AD AD8221ARZ-R7 Precision instrumentation amplifier Datasheet

Precision Instrumentation Amplifier
AD8221
CONNECTION DIAGRAM
Easy to use
Available in space-saving MSOP
Gain set with 1 external resistor (gain range 1 to 1000)
Wide power supply range: ±2.3 V to ±18 V
Temperature range for specified performance:
−40°C to +85°C
Operational up to 125°C 1
Excellent AC specifications
80 dB minimum CMRR to 10 kHz ( G = 1)
825 kHz, –3 dB bandwidth (G = 1)
2 V/μs slew rate
Low noise
8 nV/√Hz, @ 1 kHz, maximum input voltage noise
0.25 μV p-p input noise (0.1 Hz to 10 Hz)
High accuracy dc performance (AD8221BR)
90 dB minimum CMRR (G = 1)
25 μV maximum input offset voltage
0.3 μV/°C maximum input offset drift
0.4 nA maximum input bias current
–IN 1
8 +VS
RG 2
7 VOUT
RG 3
6 REF
+IN 4
AD8221
5 –VS
TOP VIEW
03149-001
FEATURES
Figure 1.
120
110
AD8221
CMRR (dB)
100
90
COMPETITOR 1
80
70
60
COMPETITOR 2
APPLICATIONS
Weigh scales
Industrial process controls
Bridge amplifiers
Precision data acquisition systems
Medical instrumentation
Strain gages
Transducer interfaces
GENERAL DESCRIPTION
The AD8221 is a gain programmable, high performance
instrumentation amplifier that delivers the industry’s highest
CMRR over frequency in its class. The CMRR of instrumentation
amplifiers on the market today falls off at 200 Hz. In contrast,
the AD8221 maintains a minimum CMRR of 80 dB to 10 kHz
for all grades at G = 1. High CMRR over frequency allows the
AD8221 to reject wideband interference and line harmonics,
greatly simplifying filter requirements. Possible applications
include precision data acquisition, biomedical analysis, and
aerospace instrumentation.
40
10
100
1k
10k
100k
FREQUENCY (Hz)
03149-002
50
Figure 2. Typical CMRR vs. Frequency for G = 1
Low voltage offset, low offset drift, low gain drift, high gain
accuracy, and high CMRR make this part an excellent choice
in applications that demand the best dc performance possible,
such as bridge signal conditioning.
Programmable gain affords the user design flexibility. A single
resistor sets the gain from 1 to 1000. The AD8221 operates on
both single and dual supplies and is well suited for applications
where ±10 V input voltages are encountered.
The AD8221 is available in a low cost 8-lead SOIC and 8-lead
MSOP, both of which offer the industry’s best performance. The
MSOP requires half the board space of the SOIC, making it ideal
for multichannel or space-constrained applications.
Performance is specified over the entire industrial temperature
range of −40°C to +85°C for all grades. Furthermore, the AD8221
is operational from −40°C to +125°C1.
1
See Typical Performance Characteristics for expected operation from
85°C to 125°C.
Rev. B
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113 ©2003–2007 Analog Devices, Inc. All rights reserved.
AD8221
TABLE OF CONTENTS
Features .............................................................................................. 1
Layout .......................................................................................... 17
Applications....................................................................................... 1
Reference Terminal .................................................................... 18
General Description ......................................................................... 1
Power Supply Regulation and Bypassing ................................ 18
Connection Diagram ....................................................................... 1
Input Bias Current Return Path ............................................... 18
Revision History ............................................................................... 2
Input Protection ......................................................................... 18
Specifications..................................................................................... 3
RF Interference ........................................................................... 19
Absolute Maximum Ratings............................................................ 8
Precision Strain Gage................................................................. 19
Thermal Characteristics .............................................................. 8
ESD Caution.................................................................................. 8
Conditioning ±10 V Signals for a +5 V Differential Input
ADC ............................................................................................. 19
Typical Performance Characteristics ............................................. 9
AC-Coupled Instrumentation Amplifier ................................ 20
Theory of Operation ...................................................................... 16
Outline Dimensions ....................................................................... 21
Gain Selection ............................................................................. 17
Ordering Guide .......................................................................... 22
REVISION HISTORY
9/07—Rev. A to Rev. B
Changes to Features.......................................................................... 1
Changes to Table 1 Layout............................................................... 3
Changes to Table 2 Layout............................................................... 5
Changes to Figure 15...................................................................... 11
Changes to Figures 32 .................................................................... 13
Changes to Figure 33, Figure 34, and Figure 35 ......................... 14
Updated Outline Dimensions ....................................................... 21
Changes to Ordering Guide .......................................................... 22
11/03—Rev. 0 to Rev. A
Changes to Features.......................................................................... 1
Changes to Specifications Section.................................................. 4
Changes to Theory of Operation Section.................................... 13
Changes to Gain Selection Section............................................... 14
10/03—Revision 0: Initial Version
Rev. B | Page 2 of 24
AD8221
SPECIFICATIONS
VS = ±15 V, VREF = 0 V, TA = 25°C, G = 1, RL = 2 kΩ, unless otherwise noted.
Table 1.
Parameter
COMMON-MODE REJECTION RATIO
CMRR DC to 60 Hz with 1 kΩ
Source Imbalance
G=1
G = 10
G = 100
G = 1000
CMRR at 10 kHz
G=1
G = 10
G = 100
G = 1000
NOISE
Voltage Noise, 1 kHz
Input Voltage Noise, eNI
Output Voltage Noise, eNO
RTI
G=1
G = 10
G = 100 to 1000
Current Noise
VOLTAGE OFFSET 1
Input Offset, VOSI
Over Temperature
Average TC
Output Offset, VOSO
Over Temperature
Average TC
Offset RTI vs. Supply (PSR)
G=1
G = 10
G = 100
G = 1000
INPUT CURRENT
Input Bias Current
Over Temperature
Average TC
Input Offset Current
Over Temperature
Average TC
REFERENCE INPUT
RIN
IIN
Voltage Range
Gain to Output
Conditions
Min
AR Grade
Typ
Max
Min
BR Grade
Typ
Max
Unit
VCM = −10 V to +10 V
80
100
120
130
90
110
130
140
dB
dB
dB
dB
80
90
100
100
80
100
110
110
dB
dB
dB
dB
VCM = −10 V to +10 V
RTI noise =
√eNI2 + (eNO/G)2
VIN+, VIN−, VREF = 0
8
75
8
75
nV/√Hz
nV/√Hz
f = 0.1 Hz to 10 Hz
2
0.5
0.25
40
6
f = 1 kHz
f = 0.1 Hz to 10 Hz
VS = ±5 V to ±15 V
T = −40°C to +85°C
2
0.5
0.25
40
6
60
86
0.4
300
0.66
6
VS = ±5 V to ±15 V
T = −40°C to +85°C
μV p-p
μV p-p
μV p-p
fA/√Hz
pA p-p
25
45
0.3
200
0.45
5
μV
μV
μV/°C
μV
mV
μV/°C
VS = ±2.3 V to ±18 V
90
110
124
130
110
120
130
140
0.5
T = −40°C to +85°C
1
0.2
T = −40°C to +85°C
VIN+, VIN−, VREF = 0
–VS
94
114
130
140
1.5
2.0
110
130
140
150
0.2
1
0.1
0.6
0.8
1
1
20
50
20
50
60
+VS
1 ± 0.0001
Rev. B | Page 3 of 24
–VS
dB
dB
dB
dB
0.4
1
0.4
0.6
60
+VS
1 ± 0.0001
nA
nA
pA/°C
nA
nA
pA/°C
kΩ
μA
V
V/V
AD8221
Parameter
POWER SUPPLY
Operating Range
Quiescent Current
Over Temperature
DYNAMIC RESPONSE
Small Signal −3 dB Bandwidth
G=1
G = 10
G = 100
G = 1000
Settling Time 0.01%
G = 1 to 100
G = 1000
Settling Time 0.001%
G = 1 to 100
G = 1000
Slew Rate
GAIN
Gain Range
Gain Error
G=1
G = 10
G = 100
G = 1000
Gain Nonlinearity
G = 1 to 10
G = 100
G = 1000
G = 1 to 100
Gain vs. Temperature
G=1
G > 12
INPUT
Input Impedance
Differential
Common Mode
Input Operating Voltage Range 3
Over Temperature
Input Operating Voltage Range
Over Temperature
OUTPUT
Output Swing
Over Temperature
Output Swing
Over Temperature
Short-Circuit Current
Conditions
Min
VS = ±2.3 V to ±18 V
±2.3
AR Grade
Typ
Max
0.9
1
T = −40°C to +85°C
±18
1
1.2
Min
BR Grade
Typ
Max
±2.3
0.9
1
±18
1
1.2
Unit
V
mA
mA
825
562
100
14.7
825
562
100
14.7
kHz
kHz
kHz
kHz
10
80
10
80
μs
μs
13
110
2
2.5
13
110
2
2.5
μs
μs
V/μs
V/μs
10 V step
10 V step
G=1
G = 5 to 100
G = 1 + (49.4 kΩ/RG)
1.5
2
1
1.5
2
1000
1
1000
V/V
0.02
0.15
0.15
0.15
%
%
%
%
VOUT ± 10 V
0.03
0.3
0.3
0.3
VOUT = −10 V to +10 V
RL = 10 kΩ
RL = 10 kΩ
RL = 10 kΩ
RL = 2 kΩ
3
5
10
10
10
15
40
95
3
5
10
10
10
15
40
95
ppm
ppm
ppm
ppm
3
10
–50
2
5
–50
ppm/°C
ppm/°C
100||2
100||2
VS = ±2.3 V to ±5 V
T = −40°C to +85°C
VS = ±5 V to ±18 V
T =−40°C to +85°C
RL = 10 kΩ
VS = ±2.3 V to ±5 V
T = −40°C to +85°C
VS = ±5 V to ±18 V
T = –40°C to +85°C
100||2
100||2
–VS + 1.9
–VS + 2.0
–VS + 1.9
–VS + 2.0
+VS − 1.1
+VS − 1.2
+VS − 1.2
+VS − 1.2
–VS + 1.9
–VS + 2.0
–VS + 1.9
–VS + 2.0
+VS − 1.1
+VS − 1.2
+VS − 1.2
+VS − 1.2
–VS + 1.1
–VS + 1.4
–VS + 1.2
–VS + 1.6
+VS − 1.2
+Vs − 1.3
+VS − 1.4
+VS − 1.5
–VS + 1.1
–VS + 1.4
–VS + 1.2
–VS + 1.6
+VS − 1.2
+VS − 1.3
+VS − 1.4
+VS − 1.5
18
Rev. B | Page 4 of 24
18
GΩ||pF
GΩ||pF
V
V
V
V
V
V
V
V
mA
AD8221
Parameter
TEMPERATURE RANGE
Specified Performance
Operating Range 4
Conditions
Min
AR Grade
Typ
Max
Min
BR Grade
Typ
Max
–40
–40
+85
+125
–40
–40
+85
+125
Unit
°C
°C
1
Total RTI VOS = (VOSI) + (VOSO/G).
Does not include the effects of external resistor RG.
One input grounded. G = 1.
4
See Typical Performance Characteristics for expected operation between 85°C to 125°C.
2
3
Table 2.
Parameter
COMMON-MODE REJECTION RATIO (CMRR)
CMRR DC to 60 Hz with 1 kΩ Source Imbalance
G=1
G = 10
G = 100
G = 1000
CMRR at 10 kHz
G=1
G = 10
G = 100
G = 1000
NOISE
Voltage Noise, 1 kHz
Input Voltage Noise, eNI
Output Voltage Noise, eNO
RTI
G=1
G = 10
G = 100 to 1000
Current Noise
VOLTAGE OFFSET 1
Input Offset, VOSI
Over Temperature
Average TC
Output Offset, VOSO
Over Temperature
Average TC
Offset RTI vs. Supply (PSR)
G=1
G = 10
G = 100
G = 1000
INPUT CURRENT
Input Bias Current
Over Temperature
Average TC
Input Offset Current
Over Temperature
Average TC
Conditions
Min
ARM Grade
Typ
Max
Unit
VCM = −10 V to +10 V
80
100
120
130
dB
dB
dB
dB
80
90
100
100
dB
dB
dB
dB
VCM = –10 V to +10 V
RTI noise = √eNI2 + (eNO/G)2
VIN+, VIN−, VREF = 0
8
75
nV/√Hz
nV/√Hz
f = 0.1 Hz to 10 Hz
2
0.5
0.25
40
6
f = 1 kHz
f = 0.1 Hz to 10 Hz
VS = ±5 V to ±15 V
T = −40°C to +85°C
μV p-p
μV p-p
μV p-p
fA/√Hz
pA p-p
70
135
0.9
600
1.00
9
VS = ±5 V to ±15 V
T = −40°C to +85°C
μV
μV
μV/°C
μV
mV
μV/°C
VS = ±2.3 V to ±18 V
90
100
120
120
100
120
140
140
0.5
T = −40°C to +85°C
3
0.3
T = −40°C to +85°C
3
Rev. B | Page 5 of 24
dB
dB
dB
dB
2
3
1
1.5
nA
nA
pA/°C
nA
nA
pA/°C
AD8221
Parameter
REFERENCE INPUT
RIN
IIN
Voltage Range
Gain to Output
POWER SUPPLY
Operating Range
Quiescent Current
Over Temperature
DYNAMIC RESPONSE
Small Signal –3 dB Bandwidth
G=1
G = 10
G = 100
G = 1000
Settling Time 0.01%
G = 1 to 100
G = 1000
Settling Time 0.001%
G = 1 to 100
G = 1000
Slew Rate
GAIN
Gain Range
Gain Error
G=1
G = 10
G = 100
G = 1000
Gain Nonlinearity
G = 1 to 10
G = 100
G = 1000
G = 1 to 100
Gain vs. Temperature
G=1
G > 12
INPUT
Input Impedance
Differential
Common Mode
Input Operating Voltage Range 3
Over Temperature
Input Operating Voltage Range
Over Temperature
OUTPUT
Output Swing
Over Temperature
Output Swing
Over Temperature
Short-Circuit Current
Conditions
Min
ARM Grade
Typ
Max
20
50
VIN+, VIN−, VREF = 0
−VS
60
+VS
kΩ
μA
V
V/V
±18
1
1.2
V
mA
mA
1 ± 0.0001
VS = ±2.3 V to ±18 V
±2.3
0.9
1
T = −40°C to +85°C
Unit
825
562
100
14.7
kHz
kHz
kHz
kHz
10
80
μs
μs
13
110
2
2.5
μs
μs
V/μs
V/μs
10 V step
10 V step
G=1
G = 5 to 100
G = 1 + (49.4 kΩ/RG)
1.5
2
1
1000
V/V
0.1
0.3
0.3
0.3
%
%
%
%
5
7
10
15
15
20
50
100
ppm
ppm
ppm
ppm
3
10
–50
ppm/°C
ppm/°C
VOUT ± 10 V
VOUT = −10 V to +10 V
RL = 10 kΩ
RL = 10 kΩ
RL = 10 kΩ
RL = 2 kΩ
100||2
100||2
VS = ±2.3 V to ±5 V
T = −40°C to +85°C
VS = ±5 V to ±18 V
T = −40°C to +85°C
RL = 10 kΩ
VS = ±2.3 V to ±5 V
T = −40°C to +85°C
VS = ±5 V to ±18 V
T = −40°C to +85°C
–VS + 1.9
–VS + 2.0
–VS + 1.9
–VS + 2.0
+VS − 1.1
+VS − 1.2
+VS − 1.2
+VS − 1.2
–VS + 1.1
–VS + 1.4
–VS + 1.2
–VS + 1.6
+VS − 1.2
+VS − 1.3
+VS − 1.4
+VS − 1.5
18
Rev. B | Page 6 of 24
GΩ/pF
GΩ/pF
V
V
V
V
V
V
V
V
mA
AD8221
Parameter
TEMPERATURE RANGE
Specified Performance
Operating Range 4
Conditions
1
Total RTI VOS = (VOSI) + (VOSO/G).
Does not include the effects of external resistor RG.
One input grounded. G = 1.
4
See Typical Performance Characteristics for expected operation between 85°C to 125°C.
2
3
Rev. B | Page 7 of 24
Min
ARM Grade
Typ
Max
−40
−40
+85
+125
Unit
°C
°C
AD8221
ABSOLUTE MAXIMUM RATINGS
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Table 3.
Parameter
Supply Voltage
Internal Power Dissipation
Output Short-Circuit Current
Input Voltage (Common-Mode)
Differential Input Voltage
Storage Temperature Range
Operating Temperature Range 1
1
Rating
±18 V
200 mW
Indefinite
±VS
±VS
−65°C to +150°C
−40°C to +125°C
THERMAL CHARACTERISTICS
Specification for a device in free air.
Temperature range for specified performance is –40°C to +85°C. See Typical
Performance Characteristics for expected operation from 85°C to 125°C.
Table 4.
Package
8-Lead SOIC, 4-Layer JEDEC Board
8-Lead MSOP, 4-Layer JEDEC Board
ESD CAUTION
Rev. B | Page 8 of 24
θJA
121
135
Unit
°C/W
°C/W
AD8221
TYPICAL PERFORMANCE CHARACTERISTICS
T = 25°C, VS = ±15 V, RL = 10 kΩ, unless otherwise noted.
1600
3500
1400
3000
1200
2500
UNITS
UNITS
1000
800
2000
1500
600
1000
400
–100
–50
0
50
100
150
CMR (µV/V)
0
–0.9
03149-003
0
–150
0.3
0.6
0.9
15
1800
1500
1200
900
600
–40
–20
0
20
40
60
INPUT OFFSET VOLTAGE (µV)
VS = ±15V
5
0
VS = ±5V
–5
–10
–15
–15
–10
–5
0
5
10
15
OUTPUT VOLTAGE (V)
Figure 4. Typical Distribution of Input Offset Voltage
Figure 7. Input Common-Mode Range vs. Output Voltage, G = 1
15
INPUT COMMON-MODE VOLTAGE (V)
3000
2500
2000
1500
1000
500
–0.5
0
0.5
1.0
INPUT BIAS CURRENT (nA)
1.5
VS = ±15V
5
0
VS = ±5V
–5
–10
–15
–15
03149-005
–1.0
10
–10
–5
0
5
OUTPUT VOLTAGE (V)
Figure 5. Typical Distribution of Input Bias Current
10
15
03149-008
0
–60
03149-004
300
10
03149-007
INPUT COMMON-MODE VOLTAGE (V)
2100
UNITS
0
Figure 6. Typical Distribution of Input Offset Current
2400
UNITS
–0.3
INPUT OFFSET CURRENT (nA)
Figure 3. Typical Distribution for CMR (G = 1)
0
–1.5
–0.6
03149-006
500
200
Figure 8. Input Common-Mode Range vs. Output Voltage, G = 100
Rev. B | Page 9 of 24
AD8221
0.80
180
0.75
160
0.70
140
0.60
VS = ±5V
0.55
120
GAIN = 10
100
GAIN = 1
60
0.45
40
–10
–5
0
5
10
15
COMMON-MODE VOLTAGE (V)
20
0.1
1
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 9. IBIAS vs. CMV
Figure 12. Positive PSRR vs. Frequency, RTI (G = 1 to 1000)
2.00
180
1.75
160
1.50
140
1.25
1.00
0.75
GAIN = 100
120
GAIN = 10
100
GAIN = 1
80
0.50
60
0.25
40
0
0.01
0.1
1
10
WARM-UP TIME (min)
20
0.1
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 10. Change in Input Offset Voltage vs. Warm-Up Time
5
1
03149-013
NEGATIVE PSRR (dB)
GAIN = 1000
03149-010
CHANGE IN INPUT OFFSET VOLTAGE (µV)
GAIN = 1000
80
0.50
0.40
–15
GAIN = 100
03149-012
POSITIVE PSRR (dB)
VS = ±15V
0.65
03149-009
INPUT BIAS CURRENT (nA)
GAIN = 1000
Figure 13. Negative PSRR vs. Frequency, RTI (G = 1 to 1000)
100k
VS = ±15V
TOTAL DRIFT 25°C – 85°C RTI (µV)
4
2
1
INPUT BIAS CURRENT
–1
–2
–3
10k
BEST AVAILABLE FET
INPUT IN-AMP GAIN = 1
1k
BEST AVAILABLE FET
INPUT IN-AMP GAIN = 1000
AD8221 GAIN = 1
100
–4
–5
–40
AD8221 GAIN = 1000
–20
0
20
40
60
80
100
120
140
TEMPERATURE (°C)
Figure 11. Input Bias Current and Offset Current vs. Temperature
10
10
100
1k
10k
100k
1M
SOURCE RESISTANCE (Ω)
Figure 14. Total Drift vs. Source Resistance
Rev. B | Page 10 of 24
10M
03149-014
0
INPUT OFFSET CURRENT
03149-011
INPUT CURRENT (nA)
3
AD8221
70
100
GAIN = 1000
80
60
60
50
GAIN = 100
40
40
CMR (µV/V)
GAIN = 10
20
10
GAIN = 1
0
20
0
–20
–40
–60
–10
–80
–20
1k
10k
100k
1M
10M
FREQUENCY (Hz)
–100
–40
03149-015
–30
100
–20
CMRR (dB)
120
100
40
60
80
100
120
140
Figure 18. CMR vs. Temperature
+VS
GAIN = 1000
–0
–0.4
INPUT VOLTAGE LIMIT (V)
REFERRED TO SUPPLY VOLTAGES
140
20
TEMPERATURE (°C)
Figure 15. Gain vs. Frequency
160
0
03149-018
GAIN (dB)
30
GAIN = 100
GAIN = 10
GAIN = 1
80
60
–0.8
–1.2
–1.6
–2.0
–2.4
+2.4
+2.0
+1.6
+1.2
+0.8
100
1k
10k
100k
1M
FREQUENCY (Hz)
+VS
GAIN = 1000
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
GAIN = 1
80
60
15
40
0.1
1
20
–0
–0.8
RL = 10kΩ
–1.2
RL = 2kΩ
–1.6
–2.0
+2.0
+1.6
RL = 2kΩ
+1.2
+0.8
RL = 10kΩ
+0.4
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
03149-017
CMRR (dB)
100
10
–0.4
GAIN = 100
GAIN = 10
5
Figure 19. Input Voltage Limit vs. Supply Voltage, G = 1
160
120
0
SUPPLY VOLTAGE (±V)
Figure 16. CMRR vs. Frequency, RTI
140
+0
03149-019
10
–VS
–VS
+0
0
5
10
15
SUPPLY VOLTAGE (±V)
Figure 17. CMRR vs. Frequency, RTI, 1 kΩ Source Imbalance
Figure 20. Output Voltage Swing vs. Supply Voltage, G = 1
Rev. B | Page 11 of 24
20
03149-020
1
03149-016
+0.4
40
0.1
AD8221
VS = ±15V
20
10
0
1
10
100
1k
10k
LOAD RESISTANCE (Ω)
–10
–8
–6
–4
–2
0
2
4
OUTPUT VOLTAGE (V)
6
10
Figure 24. Gain Nonlinearity, G = 100, RL = 10 kΩ
Figure 21. Output Voltage Swing vs. Load Resistance
+VS –0
VS = ±15V
–1
SOURCING
ERROR (100ppm/DIV)
–2
–3
+3
+2
SINKING
–VS +0
0
1
2
3
4
5
6
7
8
9
10
11
12
OUTPUT CURRENT (mA)
–10
–8
–6
–4
–2
0
2
4
OUTPUT VOLTAGE (V)
6
8
10
03149-025
+1
03149-022
Figure 25. Gain Nonlinearity, G = 1000, RL = 10 kΩ
Figure 22. Output Voltage Swing vs. Output Current, G = 1
1k
ERROR (1ppm/DIV)
VOLTAGE NOISE RTI (nV/ Hz)
VS = ±15V
GAIN = 1
100
GAIN = 10
GAIN = 100
10
GAIN = 1000
GAIN = 1000
BW LIMIT
–8
–6
–4
–2
0
2
4
OUTPUT VOLTAGE (V)
6
8
Figure 23. Gain Nonlinearity, G = 1, RL = 10 kΩ
10
1
03149-023
–10
1
10
100
1k
FREQUENCY (Hz)
10k
100k
03149-026
OUTPUT VOLTAGE SWING (V)
REFERRED TO SUPPLY VOLTAGES
8
03149-024
ERROR (10ppm/DIV)
VS = ±15V
03149-021
OUTPUT VOLTAGE SWING (V p-p)
30
Figure 26. Voltage Noise Spectral Density vs. Frequency (G = 1 to 1000)
Rev. B | Page 12 of 24
1s/DIV
5pA/DIV
Figure 27. 0.1 Hz to 10 Hz RTI Voltage Noise (G = 1)
03149-030
2µV/DIV
03149-027
AD8221
1s/DIV
Figure 30. 0.1 Hz to 10 Hz Current Noise
30
VS = ±15V
OUTPUT VOLTAGE (V p-p)
25
20
GAIN = 1
GAIN = 10, 100, 1000
15
10
1s/DIV
0
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 28. 0.1 Hz to 10 Hz RTI Voltage Noise (G = 1000)
03149-031
0.1µV/DIV
03149-028
5
Figure 31. Large Signal Frequency Response
5V/DIV
100
10
1
10
100
1k
10k
FREQUENCY (Hz)
Figure 29. Current Noise Spectral Density vs. Frequency
7.9µs TO 0.01%
8.5µs TO 0.001%
20µs/DIV
03149-032
0.002%/DIV
03149-029
CURRENT NOISE (fA/ Hz)
1k
Figure 32. Large Signal Pulse Response and Settling Time (G = 1), 0.002%/DIV
Rev. B | Page 13 of 24
AD8221
5V/DIV
0.002%/DIV
4.9µs TO 0.01%
5.6µs TO 0.001%
20µs/DIV
Figure 33. Large Signal Pulse Response and Settling Time (G = 10),
0.002%/DIV
4µs/DIV
03149-036
03149-033
20mV/DIV
Figure 36. Small Signal Response, G = 1, RL = 2 kΩ, CL = 100 pF
5V/DIV
0.002%/DIV
10.3µs TO 0.01%
13.4µs TO 0.001%
4µs/DIV
Figure 34. Large Signal Pulse Response and Settling Time (G = 100),
0.002%/DIV
03149-037
20µs/DIV
03149-034
20mV/DIV
Figure 37. Small Signal Response, G = 10, RL = 2 kΩ, CL = 100 pF
5V/DIV
0.002%/DIV
83µs TO 0.01%
112µs TO 0.001%
10µs/DIV
Figure 35. Large Signal Pulse Response and Settling Time (G = 1000),
0.002%/DIV
Rev. B | Page 14 of 24
03149-038
200µs/DIV
03149-035
20mV/DIV
Figure 38. Small Signal Response, G = 100, RL = 2 kΩ, CL = 100 pF
AD8221
SETTLING TIME (µs)
1000
2
100
SETTLED TO 0.001%
10
1
03149-039
100µs/DIV
SETTLED TO 0.001%
SETTLED TO 0.01%
5
5
10
15
20
03149-040
SETTLING TIME (µs)
10
OUTPUT VOLTAGE STEP SIZE (V)
100
Figure 41. Settling Time vs. Gain for a 10 V Step
15
0
10
GAIN
Figure 39. Small Signal Response, G = 1000, RL = 2 kΩ, CL = 100 pF
0
1
Figure 40. Settling Time vs. Step Size (G = 1)
Rev. B | Page 15 of 24
1000
03149-041
SETTLED TO 0.01%
20mV/DIV
AD8221
THEORY OF OPERATION
VB
I
I
A1
IB COMPENSATION
A2
IB COMPENSATION
10kΩ
C1
C2
+VS
10kΩ
OUTPUT
A3
10kΩ
+VS
–IN
400Ω
Q1
R2
+VS
R1 24.7kΩ
+VS
+VS
24.7kΩ
400Ω
Q2
+VS
+IN
–VS
REF
10kΩ
RG
–VS
03149-042
–VS
–VS
–VS
–VS
Figure 42. Simplified Schematic
The AD8221 is a monolithic instrumentation amplifier based
on the classic 3-op amp topology. Input transistors Q1 and Q2
are biased at a fixed current so that any differential input signal
forces the output voltages of A1 and A2 to change accordingly.
A signal applied to the input creates a current through RG, R1,
and R2, such that the outputs of A1 and A2 deliver the correct
voltage. Topologically, Q1, A1, R1 and Q2, A2, R2 can be
viewed as precision current feedback amplifiers. The amplified
differential and common-mode signals are applied to a
difference amplifier that rejects the common-mode voltage
but amplifies the differential voltage. The difference amplifier
employs innovations that result in low output offset voltage as
well as low output offset voltage drift. Laser-trimmed resistors
allow for a highly accurate in-amp with gain error typically less
than 20 ppm and CMRR that exceeds 90 dB (G = 1).
Using superbeta input transistors and an IB compensation
scheme, the AD8221 offers extremely high input impedance,
low IB, low IB drift, low IOS, low input bias current noise, and
extremely low voltage noise of 8 nV/√Hz.
B
To maintain precision even at low input levels, special attention
was given to the design and layout of the AD8221, resulting in
an in-amp whose performance satisfies the most demanding
applications.
A unique pinout enables the AD8221 to meet a CMRR
specification of 80 dB at 10 kHz (G = 1) and 110 dB at 1 kHz
(G = 1000). The balanced pinout, shown in Figure 43, reduces
the parasitics that had, in the past, adversely affected CMRR
performance. In addition, the new pinout simplifies board
layout because associated traces are grouped together. For
example, the gain setting resistor pins are adjacent to the
inputs, and the reference pin is next to the output.
B
The transfer function of the AD8221 is
G = 1+
49.4 kΩ
RG
–IN 1
8
+VS
RG 2
7
VOUT
RG 3
6
REF
+IN 4
5
–VS
AD8221
TOP VIEW
Users can easily and accurately set the gain using a single
standard resistor.
Figure 43. Pinout Diagram
Rev. B | Page 16 of 24
03149-043
B
Because the input amplifiers employ a current feedback
architecture, the gain-bandwidth product of the AD8221
increases with gain, resulting in a system that does not suffer
from the expected bandwidth loss of voltage feedback
architectures at higher gains.
AD8221
GAIN SELECTION
Grounding
Placing a resistor across the RG terminals set the gain of
AD8221, which can be calculated by referring to Table 5 or
by using the gain equation.
The output voltage of the AD8221 is developed with respect to
the potential on the reference terminal. Care should be taken to
tie REF to the appropriate local ground.
RG =
In mixed-signal environments, low level analog signals need to
be isolated from the noisy digital environment. Many ADCs
have separate analog and digital ground pins. Although it is
convenient to tie both grounds to a single ground plane, the
current traveling through the ground wires and PC board may
cause hundreds of millivolts of error. Therefore, separate analog
and digital ground returns should be used to minimize the
current flow from sensitive points to the system ground. An
example layout is shown in Figure 44 and Figure 45.
49.4 kΩ
G −1
Table 5. Gains Achieved Using 1% Resistors
1% Standard Table Value of RG (Ω)
49.9 k
12.4 k
5.49 k
2.61 k
1.00 k
499
249
100
49.9
Calculated Gain
1.990
4.984
9.998
19.93
50.40
100.0
199.4
495.0
991.0
The AD8221 defaults to G = 1 when no gain resistor is used.
Gain accuracy is determined by the absolute tolerance of RG.
The TC of the external gain resistor increases the gain drift of
the instrumentation amplifier. Gain error and gain drift are kept
to a minimum when the gain resistor is not used.
Careful board layout maximizes system performance. Traces
from the gain setting resistor to the RG pins should be kept as
short as possible to minimize parasitic inductance. To ensure
the most accurate output, the trace from the REF pin should
either be connected to the local ground of the AD8221, as shown
in Figure 46, or connected to a voltage that is referenced to the
local ground of the AD8221.
03149-044
LAYOUT
Figure 44. Top Layer of the AD8221-EVAL
Common-Mode Rejection
A well implemented layout helps to maintain the high CMRR
over frequency of the AD8221. Input source impedance and
capacitance should be closely matched. In addition, source
resistance and capacitance should be placed as close to the
inputs as permissible.
Rev. B | Page 17 of 24
03149-045
One benefit of the high CMRR over frequency of the AD8221 is
that it has greater immunity to disturbances, such as line noise
and its associated harmonics, than do typical instrumentation
amplifiers. Typically, these amplifiers have CMRR fall-off at
200 Hz; common-mode filters are often used to compensate for
this shortcoming. The AD8221 is able to reject CMRR over a
greater frequency range, reducing the need for filtering.
Figure 45. Bottom Layer of the AD8221-EVAL
AD8221
+VS
REFERENCE TERMINAL
As shown in Figure 42, the reference terminal, REF, is at one
end of a 10 kΩ resistor. The output of the instrumentation
amplifier is referenced to the voltage on the REF terminal; this
is useful when the output signal needs to be offset to a precise
midsupply level. For example, a voltage source can be tied to the
REF pin to level-shift the output so that the AD8221 can interface
with an ADC. The allowable reference voltage range is a function
of the gain, input, and supply voltage. The REF pin should not
exceed either +VS or –VS by more than 0.5 V.
AD8221
REF
–VS
TRANSFORMER
+VS
For best performance, source impedance to the REF terminal
should be kept low, because parasitic resistance can adversely
affect CMRR and gain accuracy.
AD8221
POWER SUPPLY REGULATION AND BYPASSING
REF
A stable dc voltage should be used to power the instrumentation
amplifier. Noise on the supply pins can adversely affect
performance. Bypass capacitors should be used to decouple
the amplifier.
–VS
THERMOCOUPLE
A 0.1 μF capacitor should be placed close to each supply pin.
As shown in Figure 46, a 10 μF tantalum capacitor can be used
further away from the part. In most cases, it can be shared by
other precision integrated circuits.
+VS
C
R
1
fHIGH-PASS = 2πRC
+VS
AD8221
C
R
10µF
–VS
+IN
CAPACITOR COUPLED
VOUT
AD8221
Figure 47. Creating an IBIAS Path
INPUT PROTECTION
LOAD
0.1µF
10µF
–VS
03149-046
REF
–IN
03149-047
0.1µF
REF
Figure 46. Supply Decoupling, REF, and Output Referred to Local Ground
INPUT BIAS CURRENT RETURN PATH
The input bias current of the AD8221 must have a return path
to common. When the source, such as a thermocouple, cannot
provide a return current path, one should be created, as shown
in Figure 47.
All terminals of the AD8221 are protected against ESD, 1 kV
Human Body Model. In addition, the input structure allows for
dc overload conditions below the negative supply, −VS. The
internal 400 Ω resistors limit current in the event of a negative
fault condition. However, in the case of a dc overload voltage
above the positive supply, +VS, a large current flows directly
through the ESD diode to the positive rail. Therefore, an external
resistor should be used in series with the input to limit current
for voltages above +Vs. In either scenario, the AD8221 can
safely handle a continuous 6 mA current, I = VIN/REXT for
positive overvoltage and I = VIN/(400 Ω + REXT) for negative
overvoltage.
For applications where the AD8221 encounters extreme
overload voltages, as in cardiac defibrillators, external series
resistors, and low leakage diode clamps, such as BAV199Ls,
FJH1100s, or SP720s should be used.
Rev. B | Page 18 of 24
AD8221
CD affects the difference signal, and CC affects the commonmode signal. Values of R and CC should be chosen to minimize
RFI. Mismatch between the R × CC at the positive input and the
R × CC at the negative input degrades the CMRR of the AD8221.
By using a value of CD one magnitude larger than CC, the effect
of the mismatch is reduced, and therefore, performance is
improved.
RF INTERFERENCE
RF rectification is often a problem when amplifiers are used in
applications where there are strong RF signals. The disturbance
can appear as a small dc offset voltage. High frequency signals
can be filtered with a low-pass RC network placed at the input
of the instrumentation amplifier, as shown in Figure 48. The
filter limits the input signal bandwidth according to the following
relationship:
FilterFreqDiff =
1
2πR(2CD + CC )
FilterFreqCM =
1
2πRCC
PRECISION STRAIN GAGE
The low offset and high CMRR over frequency of the AD8221
make it an excellent candidate for bridge measurements. As
shown in Figure 49, the bridge can be directly connected to
the inputs of the amplifier.
+5V
where CD ≥ 10CC.
10µF
350Ω
+IN
350Ω
CC
350Ω
R
–IN
+IN
CD
10nF
R1
499Ω
CONDITIONING ±10 V SIGNALS FOR A +5 V
DIFFERENTIAL INPUT ADC
–IN
1nF
10µF
0.1µF
There is a need in many applications to condition ±10 V signals.
However, many of today’s ADCs and digital ICs operate on
much lower, single-supply voltages. Furthermore, new ADCs
have differential inputs because they provide better commonmode rejection, noise immunity, and performance at low supply
voltages. Interfacing a ±10 V, single-ended instrumentation
amplifier to a +5 V, differential ADC can be a challenge.
Interfacing the instrumentation amplifier to the ADC requires
attenuation and a level shift. A solution is shown in Figure 50.
03149-048
CC
–15V
Figure 48. RFI Suppression
+12V
+2.5V
+12V
R3
1kΩ
0.1µF
+12V
0.1µF
C1
470pF
0.1µF
+IN
AD8022
+5V
R6
27.4Ω
REF
–IN
R1
10kΩ
10nF
10µF
–12V
–12V
R5
499Ω
DVDD
AD7723
C2
220µF
+12V
VIN(–)
AGND DGND REF1 REF2
0.1µF
0.1µF
0.1µF
AVDD
0.1µF
OP27
R2
10kΩ
+5V
(½)
VIN(+)
AD8221
+2.5V
Figure 49. Precision Strain Gage
REF
4.02kΩ
–
VOUT
AD8221
R
+
AD8221
R
1nF
4.02kΩ
10µF
350Ω
10µF
–12V
R4
1kΩ
AD8022
R7
27.4Ω
(½)
220nF
0.1µF
–12V
10nF
+5V
+VIN
10µF
0.1µF
VOUT
AD780
GND
Figure 50. Interfacing to a Differential Input ADC
Rev. B | Page 19 of 24
2.5V
22µF
03149-050
0.1µF
03149-049
+15V
0.1µF
AD8221
This topology has five benefits. In addition to level-shifting and
attenuation, very little noise is contributed to the system. Noise
from R1 and R2 is common to both of the inputs of the ADC
and is easily rejected. R5 adds a third of the dominant noise and
therefore makes a negligible contribution to the noise of the
system. The attenuator divides the noise from R3 and R4. Likewise,
its noise contribution is negligible. The fourth benefit of this
interface circuit is that the acquisition time of the AD8221 is
reduced by a factor of 2. With the help of the OP27, the AD8221
only needs to deliver one-half of the full swing; therefore, signals
can settle more quickly. Lastly, the AD8022 settles quickly,
which is helpful because the shorter the settling time, the
more bits that can be resolved when the ADC acquires data.
This configuration provides attenuation, a level-shift, and a
convenient interface with a differential input ADC while
maintaining performance.
reduces the referred input noise of the amplifier to 8 nV/√Hz.
Thus, smaller signals can be measured because the noise floor is
lower. DC offsets that would have been gained by 100 are
eliminated from the output of the AD8221 by the integrator
feedback network.
At low frequencies, the OP1177 forces the output of the AD8221 to
0 V. Once a signal exceeds fHIGH-PASS, the AD8221 outputs the
amplified input signal.
+VS
0.1µF
+IN
R
499Ω
fHIGH-PASS =
AD8221
REF
–IN
0.1µF
–VS
OP1177
+VS
Rev. B | Page 20 of 24
R
15.8kΩ
C
1µF
+VS
0.1µF
AC-COUPLED INSTRUMENTATION AMPLIFIER
Measuring small signals that are in the noise or offset of the
amplifier can be a challenge. Figure 51 shows a circuit that can
improve the resolution of small ac signals. The large gain
1
2πRC
10µF
–VS
10µF
0.1µF
–VS
Figure 51. AC-Coupled Circuit
03149-051
In this topology, an OP27 sets the reference voltage of the
AD8221. The output signal of the instrumentation amplifier is
taken across the OUT pin and the REF pin. Two 1 kΩ resistors
and a 499 Ω resistor attenuate the ±10 V signal to +4 V. An
optional capacitor, C1, can serve as an antialiasing filter. An
AD8022 is used to drive the ADC.
AD8221
OUTLINE DIMENSIONS
3.20
3.00
2.80
8
3.20
3.00
2.80
5.15
4.90
4.65
5
1
4
PIN 1
0.65 BSC
0.95
0.85
0.75
1.10 MAX
0.15
0.00
0.38
0.22
COPLANARITY
0.10
0.80
0.60
0.40
8°
0°
0.23
0.08
SEATING
PLANE
COMPLIANT TO JEDEC STANDARDS MO-187-AA
Figure 52. 8-Lead Mini Small Outline Package [MSOP]
(RM-8)
Dimensions shown in millimeters
5.00 (0.1968)
4.80 (0.1890)
8
1
5
4
1.27 (0.0500)
BSC
0.25 (0.0098)
0.10 (0.0040)
COPLANARITY
0.10
SEATING
PLANE
6.20 (0.2441)
5.80 (0.2284)
1.75 (0.0688)
1.35 (0.0532)
0.51 (0.0201)
0.31 (0.0122)
0.50 (0.0196)
0.25 (0.0099)
45°
8°
0°
0.25 (0.0098)
0.17 (0.0067)
1.27 (0.0500)
0.40 (0.0157)
COMPLIANT TO JEDEC STANDARDS MS-012-A A
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
Figure 53. 8-Lead Standard Small Outline Package [SOIC_N]
Narrow Body
(R-8)
Dimensions shown in millimeters and (inches)
Rev. B | Page 21 of 24
012407-A
4.00 (0.1574)
3.80 (0.1497)
AD8221
ORDERING GUIDE
Model
AD8221AR
AD8221AR-REEL
AD8221AR-REEL7
AD8221ARZ 2
AD8221ARZ-R72
AD8221ARZ-RL2
AD8221ARM
AD8221ARM-REEL
AD8221ARM REEL7
AD8221ARMZ2
AD8221ARMZ-R72
AD8221ARMZ-RL2
AD8221BR
AD8221BR-REEL
AD8221BR-REEL7
AD8221-EVAL
1
2
Temperature Range for
Specified Performance
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
Operating 1
Temperature Range
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
Package Description
8-Lead SOIC_N
8-Lead SOIC_N, 13" Tape and Reel
8-Lead SOIC_N, 7" Tape and Reel
8-Lead SOIC_N
8-Lead SOIC_N, 7" Tape and Reel
8-Lead SOIC_N, 13" Tape and Reel
8-Lead MSOP
8-Lead MSOP, 13" Tape and Reel
8-Lead MSOP, 7" Tape and Reel
8-Lead MSOP
8-Lead MSOP, 7" Tape and Reel
8-Lead MSOP, 13" Tape and Reel
8-Lead SOIC_N
8-Lead SOIC_N, 13" Tape and Reel
8-Lead SOIC_N, 7" Tape and Reel
Evaluation Board
See Typical Performance Characteristics for expected operation from 85°C to 125°C.
Z = RoHS Compliant Part, # denotes RoHS compliant product may be top or bottom marked.
Rev. B | Page 22 of 24
Package
Option
R-8
R-8
R-8
R-8
R-8
R-8
RM-8
RM-8
RM-8
RM-8
RM-8
RM-8
R-8
R-8
R-8
Branding
JLA
JLA
JLA
JLA#
JLA#
JLA#
AD8221
NOTES
Rev. B | Page 23 of 24
AD8221
NOTES
©2003–2007 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D03149–0–9/07(B)
Rev. B | Page 24 of 24