TELKOM
NIKA
, Vol.14, No
.2, June 20
16
, pp. 456~4
6
3
ISSN: 1693-6
930,
accredited
A
by DIKTI, De
cree No: 58/DIK
T
I/Kep/2013
DOI
:
10.12928/TELKOMNIKA.v14i1.3328
456
Re
cei
v
ed
Jan
uary 1, 2016;
Re
vised Ma
rch 29, 2016; A
c
cepted Ap
ril 11, 2016
Switch Configuration Effect on Stray Capacitance in
Electrical Capacitance Volume Tomography Hardware
Arba’i Yusuf*
1,2
,
Ha
r
r
y
S
u
d
i
by
o S
1
, Dodi Sudiana
1
,
Agus San
t
os
o Tamsir
1
,
Imamul Muttakin
2
, Wah
y
u Widada
2
, Warsi
t
o P. Taruno
2,3
1
Departme
n
t of Electrical En
gi
neer
ing, Un
iver
sit
y
of Indo
nes
i
a
, Depok, Ind
o
nesi
a
,
Kampus UI, Ko
ta Depok, Ja
w
a
Barat 16
424,
Indones
ia
2
C-T
e
ch Labs, Ed
w
a
r T
e
chnol
og
y Co, T
ange
rang, Indo
nes
i
a
,
Jl. Jalur Sutera
Kav. Spektra 23 BC No. 10-
12 Alam Suter
a
,
T
angera
ng,
Banten, Ind
o
n
e
sia
3
Departme
n
t of Ph
y
s
ics, U
n
iv
ersit
y
of Ind
o
n
e
sia, De
pok, In
don
esia,
Kampus UI, Ko
ta Depok, Ja
w
a
Barat 16
424,
Indones
ia
*Corres
p
o
ndi
n
g
author, e-ma
i
l
: arbai@c-t
ech
l
abs.com
A
b
st
r
a
ct
Electrical c
apacitance volum
e
to
m
o
graphy (ECVT) system uses six
switches in o
ne channel with
config
uratio
n r
e
se
mb
lin
g “T
”
letter, so it is calle
d
“T
-sw
i
tch
”
. T
he w
o
rki
n
g sche
m
e of the sw
itch can
be
expl
ain
ed i
n
four different
mo
des
of op
erati
on, i.e. excitati
on
mo
d
e
, dete
c
tion
mod
e
, gr
oun
d mod
e
, an
d
floatin
g
mod
e
.
T
h
is rese
arch
descri
bes the
effect of
sw
itch confi
gurati
o
n to stray cap
a
citanc
e in E
C
VT
hardw
are. Stra
y capac
itanc
e
in
trod
uces
par
asitic si
gn
al fr
om other
s
our
ces; on
e of th
em is si
gn
al fr
o
m
anoth
e
r e
l
ectro
de at fl
oati
ng
mo
de w
h
en th
e sig
nal
is
stil
l
flow
ing to
det
ection c
i
rcuit.
One ch
ann
el, t
w
o
chan
nels, thre
e chan
nels, s
o
on until thir
ty-tw
o
channel
s are conn
ected to singl
e detectio
n
circu
i
t
sequ
enti
a
lly to
investi
gate th
e
effect
of stray capac
itanc
e. Both si
mu
la
tio
n
an
d ex
peri
m
ent show
the s
t
ra
y
capac
itanc
e in
creases a
l
on
g
w
i
th additio
n
of
chann
el corre
spon
ds to 0.04
6pF
for each c
han
nel.
Ke
y
w
ords
: Stray capac
itanc
e
,
T
-
sw
itch, EC
VT
, C-V circuit
Copy
right
©
2016 Un
ive
r
sita
s Ah
mad
Dah
l
an
. All rig
h
t
s r
ese
rved
.
1. Introduc
tion
Electri
c
al
ca
pacita
n
ce vol
u
me tomo
gra
phy
(ECVT
)
is on
e of 3
D
image visua
lization
techni
que
s
b
a
se
d o
n
p
e
rmittivity distribution f
r
om
capa
citan
c
e m
easure
m
ent i
n
sid
e
3
D
se
n
s
or.
Applicatio
ns
of ECVT are
very wide from indu
stri
al
to medical field su
ch a
s
multipha
se flow,
shal
e g
a
s det
ection,
bre
a
st
and
b
r
ain
scannin
g
,
al
so
being
develo
ped fo
r
non
-radiation
full-b
ody
scanni
ng. Fig
u
re 1
sho
w
s a typical blo
c
k diag
ram
of ECVT syste
m
, which ha
s three mai
n
p
a
rt
i.e. 3D sen
s
or, data acq
u
isition sy
ste
m
, and
personal co
mput
er. Variou
s geomet
ry of
the
sen
s
o
r
s hav
e bee
n de
si
gned to
ada
pt the ECVT
for different
appli
c
ation.
There a
r
e
cube,
coni
cal, twin
-plane cylin
de
r for high pre
s
sure a
nd hi
gh tempe
r
atu
r
e appli
c
atio
n
[1]; hemisph
ere
for b
r
ea
st
scannin
g
[2]; h
e
lmet for brai
n a
c
tivi
ty sca
nning
[3]; be
nd, T-sh
ape,
half-cylinde
r for
flow imagin
g
[4]; and other
geomet
ry designs.
Figure 1. Block di
agram of
ECVT syste
m
The p
r
obl
em
in ECVT
syst
em is l
o
w
re
soluti
on, he
nce image
re
co
nstru
c
tion
is
not goo
d,
ill-po
sed
re
constructio
n
p
r
oble
m
, mu
ch mo
re
artef
a
ct, an
d the
image
attra
c
ted u
p
ward
s
and
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
1693-6
930
Switch Config
uration Effect
on Stray Cap
a
citan
c
e in El
ectri
c
al Capa
citan
c
e… (A
rba
’
i Yusuf)
457
downward
s
a
t
both end
s o
f
the sen
s
o
r
. Typically
, ECVT sen
s
o
r
h
a
s la
rge
32 e
l
ectro
d
e
s
plat
e
(4x8) in fou
r
plane
s config
uration
with e
a
ch
pl
ane ha
s eight ele
c
trode a
s
depi
ct
ed in Figu
re
1.
The configu
r
ation ha
s hi
gh se
nsitivity and high
signal-to
-
n
o
ise
ratio, but less numb
e
r of
measurement
data, he
nce
red
u
ci
ng the
image
re
so
l
u
tion. Small
electrode
co
uld in
cre
a
se
the
resolution a
n
d
numbe
r of measurem
ent
data, but red
u
ce the
sen
s
i
t
ivity and sign
al-to-noi
se rat
i
o.
To ove
r
come
these
challe
nge
s, sen
s
or
desi
gn
us
in
g small ele
c
tro
de con
n
e
c
ted
togethe
r
to
f
o
rm
a la
rge
ele
c
trode
will i
n
cre
a
se
the
num
ber of m
easu
r
eme
n
ts data
and
ima
ge resol
u
tion with
out
redu
cin
g
the
sen
s
itivity an
d si
gnal
-to-no
ise
ratio
[5
].
Another way
to incre
a
se th
e a
c
curacy i
s
by
improvin
g the
dete
c
tion
ci
rcuit e.g.
u
s
in
g qu
adrat
ure
pha
se
dete
c
tion al
gorith
m
[
6
] and
a
rra
ng
ing
the sen
s
itivity distrib
u
tion
by co
ntrolli
ng di
st
an
ce
of ele
c
trod
e
pairs [7].
Combi
n
ing
some
electrode
s to
gether ne
ed
s additio
nal el
ectro
n
ic
swit
che
s
,
whi
c
h
can
cau
s
e a
nother p
r
oble
m
su
ch a
s
inc
r
e
a
sin
g
of
st
ray
capa
cit
a
n
c
e.
The
accu
ra
cy of capa
citan
c
e
mea
s
u
r
em
ent is
influe
n
c
ed
by som
e
facto
r
s, one
of
them
is stray cap
a
c
itan
ce. Stra
y capa
citan
c
e is pa
rasiti
c signal fro
m
other
sou
r
ce
s and affe
cte
d
b
y
some fa
ctors such a
s
scre
en en
clo
s
ure, cable
c
o
nn
ec
tin
g
se
ns
or
w
i
th
d
a
t
a
ac
qu
is
itio
n
s
y
s
t
em,
and
switch
u
s
ed
for
sel
e
cting ele
c
tro
d
e
pair [8]. Us
a
ge of axial
a
nd radial
gua
rd in
the
se
n
s
or
desi
gn would
redu
ce
the fringe
effe
ct and stray
ca
pacita
n
ce, which
occu
r from the rea
r
of
electrode p
a
i
r
[9]. Coaxial cable i
s
one
of sour
ce
s of stray ca
pa
citan
c
e that is high e
nou
g
h
,
about 100 pF
per meter le
ngth. Stray capa
citan
c
e from coaxial cable ca
n be d
a
mped by put
ting
the ca
pa
citance
-
to-volta
g
e
circuit (C-V circui
t)
cl
ose to
sen
s
or. Anothe
r
sou
r
ce of st
ray
cap
a
cita
nce is switch fo
r selectin
g ele
c
trode
pair.
Thi
s
pap
er
will d
i
scuss ho
w t
he switch
co
uld
affect stray
capa
citan
c
e. Each
cha
nne
l has at le
ast
six swit
che
s
conn
ecte
d to the C-V circuit.
Some resea
r
che
r
u
s
e
a
si
ngle
C-V
ci
rcuit for e
a
ch
chann
el to
red
u
ce
stray cap
a
citan
c
e,
but
the
more th
e n
u
m
ber
of chan
nel, the mo
re
com
p
lex the
hardware, i
n
efficient, and
also i
n
tro
d
u
c
i
n
g
more
noi
se
s too. Other
rese
arche
r
s u
s
e a
sin
g
le
C-V
circuit for all
cha
n
n
e
ls, therefore
the
hard
w
a
r
e
i
s
more simpl
e
,
noise
f
r
om operational a
m
plifier can be
re
du
ce,
b
u
t
has
a
noth
e
r
probl
em that is high
stray capa
citan
c
e d
e
rived from
switch.
In
this wo
rk, the
effect of swit
ch co
nfig
uration
to stray
ca
pa
citan
c
e
i
n
E
C
VT hard
w
a
r
e
will b
e
d
e
scri
bed.
Wo
rki
n
g
sche
me
of the
swit
ch
ca
n be
explai
n
ed in
fou
r
dif
f
erent m
ode
of
operation, i.e
.
excitation
mode, d
e
tect
ion mo
de,
g
r
ound
mod
e
,
and flo
a
ting
mode. All
wil
l
be
descri
bed
in
se
ction
2.1.
From the
switch
mo
de
s, equival
ent
circuits a
r
e
examined
to
get
mathemati
c
model
s, and
then sim
u
late
d usi
ng Matla
b
with p
a
ra
m
e
ters from
da
tashe
e
t in order
to obse
r
ve th
e effect of stray capa
citan
c
e. We
u
s
ed d
a
ta acq
u
isitio
n system that
has 32
-cha
n
nel
for expe
rime
nt to prove
simulation results. A
ll cha
n
nels
con
n
e
c
ted togethe
r t
o
a sin
g
le
C-V
circuit, one
cha
nnel, two
chan
nel
s, three
ch
anne
ls, and
so
on until thirt
y
-two chan
n
e
ls
con
n
e
c
ted to singl
e C-V
circuit se
que
ntially to in
vestigate the effect of stray cap
a
citan
c
e.
2. Hard
w
a
re
De
sign
Metho
d
2.1.
S
w
i
t
ch Net
w
ork Con
f
igur
ation
Basic p
r
in
cip
l
es
of
capa
citance
sen
s
o
r
i
s
the
differen
c
e
in
p
o
tential b
e
tween t
w
o
electrode
s, a
fterwa
r
d
cap
a
citan
c
e valu
e amon
g ele
c
trod
es
ca
n
be cal
c
ul
ated
by the cha
r
ge
den
sity divided by voltage differen
c
e am
ong the
ele
c
trode
s, and wri
tten as an eq
uation [10]:
(
1
)
Whe
r
e
C
ji
is cap
a
cita
nce betwe
en
el
ectrode
i
a
nd
j
,
Q
ji
is
cha
r
g
e
on el
ectro
de
j
in
du
ce
d b
y
potential differen
c
e
bet
wee
n
V
j
-
V
i
,
V
i
i
s
p
o
tential
on
ele
c
tro
de
i
,
V
j
is
potential
on
ele
c
tro
d
e
j
.
The differe
n
c
e in p
o
tenti
a
l betwe
en t
w
o ele
c
trode
s can be o
b
t
ained by a
c
tivating pair
o
f
electrode
s
a
s
ex
citation
and
dete
c
tio
n
. Based
on
pri
n
cipl
e of
ca
pa
citan
c
e
tomog
r
ap
hy, all
electrode
s should
be
scanne
d to
get
ca
pa
cita
n
c
e
data,
hen
ce
ea
ch
ele
c
trode
ca
n a
c
t
as
excitation or
detectio
n
. It is necessa
ry for swit
ch net
work to acco
mmodate all
electrode
s, which
is
cap
able
of
co
nne
cting
each el
ectro
de to
a ex
citation
sou
r
ce
or dete
c
tion
ci
rcuit. Vari
ous
swit
ch config
uration
s
for e
a
ch el
ectr
ode
modes a
r
e
shown in Figu
re 2.
The
switch
configuration
a
s
sho
w
n
at fi
gure
2
form
e
d
a
s
the
letter
“T”
; hence, it is
call
ed
T-
sw
itch
, an
d some
re
searche
r
u
s
e
d
this notati
on [11-1
3
]. With the co
nfiguratio
n, each
electrode
can
co
nne
ct to e
x
citation sou
r
ce
or
dete
c
tion
circuit de
pendi
ng o
n
t
he given
con
t
rol
Evaluation Warning : The document was created with Spire.PDF for Python.
ISSN: 16
93-6
930
TELKOM
NIKA
Vol. 14, No. 2, June 20
16 : 456 – 46
3
458
sign
al. In this de
sig
n
we
use
d
Comple
mentary M
e
tal Oxide Se
micon
d
u
c
tor
Integrated
Ci
rcui
t
(CM
O
S IC)
DG4
70 m
anu
facture
d
fro
m
Vishay Sili
c
onix. The
swi
t
ch type in th
is chip i
s
SP
DT
(sin
gle pol
e d
ual tap), which has o
ne co
mmon conn
e
c
tion pin a
n
d
two con
n
e
c
tion pin
s
i.e. NO
(no
r
mally o
p
e
n
) a
nd
NC (n
ormally
clo
s
e
d
). Some
spe
c
ificatio
ns i
n
clude
sup
p
ly voltage 4
4
volt
,
analo
g
sign
a
l
range ±15
volt, low o
n
-resi
s
tan
c
e
3.6 ohm, off-ca
pa
citan
c
e
of 85 pF,
on-
cap
a
cita
nce of
125
pF, ca
pacita
n
ce-to
-
grou
nd of
37
pF [14]. Spe
c
ification
s
d
e
scrib
ed
above
are
con
s
id
ere
d
in
switch netwo
rk de
sig
n
.
Figure 2. Switch net
work conf
iguration for differe
nt mode
The working
scheme
of switch n
e
two
r
k ca
n
be ex
plaine
d in four differe
nt mode
s of
operation, i.e.
excitation
m
ode, d
e
tectio
n mod
e
, g
r
ou
nd mo
de, a
n
d
floating
mo
de. In ex
citation
mode: swit
ch
S
1
, S
2
, and S
6
are
clo
s
ed
wh
ere
a
s swi
t
ch S
3
, S
4
, and S
5
a
r
e o
p
ened,
hen
ce
the
electrode i
s
con
n
e
c
ted to
excitation
source, a
nd t
he si
gnal
ca
n be tran
smi
tted. In excitation
mode, cl
osed
swit
ch S
6
ha
s fun
c
tion to
prevent
sign
a
l
leakage fro
m
excitation
sou
r
ce throu
gh
swit
ch S
4
flows to virtual
earth. For d
e
tection mo
de: S
1
, S
2
, and S
6
are open
ed
wherea
s swi
t
ch
S
3
, S
4
, and S
5
are
cl
osed, hen
ce capa
ci
tance sig
nal
i
s
bei
ng conv
erted into volt
age
signal i
n
side
detectio
n
circuit. In dete
c
ti
on
circuit,
clo
s
ed
switch S
3
ha
s fu
nctio
n
to prevent th
e si
gnal
lea
k
age
from excitatio
n
sou
r
ce thro
ugh switch S
1
flows to virtu
a
l earth. G
r
o
und mod
e
: switch S
2
, S
3
, S
4
,
and S
6
a
r
e
cl
ose
d
wherea
s switch S
1
a
nd S
5
are op
end, he
nce the ele
c
trode
is conn
ecte
d
to
virtual ea
rth.
Floating m
o
d
e
: switch S
1
, S
2
, S
4
, and S
5
are ope
ned whe
r
ea
s switch
S
3
a
nd S
6
are
clo
s
ed, he
nce the electrod
e is ope
n circuit.
All config
urations shoul
d b
e
imple
m
ente
d
on
all
ele
c
trode
s. A
pat
h alo
ng
ele
c
trode
t
o
the excitation
source n
eed
s three
swit
ches a
s
well
as to the detection
circuit, therefore ea
ch
electrode
ne
eds six
CM
OS switche
s
. Accomm
o
d
a
ting
3
2
-el
e
ctrode
s req
u
ires 192
CM
OS
swit
che
s
, whi
c
h could b
e
functio
ned in
any mode of config
uratio
n.
2.2. Detec
t
ion
Ci
rcuit
The capa
cita
nce
sign
al fro
m
electrode
pairs
ne
eds t
o
be convert
ed into voltag
e sign
al
for further p
r
oce
s
sing u
s
i
ng an ele
c
tro
n
ic ci
rcui
try namely cap
a
ci
tance
-
to-volta
ge (C-V)
circuit.
The C-V ci
rcuit
is built
by
an ope
ration
al
amplif
ie
r, feedb
ack
re
si
stor,
a
nd fe
e
dba
ck capa
ci
tor
whi
c
h would
conve
r
t the current into a
c
voltage
[15
,
16] as sho
w
n in Figu
re
3. Capa
cita
nce
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
1693-6
930
Switch Config
uration Effect
on Stray Cap
a
citan
c
e in El
ectri
c
al Capa
citan
c
e… (A
rba
’
i Yusuf)
459
con
n
e
c
ted
at
the inp
u
t a
nd
output of
the
electrode
i
s
stray capa
cita
nce
(Cq
)
whi
c
h is imp
o
sed
by
scree
n
se
nso
r
, cable,
and
ele
c
tro
n
ic switch
es
[6].
Base
on
the
Kirch
hoff la
w, cu
rrent
ente
r
in
g
node
and le
a
v
ing node i
s
equal
(
i
1
=i
2
), t
hus, the volta
ge re
present
i
ng capa
citan
c
e me
asurem
ent
can b
e
retri
e
ved from:
;
(
2
)
In the equation,
is voltag
e output that repre
s
e
n
ts capa
citan
c
e measure
m
ent,
is
sinu
soi
dal voltage input injecte
d
to the electrode,
is feedba
ck resi
stor,
is feedback
cap
a
cit
o
r,
is angular fre
q
uen
cy,
is object ca
pa
citance to
be
measured. This equ
atio
n
contai
ns t
w
o
eleme
n
ts i.e
.
capa
citive
and
re
sist
ive.
Smaller
re
si
stan
ce valu
e
cau
s
e
s
gre
a
t
er
con
d
u
c
tivity
and vice versa. In the
capa
ci
tan
c
e
measurement
method,
co
ndu
ctivity will be
dampe
d by setting
≅
1
, which can b
e
made
by sele
cting suitable value
of
and
.
Figure 3. Cap
a
citan
c
e
-
to-v
ol
tage ci
rcuit (C-V circuit)
Cap
a
cita
nce being me
asu
r
ed on
C-V circuit ab
ove is actu
ally
and
, whos
e stray
cap
a
cita
nce measured in parall
e
l with
, hence total capa
citan
c
e n
a
mely standi
ng cap
a
cita
n
c
e
(
) [16]. In
the capa
citan
c
e
measurement
, stray ca
p
a
ci
tance i
s
the para
s
itic
cap
a
citan
c
e that
alway
s
p
r
e
s
e
n
t in
every m
easure
m
ent,
whi
c
h i
s
caused by
coaxial
ca
ble
alon
g
sen
s
o
r
and
d
a
ta
acq
u
isitio
n
system, CM
O
S
switch
to a
rra
nge
ea
ch
electrode
a
s
excitation an
d
dete
c
tion,
and
scree
n
sen
s
or surrou
ndi
ng ele
c
tro
d
e
.
Stray cap
a
citan
c
e
can
redu
ce th
e
measureme
n
t
sen
s
itivity in the ele
c
troni
c
circuit.
2.3.
Equiv
a
lent Circuit of S
w
i
t
ch Ne
t
w
o
r
k
Choi
ce
of the
CM
OS
swit
ch is limited
by
the n
eed
to
cover
excitatio
n
sou
r
ce
sign
al level
use
d
in syst
em, typically is below 1
5
Vp
-p. The
chosen CM
OS switch is DG
470 wi
th
spe
c
ification as de
scribe
d in
sect
io
n 2.1
.
There i
s
o
n
e
switch in
o
ne IC pa
ckag
e, so
there i
s
no
cap
a
citive
cro
sstal
k
betwee
n
switche
s
, b
u
t there i
s
ca
pacita
n
ce to
grou
nd
aroun
d 37
pF
on
e
a
ch
swit
ch termin
al. Figure 4
rep
r
e
s
ent
s equivalent
ci
rcuit of switch
network for one elect
r
o
d
e
cha
nnel, whi
c
h ha
s two
p
a
rts i.e. equi
valent swit
ch
for excitatio
n
sou
r
ce on
the left side
and
equivalent
switch fo
r det
ection
circuit
on the ri
g
h
t
side. Each
CMOS
swit
che
s
h
a
s
se
ries
comp
one
nt
C
s
,
R
s
also ha
s capa
citan
c
e
to groun
d (
C
g
).
Figure 4. Equivalent circuit of switch net
work for o
ne
electrode
Evaluation Warning : The document was created with Spire.PDF for Python.
ISSN: 16
93-6
930
TELKOM
NIKA
Vol. 14, No. 2, June 20
16 : 456 – 46
3
460
In ECVT hardwa
r
e, ea
ch
cha
nnel h
a
s
ex
citation si
g
nal indep
end
ently with ad
equate
high voltag
e, hen
ce the
excitation
circuit
is
stray-
im
m
une. Th
e pa
rt that suffers t
he mo
st impa
ct
by stray cap
a
citan
c
e in ECVT hardware is the det
ection ci
rcuit, therefo
r
e an
al
ysis in this work
focu
sed o
n
d
e
tection
circu
i
t. In detection mode, swit
ch S
4
, S
5
“on” whil
e switch S
6
“off”, one of
terminal o
n
S
6
conn
ecte
d to gro
und, h
e
n
ce th
e point
betwe
en S
4
, S
5
, S
6
conne
cted a
s
pa
rall
el
with three
C
g
and C
soff
as
de
p
i
c
t
ed
in
F
i
gu
r
e
5
.
Figure 5. Equivalent circuit with imagin
a
ry
value; (a) d
e
tection mo
d
e
; (b) floating
mode
Floating m
o
d
e
is al
so
influ
enced by
stra
y capa
citan
c
e in dete
c
tion
circuit. Swit
ch S
4
, S
5
“off” while
switc
h
S
6
“o
n”, th
erefo
r
e the
p
o
int between
S
4
, S
5
, S
6
con
necte
d a
s
p
a
rallel with th
re
e
C
g
, C
son
, and R
son
.
3.
Stra
y
Capacitanc
e on S
w
i
t
ch Net
w
o
r
k
Initial cap
a
cit
ance will
present in the
ECVT
hardware
prio
r to me
asur
em
ent p
r
o
c
ess, it is
calle
d stray
cap
a
cita
nce, whi
c
h ma
rke
d
by vo
ltage occure
nce at the C-V circuit outp
u
t. To
analyze
the
effect
of switch
to
stray cap
a
cita
nce, ci
rcuit ab
ove ne
ed
s to
be
conve
r
ted
in
impeda
nce circuit form, with all co
m
pone
nts in
compl
e
x values a
s
sho
w
n in Fig
u
re 6.
Impedan
ce
o
n
Z
1
and
Z
5
re
p
r
es
en
t ca
pa
c
i
ta
nc
e
C
g
; i
m
peda
nce on
Z
2
and
Z
4
re
pre
s
ent
switches
S
5
and S
4
that has value
R
son
//C
son
for detection m
o
d
e
and
C
soff
for floating mod
e
; impeda
nce
on
Z
3
r
e
pr
es
e
n
t
s s
w
itc
h
S
6
th
at has value
3C
g
C
soff
for d
e
tection
mod
e
and
3
C
g
C
so
n
//R
son
for floating
mode.
Figure 6. Simplification of the circuit for
analyz
i
ng the
switch effect to stray ca
pa
citan
c
e
The impe
dan
ce on e
a
ch compon
ent ca
n be cal
c
ul
ated usi
ng eq
u
a
tion as follo
ws:
(
3
)
;
(
4
)
(
5
)
(
6
)
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
1693-6
930
Switch Config
uration Effect
on Stray Cap
a
citan
c
e in El
ectri
c
al Capa
citan
c
e… (A
rba
’
i Yusuf)
461
;
(
7
)
Whe
r
e
,
,
is impeda
nce on detectio
n
mode while
,
,
is impeda
nce on
floating mode
. Moreover,
we can find the cu
rr
ent an
d voltage eq
uation on ea
ch the bran
ching
points a
s
follo
ws:
(
8
)
(
9
)
(
1
0
)
(
1
1
)
(
1
2
)
The voltage
drop to dete
c
tion electrod
e is very sm
all about 10
– 20 mV, hence
0.02
cos
2
2.5MHz was
use
d
in
simul
a
tion to an
alyze
stray
capa
citan
c
e o
n
switch net
work.
By
using (8
) until
(1
2), current
o
n
ea
ch
bran
chi
ng
p
o
i
n
ts can be calcul
ated
a
n
d
the
re
sult
s
a
r
e
sho
w
n
on
Ta
ble 1. T
he v
a
lue
s
in th
e
Table
1 a
r
e i
n
imagi
nary
and
pha
so
r f
o
rm
s in
orde
r to
facilitate further
cal
c
ulation. In the
detection mode, current from
el
ectrode
(i
1
)
i
s
about 8
4
.8 µ
A
then splitted i
n
to
i
1
, i
2
,
and
i
3
.
Conseque
ntly, current flowin
g to
i
4
dec
reas
es
to 11.6 µA. For the
floating mo
d
e
, cu
rre
nt fro
m
ele
c
trod
e
(i
1
)
i
s
ab
out
38.3 µA then
splitted i
n
to
to
i
1
, i
2
,
and
i
3
.
Con
s
e
quently
, current flo
w
i
ng to
i
4
de
cre
a
se
s to
38.9
nA. In ideal
condition
wh
e
n
floating m
o
de,
cur
r
e
n
t
i, i
1
, i
2
, i
3
, i
4
should
not flowe
d
int
o
dete
c
tion
ci
rcuit,
h
o
weve
r in fa
ct the
currents are
still
flowing i
n
to
detectio
n
ci
rcuit through
C
soff
i
n
s
w
i
t
c
h
e
s
S
5
an
d S
4
, hence
it cau
s
e
s
stray
cap
a
cit
a
nc
e.
Table 1. The
curre
n
t value
s
on ea
ch b
r
a
n
chi
ng point
s
Detection Mode
Floating Mode
9.88
10
8.4810
or
8.48
10
cos
2
1.56
1.2810
3.83
10
or
3.83
10
cos
2
1.57
1.16
10
or
1.16
10
cos
2
1.57
1.16
10
or
1.16
10
cos
2
1.57
9.88
10
7.3210
or
7.32
10
cos
2
1.56
1.2810
2.67
10
or
2.67
10
cos
2
1.57
8.11
10
6.16
10
or
6.16
10
cos
2
1.56
1.6710
2.67
10
or
2.67
10
cos
2
1.56
1.77
10
1.16
10
or
1.16
10
cos
2
1.56
3.89
10
7.5210
or
3.89
10
cos
2
3.12
Figure 7. Each cha
nnel
co
nne
cted toget
her throug
h e
l
ectro
n
ic
swit
che
s
cau
s
e
s
stray
cap
a
cita
nce; (a) e
quivalent
circuit; (b) Si
mplification of
each
cha
nne
l
Evaluation Warning : The document was created with Spire.PDF for Python.
ISSN: 16
93-6
930
TELKOM
NIKA
Vol. 14, No. 2, June 20
16 : 456 – 46
3
462
The curre
n
t
i
4
based o
n
T
able 1
is ve
ry small a
bout
38.9 nA fo
r
one
cha
nnel,
if som
e
cha
nnel
s a
r
e
con
n
e
c
ted to
gether thro
ug
h switch
es,
t
he current flo
w
ing i
n
to det
ection
ci
rcuit will
increa
se
s a
s
depict
ed on
Figure 7, h
ence incre
a
ses
stray cap
a
citan
c
e. Fig
u
re 7
(
a
)
sho
w
s
equivalent ci
rcuit; whe
r
ea
s
Fig
u
re 7(b
)
sho
w
s
sim
p
lification
of each chan
n
e
l. The aim
of
mergi
ng cha
nnel
s
is
to conne
ct small
elect
r
od
e
to
form la
rg
er
electrode
through
ele
c
tro
n
ic
swit
che
s
a
s
d
e
scrib
ed in section 1.
4. Resul
t
s
and
Analy
s
is
This
cir
c
um
st
an
ce ma
k
e
s c
u
r
r
ent
inf
l
uen
ce t
o
st
ray
ca
pa
cit
a
n
c
e is
i
4
about
3.89
10
7.52
10
. In this
c
a
s
e
,
s
w
it
c
h
network
c
i
rc
uit
c
o
nnec
ted to det
ec
tion
c
i
rc
uit
will
be an
alyze
d
. The
switch
netwo
rk conn
ected
to cha
r
ge am
plifier
or
C-V
circuit
ha
s fun
c
tion
to
conve
r
t curre
n
t into voltag
e. Impeda
nce Z
f
represe
n
ts
resi
sto
r
and cap
a
cito
r
(R
f
//C
f
) hav
ing
values of 2
2
K
Ω
and 22
pF
respe
c
tively, with voltage
excitation of
20Vp-p, impe
dan
ce Z
f
can
be
obtaine
d at
374
.2
2844
.5
Ω
.
Circuit config
uration on Fi
gure 8 is the summi
ng am
plifier circuit,
so that current flowing through
branching poi
nts
will increase the
I
f
curre
n
t. Con
s
equ
ently,
voltage sig
nal
at the output of Op-Amp in
cre
a
ses, he
n
c
e st
ray ca
pa
citan
c
e is mu
ch large
r
.
Stray capa
citance is cal
c
ulated usi
n
g
(2),
all parameters are
then simula
ted using
Matlab i
n
two
co
ndition
s. F
i
rst, id
eal
co
n
d
ition
whe
r
e
only pa
ram
e
ters b
a
sed
on
data
s
he
et a
r
e
use
d
in simu
lation. Secon
d
, adding ra
ndom current
noise a
bout
19 – 22 µA in simulatio
n
.
Experiment
o
n
ECVT h
a
rd
ware n
eed
s t
o
be
done
to
prove th
e si
m
u
lation
re
sults. Experim
en
ta
l
data is g
a
the
r
ed u
s
in
g dat
a acquisitio
n
system
DAQ
3320
1 suffici
ent for 32
-ch
annel a
c
q
u
isi
t
ion
of data. All ch
annel
s
conn
e
c
ted to
g
e
ther to a sin
g
le
C-V circuit, wit
h
one
ch
anne
l, two ch
ann
e
l
s,
three chan
ne
ls; so on unti
l
thirty-two chann
els
conn
ected to sin
g
l
e C-V ci
rcuit sequ
entially to
inv
e
st
igat
e
t
h
e ef
f
e
ct
of
st
ray
cap
a
cit
a
n
c
e.
S
u
bsequ
ently, voltage
sig
nal
at O
p
-Amp
output
is
recorded a
n
d
analyze
d
, an
d the result
shown on Figu
re 9. Total cu
rre
nt
i
4
and voltage si
gnal
at
Op-Am
p
outp
u
t can be
cal
c
ulate
d
with the followi
ng e
quation:
⋯
(
1
3
)
(
1
4
)
Figure 9. The
effect of additional ch
ann
e
l
to
ward
s: (a
)
Voltage outp
u
t magnitude;
(b) Stray
cap
a
cit
a
nc
e
Based
on
g
r
aphi
cs on
Fi
gure
9, th
e
si
mulation i
n
id
eal
con
d
ition
resulting i
n
lo
w valu
e
down to Pico
Farad in
stea
d of Femto Farad
1
10
, this is due to no noi
se ad
ded i
n
simulatio
n
an
d only pa
ra
meters in th
e data
s
he
ets use
d
in
sim
u
lation (blue
line). In fact,
the
circuit in ECVT hard
w
a
r
e
has n
o
ise from oth
e
r
so
urces
su
ch
a
s
PCB de
sig
n
, comp
one
n
t
s
layout, excitation sig
nal tha
t
passes th
ro
ugh PCB
tra
c
k, and adj
ace
n
t track in pa
rallel, whi
c
h can
cau
s
e
cap
a
ci
tance effe
ct. The CM
OS
swit
che
s
al
so ge
ne
rate
electromag
n
e
tic interfe
r
e
n
ce
(EMI) [17],
a
nd
some
g
r
o
undin
g
in
the
ci
rcuit al
so
condu
ct EMI [
18]. He
nce, the
simulatio
n
with
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
1693-6
930
Switch Config
uration Effect
on Stray Cap
a
citan
c
e in El
ectri
c
al Capa
citan
c
e… (A
rba
’
i Yusuf)
463
addition
al noi
se a
s
mentio
ned befo
r
e gi
ves re
sult
s in
value of Pico Fara
d (g
re
en line); a
nd
so
doe
s the exp
e
rime
nt results in ord
e
r of
Pico Fa
rad (red line).
5. Conclu
sion
The
switch
n
e
twork in E
C
VT is ve
ry i
m
porta
nt a
s
t
he
sign
al e
n
tran
ce f
r
om
el
ectro
de,
whe
r
e it has
four mod
e
of operatio
ns i.
e.
excitation mode, dete
c
tion mode, gro
und mod
e
, and
floating mod
e
.
Switch used
in ECVT hardwa
r
e i
s
DG
470 that ha
s
spe
c
ific p
a
ra
meters incl
ud
ing
low on
-resi
s
t
ance and lo
w on
-capa
citance. Adding
of switche
s
nece
s
sa
ry to con
n
e
c
t some
electrode
s to
gether will
in
crea
se
stray capa
citan
c
e
which
is i
ndi
cat
ed by in
crea
sing of voltag
e
at
Op-Am
p
out
put. Both of simulatio
n
and expe
ri
m
ental data
show that
ch
annel a
dditio
n
will
increa
se the
stray ca
pa
ci
tance a
s
la
rge as
0,02V
and 0,046
p
F
. Stray cap
a
citan
c
e
stro
ngly
influen
ce
s m
easure
m
ent
accuracy, se
nsitivity, and resolution. T
herefo
r
e, it is very importa
nt to
notice i
n
PCB desi
gn a
n
d
co
mpon
ent
s layout, t
hat
excitation si
gnal sho
u
ld not
pa
ss
th
ro
ugh
PCB switche
s
. Mo
reove
r
,
two p
a
rall
el tracks in
P
C
B desi
gn whi
c
h
can
cau
s
e ca
pacita
n
ce
eff
e
ct
also n
eed to
be co
nsi
dere
d
.
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