Sistemi Elettronici Integrati – B25
Lumped Modeling of
Differentially Driven Symmetric
Inductors for RF IC Design
Egidio Ragonese, Angelo Scuderi, Tonio Biondi,
Alessandro Italia, and Giuseppe Palmisano
Radio Frequency Advanced Design Center (RF-ADC)
Università di Catania
Facoltà di Ingegneria
DIEES
Catania - ITALY
Riunione Annuale GE 2006
STMicroelectronics
Catania site
Ischia, 21-23 giugno 2006
Introduction

In RF ICs symmetrical inductors are profitable
exploited instead of two separate spirals
 lower area
 full electrical symmetry
 higher Q-factor and fSR

A profitable exploitation of integrated inductors
requires simple, accurate and geometrically
scalable models

Most inductor models are developed only for
single-ended spirals, while the few models for
symmetric inductors are not validated for singleended structures
Riunione Annuale GE 2006
Ischia, 21-23 giugno 2006
Modeling of integrated inductors on Si

Both single-ended and differential inductors were
fabricated using a bipolar process supplied by
ST-Microelectronics
Turn number from 1 to 5.5, inner diameter from 50 to 150 µm
and metal width from 6 to 20 mm
Riunione Annuale GE 2006
Ischia, 21-23 giugno 2006
Modeling of integrated inductors on Si

A scalable model for both single-ended and differential inductors
 Modified -like topology (only one fitting parameter)
 Physics-based equations based on process/layout parameters
 Improved current sheet expression of LS (for sub-nH inductors)
 Novel equation for series resistance (current crowding)
Z1
K·LS
Z2
CS
K·RS
(1-2K)·LS (1-2K)·RS
COX
RG
K·LS
K·RS
COX
CG
RG
CG
K=0.16
Riunione Annuale GE 2006
Ischia, 21-23 giugno 2006
Model validation

Model validation up to 20 GHz by comparison with onwafer measurements of more than 100 spirals (covering
0.2 to 8.3 nH inductance values)

Accuracy, geometrical scalability and compactness
promote the model as a reliable time-saving design tool
Average errors on
inductance, fSR and Q
are 2%, 5%, and 7%
Riunione Annuale GE 2006
Ischia, 21-23 giugno 2006
Model exploitation:
A 5-GHz image-reject down-converter

Extensively exploitation of integrated inductors (designed
with the proposed model)

Differential inductors are used in image-rejection filters
Riunione Annuale GE 2006
Ischia, 21-23 giugno 2006
Model exploitation
A 5-GHz image-reject down-converter
Riunione Annuale GE 2006
Ischia, 21-23 giugno 2006
See you later….
Poster B25
Riunione Annuale GE 2006
Ischia, 21-23 giugno 2006