Using the EKV Model for LC- VCO Op8miza8on. Maria Helena Fino Pedro Pereira Faculty of Science and Technology Lisbon- Portugal

Transcription

1 Maria Helena Fino Pedro Pereira Faculty of Science and Technology Lisbon- Portugal

2 Outline Introduc8on Mo8va8on LC- VCO op8miza8on challenges Inductor op8miza8on EKV- based Varactor op8miza8on Overall Results Conclusions 2

3 Introduc8on The advent of ever shrinking transistor sizes makes imperious the use of compact models capable of accurately represen8ng the devices behavior. Compact models may be used in: Circuit simulators, such as Hspice. High accuracy is need. Obtained at the expense of higher complexity. Bsim6, BSIM- CMG, Analog blocks dedicated automa8c design tools Accuracy <- > efficiency depends on the design approach. Simula8on based op8miza8on loop Accuracy Model- based op8miza8on loops Efficiency 3

4 Mo8va8on The rapid evolu8on in telecommunica8ons systems is pushing electronic systems to specifica8ons where technology is driven to its limits. Design of LC- VCOs More stringent specifica8ons in terms of correlated characteris8cs such as phase- noise, area and power Adop8on of op8miza8on- based design methodologies. The possibility for exploring design trade- offs is usually implemented through Pareto- op8mal surfaces obtained by mul8- objec8ve op8miza8on procedures. Pareto surface genera8on process makes the simula8on- based op8miza8on methodology prohibi8ve Efficiency is obtained at the expense of using a simplified model Final Design tuning will be performed as a last design stage. 4

5 LC- VCO Design Intrinsic characteris8cs of the LC- VCO elements raise different modeling/ op8miza8on issues: Integrated Inductor Timely prohibi8ve electromagne8c simulator based op8miza8on procedure 2- π model adopted. Design variables are inherently discrete Varactor Need for using accurate ac=ve- device model- EKV Simplicity of implementa=on EKV- 2.6 Design variables are con=nuous + discrete Transconductance Amplifier Need for using accurate ac=ve- device model- EKV Simplicity of implementa=on EKV- 2.6 Design variables are inherently con=nuous 5

6 LC- VCO Design FLOW EKV2.6 f 0 = 2π 1 L tank C tank 2 g tank,max g active EKV2.6 V tank = 4 π 1 LC tank, max I bias g tank ω 1 LC tank, min * Pereira Pedro, Helena Fino et al," GADISI Gene8c Algorithms Applied to the Automa8c Design of Integrated Spiral Inductors, Doceis 2010, Url: hfp://dx.doi.org/ / _57 Implemented in Matlab Used Gene8c Algorithms tool box Adapted for discrete variable op8miza8on * Results are obtained in approximately 20 s 6

7 Inductor Design- 2Π Model * All element values are obtained with analy8cal equa8ons, based on geometrical and technological parameters. ** **P. Pereira, H. Fino et al., RF integrated inductor modeling and its applica8on to op8miza8on- based design,analog Integrated Circuits and Signal Processing, Springer Netherlands,Url: hfp://dx.doi.org/ /s x! *Y. Cao, et al., Frequency- independent equivalent- circuit model for on- chip spiral inductors, IEEE Journal of Solid- State Circuits, vol. 38, pp , Op=miza=on Goals/Challenges: Main Goals: Highest Q, Minimum Area, Frequency of opera8on far from the resonance frequency Design Variables are discrete Inherently discrete geometric Parameters( Number of turns, number of sides) Technological constraint geometric parameters ( w, s,..) 7

8 5nH Inductor UMC techn. Parameters Metal&Thickness& 2.8&µm& Space&betwwen&turns& 2.5&µm& Sheet&Resistance& 10&mΩ/square& Oxide&Thickness& 5.42&µm& Oxide& Thickness& between& 0.26&µm& spiral&and&underpass& Oxide&Permittivity&(ε r )& 4& Susbtrate&Thickness& 700&µm& Susbtrate&Permittivity&(ε r )& 11.9& Susbtrate&Resistivity& 28&Ω.cm& Op8miza8on Results Design Variables Constraints Further Op8miza8on Constraints*.2 d in d out 0.8 d in > 5w w" din" dout" L"" Q" n" Nside" L"" Q" (µm)" (µm)" (µm)" Asitic" Asitic" 9.25% 96.25% 4.5% 4% 179.5% 4.9nH& 4.6nH& 8.3& 8.8& *YJ. Aguilera, R. Berenguer, Design and Test of Integrated Inductors for RF Applica8ons, Kluwer Academic Publishers, ISBN ,

9 Inversion Mode Varactor Design EKV based Varactor Model *: Varactor Capacitance: C total = C GB + C GD + C GS + C S ( + C D )B extrinsic C GS = ( 2 3 " )C ox 1 x 2 rev + x rev + 0.5x #$ for ( n 1) n ( ) ( x rev + x for ) 2 ( ) ( x rev + x for ) 2 C GD = ( 2 3 " )C ox 1 x 2 for + x for + 0.5x #$ rev [ ] C GB = C ox "# $ % 1 C GS C ox C GD C ox C S ( = n 1 D )B ( )C GS ( D ) * J. Bremer, T. Peikert and W. Mathis, Analy8cal inversion- mode varactor modelling based on the EKV model and its applica8on to RF VCO design, Proc. of the 17 th - MIXDES, pp , % &' % &' x for ( rev ) = I F( R) " ( ) = " ln2 1+ exp V V P S D $ $ # # 2U T I F R γ n =1+ 2 V P +φ EKV 2.6 ( ) %% ' ' && 9

10 Inversion Mode Varactor Design EKV based Varactor Model: Varactor Capacitance: C total = C GB + C GD + C GS + C S ( + C D )B extrinsic ( ( ) + C of ) C extrinsic = 2 C ov ( Vg) + C if Vg C ov (V g ) is the parallel plate capacitance associated with the electric field in the gate- to- drain/ source overlap region. C if (V g ) is the inner fringing capacitance associated with the inner electric field emerging from metallurgical junc8on source/drain to the underside of the poly- gate. C of is the outer fringing capacitance, independent of the gate voltage, related to the electric field emerging from the sidewall of the poly- gate, ending at the source/drain region 10

11 Inversion Mode Varactor Design GA - Op8miza8on Goal? Quality Factor Q = 1 2π frc R = R poly/square 1 N 2 f Tuning Range W L N f W ( 4Lmin ) C TR = C max C min C max + C min 11

12 Inversion Mode Varactor Design- Op8miza8on TECHNOLOGICAL- PHYSICAL PARAMETERS AND OPTIMIZATION CONSTRAINTS A Capacitance (pf) Vg 12

13 Overall Results UMC130 technology Main Goal Phase- noise minimiza8on: { } =10log L Δ f # 1 16π 2 2 Δ L 2 tank ( 2π f 0 ) 4 ' 2 ' f V tank ' 2K B T # $ ' $ g L + g var +γ g d0,p + g d0,n ( ) % ( ( ( % &&( 13

14 Overall Results w = 9e- 6 din = e- 6 Nturns = dout = e- 004 Q = # FoM = L{ Δ f } 20 log f & 0 % $ Δ ( +10log P dc(mw) f ' ( ) 14

15 Conclusions Op8miza8on based methodology for LC- VCO was presented Design process efficiency is obtained by using a model based op8miza8on approach. Models used rely exclusively on geometrical and technological parameters gran8ng straight migra8on to new technologies Accuracy of results is granted by using 2- Pi model for the inductor EKV model for varactors and Gm- Amplifier. Design op8miza8on is perform in thee steps Integrated inductor op8miza8on Inherently discrete variable op8miza8on Inversion Mode Varactors Discrete +Con8nuous variable op8miza8on Gm- Amplifier op8miza8on Con8nuous variable op8miza8on Examples of LC- VCOs in UMC130 technologies for F=1.0GHz, 2.4GHz and 2.8GHz were presented and results against Hspice- RF simula8ons were presented 15