trends and perspectives in deep-submicron ic design bram nauta mesa + research institute university...
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Trends and Perspectives in deep-submicron IC design
Bram Nauta
MESA+ Research InstituteUniversity of Twente,
Enschede, The Netherlands
University of Twente IWORID 2002
Outline
• IC Technology trends
• Analog v.s. digital circuits
• How to design circuits in new technologies?
• Conclusion
IC Technology Trends
4004
8086
80286
80386
80486 P5(Pentium)
P6(Pentium Pro)
Pentium IIMerced
Doubling every 1.9 year
2.75 year
Moore’s Law Number of Transistors 80x86 Processors
The ”ITRS" Roadmap
98 2000 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 201299 2001
Advanced research (materials, architecture,..)
180
(nm)
150
130
100
200 300
300
300
300
400450
400450
Volume Production
Integration/Pilot
Basic steps/Modules
Volume Production
Volume Production
Volume Production
Basic steps/Modules 70
50
30
Precompetitive
today
Supply Voltage: Vdd
0.0
0.5
1.0
1.5
2.0
2.5
3.0
250 180 130 90 60 40 30
Technology Node (nm)
Su
pp
ly V
olt
ag
e (
V)
Minimum Maximum
Why Low Voltage?• Low power digital• No breakdown
today 2012
Threshold voltage: VT
Vdd
Vss
Ion Ioff
0 VT VDD
large Ion
small Ioff
ON OFF
Id
Vgs
VT dilemma
• Sub-threshold leakage becomes problem– low Idd during standby & test -> high VT
– fast switching -> low VT
• dual VT
• Triple well (tune VT with voltage)
Transistor speed: cut-off frequencylog [Id/Ig]
Frequencyovgg
mt CC
gf
2
1
ft is about the intrinsic transistor, not interconnectft is a measure for the speed of (analog) circuits
IdIg
0
ft
cut-off frequency
Example 30 nm Devices [Intel]
30 nm physical gate length 0.8 nm conventional SiO2(N)
mass production in 2009
Interconnect: > 6 metal layers
[Intel]
Transistor gate length 70 nm Metal-1 width 180 nm
Analog v.s. Digital Circuits
Power dissipation for analog processing
C
Vdd
0V t
Vsignal
Vpp
1/f
Idd
Vsignal
[vittoz]
N
SfTk
V
VP
pp
dd ....8min
[Vittoz, ISCAS 1990]
independent of technology
Power dissipation for digital processing
•1 bit extra -> 6dB more S/N
•operations/sec ~ n2. fsig
t
Vsignal
2n
1/f
P 300 fsig
10 SN-------
è øç ÷æ ö
log 1.76–
6-----------------------------------------------------------
è øç ÷ç ÷ç ÷ç ÷ç ÷æ ö2
Etr =
S/N in dB
depends on technology
[Vittoz, ISCAS 1990]
Energy per transition:
2
2
1ddwiretr VCE
Vdd
Idd
Cwire
Etr=10pJ for 4um 5V CMOSEtr=1pJ for 1um 3V CMOS (1990)Etr=0.1pJ for 0.18um 1.8V CMOS (2000)????? ????? (2020)
downscaling lowers digital dissipation
Signal/Noise [dB]
Pow
er d
issi
patio
n
analog
digital
IC Technology scaling
• Optimized for digital – digital = main chip area
– minimize Etr
– minimize cost per transistor
• Analog “has to live with this”– It cannot die
How to design circuits in new technologies?
Analog
• High voltage options for I/O & EEPROM– “old” transistors available in new technology
• Use the low VT – needed for digital speed anyway
• “non ideal” device behavior – gate leakage, non square law, – no real problem, better models needed
• Nominal Vdd drops – no stacking
psrr, cmrr, noise
Change analog circuits
Vdd=Vgs + Vds
Analog
• matching of MOSFETS– becomes better for same W.L
– new technology: VT drops linear with Vdd
• 1/f noise– tends to increase for minimum size MOS
f
N
ft ft ft
1/f noise Reduction: switched bias technique
Constant Bias
n-MOSFET
VON
VT
What about the Low-Frequency noise ?
VOFF
Switched Bias [Periodically switching the MOSFET “off”]
LF noise spectrum(constant DC gate bias)
Expected noise spectrum of switched bias [6 dB below] (for 50% duty cycle)
Nois
e P
ow
er(
dB
)
Frequency(log scale)Switching frequency
Measured noise spectrum of switched bias [>>6dB below](for 50% duty cycle)
1/f noise Reduction: switched bias technique
analog RF: passives components
• Inductors– many metal layers + high ohmic substrate – high Q possible
top view
analog RF: passives components
• C: use fringe caps!
cross section view
Switched opamp technique
Vsig+Vgs > Vdd
Vsig Vsig
Vgs
[Peluso, JSSC, july 97]
Vdd Vdd
Analog: strategy• Exploit the speed:
– feedback @ high frequencies– noise canceling– dynamic element matching– sigma delta AD converters @ high frequencies
• Use digital for analog– always digital on the chip– use this for: calibration, digital filtering
Digital
• transistor switching speed = no issue
• low voltage but still too high power !!!
• leakage -> dual VT
– but which VT where?
• how to manage complexity? – 100M transistors
• interconnect is speed bottleneck
interconnect 1980
substrate
interconnect 1995
substrate
interconnect 2005
substrate
Digital / interconnect
• bottleneck = wires– repeaters, synchronizers– globally asynchronous &
locally synchronous
• use analog for digital– 3D microwave techniques – “nano modems” ( more than just 1 and 0)
High-voltage digital I/O
• “high voltage” by design:
5.5V I/O in 2.5V technology ! [Annema, JSSSC,March 2001]
substrate bounce
substrate
Lbondwire
ground
Vdd
substrate bounce
substrate
Lbondwire
ground
Vdd
substrate bounce
substrate
Lbondwire
ground
Vdd
substrate bounce
• Even 100% digital chip has problems
• Decouple supply in digital ( 30% area!)– locally!
• Use package with low inductance
• Make very robust analog designs
Conclusion
conclusions
• Technology scaling > 10 years
• Scaling of analog and digital circuits fundamentally different
• problems can be solved by design
• Digital for analog and analog for digital
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