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独立行政法人日本原子力研究開発機構 研究技術情報部 研究技術情報課
〒319-1195 茨城県那珂郡東海村白方白根 2 番地 4
電話 029-282-6387, Fax 029-282-5920, E-mail:ird-support@jaea.go.jp
This report is issued irregularly by Japan Atomic Energy Agency
Inquiries about availability and/or copyright of this report should be addressed to
Intellectual Resources Section, Intellectual Resources Department,
Japan Atomic Energy Agency
2-4 Shirakata Shirane, Tokai-mura, Naka-gun, Ibaraki-ken 319-1195 Japan
Tel +81-29-282-6387, Fax +81-29-282-5920, E-mail:ird-support@jaea.go.jp
© Japan Atomic Energy Agency, 2008

+ +
2008 6 4
pH
10G1V 120
1s10V 50ch
319-1195 2-4
+

Design and Fabrication of an Ultra-High Input Impedance
Low Offset Amplifier for Electro-Chemical Measurements
Jun SAGAWA , Kiyofumi MORIYAMA +,
Tomotoshi NISHIKIZAWA and Hideo NAKAMURA +
Engineering Services Department
Nuclear Science Research Institute
Tokai Research and Development Center
Japan Atomic Energy Agency
Tokai-mura, Naka-gun, Ibaraki-ken
(Received June 4 , 2008)
Electro-chemical electrodes including pH probes, ion-selective electrodes (ISEs) etc. generally
have very high output impedances. In order to measure their outputs with generic
measurement devices like data recorders, we need impedance conversion amplifiers that
convert the ultra-high impedance signals of the probes into low-impedance input signals for
ordinary measurement devices. Although specially designed measurement devices for the
electro-chemical probes are commercially available, there are very few products that can be
applied for multi-channel time series data acquisition. Thus, we designed and fabricated an
ultra-high impedance low-offset amplifier fit for this purpose. The primary specification of
the amplifier is, input impedance >10G, input range 1V, gain 120, response time about
1s, output range 10V, output impedance 50, and it has 5 independent channels. This
report describes the originally developed design, selection of the element devices, test on the
circuit characteristics, and instruction for fabrication.
Keywords: Ultra-High Input Impedance, Electro-Chemical Measurement, pH, Ion-Selective
Electrode, Amplifier, Impedance Conversion, Analogue Circuit, Direct Current Amplifier
+Reactor Safety Research Unit, Nuclear Safety Research Center
Collaborating Engineer

1 1
1.1 1
1.2 1
1.3 2
2 3
2.1 3
2.2 7
2.2.1 A [ ] 7
2.2.2 B [ ] 10
2.2.3 C [ ] 16
3 18
3.1 18
3.2 22
3.3 24
4 26
4.1 26
4.2 27
5 42
43

Contents
1 Introduction 1
1.1 Background and Purpose 1
1.2 Design Specification 1
1.3 Challenges in Design 2
2 Circuit Design 3
2.1 Overview of the Circuit Design 3
2.2 Detail of the Circuit and Function 7
2.2.1 Block A [Ultra-High Input Impedance Low-offset Buffer Amplifier] 7
2.2.2 Block B [Offset Voltage Cancel Circuit] 10
2.2.3 Block C [Programmable Gain Amplifier Circuit] 16
3 Test on the Circuit Performance 18
3.1 Input Bias Current Impact Test 18
3.2 Input-Output Gain Accuracy Test 22
3.3 Offset Voltage Cancel Performance Test 24
4 Fabrication 26
4.1 Practice of On-Board Device Implementation 26
4.2 Selection of Elemental Devices 27
5 Summary 42
References 43

1.1
1.
1 VS R o
R i V
V
R
i
VS
(1.1)
R i R o
V VS R i >> R o
pH pH
pH
R o 1001000M
R i pH
R i 110M
2008 1
D/A
1.2

60fA
10G
2mV
1V 10V
10V
50
1,5,10,20
CH 5CH
2 2.2.2 2.3
1.3
OP
AD549LH AD549LH 60fA(25)
10T
1 I n I n
Vn Vn I n R i
2mV R i > 10T I n 2mV
/ 10T > 0.2fA
1
2

2.1
2.
2.1 2.2 5
2.1 2.2 1
5
2.1 ABC
A ··············
B ··············
C ··············
A 2
1
B 1
A
10mV
2mV
C
A B 1

151020 4
(16)
2.1
4

5
2.2(a) A

6
2.2(b) B , C

2.2
4
2.2.1 A [ ]
A 2.2(a)
A1 , A2 OP AD549LH 1
AD549LH 10|| 1T||pF
1
OP
BNC
RG174
(7) 1/101/100
AD549LH R1 R 2 (8)
AD549LH
A1 , A2 *
4.1
A3 INA114AP
2
* (Faraday Shield)
GND
108 V 100V
1/108

V
V A3 VO _ A3
V
O _ A3
( V V ) G
(2.1)
P
GND 2 GND 1
A3
(2.1)
A3
A3 (2.1) G P A3
INA114AP 6 25k
INA114AP
R 5 G P G P 1
50k/
R 5k
R 5 =5.6k G P 9.93 1
A3 15 V 12 V
G P 10
1.2 V
A1 , A2 , A3 A1 , A2 AD549LH 0.5mV 2
1.0mV(max)A3 INA114AP 0.13mV G P 10
V A1 , A2 , A3 11.3mV(max)
B A1 , A2 , A3
VR1 REF200 100
A IC100A R 6 ( R 7 )(=120)
VR1 12mV A4
A3 A.SW1 DG419 A.SW1 B
S1-ON S2-OFF
A5 A5 ISO124P (9)
[A/D PWM PWM
D/A ]
1pF 2 2pF 1
50mV(max) A5
1 VS1 2 VS2 DC/DC
BY05-15W05L DC/DC

BY05-15W05L
8mVp-p(typ)
DC/DC (P-S) 100pF(max)
A5 11 R , 12 R , 13 R ,
VR 2
G A VR 2 1/9.011/11.25
2.3 A A1 , A2 , A3
G P A3
VS VO
VOS1 A5 A1 , A2 , A3
VR 1
0 VS VO
V ( V G V ) G
(2.2)
O
S
P
OS1
G 1
O
S
OS1
A
G P A
V V V G
(2.3)
A
A5 VOS1 G A VOS1=50mV(max) 1/10 5mV(max) VOS1 A5
PWM S/N A G / 1
G P VR 2 G A
G 1
G P A
2.3 VOS1
9

2.2.2 B [ ]
2.4 2.2(b)
A5 , A6
A7 , A8 2 OP OP177FP A6 INA114AP A.SW1 A.SW2
A.SW1A.SW2 ab
ab
PIC(Peripheral Interface Controller) *PIC12F675 (10)
I/O
2.1 PIC12F675
PIC
a b
a
A.SW1 V1 GND 0V A5 , A6
SH1 CS1 V4
V V V
2
4
1
2
OS1
V V V V
1
3
3
OS2
V V V V
(2.4)
OS1
OS2
V 0 GND (2.4)
V1 3
V4 VOS1
VOS2
(2.5)
A5,A6 CS1
b
* PIC 35 8 A/D
PWM I/O

V1, V2
, V3,
V4
V1 ',
V2
',
V3
',
V4
' VS V1 '
VS
V2 '
V '
V V
(2.6)
2
S
OS1
a CS1 (2.5) V4 VOS3 0 V3'
V '
V V
(2.7)
3
OS1
OS2
V4 '(2.4),(2.6),(2.7)
V '
V 'V
'V
4
2
S
3
OS1
OS2
V V ( V V ) V V
(2.8)
OS1
OS2
OS2
S
CS1 V4 '
VOS4 0 V5
a V 5 (= V4 ')
A5 , A6
VS
V 0
VOS3 OS4
0 A7 , A8 25V(max)
0V
3
2.5 C S1
, A7 SH1 C S2
, A8 SH2 2
SH SH 2.5 SH
VS ON CS
VCS VS
OFF
VCS CS ILEAK t
ILEAK ILEAK_
SW IBIAS
ILEAK_ SW OP
IBIAS OFF t VC
t
0
LEAK
1
VC I dt
(2.9)
CS
A.SW2 ADG432BN OFF I LEAK _SW
=0.25nA(max)
A7 , A8 OP OP177FP I BIAS =2.0nA(max)

I LEAK =2.25nA(max)SH OFF t
SH 2.4 b
t =50ms VC C S =0.22 F ,
I BIAS =2.25nA , t =50ms
V C
1
2.
25nA
50ms
0.
5mV
0.
22F
SH 2
0.5mV2=1.0mV(max)
2.2(b) SH 4.4 4.5
OP
1.2
50ms2=100ms(min)

2.4
2.5
13

2.1 PIC12F675 (1/2)
;**********************************************************************************
;***** PIC12F675 Offset Voltage Cancel Circuit Switching Control Program List*******
;**********************************************************************************
LIST P=PIC12F675
INCLUDE "P12F675.INC"
;************************************************
TIME1 EQU D'199'
TIME2 EQU D'50'
TIM1_CNT EQU 20H
TIM2_CNT EQU 21H
TMP EQU 30H
IO_S EQU B'00001000'
;****************MAIN PROGRAM****************
ORG 0H
BSF STATUS,RP0
MOVLW IO_S
MOVWF TRISIO
BCF STATUS,RP0
;------------------------------------------------------------------------
LOOP CALL PATTERN_A
CALL TIMER1
CALL PATTERN_B
CALL TIMER1
CALL PATTERN_C
CALL TIMER2
CALL PATTERN_B
CALL TIMER1
CALL PATTERN_A
CALL TIMER1
CALL PATTERN_D
CALL TIMER1
CALL PATTERN_E
CALL TIMER2
CALL PATTERN_D
CALL TIMER1
GOTO LOOP
;------------------------------------------------------------------------

2.1 PIC12F675 (2/2)
PATTERN_A MOVLW B'00000000'
MOVWF GPIO
RETURN
PATTERN_B MOVLW B'00010000'
MOVWF GPIO
RETURN
PATTERN_C MOVLW B'00010010'
MOVWF GPIO
RETURN
PATTERN_D MOVLW B'00000100'
MOVWF GPIO
RETURN
PATTERN_E MOVLW B'00000101'
MOVWF GPIO
RETURN
RETURN
;******************TIMER*********************
TIMER1 MOVLW TIME1
MOVWF TIM1_CNT
LOOP1 CLRWDT
NOP
DECFSZ TIM1_CNT,1
GOTO LOOP1
RETURN
TIMER2 MOVLW TIME2
MOVWF TIM2_CNT
LOOP2 CALL TIMER1
NOP
NOP
DECFSZ TIM2_CNT,1
GOTO LOOP2
RETURN
END
;**********************************************************************************
;**********************************************************************************
;**********************************************************************************

2.2.3 C [ ]
2.2(b)A9 OP OP177FP R16 R 19 , R 22
2.6 R 16 R19 R A
R 22 R B A OP
R A /( R A R B ) OP VOUT
VOUT IN IN
A(
V V )
(2.10)
IN
V
VIN VIN
( VOUT
VIN
)
VOUT
VIN VIN (
VOUT
V )
VOUT A
IN
VIN 0 (GND) VOUT VIN
V
V
OUT
IN
A(
1)
1
1
A
1/
A
A A
VOUT
1
1
lim 1
A
V 1/
A
(2.11)
(2.12)
IN
R A , R B
VOUT
R B
(2.13)
VIN
R A
(2.11) OP A OP
A =105
(2.12)

(2.13) OP
OP A =106107 OP177FP
A =510612106
(2.13)
0.1% R 22 0.1% R 16 R 19
B A R /
R 0.14%
R 22 C 43 =1.0F
R 23 =51
50 51
2.6

3.
DL1720YOKOGAWA
DMMPC520MSANWA
3.1
OP
OP
OP
OP
3.1 ULTRA HIGH INPUT
IMPEDANCE AMPLIFIWR SYSTEM
IBIAS
OP AD549LH I BIAS =60fA(max)
IBIAS
(1.1)
V S =0 1G
R IN (= R IN , R IN )(1.1) V VS
IBIAS
R
IN
V 0 60fA
1G
60V
IBIAS R IN
R IN =0
3.2 3.1
R IN =0 3.2(a)
(d) 3.2(e)(l) RIN + RIN
1G
1 (a) peak to peak
5.4mV

2mV
(b),(c),(d)20 (d)
9.9mVp-p 120ms
2.2.2
1
10mV/20=0.5mVp-p
3.2(e)(l) (e)(h) (i)(l) 1G
20 R IN =0
1G
3.1
19

(a) (b)
(c) (d)
(e) (f)
3.2 RIN (1/2)
20

(g) (h)
(i) (j)
(k)
(l)
3.2 RIN (2/2)
21

3.2
3.3
V S , VS
VOUT PC-520MDMM
GAIN
3.1 0.20.3%
PC-520M
3.3
22

VS
VS
3.1
VOUT
V
V
OUT
S VS

3.3
2.2.2 B 3.4
2.4 V2 VOS'
V OUT (= V 5 )
3.4
3.5 CH VOS' CH2 V OUT (= V 5 )
VOS' 5V 50mV
VOS' 5V VOUT VOS'
24

(a)
(b) (c)
(d) (e)
3.5 VOS’ VOUT
25

4.
2.1 3
4.1
4.1 4.13 PCB(Printed Circuit Board)
IC
4.1 4.3 A
4.1 4.2 1 4.3
2 4.1 4.3
4.2
4.1 4.2
A1, R1 A2, R2
A1,A2 Faraday Shield
BNC
BNC
2 2.2 Guard Shield
4.4 4.7
4.4 4.6 B
R 14 , R 15 45mm

4.7 4.9 C
4.9
4.7 4.8
4.10 4.12 DC/DC
4.11 4.12
4.14 4.15
DC/DC
AC/DC
AC F.G
GND
4.2
4.1
DC/DC
4.1
R 22
0.1%0.5%
BNC
(1020)

4.3

4.5

4.6

4.8

4.9

4.12 DC/DC

4.13

Inside of Amplifier System
Front Panel Rear Panel 4.15

4.1

5.
pH
5
60fA
10G
2mV
1V 10V
10V
10mA
50
1,5,10,20
DC250V AC250V 50Hz
CH 5CH
CH CH
CH AC/DC 250V AC 50Hz
50

OP CQ
OP CQ
SPECIAL No.41CQ
1999 8 CQ
OPA128 BURR BROWN
LMC6001 National Semiconductor
OP 100 CQ
LMC662 National Semiconductor
1999 8 CQ
PIC12F629/675 MicroChip
AD549 ANALOG DEVICES
OP177 ANALOG DEVICES
ISO124 BURR BROWN
INA114 BURR BROWN
ADG432 ANALOG DEVICES
DG419 Vishay Siliconix
REF200 BURR BROWN
PS2501-1 NEC
LWT - H - SERIESE DESEI-RAMBDA
BY-L Series Bellnix

OP CQ
OP CQ
SPECIAL No.41CQ
1999 8 CQ
OPA128 BURR BROWN
LMC6001 National Semiconductor
OP 100 CQ
LMC662 National Semiconductor
1999 8 CQ
PIC12F629/675 MicroChip
AD549 ANALOG DEVICES
OP177 ANALOG DEVICES
ISO124 BURR BROWN
INA114 BURR BROWN
ADG432 ANALOG DEVICES
DG419 Vishay Siliconix
REF200 BURR BROWN
PS2501-1 NEC
LWT - H - SERIESE DESEI-RAMBDA
BY-L Series Bellnix

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