beneath a stacked-spiral inductor - 東京工業大学...2010/09/28 matsuzawa & okada lab. a...

2010/09/28Matsuzawa& Okada Lab.Matsuzawa& Okada Lab.

A 484µm2, 21GHz LC-VCO Beneath a Stacked-Spiral Inductor

Tokyo Institute of Technology, Japan

Rui Murakami, Kenichi Okada, and Akira Matsuzawa

2010/09/28 R.Murakami, Tokyo Tech

1

Matsuzawa& Okada Lab.Matsuzawa& Okada Lab.

Contents

Background

Downsizing of LC-VCO

Circuit Stacking Beneath the Inductor

Measurement Result

Summary


2


0

0.5

1

1.5

2

1999 2004 2009 2014 2019

Scaling of Supply Voltage

ITRS2000

ITRS2009

YearAs supply voltage is scaled down, low voltage circuits are needed.

Supp

ly V

olta

ge [V

]


3


Jitter (Phase noise) of Oscillators

• Ring oscillators are more susceptible to the effect of downscaling the supply voltage.

k:Boltzmann’s constantT: Absolute temperatureω0:freq.ωoffset: Offset freq.VTH:Threshold voltageM:Number of stagesQ:Quality factor of LC-tankIbias:Bias currentγn,γp:Noise factor

• LC-VCO

• Ring-VCO

[1]

[2]

[1]A. Mazzanti, et al., JSSC 2008 [2]A. Abidi, JSSC 2006

2n

biasDD2

offset

20

LCγ1k

QIVT

ωω +

⋅⋅=L

⎭⎬⎫

⎩⎨⎧

++−

⋅⋅= 1)γ(γ2kpn

THDD

DD

biasDD2

offset

20

Ring VVVM

IVT

ωω

L


4


Problem of Clock Generator

2007 2010 2013 2016 2019 2022Year

Ring-VCO

LC-VCO31.6x

15

10

5

0

Clock

6σJi

tter/C

lock

[%]

Clo

ck [G

Hz]

15

10

5

0

Ring-VCOs must be replaced with LC-VCOs

[3]

[3] K.Okada, et al., VLSIC 2009

VDD↓


5


Comparison of Oscillators

LargeAreaVery small

SmallPower cons.@high freq.

LargeGoodNoiseBadLCRing

To replace Ring-VCO by LC-VCO

inductor

core

A very small LC-VCO is desired.

The inductor occupies the dominant area in a LC-VCO.It is needed to miniaturize the Inductor

Increasing chip area will become a problem.


6


Oscillation Frequency

A 20GHz LC-VCO results in a good balance between area and phase noise

frequencyLCπ2

1=

Poor phase noise and high power consumption.

At a higher frequency, smaller inductance is needed.VCO can be designed using a small inductor.

Over 20GHz, quality factor degradation is caused by the skin effect.


7


Stacked-spiral Inductor

Stacked-spiral inductor

Mono-layer inductor

• Single layer• Wide line width• Large diameter• Low R, High Q• Large area

• Multi layer• Narrow line width• Small diameter• High R, Low Q• Ultra low space


8


Comparison the Inductors

15µm 100µmStacked-spiral Mono-layer

15.518.64.190.51Mono-layer2.829.7651.71.16Stacked-spiral

QCL

[fF]RS

[Ohm]LS

[nH]@20GHz

RS LS

CL

Area

1/44


9


Placement of Core-circuit

Insert core-circuit under the inductor.

When the Inductor is miniaturized, the core-circuit size becomes close to the area of the inductor.

Inductive coupling is a problem.


10


Inductive Coupling

parallel line eddy current

Inductance and quality factor will be degraded by inductive coupling

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛+−+⎟

⎟⎠

⎞⎜⎜⎝

⎛++= 2

2

2

2

11ln2md

md

dm

dmmM

[4] H.M.Greenhouse, TOPHAP 1974

m

d

⎟⎟⎠

⎞⎜⎜⎝

⎛

+−=⎟

⎟⎠

⎞⎜⎜⎝

⎛

+−= 2

2

22

2

122

22

22

22

1 111

QQkL

LRLkLL

ωω

[4]


11


Reducing coupling

To reduce coupling, some layout techniques are applied.

• Slit shaping interconnections• Placing inductor trace and

interconnections orthogonally


12


Analysis of Interconnection Effects

LS 3%, Q 5%down

The model of the interconnections is created and simulated the influence on LS and Q by HFSS.

2.671.14Beneath2.821.16Normal

QLS [nH]@20GHz

BeneathNormal

It corresponds 0.4dB in FoM.


13


Chip Micrograph(1)

OutputBuffer

VCO core22µm

22µm

CMOS 65nm


14


Chip Micrograph(2)

VCO core

100µm

100µm


15


Measurement Result

21GHzFreq.

0.6VVDD

206FoMA[dBc/Hz]

65nmTech.

-89.4@1MHz-110@10MHz

PN[dBc/Hz]

1.92mWpower

consumption

⎟⎠⎞

⎜⎝⎛−⎟⎟

⎠

⎞⎜⎜⎝

⎛⎟⎠⎞

⎜⎝⎛+⎟⎟

⎠

⎞⎜⎜⎝

⎛∆

−∆−= 2DC

1mmArealog10

mW1log10log20}{ P

fffFoMA o　　 [5]

[5]Shih-An Yu, et al., IEEE TCAS-II 2009


16


Performance Summary

[6]A.Tanabe, et al., RFIC 2009 [7]I.Hwang, et al., JSSC 2004[3]K.Okada, et al., VLSIC 2009

190154173173FoM

LC

195

180

0.3

4.5GHz

-109@1MHz

0.16

290000

[3]

RingLC(3D-inductor)

+Div.LC(3D-inductor)Type

182199206FoMA

3509065Tech. [nm]

3.310.6VDD [V]

0.9GHz5GHz（20GHz/4）

21GHzFreq.

-101@600kHz-103@1MHz-110@10MHzPN

9.82.81.92Power [mW]

24002597484Area [µm2]

[7][6]This Work


17


Summary

• A very compact LC-VCO with a stacked-spiral inductor and the core-circuit being placed beneath the inductor is proposed.

• To reduce coupling, interconnections are slit shaped and orthogonalized with the coil trace.

• This VCO achieves a chip area of 484µm2

equaling ring-oscillator and FoMA of 206dBc/Hz.


18


Thank you!!

beneath a stacked-spiral inductor - 東京工業大学...2010/09/28 matsuzawa & okada lab. a...

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