7. D. Zhao, K.L. Li, K.T. Chen, and H.F. Liu, Gene a ion o 10 GHz
ans o m-limi ed pulse ain om fibe ing lase using Fab y-Pe o
Semiconduc o as modula o , Elec on Le 36 (2000), 1700–1701.
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© 2003 Wiley Pe iodicals, Inc.
APPLICATION OF CAD LOAD-PULL
TECHNIQUES IN MIXER DESIGN
A u o Velazquez,
1,2
An onio Laza o,
1
Luis P adell,
1
and
Adol o Come on
1
1
Depa men o Signal Theo y and Communica ions
Technical Uni e si y o Ca alonia
Jo di Gi ona 1-3, Campus No d
Ba celona 08034 Spain
2
Depa amen o de Elec o´ nica y Telecomunicaciones
Cen o de In es igacio´ n Cien ı´fica y Educacio´ n Supe io de Ensenada
Km. 107 Ca . Tijuana-Ensenada
Ensenada, B.C. 22860 Mexico
Recei ed 30 July 2002
ABSTRACT: This wo k desc ibes he applica ion o a comme cial
CAD so wa e o implemen load-pull echniques in he design o mic o-
wa e mixe s. This me hod is used o gene a e con e sion-loss egions
when a diode is pumped and ope a ed as a mixe ci cui . Emphasis is
placed on he inclusion o image and ou -o -band e mina ions o op i-
mize he ope a ing condi ions equi ed o ob ain low con e sion loss. An
X-band 5-dB con e sion-loss mixe is designed and es ed using his
me hod. © 2003 Wiley Pe iodicals, Inc. Mic owa e Op Technol Le
36: 320–323, 2003; Published online in Wiley In e Science (www.
in e science.wiley.com). DOI 10.1002/mop.10754
Key wo ds: load pull; mixe s; mic owa es; ha monic balance; con e -
sion loss
1. INTRODUCTION
Mixe analysis and design undamen als and heo y a e desc ibed
in de ail in [1]. Howe e , one can explo e new capabili ies o e ed
by CAD ools, which allow us o adap some o he cha ac e iza-
ion and measu emen echniques by means o ci cui elemen s and
models defined as buil -in ea u es in he so wa e. As is well
known, op imum diode-mixe design equi es a ca e ul selec ion o
he impedance e mina ions p esen ed o he di e en mixing e-
quencies appea ing a diode inpu and ou pu po s [2]. Fo single
one p oduc s consis ing o a single RF inpu signal mixing wi h
he local oscilla o he ollowing equencies a e gene a ed:
IF ⫽M䡠 LO ⫾N䡠 RF, (1)
whe e
IF
⫽ou pu signal o he mixe ,
RF
⫽inpu signal o he
mixe ,
LO
⫽local oscilla o equencies o he mixe , and Mand
N⫽in ege s (0, 1, 2,...) ep esen he m
h
o n
h
ha monic o
each signal.
The basis o he load-pull echnique desc ibed he e akes he
p inciples o he expe imen al measu emen sys ems desc ibed in
[3, 4] ha a e o ien ed o amplifie design, and adap s hem o a
diode-mixe design. I consis s in he cha ac e iza ion o he diode
embedded be ween an inpu ci cula o and an ou pu une in o de
o p esen se e al dis inc loads o he diode, while i is pumped
and biased o a specific ope a ing poin . P ac ical une s a e com-
me cially a ailable, easy o use, and o ela i ely low cos . How-
e e , hey a e o limi ed use because o hei limi ed equency and
impedance ange; in addi ion, he con ol o he impedance p e-
sen ed o he image and highe o de ha monics is di ficul . The
CAD load-pull app oach does no su e om limi a ions in load
eflec ion coe ficien magni ude. By simula ing a eflec ion coe -
ficien using he one-po elemen s included as da a elemen s in he
simula ion package, uni y magni ude can be achie ed, i necessa y,
o any physical se up and a any equency. Phase and magni ude
a e con olled di ec ly by a con ol box in he HB simula ion menu.
E ec i e CAD load pull can be implemen ed i p ecise non-
linea de ice models a e a ailable (gene ally ob ained om small
signal S-pa ame e measu emen s) and hen, by using ha monic
balance analysis wi h an adequa e numbe o LO ha monics, we
can ob ain he con e sion loss alue associa ed o each une
posi ion and, in his way, we can ha e a g aphical iew on he
Smi h Cha o he con e sion loss capabili ies o a gi en de ice
and ope a ing condi ions. A CAD load-pull s a is ical analysis has
been epo ed [5] o e i y he op imized pa ame e s o esis i e
FET mixe s, and in his pape we use he CAD load-pull echnique
o es ablish con e sion loss egions on a Smi h Cha om which
we can ollow a sys ema ic design and implemen a ion o mic o-
wa e diode mixe s.
2. LOAD PULL SETUP
Wi h he nonlinea simula ion se up shown in Figu e 1, we imple-
men he load-pull me hod o de e mine he con e sion loss e-
gions. The dependency o diode pe o mance on ou pu impedance
is examined by applying a fixed RF powe and pumping he diode
wi h a fixed LO powe o se specific ope a ing condi ions and
de e mine i s con e sion loss o a gi en numbe o load e mina-
ions.
In Figu e 1 he de ice unde es (DUT) includes he diode and
bias s uc u es used o p o ide DC ol age and cu en , as well as
he coupling s uc u e o RF (
2
) and local oscilla o (
1
) signals.
Va ia ion o he ou pu load is ca ied ou by he one-po elemen ,
implemen ed as a une , which allows he defini ion o a se o
impedances o eflec ion coe ficien s ha will be p esen ed as a
load impedance o he diode a he a ious mixing equencies,
including he image and sum-mixing p oduc s. The DUT is
pumped o an adequa e powe le el om a local oscilla o and hen
biased o se he ope a ing condi ions as a mixe de ice.
The comme cial so wa e Ad anced Design Sys em (ADS) [6]
is used, mainly because i in eg a es he schema ic and layou
simula ions ea u es in he same design en i onmen , which allows
us o make linea and nonlinea ci cui analysis and op imiza ion;
also, we can pe o m di ec elec omagne ic analysis o he passi e
s uc u es using Momen um, he 2.5-D elec omagne ic simula o
included as a companion o ADS.
Figu e 1 Load-pull simula ion se up
320 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 36, No. 4, Feb ua y 20 2003
2.1 Diode Model
One essen ial and key elemen when using his app oach is he
diode model shown in Figu e 2, which ep esen s he beha io o
he de ice a bo h DC and RF ope a ing condi ions. By using he
basic diode equa ions
Idiode ⫽Iss
䡠
冉
exp
冉
V
nkTB
冊
⫺1
冊
, (2)
Cj⫽Cj0
冑
1⫺共V/Vbi兲, (3)
we fi and op imize expe imen ally measu ed da a o ob ain pa-
ame e alues ha will be in oduced in a symbolically defined
de ice (SDD) elemen o , al e na i ely, use hose pa ame e alues
di ec ly as pa ame e s o he esiden ADS nonlinea diode model,
as shown in Figu e 3. These pa ame e s in conjunc ion wi h he
pa asi ic alues ex ac ed om measu ed da a gi e us a p ecise and
eliable de ice model o be used in all he nonlinea analysis and
mixe simula ions. By means o he Ma lab unc ion FMINS we se
ini ial alues o he pa ame e s defined in Eqs. 1 and 2, e alua e
he equa ions, and compa e he esul s wi h expe imen ally mea-
su ed alues. We minimize he e o unc ion un il a global min-
imum is ound and hen use hese new pa ame e s o e alua e he
equa ions and compa e wi h expe imen al cu es. Final pa ame e
alues o MA40417 a e: R
s
⫽6.5 ⍀,L
s
⫽0.13 nH, C
p
⫽10
F, I
ss
⫽0.421 pA; C
jo
⫽0.0239 pF, N⫽1.3, and V
bi
⫽0.85
V. When hose pa ame e s a e used o e alua e he model, he
compa ison o measu ed and fi ed da a shows e y good ag ee-
men .
The equa ions equi ed by he so wa e o p ocess he une
unc ions a e associa ed wi h con ol elemen s and HB analysis
dialog boxes. Va iables a e defined o sweep magni ude and phase
alues be ween a minimum and maximum, depending on he
desi ed egion in he Smi h Cha , o map load- eflec ion coe fi-
cien s. Also, o be consis en wi h he basic heo y on mixe design
[2], we ha e o p esen adequa e load e mina ions a he di e en
mixing p oduc s; his ask is pe o med by defining he e mina-
ions (sho o open ci cui s) associa ed wi h each known mixing
p oduc . In pa icula , i is known ha o he “Y” ype mixe
defined in [1], all he ou -o -band equencies mus be sho ci -
cui ed and he bes con e sion loss is ob ained by e mina ing he
image equency in open ci cui , al hough o he e mina ions could
be used. In ac , se e al combina ions o sho - and open-ci cui ed
e mina ions a hose equencies we e es ed o de e mine he bes
condi ions o minimum con e sion loss.
Rega ding he block diag am in Figu e 1, by means o V
load
and V
sou ce
in he se up, we define con e sion loss by sub ac ing
he app op ia e mixing p oduc s. This can be done di ec ly in he
ci cui page by defining a measu emen equa ion o in he da a
windows as a gene al equa ion, o show all g aphic in o ma ion
needed by using he basic equa ion:
L⫽dBm共mix共Vload,兵1⫺1其兲兲 ⫺dBm共mix共Vsou ce,兵0, 1其兲兲.
(4)
Also, o comple e he in o ma ion we can ge he sou ce and load
impedances associa ed wi h each con e sion loss alue using he
app op ia e indexing o he a iables used o ep esen hose quan-
i ies. We define he eflec ion coe ficien a he inpu by means o :
⌫in ⫽mix共V e ,兵0, 1其兲
mix共Vsou ce,兵0, 1其兲 . (5)
3. CONVERSION LOSS REGIONS
By defining se e al alues o eflec ion coe ficien s on he Smi h
Cha , we can plo egions o con e sion loss alue. Con e sion
loss (CL) cha ac e iza ion is made by applying load-pull ech-
niques a adio equency (RF) and in e media e equency (IF),
and sweeping he load impedance be ween gi en alues. In his
way, o each impedance poin a he IF po , one can de e mine
he co esponding sou ce impedance h ough he inpu ci cula o
Figu e 2 Nonlinea Scho ky diode model
Figu e 3 Nonlinea diode model o ADS using: (a) SDD; (b) diode
model elemen
Figu e 4 Con e sion loss egions. [Colo figu e can be iewed in he
online issue, which is a ailable a www.in e science.wiley.com.]
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 36, No. 4, Feb ua y 20 2003 321
as shown by V
e
in Figu e 1. We apply his p ocess o s udy he
MA40417 diode whose model was ob ained om DC and S-
pa ame e measu emen s using a J-Mic o mic os ip- o-on wa e
coplana ansi ion as desc ibed in sec ion 2.
As can be seen, o he pa icula ope a ing condi ions in ou
example, he alue o minimum con e sion loss is he poin
ma ked as CL
min
, which co esponds o a single poin in he
impedance cha . Fo con e sion loss alues be ween CL
min
and
one dB highe , we ha e egion I, which co esponds o he locus o
load impedances associa ed o a ious une posi ions. Fo CL
alues be ween CL
min
and wo dB highe , we ha e egion II and,
simila ly, o con e sion loss alue om CL
min
up o 3 dB highe ,
we ha e egion III.
By knowing he sou ce and load impedances, i is possible o
syn hesize ma ching ne wo ks so ha he DUT will be able o
p o ide low con e sion loss as a mixe . The impedance alues
selec ion o ob ain low con e sion loss is made by means o
indexing he a iables in he impedance domain p esen ed o all
he une posi ions. Once his is done, he impedance in o ma ion
can be abula ed o sa ed o u he p ocessing.
4. APPLICATION TO MIXER DESIGN
Wi h his in o ma ion a hand, we can p oceed o selec he
impedance poin s ha mee ou needs and om which we can
syn hesize he co esponding inpu and ou pu ma ching ne wo ks.
This means ha we ha e o a oid imp ac ical impedance alues
inside hose con e sion loss egions o simpli y he syn hesis
p ocess and ob ain physically ealizable ne wo ks. Fo example,
we ake a poin om egion III, co esponding o a con e sion loss
alue o 4.0 dB, and syn hesize he inpu - and ou pu -ma ching
ne wo ks.
To implemen he mixe , in his s udy a wo-sec ion spu line
fil e is used a he RF inpu o ejec he image equency wi h less
han 1-dB RF a enua ion. To couple he pump LO signal, we use
a di ec ional fil e cen e ed a he local oscilla o equency and a
ma ching and fil e ing s uc u e a he in e media e equency
ou pu . The equi ed RF impedance is nea ly eal, so ha i can be
implemen ed wi h a ape ed line ans o me . A
␭
/4 sho ed s ub is
placed o DC e u n. Two adial s ubs a e used o sho ci cui he
diode a he LO and 2
nd
LO ha monic equencies. We e ified he
equency esponse o he fil e s using elec omagne ic analysis by
means o he 2.5-D Momen um capabili ies in eg a ed in ADS o
ob ain e y good ag eemen wi h he expe imen al esul s.
Using he so wa e o analyze his s uc u e, i was ound ha
good con e sion loss pe o mance could be ob ained wi h he
applica ion o he desc ibed me hodology. Based on hose esul s,
a single diode mixe was implemen ed using Cuclad 10-mil sub-
s a e. The comple e mixe layou is shown in Figu e 5.
Expe imen al esul s shown in Figu e 6 indica es ha his mixe
has minimum con e sion loss o 5.56 dB when i is pumped a
9-dBm LO powe and 11.02-GHz LO equency. DC bias (V
dc
⫽
⫺0.7 V, I
dc
⫽2 mA) is applied h ough he IF po . The
di e ences ound can be a ibu ed o sligh de ia ions in he inpu
fil e cen e equency and inc eased losses as can be obse ed in
he e u n losses a bo h he RF and IF po s, as shown in Figu e
7. The pe o mance o he ealized mixe is in good ag eemen
wi h ha p edic ed by he simula ion se up.
5. CONCLUSION
In his pape , we p esen ed he adap a ion o a load-pull echnique
as a ool o mixe design. Wi h he aid o he con e sion-loss
egions, one can selec he mos app op ia e load impedance o a
gi en con e sion-loss alue. A CAD echnique was used o de e -
mine he load and sou ce eflec ion coe ficien s while cha ac e iz-
ing diode pe o mance. The conjunc ion o a powe ul so wa e
package ha allows ull nonlinea analysis and simula ion wi h he
Figu e 5 Layou o he X-band mixe
Figu e 6 F equency esponse o X-band mixe
Figu e 7 Re u n loss a RF and IF po
322 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 36, No. 4, Feb ua y 20 2003
basic heo y is a echnique han can be applied o easily and
quickly achie e an op imized mixe design. This me hod can be
gene alized o o he mixe s uc u es om he de ice’s nonlinea
model.
ACKNOWLEDGMENTS
This wo k has been pa ially suppo ed unde g an s 2FD97-0960-
C05-05 and 2FD97-1769-C04-03 (CICYT-FEDER) and a schol-
a ship om CONACyT (Me´xico). A. Vela´zquez is on lea e o
absence om he Dp o. de Elec o´nica y Telecomunicaciones,
CICESE, Me´xico.
REFERENCES
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nd
Ed., A ech House, No wood,
MA, 1993.
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MA, 1971.
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load-pull measu emen s based on six po echniques, IEEE T ans
Mic owa e Theo y Techniques MTT-46 (1998), 2068–2073.
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(1998), 1201–1208.
5. J.F. Villemaze and M. Soula d, A s a is ical load pull o mixe design
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6. Ad anced Design Sys em, Release 1.5, Agilen Technologies, San a
Cla a, CA.
© 2003 Wiley Pe iodicals, Inc.
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 36, No. 4, Feb ua y 20 2003 323