TELKOM
NIKA Indonesia
n
Journal of
Electrical En
gineering
Vol.12, No.5, May 2014, pp
. 3713 ~ 37
1
8
DOI: http://dx.doi.org/10.11591/telkomni
ka.v12i5.5004
3713
Re
cei
v
ed O
c
t
ober 3
0
, 201
3; Revi
se
d Decem
b
e
r
20, 2013; Accept
ed Ja
nua
ry 7,
2014
Accurate Low-Current Measur
e
ment Circuit for
Multimeters and Oscillograps
Shuqin Gen
g
*, Chen Liu,
Jinhui Wan
g
, Ligang Ho
u, Ying Yuan
Dep
a
rtment of Electron
ic Information a
nd C
o
ntrol Eng
i
n
eeri
ng, Beij
ing U
n
i
v
ersit
y
of T
e
chnol
og
y 1
509
#,
Beijing Univers
i
t
y
of T
e
chnology
,
100hao, Ping
ley
u
anlu, Chaoy
ang dist
rict, Beijing, China
*Corres
p
o
ndi
n
g
author, e-ma
i
l
: gengs
hu
qin
@
bjut.e
du.cn
A
b
st
r
a
ct
A simp
le a
n
d
high-
precis
io
n cu
rrent-to-v
o
ltag
e (I/V) converter circ
ui
t for multi
m
et
ers an
d
oscill
ogr
aphs
i
s
prese
n
ted
in
this pa
per. T
h
e I/V conver
ter
measur
es the
electric c
u
rre
n
t
w
i
th uA an
d
n
A
selecta
b
le ra
ng
es in the frequ
ency ran
ge fro
m
dir
e
ct cu
rren
t
to 1MH
z
. C
i
rc
uit techno
lo
gy is also disc
usse
d.
System Archite
c
ture is presen
ted and
d
ual p
o
larity pow
er is
desig
ned. Po
w
e
r detector circuit is expla
i
n
e
d
.
Measur
e
m
ent
data ar
e o
b
tai
n
ed. Li
ne
arity a
nd the
error
ar
e an
aly
z
e
d
. T
h
e typica
l acc
u
r
a
cy of the
μ
Cur
r
ent
is hi
gher
by 0.
085
% in
the
μ
A and
nA ra
ng
es.
μ
Curre
nt c
an b
e
us
ed
in
detectin
g
l
o
w
uA and
nA i
n
cu
rren
t
systems, chi
p
s
,
and modu
les.
Ke
y
w
ords
:
I/V converter, low
current, hig
h
pr
ecisio
n, measu
r
ement
Copy
right
©
2014 In
stitu
t
e o
f
Ad
van
ced
En
g
i
n
eerin
g and
Scien
ce. All
rig
h
t
s reser
ve
d
.
1. Introduc
tion
Accu
rately m
easurin
g the
slee
p an
d o
p
e
rating
curre
n
t of a mi
crocontrolle
r [1] a
nd oth
e
r
module
s
of
embed
ded
systems i
s
a
comm
on ta
sk. Nu
merou
s
mea
s
ureme
n
t appli
c
ation
s
of
high-i
m
ped
an
ce devi
c
e
s
such a
s
ultrasound pi
ezoel
ectro
n
ic t
r
an
sducers are u
s
ed in
“surfa
ce
”
microscopy [2-5]. Tuning forks, torsion
oscillators
, and elect
r
ostatically dr
iven
grids are types of
useful
experi
m
ental tool
s for stu
d
ying
the phy
si
cal
prop
ertie
s
o
f
quantum li
quid
s
an
d ot
her
system
s at low an
d very
low tempe
r
ature
s
[6]. Lowe
r
su
pply
voltages for current batt
e
ry-
powere
d
circuits co
rrespo
nd to greate
r
req
u
ir
e
m
en
ts for accu
rately measu
r
ing the sup
p
l
y
c
u
rrent [7].
Ho
wever, in
our
experim
e
n
t, the end n
ode of
wirele
ss se
nsor net
works will
not
tran
smit
or
re
ceive
d
a
ta when
th
e en
d-n
ode
curre
n
t of
wi
rele
ss sen
s
o
r
n
e
two
r
ks i
s
m
onitored
by
multimeter.
Howeve
r, the
e
nd n
ode
fun
c
tions
we
ll
wh
en the
en
d-n
ode
cu
rrent i
s
n
o
t mo
nitored.
The
sam
e
probl
em
occurs the
whe
n
the
multi
m
eter i
s
ch
ange
d. The
re
ason fo
r this
phen
omen
on
is that th
e b
u
rde
n
voltag
e is typi
ca
lly
spe
c
ified i
n
mV/A. The value
cha
nge
s with
varying
cu
rre
nt ra
nge
s. T
hus, th
e b
u
rden
volta
ge
may have
1
m
V/A, 1mV/mA, or
1mV/
μ
A.
Multimeters with good p
e
r
forma
n
ces
will at leas
t decrea
s
e the
value to 0.1 mV/uA. During
transmissio
n, the
system
cu
rr
ent i
s
approximatel
y 16mA, a
n
d
4
-
, 4.5
-
,
5-, a
nd
6-di
git
multimeters will decre
ase
the value to
1.6V, t
hus ca
usin
g dysfun
ction to the end-n
ode
syst
em.
Jon
e
s [1] en
cou
n
tere
d this pro
b
lem in
the past an
d desig
ned
an adapte
r
for multimeters.
Ho
wever, th
e
battery volta
ge di
re
ctly su
pplie
s po
we
r
to the
circuit. Thu
s
, a
de
crea
sing
batte
ry
voltage influe
nce
s
mea
s
u
r
ement pe
rformance. An
additional feat
ure is the nA
current ra
ng
e,
whi
c
h i
s
not f
ound i
n
mo
st multim
eters. Measuri
ng th
e cu
rrent with
prob
es i
s
n
o
t
conveni
ent for
oscillog
r
ap
hs.
Such
a
s
sp
eaki
ng voi
c
e
and
huma
n
body move
ment cau
s
ed
by vibration
will
affect the me
asu
r
em
ent in
strum
ent.
To achieve n
o
ise
redu
ctio
n as far
as
possibl
e, cu
rrent ad
dition
of vibration isolatio
n
device in the circuit, fixtures, while out
si
de of t
he instrume
nt incre
a
se
d shiel
d
in
g box to redu
ce
the slight vi
bration
on
measurement
result of
external interf
eren
ce, the
cost of hi
gher
impleme
n
tation is more co
mplex [8]. Thus, we aim
to
improve the desi
gn ci
rcuit in this study for
conve
n
ient conne
ction
with oscillog
r
ap
hs.
Evaluation Warning : The document was created with Spire.PDF for Python.
ISSN: 23
02-4
046
TELKOM
NI
KA
Vol. 12, No. 5, May 2014: 3713 – 37
18
3714
2. Sy
stem Architec
ture
Low-current
monitor
s
y
s
t
ems
mus
t
hav
e low
nois
e
,
low drift, and ul
tra-low offs
et.
The
curre
n
t mea
s
urem
ent sy
stem archite
c
tu
re i
s
sho
w
n
as Fi
gure 1.
The
system i
s
con
s
iste
d o
f
a
low
cu
rre
nt [9], an a
c
tive cu
rre
nt-to-vo
ltage (I/V
)
co
nverter, a
bat
tery, a low
dropout
(L
DO),
a
power
dete
c
tor, an
d a d
u
a
l pola
r
ity po
wer supply.
The d
ual p
o
l
a
rity po
wer supply for th
e
I/V
conve
r
ter.
Th
e I/V circuit
module
mu
st
be
highl
y
p
r
eci
s
e.
The
output
can
b
e
conn
ecte
d
to
multimeters o
r
o
scill
ograph
s, and
the I/
V circui
t m
o
d
u
le ha
s t
w
o I
/
V chan
nel
s f
o
r
cha
ngin
g
the
measurement
range
(uA/n
A
).
Figure 1. Block
Diag
ram o
f
a Low-cu
rre
nt A
dapter System for Multi
m
eters and O
scill
ograph
s
2.1. I/V Con
v
erter Mo
dule
Figure
2
sho
w
s
the sch
e
m
atic of a non-inve
rting l
oop amplifie
r. Suppose th
e closed-
loop a
m
plifier use
s
an id
ea
l ope
rational
amplifier
(op
amp). An i
n
finite ope
n-lo
o
p
gain Av
cau
s
e
s
op amp
s
to h
a
ve almo
st zero in
put differential vo
lta
ge, thus, the
relation
shi
p
b
e
twee
n the in
put
and outp
u
t voltages i
s
as fo
llows:
in
in
in
/
1
*
4
9
/
1
1
*
5
0
ou
t
f
VR
R
V
V
V
（）
(1)
Whe
r
e
the
re
sisto
r
R
and
t
he fee
dba
ck
resi
stor Rf
ca
n be
a
value
of IK
Ω
and IM
Ω
, respec
tively,
with a magnifi
cation rang
e of 0 to 100.
Figure 2. Sch
e
matic of a Simple
Several
ele
m
ents i
n
flue
nce
data
accuracy,
su
ch
as the
noi
se
pro
d
u
c
ed
by the
electrometri
c amplifier, pre
c
isi
on
of the
scaling
re
si
stor, ci
rcuit
of t
he me
asured
cu
rrent, ci
rcuit
techni
que
s,
measurement
enviro
n
me
nt, and
cable
s
.
The o
p
a
m
p i
nput imp
eda
n
c
e i
s
not infini
te,
and the re
si
stance
Rf is subje
c
t to the limits
of the amplifier inp
u
t impedan
ce. The prima
r
y
factors affecti
ng the se
nsit
ivit
y of the micro
-
curre
n
t measurement
are op am
p bias
curre
n
t Ib,
noise-voltage, and zero-point drift. The instantane
ous value of the input
noise current of
th
e
amplifier i
s
b
a
se
d on
the
curre
n
t ori
g
in
ating fr
om
co
nstru
c
ting
an
d ci
rcuit ele
m
ents,
su
ch
as
leakage of i
n
sul
a
tors, ca
bles, a
nd p
r
i
n
ted ci
rcuit boards
(PCB
s) d
u
ri
ng tra
n
smi
ssi
on. T
h
e
instanta
neo
u
s
value
of the noi
se
cu
rrent of
the
amplifier i
s
based o
n
th
e cu
rrent of
th
e
instanta
neo
u
s
value of thermal noi
se vo
ltage of
the scalin
g re
sisto
r
and the in
stantane
ou
s value
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
2302-4
046
Accu
rate L
o
w-Cu
rrent Mea
s
urem
ent Circuit
for Multi
m
eters and O
scill
ograp
s (S
huqin G
eng
)
3715
of input noise
voltage of the amplifier a
n
d
the input offset voltage of
the amplifier.
MAX4239 i
s
one of the M
a
xim int
egrated produ
cts,
CA in USA.
It is an
ultra
-
lo
w offset,
low
nois
e
, low drift, and ul
tra-high-prec
is
ion amplifier that offe
rs near-zero dire
c
t
c
u
rrent
(DC)
offset and
d
r
ift by paten
ted auto
c
orrelating
ze
roi
ng techniq
u
e
s. Thi
s
me
thod con
s
ta
ntly
measures and compensates
for the input offs
et, thus eliminatin
g drift, temperature,
and 1/f noise
effects over ti
me. Device
feature
rail-to
-rail
out
put
s, operate
from a
si
ngle
2.7V
to 5.5V
supp
ly,
and
co
nsume
only 6
0
0
μ
A.
An a
c
tive-lo
w
sh
utdo
wn
m
ode
de
cre
a
se
s the
supply
curre
n
t to 0.1
μ
A
[10].
Given that an
ammeter wit
h
an active I/V c
onverte
r d
oes n
o
t have
the short
c
o
m
ings of
an ammete
r with a passiv
e
I/V converter (i.e., ex
ce
ssive inp
u
t re
sista
n
ce and
a shunt volta
ge)
[11], a feedba
ck
stru
cture is sel
e
ct
e
d
for this low-cu
rrent adapte
r
.
Figure 3
sho
w
s th
e sch
e
m
atic of the I
/
V c
onverte
r.
A low
curre
n
t passe
s th
rough th
e
resi
stan
ce, th
us
cha
nging
the cu
rrent to ui. The
ui
then multiplie
s the am
plification fa
ctor
o
f
MAX4239, th
us
re
sulting i
n
Vout. Two
curre
n
t ran
g
e
s
a
r
e d
e
fined
by the sh
unt
re
sisto
r
on
e
a
ch
rang
e and th
e gain of MAX4239.
Figure 3. I/V
Conve
r
ter
Circuit
R9
(20 K 0.
1
%
) is the
shu
n
t re
sisto
r
for t
he nA rang
e, R9 p
r
ovid
e
s
a b
u
rden v
o
ltage of
20
μ
V/nA (1
nA*20 K). T
he 20
μ
V
sig
nal an
d 1m
V (20 uV*
5
0
)
is the i
npu
t and outp
u
t of
MAX4239, re
spe
c
tively. The o
scill
ogra
ph o
r
mult
im
eter
will di
spl
a
y 1mV. R10
(20
R 0.1%
) is
swit
che
d
in t
he
μ
A rang
e by SW1B, which p
r
ovide
s
a burde
n voltage of 20
μ
V/
μ
A (1
μ
A*20 R).
S
W
1A
s
e
le
ct
s w
h
ic
h s
h
u
n
t
resi
st
o
r
is
f
ed t
h
ro
u
g
h
the amplifie
r. Table
1 shows the
cu
rrent
rang
e.
Table 1. Unit
of I/V and I
in
-m
a
x
Unit I/V
Iin-max
uA 1mV/uA
±2200uA
nA 1mV/nA
±2200nA
2.2. LDO Voltage
Regula
t
or
A stable volta
ge can
redu
ce the ne
gative e
ffects on measurement
ac
cu
ra
cy; he
nce,
we
cho
o
se the v
o
ltage
regul
ator
chip
s. Th
e
HT73
50 i
s
o
n
e
of the
HOL
T
EK Taiwa
n
Compl
e
me
ntary
Metal Oxide
Semico
ndu
ct
or (CM
O
S) L
D
O voltag
e r
egulato
r
s. It i
s
u
s
ed
in thi
s
devi
c
e. Thi
s
voltage re
gul
ator can deli
v
er up to 25
0m
A of cu
rre
nt while
con
s
uming o
n
ly 4
μ
A of quiescent
curre
n
t (typical). A se
ries
of four al
kalin
e batte
rie
s
a
r
e use
d
in this device. Th
e device
can
u
s
e
lithium battery, which re
sults in low
cut-off vo
ltage. The alkalin
e battery is
a gree
n devi
c
e,
whe
r
ea
s lithiu
m
battery cau
s
e
s
poll
u
tion.
The inp
u
t an
d output volta
ges
of this d
e
vice is
6 an
d
5
V, respe
c
tivel
y
. Both the dropout voltage
and tempe
r
a
t
ure co
efficie
n
t are low.
Evaluation Warning : The document was created with Spire.PDF for Python.
ISSN: 23
02-4
046
TELKOM
NI
KA
Vol. 12, No. 5, May 2014: 3713 – 37
18
3716
2.3. Dual Polarit
y
Po
w
e
r
The I/V con
v
erter
need
s a bal
an
ced
dual
pola
r
ity powe
r
. M
C
P600
2 i
s
o
ne of th
e
Microchip T
e
chn
o
logy In
c. USA, whi
c
h
is a
n
op
amp
that ha
s a
1
M
Hz gai
n ba
ndwi
d
th p
r
od
uct
and a
90°
ph
ase
margin
(typ.). This
op
amp al
so m
a
i
n
tains
a 45
°
pha
se m
a
rgi
n
(typ.) with
a
500
pF ca
pa
citive load. R1 a
n
d
R2 di
stribute
the ba
ttery voltage. MCP6
002 supp
ort
s
rail-to
-rail inp
u
t
and outp
u
t swing
s
. The
d
ual pola
r
ity in this device i
s
2.5 an
d
−
2.5 V. This op
amp is
de
sig
ned
with the adv
anced CM
O
S
process, which h
a
s a
p
o
we
r su
pply rang
e of 1.8 V to 5.5 V.
The
output voltag
e rang
e of the MCP60
02 op amp is VDD
−
25 mV (min.) and VS
S + 25 mV (max.)
whe
n
RL
= 1
0
k
Ω
a
nd is
con
n
e
c
ted to
VDD/2 an
d V
DD
= 5.5V. The MCP6
0
01/2/4 op am
p is
desi
gne
d to prevent pha
se
reversal
whe
n
the
input pi
ns exceed th
e sup
p
ly voltages [12].
2.4 Po
w
e
r Detec
t
or
Desi
gn
Figure 4
sho
w
s th
e po
we
r and po
we
r d
e
tector
sche
matic. Anoth
e
r OA of M
C
P6002
can
detect
and
de
termine
the b
a
ttery voltage
. Whe
n
the
b
a
ttery
ene
rgy is sufficient a
nd
the device
is
turned
on, the output voltage of IC1B
is high
er
tha
n
the thre
sho
l
d voltage of Q1. The outp
u
t
voltage will
tu
rn o
n
Q
1
an
d
the g
r
een
L
E
D will
be
co
me b
r
ight. When the
batte
ry voltage i
s
l
o
w,
the output vol
t
age of IC1B
will be
lower than the threshold of
Q1
and Q1
will be t
u
rned off. The
use
r
can
cha
nge th
e batt
e
ry when
the
red
LE
D be
come
s
bri
ght
. Thre
e
zero
re
sista
n
ces
are
pre
s
ent an
d a
r
e used to ma
ke hol
es a
nd interconn
ect comp
one
nts conve
n
iently.
Figure 4. Power a
nd Po
wer Dete
cto
r
Schem
atic
2.5 Circuit T
echnique
Circuit te
chn
o
l
ogy is im
port
ant for a
c
hi
eving hig
h
p
r
e
c
i
s
ion, m
e
a
s
uri
ng lo
w curren
ts, and
cho
o
si
ng hig
h
-pe
r
forman
ce op amp
s
.
Rea
s
o
nable
and reliable
circuit elem
e
n
ts sh
ould b
e
sele
cted, such a
s
hig
h
-resi
stan
ce
pre
c
isi
on an
d low-noi
se
platinum resi
stan
ce, t
anta
l
um ca
pa
citors for l
o
w n
o
ise, an
d hi
gh
insul
a
tion
ma
terials su
ch as
comp
osite
-
co
ated
cop
p
e
r for PCB u
s
e [13, 14]. Short overhe
ad
microwave-shielde
d
cabli
ng
can
be
used a
s
i
nput a
nd o
u
tput
sig
nal line
s
. P
C
B su
rface le
a
k
ag
e
effects
need
to be
con
s
id
ered
in a
ppli
c
ation
s
whe
r
e low inp
u
t-b
i
as
cu
rre
nt is criti
c
al. Surf
ace
leakage i
s
ca
use
d
by hu
m
i
dity, dust, or other
co
nta
m
inants on t
he bo
ard.
Th
e use of a
g
uard
ring aro
und
sen
s
itive
pin
s
i
s
the ea
si
est way
to
redu
ce
su
rface lea
k
ag
e. T
he gu
ard ri
n
g
is
biased at th
e sam
e
voltage a
s
the
sen
s
itive pins. In ord
e
r to shield t
he ci
rcuit from
electroma
gne
tic interferen
ce, the entire circuit
was
enclos
ed within a metal s
h
ield
box [15].
3. Measurem
e
nts
Measurement
s a
r
e
perfo
rmed in
a l
a
b
o
rato
ry
to d
e
t
ermine
the
cha
r
a
c
teri
stics of th
e
circuit pe
rformance. The
Keithley Mod
e
l 240
0 of Ke
it
hley
I
n
st
ru
ment
s I
n
c.
in
U.
S
.
A
.
serv
e
s
a
s
the con
s
tant
curre
n
t sou
r
ce of th
e I/V
conve
r
ter,
an
d FL
UKE 8
5
08A referen
c
e multimete
r
is
use
d
a
s
th
e
output voltag
e dete
c
tor.
T
he exp
e
rim
e
ntal environm
ent tempe
r
at
ure fo
r
dete
c
ting
nA and
uA
pa
ramete
rs are 1
8
.5
and
18.9°
C,
re
spe
c
tively. We
co
ndu
cted five
ci
rcle
measurement
s, and e
a
ch
step i
s
app
ro
ximately
100
uA. Figure
5
and Fig
u
re
6
sho
w
the lo
w-
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
2302-4
046
Accu
rate L
o
w-Cu
rrent Mea
s
urem
ent Circuit
for Multi
m
eters and O
scill
ograp
s (S
huqin G
eng
)
3717
curre
n
t dete
c
tor ave
r
ag
e
e
x
perime
n
tal
result
s of
the five circle
s for t
he uA and nA param
eters.
The typical a
c
cura
cy of th
e
μ
Cu
rrent i
s
better tha
n
0.085% in th
e
μ
A and
nA
ran
g
e
s
. Figu
re 5
and 6
presen
t the DC cha
r
acteri
st
ics
of the average
output
voltag
e of the I/V converte
r for t
h
e
f
i
v
e
circle
s.
Figure 5. DC
Cha
r
a
c
teri
stics of the I/V
Conve
r
ter for
the Input uA Curre
n
t
Figure 6. DC
Cha
r
a
c
teri
stics of the I/V
Conve
r
ter for
the Input nA Curre
n
t
From
Fi
gu
re 5
and 6,
we can se
e
that with
the
I
in
in
cre
a
si
ng,
V
out
is Lin
ear increa
sing.
DC
cha
r
a
c
teristics of the I/V converte
r for the in
p
u
t nA and uA cu
rrent is g
ood.
Method of le
ast
squ
a
re
s i
s
u
s
ed to fitting li
ne [16] for t
h
e five circle
measurement
data
.
Th
e ratio is 0.0
010
0
1
for
uA and 0.001
000 for nA.
∆
=
(V
out
/1000
- I
in
)/ I
in
(2)
Figure 7. Erro
r of the Input uA Current
Figure 8. Erro
r of the Input nA Current
Figure 7
sh
o
w
s t
he me
asurem
ent data
error
rate
. It
is
cal
c
ulate
d
by (2
) with
the five
circile
s avera
ge value of e
x
perime
n
t dat
a. The e
rro
r rate increa
se
s with incre
a
si
ng input
cu
rre
nt.
From Fig
u
re
7, we can
se
e that when
the input
cu
rrent passe
s the 1400
uA
, the error rate
is
about 0.0
7
2
%
, which is
caused by the
denomi
nato
r
i
n
crea
sein
g fa
ster th
an the
nume
r
ator of
(2).
Phenom
eno
n
of nA is the
same
as th
e
curre
n
t of uA.The high
est
error
rate
Δ
of uA is 0.08
5
%
,
whi
c
h can sa
tisfy most low-cu
rre
nt systems. Wh
en the cu
rrent of
uA bec
o
m
es small, the erro
r
rate i
s
be
co
me sm
all too
,
which is ne
ar the
ze
ro.
From Fi
gu
re
8, we
can
see that with
the
curre
n
t incre
a
sin
g
, the error rate be
co
mes
sm
all; when the
cu
rre
nt of
nA passe
s 140
0nA,
the
error
rate
be
come
s l
e
ss t
han 0.0
2
%. Ho
wever, F
r
o
m
Figu
re 8,
we
can
al
so
see th
at with
the
curre
n
t beco
m
es
small, the error rate b
e
com
e
s la
r
g
e
reversely, which i
s
ca
use
d
by the pre
c
i
s
ion
Evaluation Warning : The document was created with Spire.PDF for Python.
ISSN: 23
02-4
046
TELKOM
NI
KA
Vol. 12, No. 5, May 2014: 3713 – 37
18
3718
o
f
re
siste
n
ce, the offset voltage, noise a
nd PCB
lea
k
age current.
Offset adju
s
t
m
ent circuit
s
can
be u
s
ed to i
m
prove th
e p
r
esitio
n.The h
i
ghe
st error
rate
Δ
of nA is 0.1%, which
can
sati
sfy most
low-cu
rrent systems.
4. Conclusio
n
We have
pre
s
ente
d
the I/V converte
r circuit
a
nd it
s
t
e
chni
cal
cha
r
act
e
ri
st
ic
s wi
t
h
t
w
o-
cha
nnel
rang
es. T
he
esse
ntial featu
r
e
s
of the I/V
con
v
erter are
its simpli
city
an
d
high p
r
e
c
isi
o
n
with a f
r
eq
ue
ncy rang
e of
1MHz. T
he
dual p
o
la
ri
ty power
and
p
o
we
r d
e
tecto
r
is conveni
e
n
tly
use
d
. The measurement
data are a
nalyse
d
and
e
rro
r rate i
s
low. Ci
rcui
t techniqu
es are
importa
nt for the reali
z
atio
n of high pre
s
iti
on of I/V converte
r. The
highe
st error rate
Δ
of uA i
s
0.085%, whi
c
h ca
n satisfy most lo
w-cu
rre
nt system
s. The hi
ghe
st error
rate
Δ
of nA is 0.
1%,
whi
c
h
ca
n
sat
i
sf
y
mo
st
lo
w-
cur
r
e
n
t
sy
st
e
m
s.
Th
e
Li
ne
arity is an
alized. Th
e I/V converte
r i
s
u
s
ed
in the detecti
on of low uA and nA cu
rr
e
n
t system
s, chips, an
d mo
dule
s
.
Ackn
o
w
l
e
dg
ements
This work wa
s su
ppo
rted i
n
part by the National Natural Scie
nce Found
ation o
f
China
(Grant No. 6
0976
028 a
n
d
61204
040
), Beijing Muni
cipal Natu
ral S
c
ien
c
e F
oun
d
a
tion (G
rant
No.
4123
092
), and Advance
d
Technolo
g
y
Foundat
io
n (Grant No
. 002000
514
3120
04 an
d
No.
0020
0051
431
1013
).
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