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A 2GHz merged CMOS LNA and mixer for WCDMA

Karimi-Sanjaani, Ali; Sjöland, Henrik; Abidi, Asad

Published in:Symposium on VLSI Circuits, 2001. Digest of Technical Papers.

DOI:10.1109/VLSIC.2001.934180

Published: 2001-01-01

Link to publication

Citation for published version (APA):Karimi-Sanjaani, A., Sjöland, H., & Abidi, A. (2001). A 2GHz merged CMOS LNA and mixer for WCDMA. InSymposium on VLSI Circuits, 2001. Digest of Technical Papers. (pp. 19-22). IEEE--Institute of Electrical andElectronics Engineers Inc.. DOI: 10.1109/VLSIC.2001.934180

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2-4

A 2 G H z Merged CMOS LNA and Mixer for W C D M A

Ali Karimi-Sanjaani, liknrik Sjold*, Asad A Abidi Elec t r i ca l E n g i n e e r i n g D e p a r t m e n t

Un ive r s i ty of Ca l i fo rn ia , L o s A n g e l e s , C A 90095-1594 'Lund Unive r s i ty , S w e d e n

Abstract

A m e r g e d L N A a n d m i x e r w i t h an on -ch ip V C O is fabr i - cated in 0 .35 k m CMOS for a 2 .1 G H z W C D M A receiver. T h e f ron t - end c o n s u m e s 8 m A f r o m 2.7V a n d gives N F of 3 .2dB, conve r s ion ga in o f 24 .2 d B , a n d i n p u t I P 3 of - 1 . S d B m . T h e V C O c o n s u m e s 3 m A whi l e ach iev ing phase noise o f -128.4 a n d -138.5 d B c / H z a t offsets o f 5 a n d 1 5 M H z , respectively.

Front-End Architecture

N o i s e a n d l inear i ty r e q u i r e m e n t s a re very d e m a n d i n g in W C D M A receivers [ l ] . T h e z e r o - I F a r c h i t e c t u r e is o f i n t e re s t because Ilf noise a n d DC offset can b e f i l tered wi th l i t t le i m p a c t on t h e 5 M H z wide s p r e a d - s p e c t r u m signal [2]. T h i s pape r revis i ts t h e idea of s h a r i n g bias c u r r e n t t o i n t r o d u c e a m e r g e d L N A a n d m i x e r w h i c h achieves very good d y n a m i c r a n g e w i t h less p o w e r c o m p a r e d t o t h e conven t iona l cascade L N A a n d mixe r s .

F ig . 1 s h o w s t h e m e r g e d L N A a n d q u a d r a t u r e mixe r s . Risks wi th th i s t opo logy a r e lower ga in a n d lower L O - R F isola- t ion. However , w i th ca re fu l des ign , t h e f ron t - end is s h o w n to sat isfy 3 G W C D M A specif icat ions.

Low Noise Amplifier

T h e N F of a 3G receiver s h o u l d b e 5-6 d B , w h i c h impl i e s t h a t if t h e conve r s ion ga in o f t h e receiver f ron t - end is a b o u t 20 d B , i ts o w n N F is 3 d B . T h e c o m m o n - s o u r c e ( C S ) L N A de - e m p h a s i z e s FET no i se by t h e vol tage ga in t h r o u g h t h e i n p u t m a t c h i n g c i r cu i t . A t i m p e d a n c e m a t c h t h e no i se factor (F) is given b y F = 1 + y . a/( 1 + L / L ) , which p o i n t s t o sma l l

s o u r c e d e g e n e r a t i o n (L,) for lower noise f igure. T h i s is imp le - m e n t e d in th i s d i f f e ren t i a l L N A as a pa i r of 0 . 7 8 n H on-ch ip induc to r s , each real ized by 1 .5 t u r n s o f M e t a l - 4 layer w i th 1.4R resis tance.

T h e p a d capac i t ance (60fF) is i n c l u d e d in t h e i n p u t m a t c h - ing ne twork . M e t a l r o u t i n g o f ga t e a n d s o u r c e o f L N A transis- t o r s t o t h e p a d s also c o n t r i b u t e to noise . T h e h ighe r t h e qua l i t y factor (Q) of t h e i n p u t c i r cu i t , t h e lower t h e t h e r m a l noise , b u t t h e h i g h e r t h e ga t e i n d u c e d noise . I t ' s been f o u n d b y s imula- t i ons t h a t t h e lowest F is a t t h e p o i n t t h a t t h e t h e r m a l no i se a n d the ga t e i n d u c e d noise have t h e s a m e s h a r e o f i n p u t r e fe r r ed noise. S i m u l a t i o n s s h o w e d t h a t a s i ze of 2 0 0 p m / 0 . 3 5 p m for L N A t r ans i s to r s wou ld m a k e t h e s h a r e of t h e r m a l no i se to b e 21% a n d t h e s h a r e o f ga t e i n d u c e d no i se to be 22.4O/o. T h e d y n a m i c r a n g e ( D R ) o f a CS d e g e n e r a t e d L N A is c o n s t a n t a t a given c u r r e n t , a n d s l ides u p o r d o w n wi th Lg. A bias c u r r e n t o f 4 m A in each s ide o f L N A gives t h e D R n e e d e d for who le f ron t - e n d .

T w o m i x e r s d r iven by q u a d r a t u r e L O phases c o m m u t a t e t h e L N A o u t p u t c u r r e n t . A s t h e r e a r e n o add i t iona l t r ans i s to r s in t h e L N A p a t h , t h i s gives bes t overal l linearity. A resis tor load

g J

f u r t h e r lowers noise. A large m i x e r F E T size ( 1 0 0 / 0 , 3 5 p m ) p r o m o t e s fas ter swi t ch ing , w h i c h lowers non l inea r i ty d u e to s igna l -dependen t c u r r e n t divis ion d u r i n g c u r r e n t t r ans i t i on . T h e on -ch ip L O d r ives t h e m i x e r w i th 1 volt peak.

Accord ing to [ 3 ] , slowly va ry ing flicker noise a t t he ga t e o f m i x e r F E T s a p p e a r s un t r ans l a t ed in f r e q u e n c y at t h e mixe r o u t p u t t h r o u g h two m e c h a n i s m s : by m o d u l a t i n g the ze ro - c ros s ing of t he tail c u r r e n t (d i r ec t m e c h a n i s m ) , a n d by induc - ing c u r r e n t in the tail capac i t ance ( ind i r ec t m e c h a n i s m ) . L a r g e L O a m p l i t u d e lowers t h e d i r ec t m e c h a n i s m . T h i s c i rcui t fea- t u re s a new m e t h o d to lower t h e ind i r ec t m e c h a n i s m . A differ- ent ia l i n d u c t o r be tween t h e two L N A o u t p u t s t u n e s o u t t he tail capaci tance. N o w on ly t h e d i r ec t m e c h a n i s m rema ins , a n d the total flicker noise spec t r a l dens i ty a t t h e m i x e r o u t p u t is low- e red by a b o u t 3 5 % .

Properties of Merged Quadrature Mixers

T h e m e r g e d q u a d r a t u r e mixe r s , coup led a t t h e tails o f t he two different ia l pairs , behave d i f f e ren t ly t h a n t w o i n d e p e n d e n t mixe r s . I n add i t ion to t h e d o w n c o n v e r t e d s ignal , a s t r o n g c o m - p o n e n t a t t he 2"d h a r m o n i c of t h e LO a p p e a r s a t each load resistor. A capac i to r o f 7 p F is c o n n e c t e d across t h e SOOR mixer load to pas s t h e 5 M H z - w i d e d o w n c o n v e r t e d c h a n n e l b u t s u p - p re s s t h i s c o m p o n e n t a t 4.2 G H z .

Also, as q u a d r a t u r e phases o f t h e LO i n d u c e t h e vol tage r ipp le a t t h e m e r g e d sources of t h e m i x e r different ia l pairs , t he m a g n i t u d e o f t h e r ipp le is lower than in a conven t iona l mixer , b u t its d o m i n a n t c o m p o n e n t lies a t t h e 41h h a r m o n i c o f t h e LO.

Every q u a r t e r pe r iod o f t h e LO, o n e o f t he fou r FETs a t t ached to each L N A dra in c o n d u c t s i n sequence . T h e large LO a m p l i t u d e used h e r e forces t h e c o n d u c t i n g FET in to t r i - ode. I t is f o u n d t h r o u g h s imula t ion t h a t t h e capaci tance a t t he L N A d r a i n , w h e n sequen t i a l ly swi t ched i n t o t h e four 7 p F filter capac i to r s a t t h e m i x e r o u t p u t s , acqu i r e s a vol tage r ipp le a t t he LO f u n d a m e n t a l . T h i s is potent ia l ly a s e r ious p rob lem, because i t can coup le t h r o u g h t h e C G D of t h e L N A F E T s to the receiver i n p u t a n d r ad ia t e i n -band . W C D M A restr ic ts t he LO radiat ion to -60 d B m . S i m u l a t i o n s show t h a t t he L O f e e d t h r o u g h to t h e a n t e n n a a t each t e r m i n a l of t h e L N A is less t han -78.3 d B m across t h e b a n d , a n d as th i s is a c o m m o n - m o d e s ignal , it is f u r t h e r s u p p r e s s e d b y t h e i n p u t ba lun .

On-Chip V C O A 3 m A V C O has been des igned to fulfill W C D M A phase

noise specif icat ions with a f u l l y on -ch ip r e sona to r (F ig . 3(a)) . T h e osci l la tor is t u n e d with a s ing le 1 8 . 2 n H different ia l spiral i n d u c t o r w i th Q o f 7 , a n d a M O S F E T varactor . I t has 2 0 0 M H z t u n i n g r ange cen te red a t 2 . 1 4 G H z . I t s phase noise a t t h e offset of 5 a n d I S M H z is -128.4 a n d - 1 3 8 . 5 d B c l H z respect ively (F ig . 3 (c ) ) . A n R C po lyphase filter w i th two s tages t u n e d to 2.27

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G H z a n d 1.73 G H z gene ra t e s q u a d r a t u r e phases . A buffer , Fig. 3 (b ) , is i n se r t ed be tween t h e V C O a n d po lyphase filter to pre- ven t t h e r e sona to r f rom be ing loaded by t h e po lyphase filter o r pul led by the mixer .

Experimental Results and Discussion

T h e f ron t - end I C was fabricated in 0 .35 -pm B i C M O S 6 M from S T Mic roe lec t ron ic s us ing on ly M O S F E T s (F ig . 3 ) . T h e IC is m o u n t e d in a s t anda rd mic rowave package. A 2 p F c h i p capaci tor is slid a long a different ia l mic ros t r ip t r ansmiss ion l ine o n t h e P C boa rd , a b o u t 2 c m long, un t i l t h e i n p u t i m p e d a n c e is satisfactorily m a t c h e d ( F i g . 4 ) . F ig . 5 s h o w s t h e different ia l s I 1 for fou r d i f f e ren t c h i p s t e s t ed .

T h e N F is d e - e m b e d d e d wi th p r o p e r p r o c e d u r e s [4]. F ig . 6 shows the gain a n d N F m e a s u r e d by a noise f igu re m e t e r a t an o u t p u t I F o f 1 2 M H z . Af t e r ca l ib ra t ion , N F a t lower f r equen- cies is m e a s u r e d o n a s p e c t r u m analyzer . S y s t e m s imula t ions show t h a t a h ighpass filter w i th a cu to f f f r equency of 5 k H z

14 6.9 6 . 9 10.3 61 0.5~ SiGe 5 G H z (merged) BJT ‘#LAN PI

A n on-ch ip V C O fulfilling phase noise specif icat ions for W C D M A R X dr ives t h e mixe r t h r o u g h a po lyphase filter to gene ra t e q u a d r a t u r e phases .

T h i s p r o t o t y p e gives substant ia l ly h ighe r d y n a m i c r ange pe r u n i t power c o n s u m p t i o n than previously publ ished s imilar topologies .

5 5

Table 1: Front-end measured and simulated specifications.

. . ~.

does n o t d e g r a d e B E R of t h e 5 M H z - w i d e channe l cen te red a t Table 2: ComDarison with o t h e r recent L N A & mixers (some merged) D C . F l i cke r noise (F ig . 7 ) d e g r a d e s t h e in t eg ra t ed noise f rom 5 k H z to 5 M H z by on ly 0 .2dB. M e a s u r e d L O f e e d t h r o u g h to t h e a n t e n n a lies in t h e r a n g e o f - 7 6 to - 7 1 d B m over t h e 2 . 1 1 G H z to 2.17 G H z b a n d . I I P 3 m e a s u r e d o n four c h i p s var ies f rom + 3 d B m to - 3 d B m , wi th an average o f - 1 . 5 d B m (F ig . 8). T a b l e 1 c o m p a r e s m e a s u r e d r e su l t s w i th s imula t ions . S e c o n d - o r d e r i n t e rcep t p o i n t ( I I P 2 ) c a n n o t be s imula t ed , b u t is m e a s u r e d to be + 4 7 d B m which is suff ic ient [ l ] .

T h i s f r o n t e n d , w h e n cascaded wi th baseband circui ts with N F of a t m o s t 1 7 d B a n d an I I P 3 o f a t least + 6 d B m , will satisfy the W C D M A receiver specif icat ions [1],[5]. T h e s e f igures a re a t ta inable in p rac t i ce ; for example , baseband circui ts desc r ibed in [2] show N F of 12 .7dB a n d I I P 3 o f t 1 4 d B m .

ples t h r o u g h t h e i m p e r f e c t d u p l e x e r t o t h e receiver i n p u t [ I ] . A l t h o u g h th i s f e e d t h r o u g h lies in t h e T X b a n d , it potent ia l ly overloads t h e f r o n t e n d a n d desens i t i ze s r ecep t ion in t h e R X b a n d . T h e receiver m u s t b e suff ic ient ly l inear t o gua rd aga ins t t h i s eventual i ty . A s s u m i n g peak PA o u t p u t of t 2 4 d B m a n d 5 8 d B a r t e n u a t i o n of T X R X f e e d t h r o u g h in the d u p l e x e r a n d f i l ter , the h ighes t leakage t h e L N A i n p u t is -32 d B m , T h e

[ I ] Mobile Equipment,” Micromuue Journul, Feb. 2000.

0. K . Jensen, e t a l . , “RF Receiver Requirements for 3G W-CDMA

I n fu’ l -duplex W C D M A t h e p o w e r amp1if ier Ou tpu t [2] A , Parssinen, et “A 2.GHz Wide-Band Direct Conversion Receiver for W C D M A Applications,” f E E E Journal ofSo l id -Stare Clr-

[3] H. Darabi and A.A. Abidi, “Noise in R F - C M O S Mixers: A S i m - ple Physical Model,” f E E E Journal ofSolid-Stnte Ctrcuits, vol. 35, no. 1, PP. 15-251Jan. 2000. [4] A. A. Abidi, J. C . Leete, “De-Embedding the Noise Figure ofDif- ferential Amplifiers,” I E E E Journal ofSol id-Stute Circuifs, vol. 3 4 , no . 6, pp. 882-5, June 1999.

34, no. 12, pp. 1893-1903, Dec. 1999.

I d B gain compress ion level is one - th i rd of t h e I I P 3 s ignal level T h i r d G e n e r a t i o n P a r t n e r s h i p P r o j e c t (3GPP), R a d i o T r a n s - [61. i f a W C D M A front -end has a n ‘Ip3 O f a t l e a s t -22.4 mission and Reception(FDD),” Technical Specification 25.101, Vol. d B m , PA f e e d t h r o u g h will n o t desens i t i ze i t .

O t h e r s , too, have invest igated ways to m e r g e t h e L N A a n d mixe r ; for example , [7-91. W e de f ine a f i gu re of m e r i t ( F O M ) to c o m p a r e t h e p e r f o r m a n c e of t hese var ious f ron t - ends . T h i s F O M norma l i zes t h e d y n a m i c r a n g e ( D R ) to the power c o n - s u m p t i o n of t h e f r o n t e n d :

I IP3 D R = - = ~ - 1 ‘ d c

3.3.0, June 2000, [Online], http://www.3gpp.org. [6] R. G . Meyer, e t al : , “Blocking and Desensitization in R F Amplifi- ers,” f E E E Journal o / S o l i d - S t u t e Clrcutts, vol. 30, no. 8, pp. 944-946, Aug. I Y 9 5 . [7i A. R. Shahani, “A 12-mW Wide Dynamic Range CMOS Front-End for a Portable G P S Receiver,” f E E E Journal of Sol id-S ta te Circuits, vol. 32, no. 12, pp. 2061-70, Dec. 1997. [8] J. R . Long, et a / . , “A 5.1-5.8GHz Low-Power image-Reject Down

F o M ( d B ) = log((^ !{331n&y!1dc> converter in SiGe Technology,” IEEE 1999 B C T M , pp. 67-70. \ , ~~

Tab le 2 c o m p a r e s t h e F O M o f the relevant compe t ing [yl A-S. Porret, e t al. , “A IV, I m W , 434 M H z FSK Receiver fully inte- grated in a Standard Digital C M O S Process,” I E E E 2000 Custom f n t e - Xruted Circuits Conference, May 2000, pp. 171-4. c i rcui ts .

~~

Conclusions [IO] J , Ryynanen, e f a l . , “An R F Front-End for the Direct-Conversion W C D M A Receiver,” 1999 IEEE R u d i o Frequency Integrated Circuits sym- posium, June 1999, pp. 21-4. [ I l l F. Behbahani, e t u l . , “A 2 .4GHz Low-IF Receiver for Wideband W L A N i n 0,6-pm CMOS”, I , ~ , ~ E J ~ , ~ ~ ~ ~ / o f .yo i id-Srote C ~ r c u i r s , vol. 3 5 , no. 12, pp. 1 ~ 0 8 . 1 ~ 1 6 , D ~ C . 2000.

A m e r g e d L N A - m i x e r topology is proposed to o b t a i n the high d y n a m i c r ange a t low p o w e r c o n s u m p t i o n r equ i r ed in a W C D M A receiver. F l i cke r no i se is cha rac t e r i zed , a n d negligi- bly d e g r a d e s sensitivity. Spec ia l issues of LO f e e d t h r o u g h tha t arise by m e r g i n g q u a d r a t u r e m i x e r s in th i s way a re addres sed .

2001 Symposium on VLSl Circuits Digest of Technical Papers 20

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I 1 I ,

L L

R F h t - T F - R F i n - matching 2M)bm 0.75nH A n - c h i p inductors-

bond wire network

6)

Fig. 1. Merged LNA and Mixer for 2.14 GHz direct conversion front-end

I I

Fig. 3. Test chip photo

Packaged Chip

50

mrcrusrrip-ry e rrnnsrnissron L e . 7

Fig. 4. Matching circuit with sliding capacitor on a differential transmission line.

-15 .

-20 . 5.

z -25 .

c

-30 .

-35 . -40.

~~~

2.1 2.11 2.12 2.13 2.14 2.15 2.16 2.17 Freq (GHz)

Fig. 5 . Input Matching ( s I , ) Measurements vs. Simulations

Frequency (Hr)

(c)

Fig. 2. (a) VCO circuit. (b) VCO buffer. (c) Measured phase noise at 2.1 GHz, with WCDMA RX phase noise specs overlaid.

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I # I F frequency = 1 5 M H Z 18 1900 1950 2000 2050 2100 2150 2200 2250 2300

LO frequency (MHr) 5.5

1

2.5 : : I F = I Z M H Z :

1 o3 lo4 1 o5 1 o6 10' l o 8 IF frequency (Hz)

Fig. 7 . L o w frequency Noise Measurement vs. Simulations

Receiver 3rd order Input Intercept Point

* / ' /

60

40 ...... ;. ..... .:. ..... .:. ..... .:_ . ..... c . ./ ...

.. .... ....... , e-?- ;@-- I ......... _, ...... .. ...... .......

.. , ...... .*. ... .&/.... ............. L ....... : y :

. .:. .... -8. . . . . . . . . . . . . * . . . . . . . a . . ......

_ . , : . . p . . . . . . . . . . . . , . . . . . . . . . . . . . . d , I - - ~ - - - -

: d .

&."' . -40 -30 -20 -10 0 10

Input Power (dBm)

Fig. 8 . Input 3rd Order Intercept Point.

dBm

2001 Symposium on VLSl Circuits Digest of Technical Papers 22

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