ECE194J /594J notes, M. Rodwell, copyrihted 2011 Mixed-Sinal IC Desin Notes set 1: Quick Summary of Device Models Mark Rodwell University of California, Santa Barbara rodwell@ece.ucsb.edu 805-893-3244, 805-893-3262 fax
Backround / Review ECE194J /594J notes, M. Rodwell, copyrihted 2011 This material was covered in ECE145A Quickly review key information. Transistor models Interconnect models 2 - port parameters If reater detail is required, please refer to the ECE145a online notes.
Transmission Lines ECE194J /594J notes, M. Rodwell, copyrihted 2011
Transmission Lines for On-Wafer Wirin ECE194J /594J notes, M. Rodwell, copyrihted 2011 microstrip line eometry voltaes currents W +V I H 0V I characteristic impedance : whereη 377Ω and 0 propaation velocity : v = where c is the speed of liht. Z o c ε r η 0 ε r H H + W These are approximate relationships : learn how to use ADS
ECE194J /594J notes, M. Rodwell, copyrihted 2011 Transmission Lines: Waves, Voltae, Current Z s Ldz V en Cdz Z L V ( z, t) = V V I( z, t) = where Z o = and v = 1/ + + ( t ( t Z z / v) o + V z / v) V ( t ( t + Z L / C characteristic impedance LC propaation velocity + z / v) forward and reverse wave voltaes o z / v) forward and reverse wave currents
Reflections ECE194J /594J notes, M. Rodwell, copyrihted 2011 Z s V en Z L At end of V At beinnin of line : V + and = ΓV T s l = ΓV s = + line : where Γ Z + T V o Z + o s Z en s l = where ( Zl Zo ) ( Z Z ) l Γ s o = 1 + 1 load reflection coefficient ( Zs Zo ) ( Z Z ) source transmission coefficient s o 1 source reflection coefficient + 1
Pulse Reflections on Transmission Lines ECE194J /594J notes, M. Rodwell, copyrihted 2011
Relatin Lumped and Distributed Circuits ECE194J /594J notes, M. Rodwell, copyrihted 2011 L = Z τ, = τ Z 0 C / 0 Approximate model L /( R L + R ) << ( R R ) C s nelect inductor RC circuit charin. L s
ECE194J /594J notes, M. Rodwell, copyrihted 2011 Short Tramission Lines Can Be Modeled as L's and C's L = Z τ, = τ Z 0 C / 0 Hih - Z0 line : lare L, small C. approximately an inductor Low - Z 0 line : lare C, small L. approximately a capacitor.
Skin effect loss ECE194J /594J notes, M. Rodwell, copyrihted 2011 W H ~W +2H Current penetrates the conductor by one skin depth δ = ωµσ / 2 where σ is the conductivity. Line has added series resistance per unit lenth 1 (1 + j) Z surface =, where P is the effective current P δσ - carryin periphery.
ECE194J /594J notes, M. Rodwell, copyrihted 2011 packae resonance and roundin
What is Ground Bounce? ECE194J /594J notes, M. Rodwell, copyrihted 2011 input buffer ADC diital sections L round round bounce noise V in round return currents "Ground" simply means a reference potential shared between many circuit paths. To the extent that it has nonzero impedance, circuits will couple in unexpected ways RFI, resonance, oscillation, frequently result from poor round systems
ECE194J /594J notes, M. Rodwell, copyrihted 2011 Ground Bounce on an IC: break in a round plane sinal line sinal line line 1 round round line 2 round plane common-lead inductance couplin / EMI due to poor round system interity is common in hih-frequency systems whether on PC boards...or on ICs.
ECE194J /594J notes, M. Rodwell, copyrihted 2011 Ground Bounce: IC Packain with Top-Surface-Only Ground Peripheral roundin allows parallel plate mode resonance die dimensions must be <0.4mm at 100GHz Bond wire inductance aravates the effect: resonates with throuh-wafer capacitance at 5-20 GHz peripheral bond inductances IC: parallel-plane transmission line peripheral bond inductances
ECE194J /594J notes, M. Rodwell, copyrihted 2011 power-supply resonance
Power Supply Resonance ECE194J /594J notes, M. Rodwell, copyrihted 2011 f = 1/ 2π L bond C on
ECE194J /594J notes, M. Rodwell, copyrihted 2011 Power Supply Resonances; Power Supply Dampin 80 power supply impedance, Ohms 70 60 50 40 30 20 10 0 0 20 40 60 80 100 Frequency (GHz) 90 GHz--local resonance between power supply capacitance and supply lead inductance ~N*5GHz resonances--lobal standin wave on power supply bus Power supply is certain to resonate: we must model, simulate, and add damplin durin desin.
Standard cell showin power buses ECE194J /594J notes, M. Rodwell, copyrihted 2011
ECE194J /594J notes, M. Rodwell, copyrihted 2011 Interconnects: Summary, Desin Stratey
IC Interconnects -- Thin-Film Microstrip ECE194J /594J notes, M. Rodwell, copyrihted 2011 narrow line spacin IC density no substrate radiation, no substrate losses fewer breaks in round plane than CPW... but round breaks at device placements still have problem with packae roundin InP mm-wave PA (Rockwell)...need to flip-chip bond W thin dielectrics narrow lines hih line losses low current capability no hih-z o lines Z ~ ε η1/ o o 2 r H W + H H
IC Interconnects -- Inverted Thin-Film Microstrip ECE194J /594J notes, M. Rodwell, copyrihted 2011 narrow line spacin IC density Some substrate radiation / substrate losses No breaks in round plane... no round breaks at device placements still have problem with packae roundin InP 150 GHz master-slave latch...need to flip-chip bond thin dielectrics narrow lines hih line losses low current capability no hih-z o lines InP 8 GHz clock rate delta-sima ADC
ECE194J /594J notes, M. Rodwell, copyrihted 2011 VLSI Interconnects with Ground Interity & Controlled Z o narrow line spacin IC density no substrate radiation, no substrate losses neliible breaks in round plane neliible round breaks @ device placements still have problem with packae roundin...need to flip-chip bond thin dielectrics narrow lines hih line losses low current capability no hih-z o lines
ECE194J /594J notes, M. Rodwell, copyrihted 2011 No clean round return? interconnects can't be modeled! 35 GHz static divider interconnects have no clear local round return interconnect inductance is non-local interconnect inductance has no compact model 8 GHz clock-rate delta-sima ADC thin-film microstrip wirin every interconnect can be modeled as microstrip some interconnects are terminated in their Zo some interconnects are not terminated...but ALL are precisely modeled InP 8 GHz clock rate delta-sima ADC
ECE194J /594J notes, M. Rodwell, copyrihted 2011 Active Devices: Bipolar Transistors
HBT Physical Structure ECE194J /594J notes, M. Rodwell, copyrihted 2011
Physical structure, symbolic ECE194J /594J notes, M. Rodwell, copyrihted 2011 Device Stripe Lenth = LE perpendicular to drawin W eb W e W b,cont emitter contact EB rade base BC rade base contact emitter base contact collector N- drift collector collector contact T b N+ sub collector W under T c semi-insulatin InP substrate W c
Bipolar Transistor: DC characteristics: common-emitter ECE194J /594J notes, M. Rodwell, copyrihted 2011 I c, I b (A) 10-2 10-4 10-6 10-8 10-10 I c I b ma/µm 2 20 15 10 5 V ce, sat J max I = β c I b 10-12 0 0.25 0.5 0.75 1 V be (V) 0 0 1 2 3 4 V ce HBTs have a maximum operatin current density This is set by : Kirk effect, J max Maximum power density.. V br,ceo More information in desin project documentation.
HBT hybrid-pi equivalent-circuit model ECE194J /594J notes, M. Rodwell, copyrihted 2011 C = qi R = β / τ be mo f m = = τ b mo mo c / + τ exp( nkt c jωτ c ) B R bb C cbx C cbi R c C R be V be m V be e -jωτ c C be,diff = m τ f C je R ex E Given N ( C ) je, Ccbi, Ccbx vary in proportion to N finerle, ( R, R, R, I ) vary in proportion to1/ N L. bb ex finer c HBT finers of emitter lenth L c, max finer E E :
ECE194J /594J notes, M. Rodwell, copyrihted 2011 Active Devices: MOSFETs
MOSFETS ECE194J /594J notes, M. Rodwell, copyrihted 2011 Cross-Section Layout (multi-finer) ate oxide ate metal (silicide) N+ poly ate dielectric sidewall W G S D S D S D S source contact (silicide) drain contact (silicide) G N+ source N+ drain P substrate ate dielectric inversion layer P substrate N+ polysilicon ate
MOSFET DC Characteristics ECE194J /594J notes, M. Rodwell, copyrihted 2011 I D I d mobility-limited increasin V GS velocity-limited V DS V th For drain voltaes larer than the knee voltae : V s mobility limited current 2 I c W ( V V ) / 2L D, µ = µ ox s velocity limited current I = c W v ( V th V D, v ox sat s th ) Generalized Expression I I D D, v 2 I + I D D, µ = 1
Knee Voltae: Mobility-Limited Case ECE194J /594J notes, M. Rodwell, copyrihted 2011 The knee voltae defines the boundary between I D Ohmic constant-current the Ohmicand constant - current reions increasin V GS In the mobility - limited reime, the knee in curve occurs when V d = V ds V s = V th V GD =V th V DS The Knee Voltae is further increased by voltae drops across the parasitic source & drain resistances. V GD =V th I D R D I D R S
Knee Voltae: Velocity-Limited Case ECE194J /594J notes, M. Rodwell, copyrihted 2011 In the velocity - limited reime, occurs when V = v ds sat L / µ the knee in curve V DS =v sat L /µ Aain, the Knee Voltae is further increased by voltae drops across the parasitic source & drain resistances. I D R D V DS =v sat L /µ I D R S
MOSFET Transconductance mobility limited I D, µ = µ c m = ox W I V D GS ( V s = µ c V ox th W ) 2 ( V / 2L s V th ) / L I d V ECE194J /594J notes, M. Rodwell, copyrihted 2011 V th V s mobility-limited velocity limited I D, v = m c = ox W v I V D GS sat ( V = c s ox V W v th ) sat m V velocity-limited V th V s
ECE194J /594J notes, M. Rodwell, copyrihted 2011 Linear vs. Square-Law Characteristics: 90 nm
90 nm MOSFET DC Characteristics ECE194J /594J notes, M. Rodwell, copyrihted 2011 N - channel V m th / W = c ox v sat = 0.6 V 1/ λ ~ 3V = 1.4 ms/μm = 1.4 S / mm P - channel m V th / W = = c ox v sat = 0.7 ms/μm 0.6 V 1/ λ ~ 3V = 0.7 S / mm
Device Structure and Model ECE194J /594J notes, M. Rodwell, copyrihted 2011 G S D S D S D S G R R i C d m V s G ds R d D W C s V s C db G C sb R s S N C C G R m s d ds i = # ate finers, W = ate width ε ~ v T eq eq NW NW ~ 1/ m eff ε ~ L T ε ( NW ) or µ ( NW )( V V ) ( NW ) T eq R R R C C d s sb db 1/ NW NW NW s ~ ρ s W 12L N 1/ NW + th Rend 2N G Increase f max usin - short ate finers R R i C s - amplesubstrate contacts C d V s R s S m V s C sb G ds D C db
Oversimplified Model ECE194J /594J notes, M. Rodwell, copyrihted 2011 For rouh hand analysis, etc C G R mx sx dsx in ~ 1+ ~ R s m m C ~ 1+ s G ~ 1+ m ds m + R R s R R s s + R i G R R i C s C d V s R s S m V s C sb G ds D C db G R in C d mx V s G dsx D Approximate cutoff frequencies 1/ 2πf f max τ ~ 2 ~ C s ( R / s m + R + C d f + R ) G i / τ m ds + ( R s + 2πR + R C d d ) C d C sx V s C sb C db S
End ECE194J /594J notes, M. Rodwell, copyrihted 2011