ese370: circuit-level modeling, design, and …ese370/fall2019/handouts/lec...ese370: circuit-level...
TRANSCRIPT
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ESE370: Circuit-Level Modeling, Design, and Optimization for Digital Systems
Lec 15: October 7, 2019 Energy and Power Basics
Penn ESE 370 Fall 2019 - Khanna
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Previously
! Where capacitance arises " Device materials
! What drives delay " Equivalent drive resistance and load capacitance
! Optimize delay " τ-estimate " Transistor sizing " Fanin/fanout " Drive in stages
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Today
! Power Sources " Static power " Switching power
" Dynamic switching power " Short circuit power
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Power
! P = I×V
! Tricky part: " Understanding I " (pairing with correct V)
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Inverter Current Simplification
Penn ESE 370 Fall 2019 - Khanna 5
! What is Ipwr,gnd? " 0V " 140mV " 400mV " 500mV " 600mV " 860mV " 1V
" From preclass – see next two slides
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Preclass (1/2)
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Preclass (2/2)
Penn ESE 370 Fall 2019 - Khanna 7
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Inverter Current Simplification
! What is Ipwr,gnd? " 0V " 140mV " 400mV " 500mV " 600mV " 860mV " 1V
Penn ESE 370 Fall 2019 - Khanna 8
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Understanding Currents
Static Power
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Operating Modes
! Steady-State: What modes are the transistors in? " Vin=Vdd
" Vin=Gnd
! What current flows in steady state?
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Operating Modes
! Steady-State: Vin=Vdd
" PMOS: subthreshold " NMOS: resistive
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Operating Modes
! Steady-State: Vin=Vdd
" PMOS: subthreshold " NMOS: resistive
12
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Penn ESE 370 Fall 2019 - Khanna
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Operating Modes
! Steady-State: Vin=Vdd
" PMOS: subthreshold " NMOS: resistive
13
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IDSp = −IS#WL
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Which current determines Istatic ?
Penn ESE 370 Fall 2019 - Khanna
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Operating Modes
! Steady-State: Vin=Vdd
" PMOS: subthreshold " NMOS: resistive
14
€
IDSp = −IS#WL
$
% &
'
( ) e
−VGS −VTnkT / q
$
% &
'
( )
1− eVDSkT / q$
% &
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( )
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( ) ) 1− λVDS( )
IDSn = µnCOXWL
!
"#
$
%& VGS −VT( )VDS −
VDS2
2(
)*
+
,-
Which current determines Istatic ?
Penn ESE 370 Fall 2019 - Khanna
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Static Power
! P = I×V ! What V should we use?
" Where is the static current flowing?
15 Penn ESE 370 Fall 2019 - Khanna
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Data Dependent?
! How does the binary value of the input impact Istatic?
16 Penn ESE 370 Fall 2018 - Khanna
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Data Dependent?
! How does the binary value of input impact Istatic?
17
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Penn ESE 370 Fall 2018 - Khanna
Out
1
2
1
2
1
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A
B
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Data Dependent Leakage Current
Penn ESE 370 Fall 2018 - Khanna 18
ACM Great Lakes Symposium on VLSI Stresa, I. (n.d.). Analysis of data dependence of leakage current in CMOS cryptographic hardware. In GLSVLSI ’07 proceedings of the 2007 ACM Great Lakes Symposium
on VLSI : Stresa - Lago Maggiore, Italy, March 11-13, 2007 /. New York, N.Y. :: Association for Computing Machinery. https://doi.org/10.1145/1228784.1228808
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Understanding Currents
Dynamic Switching Currents
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Power: During Switching
! P = IV ! Input switch: 1#0 ! Where does I go?
" Vin=Gnd
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Power: During Switching
! P = IV ! Input switch: 1#0 ! Where does I go?
" Vin=Gnd
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Power: During Switching
! P = IV ! Input switch: 1#0 ! Where does I go?
" Vin=Gnd
22
Subtheshold Leakage
Idyn (Saturation/Linear)
Penn ESE 370 Fall 2019 - Khanna
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Power: During Switching
! P = IV ! Input switch 0#1 ! Where does I go?
" Vin=Vdd
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Power: During Switching
! P = IV ! Input switch 0#1 ! Where does I go?
" Vin=Vdd
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Power: During Switching
! P = IV ! Input switch 0#1 ! Where does I go?
" Vin=Vdd
25
Subtheshold Leakage
Idyn (Saturation/Linear)
Penn ESE 370 Fall 2019 - Khanna
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Switching Currents
! Dynamic current flow:
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Understanding Currents
Short Circuit Currents
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Power: During Switching
! P = IV ! Where does I go?
" Vin=Vdd/2 " And Vdd>Vthn+|Vthp|
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Power: During Switching
! P = IV ! Where does I go?
" Vin=Vdd/2 " And Vdd>Vthn+|Vthp|
29
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1
Vou
t
Vin
CMOS Inverter DC Transfer
Linear/Saturation
Penn ESE 370 Fall 2019 - Khanna
Linear/Saturation
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Switching Currents
! Dynamic current flow:
! If both transistor on: " Current path from Vdd
to Gnd " Short circuit current
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Currents Summary
! Current (I) changes over time ! At least two components
" Istatic – no switching " Iswitch – when switching
" Idyn and Isc
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Currents Summary
! Current (I) changes over time ! At least two components
" Istatic – no switching " Iswitch – when switching
" Idyn and Isc
32
VRAMP
CLK
φ
ramp_enable
Penn ESE 370 Fall 2019 - Khanna
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Switching
Dynamic Power
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Switching Currents
! Itotal(t) = Istatic(t)+Iswitch(t)
! Iswitch(t) = Isc(t) + Idyn(t)
34
Isc
Istatic
Idyn
Penn ESE 370 Fall 2019 - Khanna
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Charging
! Idyn(t) – why is it changing? " Ids = f(Vds,Vgs) " and Vgs, Vds changing
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Penn ESE 370 Fall 2019 - Khanna
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Switching Energy – focus on Idyn(t)
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Isc
Istatic
Idyn
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Switching Energy – focus on Idyn(t)
E = P(t)dt∫= I(t)Vdd dt∫=Vdd I(t)dt∫
37
Idyn
Penn ESE 370 Fall 2019 - Khanna
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Switching Energy
38
! Do we know what this is?
Idyn
Idyn (t)dt∫
E = P(t)dt∫= I(t)Vdd dt∫=Vdd I(t)dt∫
Penn ESE 370 Fall 2019 - Khanna
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Switching Energy
39
! Do we know what this is?
Idyn
E = P(t)dt∫= I(t)Vdd dt∫=Vdd I(t)dt∫
Penn ESE 370 Fall 2019 - Khanna
Q = Idyn (t)dt∫
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Switching Energy
40
! Do we know what this is?
! What is Q? Idyn
E = P(t)dt∫= I(t)Vdd dt∫=Vdd I(t)dt∫
Penn ESE 370 Fall 2019 - Khanna
Q = Idyn (t)dt∫
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Switching Energy
41
! Do we know what this is?
! What is Q? Idyn
E = P(t)dt∫= I(t)Vdd dt∫=Vdd I(t)dt∫
Penn ESE 370 Fall 2019 - Khanna
Q = Idyn (t)dt∫=CV
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Switching Energy
42
! Do we know what this is?
! What is Q? Idyn
E = P(t)dt∫= I(t)Vdd dt∫=Vdd I(t)dt∫
Penn ESE 370 Fall 2019 - Khanna
Q = Idyn (t)dt∫=CV
€
E = CVdd2
Capacitor charging energy
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Switching Power
! Every time output switches 0#1 pay: " E = CV2
! Pdyn = (# 0#1 trans) × CV2 / time
! # 0#1 trans = ½ # of transitions
! Pdyn = (# trans) × ½CV2 / time
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Data Dependent Activity
! Consider an 8b counter " How often do each of the following switch?
" Low bit? " High bit?
! Assuming random inputs " Activity at output of nand2? " Activity at output of xor2?
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Gate Output Switching (random inputs)
45
0
1
P(outi!=outi+1)=P(outi=0)*P(outi+1=1)+P(outi=1)*P(outi+1=0)
i i+1
Output states
Probablity of output switch of nand4? Probablity of output switch of xor4?
Penn ESE 370 Fall 2018 - Khanna
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Charging Power
! Pdyn = (# trans) × ½CV2 / time ! Often like to think about switching frequency ! Useful to consider per clock cycle
" Frequency f = 1/clock-period = clock-cycles/time
! Pdyn = (#trans/clock-cycle) ½CV2 f
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Charging Power
! Pdyn = (#0#1 trans) × CV2 / time ! Often like to think about switching frequency ! Useful to consider per clock cycle
" Frequency f = 1/clock-period = clock-cycles/time
! Pdyn = (#0#1 trans/clock-cycle) CV2 f
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Dynamic Power
! Pdyn = (#0#1 trans/clock-cycle) CV2 f ! Let a = activity factor
a = average #tran0#1/clock a = probability of #tran0#1
! Pdyn = aCV2 f
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Activity Factor
! Let a = activity factor " a = average #tran0#1/clock " a = probability of #tran0#1
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a = p(outi = 0)p(outi+1 =1)
a = N0
2NN12N
=N0 (2
N − N0 )22N
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Switching
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Short Circuit Power
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Short Circuit Power
! Between VTN and Vdd - VTP
" Both N and P devices conducting
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Short Circuit Power
! Between VTN and Vdd - VTP
" Both N and P devices conducting
! Roughly:
52
Isc
Penn ESE 370 Fall 2019 - Khanna
Vin
time
Vout
Isdp
time
time
time
Vthn
Vdd
Vdd
Vdd-Vthp
Isc
tsc tsc
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Peak Current
! Ipeak around Vdd/2 " If |VTN|=|VTP| and sized equal rise/fall
53
€
IDS ≈νsatCOXW VGS −VT −VDSAT
2%
& '
(
) *
Penn ESE 370 Fall 2019 - Khanna
Vin
time
Vout
Isdp
time
time
time
Vthn
Vdd
Vdd
Vdd-Vthp
Isc
tsc tsc
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Peak Current
! Ipeak around Vdd/2 " If |VTN|=|VTP| and sized equal rise/fall
54
€
IDS ≈νsatCOXW VGS −VT −VDSAT
2%
& '
(
) *
€
I(t)dt∫ ≈ Ipeak × tsc ×12%
& ' (
) *
Penn ESE 370 Fall 2019 - Khanna
Vin
time
Vout
Isdp
time
time
time
Vthn
Vdd
Vdd
Vdd-Vthp
Isc
tsc tsc
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Vin
time
Vout
Isdp
time
time
time
Vthn
Vdd
Vdd
Vdd-Vthp
Isc
tsc tsc
Peak Current
! Ipeak around Vdd/2 " If |VTN|=|VTP| and sized equal rise/fall
55
€
IDS ≈νsatCOXW VGS −VT −VDSAT
2%
& '
(
) *
€
I(t)dt∫ ≈ Ipeak × tsc ×12%
& ' (
) *
€
E =Vdd × Ipeak × tsc ×12#
$ % &
' (
Penn ESE 370 Fall 2019 - Khanna
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Short Circuit Energy
! Make it look like switching an equivalent capacitance, CSC
" Q=I×t " Q=CV
56
E =Vdd × I peak × tsc ×12"
#$%
&'
"
#$
%
&'
E =Vdd ×QSC
E =Vdd × (CSCVdd ) =CSCV2dd
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Short Circuit Energy
! Make it look like switching an equivalent capacitance, CSC
" Q=I×t " Q=CV
57
E =Vdd × I peak × tsc ×12"
#$%
&'
"
#$
%
&'
E =Vdd ×QSC
E =Vdd × (CSCVdd ) =CSCV2dd
Penn ESE 370 Fall 2019 - Khanna
CSC =I peaktsc2Vdd
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Short Circuit Energy
! Every time switch (0#1 and 1#0) " Also dissipate short-circuit energy: E = CscV2
" Ccs “fake” capacitance (for accounting)
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Total Power
! Ptot = Pstatic + Psc + Pdyn
! Pdyn + Psc = aCloadV2f+2aCscV2f
! Ptot ≈ a(Cload+2Csc)V2f+VI’s(W/L)e-Vt/(nkT/q)
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Switching Waveforms
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Switching Waveforms
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Switching Waveforms
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Switching Waveforms
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Switching Waveforms
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Ideas
! Three components of power " Static " Dynamic " Short-circuit
! Ptot = Pstatic + Pdyn+ Psc
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Admin
! HW6 due Friday
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