FREQUENCY TUNING
LOOP
FOR
VCOS
B.
Lina es-Ba anco’,
A.
Rod iguez-Vbquez2,
E.
Shchez-Sinencio’ and
J.
L. Hue as2
’
Depa men
o
Elec ical Enginee ing
Texas A&M Uni e si y, College S a ion,
TX
77843-USA Dp o. de Diseiio Analbgico,
Cen o Nacional de Mic oelec bnica, 41012-Se illa,
Spain
Abs ac -Fo
a
Vol age Con olled Oscilla o
(VCO) he oscilla ing equency
is
con olled by
an ex e nal inpu . The ela ionship be ween he
oscilla ing equency and he inpu con ol ol -
age
is,
in mos cases, expec ed o be linea and
independen o pa asi ics, p ocess pa ame e s,
empe a u e, and o he non-ideali i es. In his
pape we in oduce
a
equency uning ci cui
o VCOs
so
4a
he Anal ela ionship be ween
oscilla ing equency and inpu con ol ol age is
Axed and independen o he p e ious men ioned
non-ideali ies. This uning loop is applied o an
OTA-C sinusoidal VCO. Such an oscilla o has
an ou pu equency-inpu ol age ela ionship
ha depends on empe a u e, p ocess pa ame-
e s, and e en ampli ude o he oscilla ions.
I
is
shown ha by adding he uning loop all hese
non-ideal dependences will be minimized.
I.
INTRODUCTION
Vol age Con olled Oscilla o s a e key componen s
in many signal p ocessing and communica ion sys ems
[l-31,
and a e
also
used o he uning o monoli hic
il e s
[4-91.
They alsomay be used o ins umen a ion
applica ions
[2].
In many cases i is necessa y ha he
ela ionship be ween he ac ual oscilla ing equency o
he VCO and i s inpu con ol ol age is e y p ecise and
does no change wi h empe a u e, p ocess pa ame e s
o
pa asi ics.
Conside a ce ain VCO (sinusoidal, iangula ,
o
squa e wa e,) ha has an “uncon olled” inpu ol age-
ou pu equency cha ac e is ics. We will show ha by
adding he equency uning loop desc ibed in his pa-
pe he inpu ol ageou pu equency ela ionship can
be made e y linea and comple ely independen o sec-
onda y pa ame e s ( empe a u e, ampli ude, pa asi ics,
and p ocess pa ame e s) wi hin he uning ange o he
o iginal VCO.
The uning loop p oposed in his pape is alid o
any ype o VCO. We a e going o e i y i s ope a ion
by applying i o an OTA-C sinusoidal VCO
[lo].
Sinusoidal OTA-C VCOs ha e
a
nonlinea inpu
ol ageou pu equency ela ionship ha depends on
p ocess pa ame e s, empe a u e, pa asi ic componen s
and e en ampli ude
o
he oscilla ions. By adding he
p oposed uning loop we will show ha his ela ionship
will become linea and independen
o
he p e iously
men ioned pa ame e s.
11.
THE FREQUENCY TUNING
LOOP
Figu e
1
shows he basic s uc u e o he equency
uning loop
[11,12].
co
“OU?
I
Squa e- wa e
Con e e
F equency
Di ide
by
N
(Op ional)
Fig.
1.
Block Diag am o F equency Con ol Loop.
The ou pu o he oscilla o (i no squa e) is con-
e ed o a squa e wa e, di ided by
N
(op ional) and
applied o a F equency- wVol age (FTV) con e e .
Usually he maximum ope a ing equency o
an
oscil-
la o is highe han he maximum possible equency
in a F equency- o-Vol age Con e o .
Fo
his eason
he inclusion o he equency di ide in Fig.
1
is many
imes manda o y.
As we will see in he nex sec ion, he FTV con-
e e is a de ice such ha i
in
is he equency o i s
inpu signal, i s ou pu ol age will be gi en by
in
REF
Vz
=
n
VBIAS-
Whe e
n
is
a
posi i e in ege ,
VBlAS
is
a
e e ence ol -
age and
REF
he equency o a e e ence squa e wa e
CH
30064/91/0000
-
2617
$1.00
C
IEEE
signal (like
a
c ys al oscilla o ). I
is he ou pu e-
quency o he VCO and a equency di ide is used wi h
a
a e
N,
hen
in
=
/N.
I
p-'
is he ime cons an
o he in eg a o , i s ou pu ol age will be gi en by:
V
=
~( co
-
z)
(2)
On he o he hand, o
a
CMOS OTA-C sinusoidal
os-
cilla o we ha e
1131,
(3)
K
=
e
=
-(V
-
ih)
2*
c
2TC
whe e
K
and
V h
a e gi en by he opology and an-
sis o geome ies o he OTAs used
as
well
as
by he
p ocess pa ame e s.
Sol ing equa ions
(l),
(2)
and
(3)
yields,
Vco
-
VBIAS-
N REF
which has a s able s a iona y poin
(!$
<
0)
cha ac-
e ized by
N Vco
=
REF-
~VBIAS
(5)
The ela ion be ween
(ou pu equency) and
V,,
(in-
pu ol age) is shown in Fig.
2.
No e ha i is linea
and i depends only on
REF,
VBIAS,
n
and
N.
In he nex Sec ion we will gi e he implemen a ion
de ails o he FTV con e e , which is he key compo-
nen o he equency uning loop.
,
Fig.
2.
Fkequency s con ol ol age ela ionship o
V,,
wi h equency uning
loop.
111.
The
FTV
Con e e
Conside he ci cui eo Fig.
3.
I con ains
a
monos-
able ha p oduces a pulse o du a ion
o
=
1
Du ing his pulse, capaci o C is cha ged by a cu en
go
(~~VBIAS
-
z).
The es
o
he ime i is discha ged
by
goV,.
The wa e o m ha esul s a he capaci o
u( )
is shown in Fig.
4.
Fo each cycle
o
u( ),
Vz( )
is
he peak alue o
u( )
o he p e ious cycle. Two
consecu i e peak alues a e ela ed by
2 REF
'
V,( +nT)
=
V,( )-g"Vz(NT- o)+g"(2n ~~~s- z) ,
whe e
T
=
1/
.
I
is cons an and he FTV con e e
C C
(6)
eaches i s s eady s a e, hen
Vz(
+
NT)
=
Vz( ),
i.e.,
A
s abili y condi ion o he s eady s a e can be ob-
ained by w i ing
(6)
in he Z-domain and making he
poles o be inside he uni y ci cle. The esul ing condi-
ion is
[E],
(8)
Ngo
'2C
A
con enien IC implemen a ion o his FTV con e e
is shown in Fig.
5.
To imp o e he ime esponse, he
swi ch o Fig.
3
has been eplaced by a di e en ial pai
and cu en mi o s. The cu en sou ces a e imple-
men ed wi h linea ized OTAs.
o
=
,
--I+
MONOSTABLE
N
I
1
4
De ec o
Uj , Peak
&-
-
-
Fig.
3.
Fkequency- o-Vol age Con e e
-
u( )
Fig.
4.
Time wa e o ms o
U(
)
inside he FTV
Con e e , and o
Vx( ),
i s ou pu .
s
1.
--cHc
Ju-l-
V,
I J
Fig.
5.
CMOS Ci cui Implemen a ion o FTV
Con e e
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The monos able has o p o ide
a
pulse o du a ion
o
=
1/2 REF. such
a
ci cui is shown in Fig.
6.
The
du a ion o he ou pu pulse
o
is gi en by he ime i
akes o
cha ge
capaci o
CI
om OV o VREF by he
cu en
IREF.
VREF is gi en by he ol age o which
Cz
is cha ged, s a ing a OV by a cu en
IREF
du ing
a
ime
o
=
1/2 REF. The e o e, i he wo ci cui s
enclosed by b oken lines in Fig.
6
a e pe ec ly ma ched,
he du a ion
o
he monos able ou pu pulse will be
o
=
1/2 REF, independen o
IREF
and
cl
=
cz
=
c.
I
he e is
a
misma ch be ween he wo ci cui s he wid h
o he monos able ou pu pulse will no be equal o hal
he pe iod o e e ence signal
REF.
Howe e , besides
his, he ope a ion and cha ac e is ics o he uning loop
s ill emain basically in a ian .
---------------
_L
ICIl
I1
I-
-
-
a
____--
M. Chcd
ChUi .
- c--c
I.
Fig.
6.
Block Diag am o Monos able wi h Ou pu
Pulse Wid h Con olled by an Ex e nal
Squa e Wa e Signal o P ecise F equency.
IV. EXPERIMENTAL RESULTS
In o de o es heop oposed equency uning loop
s a egy we used a sinusoidal OTA-C oscilla o [10,12].
I s equency dependence is shown in Fig. 7. No e ha
he ela ionship be ween ou pu equency and inpu
ol age (Bias Vol age) is nonlinea and changes wi h
he ampli ude o he oscilla ions.
A
disc e e equency uning loop was implemen ed
a ound he p e ious
CMOS
OTA-C oscilla o . Since
he ou pu equency gdes o e 13MHz, a as compa a-
o (CM710C) was used o con e he sinusoid o a
squa e wa e signal. Fo he monos able a con en ional
555
ime was used. In his case, he wid h o i s ou pu
pulse is no con olled by an ex e nal equency e e -
ence, bu by a p ecise RC cons an . Also, since his
ci cui has e y bad ime esponse (p opaga ion imes
a e a ound lOOns he ou pu o he oscilla o had o be
di ided by 32. The esul ing ou pu equency-inpu
ol age ela ionship o he
VCO
wi h equency uning
loop is shown in Fig.
8.
This cha ac e is ic is he same
o di e en alues o he oscilla ing ampli udes, o di -
.O
Bias
Vd og.
( ol s)
Fig.
7. F equency s Bias Vol age
o
sinusoidal
OTA-C Oscilla o wi hou equency uning
loop.
e en empe a u es and o di e en IC chips. A his
ime we do no ha e a ailable a comple e IC p o o ype
o quan i y he deg ee o linea i y,
which
is highly de-
penden on he implemen a ion.
14.0'
13.0.
12.0,
11.0
CI
Y
E"
'"5
8.
;:5
1
6.0
5.0-
4.0.
3.0.
2.0
+
1:O
1:1 1:2
1.3
114
115
1.6 1.7
F oquoncy
Con ol
V&ap
(Vdb)
Fig.
8.
Measu ed Oscilla ion F equency s
F equency Con ol Vol age o VCO
wi h F equency Tuning Loop.
V. CONCLUSIONS
A
equency uning loop o VCOs is p esen ed ha
compensa es o empe a u e, p ocess pa ame e s, am-
pli ude, and pa asi ics in luence in he o iginal ou pu
equency-inpu ol age ela ionship. This uning loop
can be applied o any ype o VCO. I s iabili y has been
demons a ed, by applying i o a sinusoidal OTA-C
VCO. The uning loop was cons uc ed using a b ead-
boa d p o o ype, bu i can be in eg a ed oge he wi h
he oscilla o in he same IC die [14].
2619
VI.
REFERENCES
[
11
K.K. Cla ke and D.J. Hess, “Communica ion Ci -
cui s: Analysis and Design”,
Addison Wesley
1978.
[
21 Analog De ices, “Nonlinea Ci cui s Handbook”,
Ed.
D.
E.
Sheingold,
Analog De ices Inc. 1976.
[
31
B.P. La hi, “Mode n Digi al and Analog
Commu-
nica ion Sys ems”,
Hol Rineha , and Wins on,
1983.
[
41 T.L. B ooks and P.M. VanPe eghem, “Simul ane-
ous
‘hning
and Signal P ocessing in In eg a ed
Con inuous-Time Fil e : The Co ela ed Tuning
Loop”,
P oc.
o
he
1989
IEEE In .
Symp.
Ci c.
Sys .,
pp. 651454, 1989.
[
51
F.
K ummenache and
N.
Joehl, “A 4-MHz CMOS
Con inuous-Time Fil e wi h On-Chip Au oma ic
Tuning”,
IEEE Jou nal
o
Solid-S a e Ci cui s,
Vol.
23,
No.
3, June 1988.
[
61 C.S. Pa k and R. Schaumann, “Design
o
a 4-MHz
Analog In eg a ed CMOS T ansconduc ance-C
Bandpass Fil e ”,
IEEE
J.
Solid-S a e Ci cui s,
Vol.
23,
NO.
4, pp. 987-996, Augus 1988.
[
71 W.J.A. Hey, K. Hoen and
E.
See inck, “Accu a e
Au oma ic Tuning Ci cui
o
Bipola In eg a ed
Fil e s”,
P oc.
o
he
1990
IEEE In . Symp. Ci c.
Sys .,
pp. 1159-1162, 1990.
[
81
Y.
Tsi idis, M. Banu, and J. Khou y, “Con inuous-
Time MOSFET-C Fil e s in VLSI,”
IEEE J. Solid-
S a e Ci cui s,
Vol. SC-21, pi. 15-30, Feb ua y
1986.
[
91
R.
Schaumann, M.
S.
Ghausi, K. R. Lake ,
“Design
o
Analog Fil e s, Passi e, Ac i e RC and Swi ched
Capaci o ,
P en ice Hall, Englewood Cli s, 1990.
[lo]
B. Lina es-Ba anco, A. Rod iguez-VQzquez,
E.
Sbchez-Sinencio and J.L. Hue as, “CMOS OTA-
C High-Fkequency Sinusoidal Oscilla o s”,
IEEE
J.Solid-S a e Ci cyii s,
Vol. 26, No. 2, pp. 160-
165, Feb ua y 1991.
[ll]
Da e1 Sys em Inco po a ion, “Designe ’s Guide o
V/F Con e e s”, 1976.
[12] B. Lina es-Ba anco, “Design
o
High Fkequency
T ansconduc ance Mode CMOS Vol age Con olled
Oscilla o s”, Ph.D. Disse a ion,
Uni e si y
o
Se ille,
May 1990 (a ailable in English upon e-
ques ).
[13]
A.
Rod iguez-Vkquez, B. Lina es-Ba anco, J.L.
Hue as and E. Shchez-Sinencio, “On he Design
o
Vol age Con olled Sinusoidal Oscilla o s Using
OTAs”,
IEEE lhnsac ions on Ci cui s and
Sys-
em,
Vol. 37,
No.
2,
pp. 198-211, Feb ua y 1990.
141
T.
P.
Lin, and R.
G.
Meye , “A 250-MHz Mono-
li hic Vol age-Con olled Oscilla o wi h Low Tem-
pe a u e Coe ;cien ,”
IEEE J.
o
Solid-S a e Ci -
cui s,
Vol. 25,
NO.
2,
pp. 555-561, Ap il 1990.
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