After Tech. Mapping
0
10
20
30
40
50
60
70
80
Pow
er(m
W),
Rat
io
h=26
h=3 h=310
h=4 h=5 h=315
h=4 h=5 h=520
h=6 h=7 h=8
Fanin, Height
K 1=3, k 2=3
SIS+LEVEL MAPSIS+OURS+LEVEL MAPImprovement Ratio
7. Circuit Level Design
Buffer Chain• Delay analysis of buffer chain • Delay analysis considering parasitic
capacitance,Cp
input
stage 1 stage 1stage (i- 1) stage i stage n
s ize 1 size s ize i- 2 size i- 1 s ize n- 1
C in C ini- 1C in iC in C in=nC in
)/ln()( , 72.2)(
0)()ln(
)/ln()ln(
)/ln(
)(
)/( )/(
0
1 100
1
inLoptimumoptimum
d
inLd
inL
inn
L
n
k
n
kdd
kk
CCne
T
CCtT
CCn
CC
tntktT
LWLW
) : (typical 10~21
11) (
) (
21
1
1
2
122
1
e
Eff
CCfVPP
CCfVfVCP
CCC
nn
n
nn
kpinddkT
pini
ddddkk
pk
ink
k
Ck,Pk: stage k buffer output 의 total capacitance, power
PT: buffer chain 의 power consumption
Pn: load capacitance CL 의 power consumption
Eff: power efficiency pn/pT
Slew Rate• Determining rise/fall time
P eriod Ttr tf
t1 t3t2
V in
Vdd+Vtp
Imax
Imean
V tn
Ishort
fr
tddddmeanSC
ttntpp
t
ttin
t
tshort
t
t
t
tshortshortmean
tt
fVVVIP
VVV
dtVVT
dttIT
dttIdttIT
I
where,
)2(2
, where,
)(2
4
)(4
)()(2
3
n
22
1
2
1
2
1
3
2
Slew Rate(Cont’d)• Power consumption of Short circuit current in Oscillation Circuit
Vdd
Vdd
Vo
V i
Vdd
Vdd
Vo
V i
VoV i
Pass Transistor Logic• Reducing Area/Power
– Macro cell(Large part in chip area) XOR/XNOR/MUX(Primitive) Pass Tr. Logic
– Not using charge/discharge scheme Appropriate in Low Power Logic
• Pass Tr logic Family– CPL (Complementary Pass
Transistor Logic)– DPL (Dual Pass Transistor Logic)– SRPL (Swing Restored Pass
Transistor Logic)
• CPL– Basic Scheme
– Inverter Buffering
A
ABAB
B
ABB
B
A
ABAB
B
B
ABB
VddVdd
p- M OS Latch
Pass Transistor Logic(Cont’d)• DPL
– Pass Tr Network + Dual p-MOS– Enables rail-to-rail swing– Characteristics
• Increasing input capacitance(delay)
• Increasing driving ability for existing 2 ON-path
• equals CPL in input loading capacitance
• SRPL– Pass Tr network + Cross
coupled inverter– Restoring logic level– Inverter size must not be too
big
AB
B
A
B
AA B
A
B
AB
n-M O S C P Lnetw ork
Dynamic Logic• Using Precharge/Evaluation scheme• Family
– Domino logic– NORA(NO RAce) logic
• Characteristics– Decreasing input loading
capacitance– Power consumption in precharge
clock– Increasing useless switching in
precharging period
• Basic architecture of Domino logic
A
B
clk
C in C L
A
P1
N1
NLogic Blockc lk
B
A
precharge evaluation
Input Pin Ordering• Reorder the equivalent inputs to a
transistor based on critical path delays and power consumption
• N- input Primitive CMOS logic– symmetrical in function level– antisymmetrical in Tr level
• capacitance of output stage• body effect
• Scheme– The signal that has many transition
must be far from output– If it is hard to estimate switching
frequency, we must determine pin ordering considering path and path delay balance from primary input to input of Tr.
• Example of N-input CMOS logic
A
D
C L
C
B
C 3
C 1
C 2
Experimentd with gate array of TIFor a 4-input NAND gate in TI’s BiCMOS gate array library (with a load of 13 inverters), the delay varies by 20% while power dissipation by 10% between a good and bad ordering
INPUT PIN Reordering
CL
A B C D
C
A
B
D
CB
CC
CD
VDD
MPA MPB MPC
MPD
MNA
MNB
MNC
MND
1 1
1 1
1 1
1 1
1
1
1
1
(a) (b) (c) (d)
Simulation result ( tcycle=50ns, tf/tr=1ns)
: A 가 critical input 인 경우 =38.4uW,
D 가 critical input 인 경우 =47.2uW
Sensitization• Example
• Definition– sensitization : input signal that
forces output transition event– sensitization vector : the other
inputs if one signal is sensitized
X1
X3
X2
),,,1,,,( ),,,0,,,(
][ ][
11
11
10
nili
nili
XXi
XXXXfXXXXf
ffXY
ii
32332
101
][ ][ 11
XXXXX
ffXY
XX
321 )( XXXY
Sensitization(Cont’d)• Considering Sensitization in
Combinational logic:Remove unnecessary transitions in the C.L
• Considering Sensitization in Sequential logic: Also reduces the power consumption in the flip-flops.C om binationa l
LogicXn
E
QY
C om binationa lLog ic
X1
Xn
E
Q Y
C om binationa lLogic
X1
Xn
E
Q Y
Com binationalLogic
Q YD Q
D Q
c lk
X1
Xn
D Q
D Q
E
TTL-Compatible• TTL level signal CMOS
input• Characteristic Curve of CMOS
Inverter
Vdd= 3.3V
Vdd= 3.3V
Vo
V i
1.4V
V IL= 0.8V V IH= 2.0V Vdd= 3.3VV i
Vo Ileak= avg(Id1, Id2)
IDTTL1 IDTTL2
Vdd
V in
TTL INP U T
padinput compatible TTL ofnumber : e wher)( 21
TTL
DTTLDTTLddTTLTTL
NIIVNP
TTL Compatible(Cont’d)• CMOS output signal TTL input
– Because of sink current IOL,
CMOS gets a large amount of heat
– Increased chip operating temperature
– Power consumption of whole system
C hip B oundary C hip B oundary
Input Pad
O utput Pad
VOL
IO L
INPUT PIN Reordering◈ To reduce the power dissipation one should place the
input with low transition density near the ground end.
(a) If MNA turns off , only CL needs to be charged (b) If MND turns off , all CL, CB, CC and CD needs to be charged (c) If the critical input is rising and placed near output node, the initial charge of CB, CC and CD are zero and the delay time of CL discharging is less than (d) (d) If the critical input is rising and placed near ground end, the charge of CB, CC and CD must dischagge before the charge of CL discharge to zero
저전력 Booth Multiplier 설계
성균관대학교전기전자컴퓨터공학부
김 진 혁 , 이 준 성 , 조 준 동
Modified Booth 곱셈기
R ecoded D ig it O peration on X
0 : Add 0 to the partia l p roduct
+1 : Add X to the partia l product
+2 : Sh ift le ft X one position and add it
to the partia l p roduct
-1 : Add two ’s com plem ent o f X to the
partia l product
-2 : Take two ’s com plem ent of X and
shift le ft one position
Y 2i+1 Y 2i Y 2I-1 R ecoded O peration D igit on X
0 0 0 0 0X 0 0 1 +1 +1X 0 1 0 +1 +1X 0 1 1 +2 +2X 1 0 0 -2 -2X 1 0 1 -1 -1X 1 1 0 -1 -1X 1 1 1 0 0X
• Multibit Recoding 을 사용하여 부분합의 갯수를 1/2 로 줄여 고속의 곱셈을 가능하게 한다 . • 피승수 (multiplicand) : X , 승수 (multiplier) : Y
Recoded digit = Y2i-1 + Y2i -2Y2i+1 ( Y-1=0 )
< Generation and operation of recoded digit >
Modified Booth 곱셈기 - 예
• Example
10010101 = X01101001 = Y
1111111110010101000000110101100000011010111100101010
1101010000011101 = P ( - 11235)
(- 107)(+105) Operation B its recoded
+ 1- 2- 1+ 2
010100101011sign
extension
Wallace Tree - 4:2 CompressorX 7Y 7
X 0Y 0
..............
.............. : Zero: B it jum ping leve l: partia l p roduct: b it generated by
com pressor
1st s tage
2nd stage
Tw o sum m ands tobe added
(a)
4*8 P artia l P roduct genera to rs
8 4-2 com pressors
4*8 P artia l P roduct genera to rs
8 4-2 com pressors
16-b it adder
11 4 -2 com pressors
1st s tage(b lock A )
1st s tage(b lock B )
2nd stage(b lock C )
X3 , X2 , X1 , X0
X7 , X6 , X5 , X4
8
4
4Y
P0P15
(b)
Multipliers - Area
• 16-bit Multiplier Area
Multipliertype
Area(mm2) Gate count
Array 4.2 2,378
Wallace 8.1 2,544
Modified booth 8.5 3,375
Multiplier - Delay
• Average Power Dissipation (16-bit)
Multipliertype
Power(mW) Logictransitions
Array 43.5 7,224
Wallace 32.0 3,793
Modified booth 41.3 3,993
Multiplier - Power
• Worst-Case Delay (16-bit)
Multipliertype
Delay(ns) Gatedelays
Array 92.6 50
Wallace 54.1 35
Modified booth 45.4 32
Instruction Level Power Analysis
• Estimate power dissipation of instruction sequences and power dissipation of a program
• Eb : base cost of individual instructions
Es : circuit state change effects
• EM : the overall energy cost of a program
Bi : the base cost of type i instruction
Ni : the number of type i instruction
Oi,j : the cost occurred when a type i instruction is followed by
a type j instruction Ni,j : the number of occurrences when a type i instruction is
immediately followed by a type j instruction
E B Nb i i E O Ns i j i j , ,
E E EM b s
Instruction ordering
• Develop a technique of operand swapping• Recoding weight : necessary operation cost of operands
• Wtotal : total recoding weight of input operand
Wi : weight of individual recoded digit i in Booth Multiplier
Wb : base weight of an instruction
Winter : inter-operation weight of instructions
• Therefore, if an operand has lower Wtotal , put it in the second
input(multiplier).
W Wtotal ii
W W Wi b er int
RESULT
Circuit State Effects[pJ]when switchedInstruction
NameBasecost[pJ]
LOAD ADD 2’scomplement
SHIFT
LOAD 1.46 0.18 1.20 1.08 0.73
ADD 0.86 0.31 0.49 0.61
2’scomplement
0.77 0.27 0.34
SHIFT 0.29 0.15
< 4 by 4 multiplier >
Circuit State Effects[pJ]when switchedInstruction
NameBasecost[pJ]
LOAD ADD 2’scomplement
SHIFT
LOAD 3.25 0.40 2.67 2.38 1.63
ADD 1.91 0.58 1.11 1.44
2’scomplement
1.72 0.55 0.78
SHIFT 0.65 0.38
< 8 by 8 multiplier >Circuit State Effects[pJ]
when switchedInstructionName
Basecost[pJ]
LOAD ADD 2’scomplement
SHIFT
LOAD 4.81 0.59 3.96 3.57 2.40
ADD 2.83 1.02 1.63 2.12
2’scomplement
2.55 1.00 1.14
SHIFT 0.96 0.78
< 12 by 12 multiplier >
Conclusion
02468
1012
4bit
8bit
12bi
tav
erag
e
0
5
10
15
20
25
30
35
4bit
8bit
12bi
t
circuitstateseffects notconsideredcircuitstateseffe c t sconsidered
Power[pJ]
bits bits
% of instances with circuit states effects
4.0% reduction
12.0% reduction
9.0% reduction
8. Layout Level Design
• Constant scaled wire increases coupling capacitance by S and wire resistance
by S• Supply Voltage by 1/S, Theshold Voltage by 1/S, Current Drive by 1/S• Gate Capaitance by 1/S, Gate Delay by 1/S• Global Interconnection Delay, RC load+para by S• Interconnect Delay: 50-70% of Clock Cycle• Area: 1/S2
• Power dissipation by 1/S - 1/S2
• ( P = nCVdd2f, where nC is the sum of capacitance times #transitions)
• SIA (Semiconductor Industry Association): On 2007, physical limitation: 0.1 m
20 billion transistors, 10 sqare centimeters, 12 or 16 inch wafer
Device Scaling of Factor of S
Delay Variations at Low-Voltage
• At high supply voltage, the delay increases with temperature (mobility is decreasing with temperature) while at very low supply voltages the delay decreases with temperature (VT is decreasing with temperature).
• At low supply voltages, the delay ratio between large and minimum transistor widths W increases in several factors.
• Delay balancing of clock trees based on wire snaking in order to avoid clock-skew. In this case, at low supply voltages, slightly VT variations can significantly modify the delay balancing.
Quarter Micron Challenge• Computers/peripherals (SOC): 1996 ($50 Billion) 1999 ($70 Billion)• Wiring dominates delay: wire R comparable to gate driver R; wire/wire coupling
C > C to ground• Push beyond 0.07 micron• Quest for area(past), speed-speed (now), power-power-power(future)• Accelerated increases of clock frequencies• Signal integrity-based tools• Design styles (chip + packages)• System-level design(system partitioning)• Synthesis with multiple constraints (power,area,timing)• Partitioning/MCM• Increasing speed limits complicate clock and power distribution• Design bounded by wires, vias, via resistance, coupling• Reverse scaling: adding area/spacing as needed: widening, thickening of wires,
metal shielding & noise avoidance - adding metal
CLOCK POWER CONSUMPTION
•Clock power consumption is as large as the logic power; Clock Signal carrying the heaviest load and switching at high frequency, clock distribution is a major source of power dissipation.• In a microprocessor, 18% of the total power is consumed by clocking• Clock distribution is designed as a hierarchical clock tree, according to the decomposition principle.
Power Consumption per block in typical microprocessor
Crosstalk
Solution for Clock Skew• Dynamic Effects on Skew
Capacitance Coupling• Supply Voltage Deviation (Clock
driver and receiver voltage difference)
• Capacitance deviation by circuit operation
• Global and local temperature• Layout Issues: clocks routed first• Must aware of all sources of delay• Increased spacing• Wider wires• Insert buffers• Specialized clock need net
matching• Two approaches: Single Driver, H-
tree driver
• Gated Clocks: The local clocks that are conditionally enabled so that the registers are only clocked during the write cycles. The clock is partitioned in different blocks and each block is clocked with its own clock.
• Gating the clocks to infrequently used blocks does not provide and acceptable level of power savings
• Divide the basic clock frequency to provide the lowest clock frequency needed to different parts of the circuit
• Clock Distribution: large clock buffer waste power. Use smaller clock buffers with a well-balanced clock tree.
PowerPC Clocking Scheme
CLOCK DRIVERS IN THE DEC ALPHA 21164
DRIVER for PADS or LARGE CAPACITANCES
Off-chip power (drivers and pads) are increasing and is very difficult to reduce such a power, as the pads or drivers sizes cannot be decreased with the new technologies.
Layout-Driven Resynthesis for Lower Power
Low Power Process• Dynamic Power Dissipation
Vdd
V in Vo
C ovpC ovn
C djp
C djn
DrainW
D
C jbC jsw
)(2 ,
)(
)(
)(2
0
1
1
2
2
DWPDWA
PCACCWCC
CC
LWCC
VVI
fVCP
DD
DjswDjdj
GDov
m
jjgatein
n
ioxgate
tgsds
ddLd
Crosstalk• In deep-submicron layouts, some of the netlengths for connection between
modules can be so long that they have a resistance which is comparable to the resistance of the driver.
• Each net in the mixed analog/digital circuits is identified depending upon its crosstalk sensitivity– 1. Noisy = high impedance signal that can disturb other signals, e.g., clock
signals.– 2. High-Sensitivity = high impedance analog nets; the most noise sensitive
nets such as the input nets to operational amplifiers.– 3. Mid-Sensitivity = low/medium impedance analog nets.– 4. Low-Sensitivity = digital nets that directly affect the analog part in some
cells such as control signals.– 5. Non-Sensitivity = The most noise insensitive nets such as pure digital nets,
• The crosstalk between two interconnection wires also depends on the frequencies (i.e., signal activities) of the signals traveling on the wires. Recently, deep-submicron designs require crosstalk-free channel routing.
Power Measure in Layout• The average dynamic power consumed by a CMOS gate is given below,
where C_l is the load capacity at the output of the node, V_dd is the supply voltage, T_cycle is the global clock period, N is the number of transitions of the gate output per clock cycle, C_g is the load capacity due to input capacitance of fanout gates, and C_w is the load capacity due to the interconnection tree formed between the driver and its fanout gates.
• Pav = (0.5 Vdd2) / (Tcycle Cl N) = (0.5 Vdd
2) / (Tcycle (Cg + Cw )N)• Logic synthesis for low power attempts to minimize SUMi Cgi Ni
• Physical design for low power tries to minimize SUMi Cwi Ni
• . Here Cwi consists of Cxi + CsI, where Cxi is the capacitance of net i due to its crosstalk, and CsI is the substrate capacitance of net i. For low power layout applications, power dissipation due to crosstalk is minimized by ensuring that wires carrying high activity signals are placed sufficiently far from the other wires. Similarly, power dissipation due to substrate capacitance is proportional to the wirelength and its signal activity.
이중 전압을 이용한 저전력 레이아웃 설계
성균관대학교전기전자컴퓨터공학부
김 진 혁 , 이 준 성 , 조 준 동
목 차• 연구목적• 연구배경• Clustered Voltage Scaling 구조• Row by Row Power Supply 구조• Mix-And-Match Power Supply 구조• Level Converter 구조• Mix-And-Match Power Supply 설계흐름• 실험결과• 결론
연 구 목 적 및 배경• 조합회로의 전력 소모량을 줄이는
이중 전압 레이아웃 기법 제안
• 이중 전압 셀을 사용할 때 , 한 cell row 에 같은 전압의 cell 이 배치되면서 증가하는 wiring 과 track 의 수를 줄임
• 최소 트랜지스터 개수를 사용하는 Level Converter 회로의 구현
• 디바이스의 성능을 유지하면서 이중 전압을 사용하는 Clustered Voltage Scaling [Usami, ’95] 을 적용
• 제안된 Mix-And-Match Power Supply 레이 아웃 구조는 기존의 Row by Row Power Supply [Usami, ’97] 레이 아웃 구조를 개선하여 전력과 면적을 줄임
Clustered Voltage Scaling• 저전력 netlist 를 생성
F/F
F/F
F/F
LC 2
G 1
G 2G 3G 4
G 5
G 6
G 7G 8
LC 1
G 11 G 9G 10
S lack(S i) = R i - A i
S 1> 0S 3> 0S 4> 0
S 5>0
S 6>0
S 9>0S 7< 0
S 10< 0
S 11< 0
S 8< 0
: VDDL
: VDDH
: Level C onverter
S 2<0
VDDHVDDL
VDDH
VDDHVDDL
standard cell
s tandard cell
module
VS SVDDH cell
VS S
VDDL
VDDL cell
standard cell
VDDH cell
VDDL cell
Row by Row Power Supply 구조
Mix-And-Match Power Supply 구조
VDDHVDDL
VDDHVDDL
standard cell
s tandard cell
module
standard cellVDDH
cellVDDL
cell
VDDH cell
VDDL cell
VDDL cellVDDH cellVS S
VDDLVDDH
VSS
VDDLVDDH
VDDH
module
VDDHVDDL
module
VDDH
VDDL
module
구 조 비 교
Conventional RRPS MAMPS Circuit
Level Converter 구조• Transistor 의 갯수 : 6 개 4 개 • 전력과 면적면에서 효과적
기 존 제 안
VS S / VDDL
Vth= 1.5V
VS S / VDDH
Vth= 2.0V
VDDHVDDH
INVDDL
VDDH
O U T
Mix-And-Match Power Supply Design Flow
Physical placem ent
Assign supply voltage to each cell
Routing
Synthesis tim ing, power and area
Single voltage netlist
Netlist with m ultiple supply voltage
Multiple voltage scaling
(O P U S )
(Aquarius XO )
(P owerM ill)
Area (% )
C onventionalc ircuit RR P S M AM P S
15% 10%
100
power (% )
C onventionalc ircuit RR P S M AM P S
47%
2%
100
실 험 결 과
전체 Power 전체 Area
결 론
• 단일 전압 회로와 비교하여 49.4% 의 Power 감소를 얻은 반면 5.6% 의 Area overhead 가 발생
• 기존의 RRPS 구조보다 10% 의 Area 감소와 2% 의 Power 감소
• 제안된 Level Converter 는 기존의 Level Converter 보다 30% 의 Area 감소와 35% 의 Power 감소
9. CAD tools
Low Power Design Tools• Transistor Level Tools (5-10% of silicon)
– SPICE, PowerMill(Epic), ADM(Avanti/Anagram), Lsim Power Analyst(mentor)• Logic Level Tools (10-15%)
– Design Power and PowerGate (Synopsys), WattWatcher/Gate (Sente), PowerSim (System Sciences), POET (Viewlogic), and QuickPower (Mentor)
• Architectural (RTL) Level Tools (20-25%)– WattWatcher/Architect (Sente): 20-25% accuracy
• Behavioral (spreadsheet) Level Tools (50-100%)– Active area of academic research
Commercial synthesis systems
Research synthesis systems A - Architectural synthesis.
L - Logic synthesis.
Low-Power CAD sites• Alternative System Concepts, Inc, : 7X power reduction throigh optimization,
contact http://www.ee.princeton.edu and Jake Karrfalt at [email protected] or (603) 437-2234. Reduction of glitch and clock power; modeling and optimization of interconnect power; power optimization for data-dominated designs with limited control flow.
• Mentor Graphics QuickPower: Hierarchical of determining overall benet of exchanging the blocks for lower power. powering down or disabling blocks when not in use by gated-clock
• choose candidates for power-down Calculate the effect of the power-down logic http://www.mentorg.com
• Synopsys's Power Compiler http://www.synopsys.com/products/power/power_ds
• Sente's WattWatcher/Architect (first commerical tool operating at the architecture level(20-25 %accuracy). http://www.powereda.com
• Behavioral Tool: Hyper-LP (Optimization), Explore (Estimation) by J. Rabaey
Design Power(Synopsys)• DesignPower(TM) provides a single, integrated environment for power
analysis in multiple phases of the design process: – Early, quick feedback at the HDL or gate level through probabilistic
analysis. – Improved accuracy through simulation-based analysis for gate level
and library exploration. • DesignPower estimates switching, internal cell and leakage power. It accepts
user-defined probabilities, simulation toggle data or a combination of both as input. DesignPower propagates switching information through sequential devices, including flip-flops and latches.
• It supports sequential, hierarchical, gated-clock, and multiple-clock designs. For simulation toggle data, it links directly to Verilog and VHDL simulators, including Synopsys' VSS.
10. References
References[1] Gary K. Yeap, "Practical Low Power Digital VLSI Design",
Kluwer Academic Publishers.[2] Jan M. Rabaey, Massoud Pedram, "Low Power Design Methodologies",
Kluwer Academic Publishers.[3] Abdellatif Bellaouar, Mohamed I. Elmasry, "Low-Power Digital VLSI Design
Circuits And Systems", Kluwer Academic Publishers.[4] Anantha P. Chandrakasan, Robert W. Brodersen, "Low Power Digital CMOS Design", Kluwer Academic Publishers.[5] Dr. Ralph Cavin, Dr. Wentai Liu, "1996 Emerging Technologies : Designing Low Power Digital Systems"[6] Muhammad S. Elrabaa, Issam S. Abu-Khater, Mohamed I. Elmasry, "Advanced Low-Power Digital Circuit Techniques", Kluwer Academic Publishers.
References• [BFKea94] R. Bechade, R. Flaker, B. Kaumann, and et. al. A 32b 66 mhz 1.8W
Microprocessor". In IEEE Int. Solid-State Circuit Conference, pages 208-209, 1994.
• [BM95] Bohr and T. Mark. Interconnect Scaling - The real limiter to high performance ULSI". In proceedings of 1995 IEEE international electron devices meeting, pages 241-242, 1995.
• [BSM94] L. Benini, P. Siegel, and G. De Micheli. Saving Power by Synthesizing Gated Clocks for Sequential Circuits". IEEE Design and Test of Computers, 11(4):32-41, 1994.
• [GH95] S. Ganguly and S. Hojat. Clock Distribution Design and Verification for PowerPC Microprocessor". In International Conference on Computer-Aided Design, page Issues in Clock Designs, 1995.
• [MGR96] R. Mehra, L. M. Guerra, and J. Rabaey. Low Power Architecture Synthesis and the Impact of Exploiting Locality". In Journal of VLSI Signal Processing,, 1996.