VIHDC
VILDC
VILAC
=
VREF
- VSAT
AT * ASAT , AA++
t'T tINTtT
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8/21/2019 Gervasi Timing
13/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
Applying CTM to Setup & -old
* Relate inp+t signals (data, address,
co$$and) to re/erence (clock, stro&e)
* Assert t#$a. and t#$in characteristics* Ass+$e inp+ts and re/erences $ay have
di//erent inp+t slew rates
* +tco$e is a $atri. o/ deratings
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8/21/2019 Gervasi Timing
14/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
CTM Setup Time +efinition
>N?U#
Set+p
C3CB
C3CB
Set+p ; t#$a. o/ inp+t 7 t#$in o/ re/erence
t#$a.
t#$in
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8/21/2019 Gervasi Timing
15/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
CTM -old Time +efinition
>N?U#
@old
C3CB
C3CB
@old ; t#$a. o/ re/erence 7 t#$in o/ inp+t
t#$in
t#$a.
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8/21/2019 Gervasi Timing
16/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
-ow does this help.?
#he Charge #rans/er Model gives a higher acc+racy /orset+p and hold relationships
>t also provides a way to acc+rately descri&e derating/or inp+t slew rate
Charge #rans/er Model gives a $ethod /or analyFing
non1$onotonic transitions
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8/21/2019 Gervasi Timing
17/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
/ample0 ++R1 Input +erating Ta"les
2'00'
0'
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8/21/2019 Gervasi Timing
18/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
+erating 2sing Charge Transfer
* Users contin+e to +se 4R-5 crossing /or single endedand crosspoint o/ di//erential pair /or $eas+re$ent
* Herating ta&les correlate $eas+re$ent to re6+iredset+p hold ti$es
* !oot1ti$eK slew rate calc+lations $ay &e needed,e'g' $od+les st+//ed and total loading
∴#he Charge #rans/er Model red+ces syste$develop$ent cost &y ena&ling $ore co$ple. ti$inganalysis
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8/21/2019 Gervasi Timing
19/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
Non3Monotonic Transitions
* 3ine re/lections in co$ple. syste$ loading or end1
+ser con/ig+ra&le syste$s ca+se shelves or ring&ack,
/or e.a$pleG
Memory
Controller
Hata &+s
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8/21/2019 Gervasi Timing
20/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
Charge Transfer Model for Non3Monotonic Transitions
VREF
VIHAC
=
VREF
+ VSAT
VIHDC
VILDC
VILAC
=
VREF
- VSAT
t'T tINT
tT
Accumulated chargereaches m(3ps needed
to trigger input
Ring"ac4 hereshould not matter
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8/21/2019 Gervasi Timing
21/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
Ring"ac4 "elow accumulation threshold
VREF
VIHAC
= VREF
+ VSAT
VIHDC
VILDC
VILAC
=
VREF
- VSAT
t'T
A5
A1
A6
Charge Accumulation *
A5 7 A1 , A6
tINT
tT
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8/21/2019 Gervasi Timing
22/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
Ne/t 8eneration Models
* CharacteriFe and co$&ine inp+t types
7 here t-I# is the sa$e and only t>N# is di//erent
* More co$ple. geo$etrical area calc+lations
* More acc+racy in acc+$+lation sat+ration points
* Non1linearities in charge acc+$+lation
* Model /or gro+nd &o+nce
* Model /or power s+pply noise
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8/21/2019 Gervasi Timing
23/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
Summary
* Charge #rans/er Model separates inp+t signalcharacteristics 7 Slew rate dependent
7 Slew rate independent
* Single ended and di//erential deratedi//erently
* Matri. derating ta&les needed to handle C#M* Non1$onotonics can &e dealt with
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8/21/2019 Gervasi Timing
24/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
Call to Action
* -.tend >!>S $odels with C#M* Need logic analysis tools /or calc+lating
charge acc+$+lation 7 Acc+$+lation threshold 7 Sat+ration threshold 7 Co$prehend set+p hold ti$ing derating
* $41ps acc+$+lation area
* 3ine +p or $ark t#($in) t#($a.)* Single ended vers+s di//erential acc+$+lation
* 3ooking ahead 7 Algorith$ic acc+$+lation $odel
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8/21/2019 Gervasi Timing
25/25
Mark Sherwood and Associates All rights reserved Copyright JANUAR
When Timing-Is-Everything …
Than4 9ou