Philips Semiconductors B.V.
Low cost DECT Power Amplifier
PH9 7005
Prelim in ary A pplication No te
RNR-T4 5-97-M-0 931
Au th or
L.C. Colussi
Novemb er 2 1, 19 97
Discre te Se micon ducto rs Nijmege n
Gerstwe g 2, 65 34 AE Nijme gen
Th e Netherland s
Key words
PA, DECT, DPO, BFG4 25W, BFG2 1W
Abs trac t
Ap plicatio n of n ew
5
th
gen eration
discrete bipo la r RF tra nsistors facilitates d esign o f a low cost
two-stage p owe r amp lifier fo r DECT syste ms, h aving a p owe r gain of 26 dB a nd an overall
efficie ncy b ette r than 4 0%. The amp lifie r ope ra te s fr om a sing le supp ly volta ge, in clude s bias
circuitry for loa d pow er ad ju stmen t an d on/off switch in g and is mou nted on a b ilayer p cb,
requ irin g 10 x 20 mm . A descrip tion is given of the circu it desig n and the b oard layo ut, includ in g
mea sureme nt results.
Philips Semiconductors B.V.
PH97005
Low cost DECT Power Amplifier
INTRODU CTION
Th is n ote des crib es the ap pl ic atio n of two of th e new
5
th
gen er ation
si li co n bi pol ar RF tr an si stor s
i n SOT3 43R pl as ti c SMD p ack age i n a two- stage p owe r amp li fi er (PA ), des ig ned for u se i n
DEC T cor dl es s te le pho ne sy stems . Th ese tra ns is to rs , man ufactur ed ac co rd ing to the ne w
do ubl e- po ly
proce ss, are cha ra cter is ed by the ir h ig h tran si ti on fr equ enc y (f
T
> 20 GH z) at lo w
su ppl y voltag es , re sul tin g in a s upe ri or powe r ga in at mi cr owav e fr eq uen ci es, usu al ly a fi el d
de di cated to GaA s- dev ic es. Two l ay er s of p ol ysi l ic on ar e us ed: one for c ontac ting the b ase ,
yi el di ng a l ow ba se resi s tan ce a nd one to for m the e mitter , re su lti ng in a s te ep em itte r do pe
pr ofi le an d an effecti ve em itter wi dth of 0 .5
µ
m. A bu ri ed N-l aye r (c ol l ector ) is pl ace d wi th in a P-
su bstr ate, wh ic h is con nec te d to the e mitter pa ck age l ea d, wh ic h ena bl es th e di e to b e pl ace d
on the g rou nd pl an e, r ed uci ng e mitter i nd uctan ce an d th erm al resi s ta nce . Fi gu re 1 sh ows a
cr os s se ctio n of a
do ubl e- po ly
bur i ed la ye r tran si stor .
1
2
3
4
Fig u re 1 : Cro ss sectio n an d p acka g e of th e d ou b le -p o ly b u ried la yer RF t ra nsisto rs.
bas e
e mitt er
c ol le ct or
e mitt er
Wi th o nl y two
do ubl e- po ly
tran si stor s a comp le te a mpl ifi er l i ne- up ca n be real i sed , offer in g
26 d Bm of o utput powe r wi th mo re tha n 26 dB po wer g ai n. Th e ampl i fi er req ui re s a si ngl e
su ppl y voltag e of 3 .6 V a nd typi ca ll y ha s 44% effic ie ncy . The bi as in g c i rc ui try us es on ly o ne
NPN tra ns is to r pai r , whi c h a ls o pe rfor ms lo ad po wer a dj ustme nt an d on/off s wi tc hi ng func ti on s.
Th ank s to the l ow c ompo nen t co unt and s imp le ma tc hi ng ne tw ork s the en ti re a mpl ifi er
( in cl udi ng b ia s part) onl y mea su res 1 0 x 20 mm.
As c ompa re d to a p rev i ous d emon stra ti on b oard, P H960 60 (Pre li mi nar y Ap pl ic atio n Note
RNR-T4 5-96 -T-83 8) thi s on e offer s lowe r add iti ona l co mpo nent co unt, bu t is le ss s ui ta bl e fo r
PHS a ppl i cati on.
Th e mai n fe atur es of th e PA ar e:
- l ow co mpon ent co unt
- s mal l si ze
- h ig h effi ci en cy
- s in gl e sup pl y ope ra ti on
RNR-T45-97-M-0931
Philips Semiconductors B.V.
PH97005
Low cost DECT Power Amplifier
CHAR ACTER IS TIC S
(unless otherwise specified the operating frequency is 1. 89 GHz, the supply voltage is 3.6 V, the input
power is 0 dBm and the period is 10 ms with a duty cycle of 1:8)
Pa rame te r
Gener al para meters
Su ppl y vo ltag e (Vs )
Con tr ol vol tage (Vc )
Fr eq uen cy rang e
Ty pe of ope ra ti on
So urc e an d l oa d im peda nc e
Po wer g ai n (G
p
)
Outpu t po wer ( P
o
)
Av g. s upp ly c ur re nt
Effic ie ncy
Inpu t VSWR
Isol ati on
(r ela tive t o in pu t po wer )
Sp uri ou s
Le aka ge cu rren t in o ff- state
Har mon ic s: 2
nd
3
rd
Lo ad mi sma tc h:
Pr in te d ci rc ui t bo ard
Di men si ons
Tab le 1:
Specifica tion
3.2
≤
3 .6
≤
4 .2 V
on s ta te : 3.6 V
off s ta te : 0 V
1.88 - 1.9 2 GHz
pu ls ed
50
Ω
≥
26 dB
≥
26 dB m
11 mA
≥
40%
2 :1
≥
50 dB
≤
-6 0 dBc
≤
10
µA
≤
-3 0 dBm
≤
-3 0 dBm
No de gr ada ti on
FR4 b il ay er
(h = 0. 7;
ε
r
= 4. 6;
ta n
δ=
0. 02 )
Ty pical
Condition
du ty c yc le
≤
50%
26 .3 d B
26 .3 d Bm
44 %
57 d B
P
o
= 26 dB m
P
o
= 26 d Bm
P
o
= 26 d Bm
Vc = 0 V
V
s
= 3.2..4 .2 V
VSWR 6 : 1, al l p has es
Vc = 0 V
- 34 dBm
- 13 dBm
P
o
= 26 d Bm, V
s
≤
4.5 V
VSWR 6 : 1, al l p has es
10 x 2 0 mm
(in clu din g bias circu it ry)
Cha ra cte ristics o f th e DE CT P A PH97 0 05 .
RNR-T45-97-M-0931
Philips Semiconductors B.V.
PH97005
Low cost DECT Power Amplifier
CIRCUIT DES CRIP TION
Fi gu re 2 s hows c i rcu it di agr am of th e DECT PA i nc lu di ng bo th RF tr ans is to rs , match in g ci rc ui ts
an d bi asi ng c ir cu it. The ap pen di x con ta in s th e part l is t o f th e dem o b oard.
Vs
Vc
R7
R4
Q3a
R5
R2
Q3b
R6
TL3
C4
TL8
TL7
R1
C1
RF in
TL1
C2
Q1
C3
C5
C10
TL2
TL4
TL5
TL6
Q2
C11
RF out
C6
R5
C8
C12
R3
C7
C9
C13
Fig u re 2 : Circu it
d ia g ra m o f t he DECT PA d e mo bo a rd P H9 7 00 5 .
RF tra nsist or s
Th e RF ch ain o f the PA c ons is ts o f two tran si stor s ta ges : a BFG425 W (Q1) wid eba nd tra nsi stor ,
op er atin g i n cla ss A an d a B FG21 W (Q2) , o peratin g in c la ss AB .
In acc or dan ce wi th the a bov e se tti ngs the me asu re d sou rc e and l oad i mp edan ce s of b oth
tra nsi stor s are gi ve n in tabl e 2.
Tr ans is tor
BFG425 W
(V
ce
= 3. 6 V; Ic= 30 m A; f= 1. 89 G Hz)
Sourc e impeda nce (Z
s
)
12 + 0 .7 j
Ω
8 - 4 .5 j
Ω
Load impedanc e (Z
l
)
52 + 1 02 j
Ω
12 - 3.5 j
Ω
BFG21W
(V
ce
= 3. 6 V; P
o
= 26 d B m; f =1 .8 9 GHz)
Tab le 2 : S ou rce a n d lo ad imp ed a n ce s o f th e ap p lie d RF tr an sist or s.
Sma ll si gna l S- par ame te r da ta for the B FG42 5W as wel l a s la rg e si gna l Sp ic e par ame te rs o f
bo th the BFG42 5W a nd the BFG21W are av ail ab le o n fl op py di sc .
Th e RF tr an si stor s hav e tw o emi tter s lead s, wh ic h hav e to b e careful l y groun ded to en sure
stab le o perati on and p erfo rma nce a cc ord in g to s pec ifi cati on. Typ ic al l y, the i ndu ctan ce of th e
vi as h as to be kept b el ow 0.1 nH.
RNR-T45-97-M-0931
Philips Semiconductors B.V.
PH97005
Low cost DECT Power Amplifier
Impedanc e matc hing
Th e imp eda nce ma tc hi ng pa rt con si sts of th ree s epa ra te s ecti ons : the inpu t, th e in te rs ta ge an d
the ou tp ut ma tc hi ng ne two rk s. The pu rp ose o f thes e networ ks is to en abl e th e RF tran si stor s to
gi ve o ptimu m p erfo rma nce w ith re spe ct to po wer g ai n, o utput powe r an d effi ci en cy. Fortuna te ly ,
the imped anc e le vel s of th e app li ed
do ubl e- po ly
tran si stor s are n ot e xc epti ona ll y hi gh o r lo w, s o
they ’re ra th er e asy to ma tc h.
Dec ou pl in g i s d one by usi ng c apa ci to rs C1 , C4 , C6, C8, C 11 an d C12, whi ch a re seri es
r eso nan t at 1.9 GHz. C apa ci to rs C7 (wi th res is to r R3 ) and C 9 are u sed to su ppr es s lo w
fre que ncy i ns ta bi li ty.
At th e inp ut s i de sh unt cap aci tor C2 a nd se ri es
tra nsmi ss io n li ne TL1 matc h the 5 0
Ω
sou rc e to the
ba se of Q1. B ase res is to r R1 is us ed fo r bi as in g and
ha s no effect on match in g.
input Q1
TL1
C2
Fig . 3a : In pu t mat ching .
Be twe en the co ll ec to r of Q1 and the b ase o f Q2
match in g is d one b y se ri es tra nsm is si on lin e TL2 , sh unt
ca pac itor C3 and s er ie s tr an smi ss io n li ne s TL4 a nd
TL 6. B oth s hu nt c apa ci to rs C3 a nd C5 (par tly )
co mpen sa te the influ enc e of b ia s stubs TL3 a nd TL5 ,
whi c h are b oth sho rter th an a qua rter wave le ngth.
input Q2
TL5/C5
TL3
output Q1
C3
TL2
TL4/TL6
Fig . 3b : In te rsta ge m at ch ing .
Th e outpu t match i s do ne by s er ie s tr an smi ss io n li ne
TL 7 and s hun t ca pac itor C10. Aga in thi s ca pac itor al so
co mpen sa te s th e in fl uen ce o f bi as s tu b TL6 .
TL7
output Q2
C10
Fig . 3c: Ou tp ut ma tch in g .
RNR-T45-97-M-0931
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