Precision Instrumentation Amplifier
AD8221
FEATURES
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
CONNECTION DIAGRAM
–IN
1
R
G
2
R
G
3
+IN
4
8
+V
S
7
V
OUT
6
REF
AD8221
TOP VIEW
Figure 1.
120
110
100
90
COMPETITOR 1
80
70
60
COMPETITOR 2
50
40
AD8221
CMRR (dB)
03149-001
5
–V
S
APPLICATIONS
Weigh scales
Industrial process controls
Bridge amplifiers
Precision data acquisition systems
Medical instrumentation
Strain gages
Transducer interfaces
10
100
1k
FREQUENCY (Hz)
10k
100k
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°C
1
.
1
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.
See Typical Performance Characteristics for expected operation from
85°C to 125°C.
Rev. C
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.
www.analog.com
Tel: 781.329.4700
Fax: 781.461.3113 ©2003–2011 Analog Devices, Inc. All rights reserved.
03149-002
AD8221
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
General Description ......................................................................... 1
Connection Diagram ....................................................................... 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Absolute Maximum Ratings ............................................................ 8
Thermal Characteristics .............................................................. 8
ESD Caution .................................................................................. 8
Pin Configuration and Function Descriptions ............................. 9
Typical Performance Characteristics ........................................... 10
Theory of Operation ...................................................................... 17
Gain Selection ............................................................................. 18
Layout .......................................................................................... 18
Reference Terminal .................................................................... 19
Power Supply Regulation and Bypassing ................................ 19
Input Bias Current Return Path ............................................... 19
Input Protection ......................................................................... 19
RF Interference ........................................................................... 20
Precision Strain Gage ................................................................. 20
Conditioning ±10 V Signals for a +5 V Differential Input
ADC ............................................................................................. 20
AC-Coupled Instrumentation Amplifier ................................ 21
Die Information .............................................................................. 22
Outline Dimensions ....................................................................... 23
Ordering Guide .......................................................................... 24
REVISION HISTORY
3/11—Rev. B to Rev. C
Added Pin Configuration and Function Descriptions Section .. 9
Added Die Information Section ................................................... 22
Updated Outline Dimensions ....................................................... 23
Changes to Ordering Guide .......................................................... 24
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. C | Page 2 of 24
AD8221
SPECIFICATIONS
V
S
= ±15 V, V
REF
= 0 V, T
A
= 25°C, G = 1, R
L
= 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, e
NI
Output Voltage Noise, e
NO
RTI
G=1
G = 10
G = 100 to 1000
Current Noise
VOLTAGE OFFSET
1
Input Offset, V
OSI
Over Temperature
Average TC
Output Offset, V
OSO
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
R
IN
I
IN
Voltage Range
Gain to Output
Conditions
V
CM
= −10 V to +10 V
80
100
120
130
V
CM
= −10 V to +10 V
80
90
100
100
RTI noise =
√e
NI2
+ (e
NO
/G)
2
V
IN+
, V
IN−
, V
REF
= 0
f = 0.1 Hz to 10 Hz
2
0.5
0.25
40
6
60
86
0.4
300
0.66
6
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
1
20
50
1.5
2.0
0.6
0.8
94
114
130
140
110
130
140
150
0.2
1
0.1
1
20
50
0.4
1
0.4
0.6
2
0.5
0.25
40
6
25
45
0.3
200
0.45
5
µV p-p
µV p-p
µV p-p
fA/√Hz
pA p-p
µV
µV
µV/°C
µV
mV
µV/°C
dB
dB
dB
dB
nA
nA
pA/°C
nA
nA
pA/°C
kΩ
µA
V
V/V
8
75
8
75
nV/√Hz
nV/√Hz
80
100
110
110
dB
dB
dB
dB
90
110
130
140
dB
dB
dB
dB
Min
AR Grade
Typ
Max
Min
BR Grade
Typ
Max
Unit
f = 1 kHz
f = 0.1 Hz to 10 Hz
V
S
= ±5 V to ±15 V
T = −40°C to +85°C
V
S
= ±5 V to ±15 V
T = −40°C to +85°C
V
S
= ±2.3 V to ±18 V
V
IN+
, V
IN−
, V
REF
= 0
–V
S
60
+V
S
1 ± 0.0001
–V
S
60
+V
S
1 ± 0.0001
Rev. C | Page 3 of 24
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 > 1
2
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
V
S
= ±2.3 V to ±18 V
T = −40°C to +85°C
Min
±2.3
0.9
1
AR Grade
Typ
Max
±18
1
1.2
Min
±2.3
0.9
1
BR Grade
Typ
Max
±18
1
1.2
Unit
V
mA
mA
825
562
100
14.7
10 V step
10
80
10 V step
13
110
2
2.5
1000
0.03
0.3
0.3
0.3
V
OUT
= −10 V to +10 V
R
L
= 10 kΩ
R
L
= 10 kΩ
R
L
= 10 kΩ
R
L
= 2 kΩ
3
5
10
10
3
10
15
40
95
10
–50
825
562
100
14.7
10
80
13
110
2
2.5
1000
0.02
0.15
0.15
0.15
3
5
10
10
2
10
15
40
95
5
–50
kHz
kHz
kHz
kHz
µs
µs
µs
µs
V/µs
V/µs
V/V
%
%
%
%
ppm
ppm
ppm
ppm
ppm/°C
ppm/°C
G=1
G = 5 to 100
G = 1 + (49.4 kΩ/R
G
)
V
OUT
± 10 V
1.5
2
1
1.5
2
1
100||2
100||2
V
S
= ±2.3 V to ±5 V
T = −40°C to +85°C
V
S
= ±5 V to ±18 V
T =−40°C to +85°C
R
L
= 10 kΩ
V
S
= ±2.3 V to ±5 V
T = −40°C to +85°C
V
S
= ±5 V to ±18 V
T = –40°C to +85°C
–V
S
+ 1.9
–V
S
+ 2.0
–V
S
+ 1.9
–V
S
+ 2.0
–V
S
+ 1.1
–V
S
+ 1.4
–V
S
+ 1.2
–V
S
+ 1.6
18
+V
S
− 1.1
+V
S
− 1.2
+V
S
− 1.2
+V
S
− 1.2
+V
S
− 1.2
+Vs − 1.3
+V
S
− 1.4
+V
S
− 1.5
–V
S
+ 1.9
–V
S
+ 2.0
–V
S
+ 1.9
–V
S
+ 2.0
–V
S
+ 1.1
–V
S
+ 1.4
–V
S
+ 1.2
–V
S
+ 1.6
100||2
100||2
+V
S
− 1.1
+V
S
− 1.2
+V
S
− 1.2
+V
S
− 1.2
+V
S
− 1.2
+V
S
− 1.3
+V
S
− 1.4
+V
S
− 1.5
18
GΩ||pF
GΩ||pF
V
V
V
V
V
V
V
V
mA
Rev. C | Page 4 of 24
AD8221
Parameter
TEMPERATURE RANGE
Specified Performance
Operating Range
4
1
2
Conditions
Min
–40
–40
AR Grade
Typ
Max
+85
+125
Min
–40
–40
BR Grade
Typ
Max
+85
+125
Unit
°C
°C
Total RTI V
OS
= (V
OSI
) + (V
OSO
/G).
Does not include the effects of external resistor R
G
.
3
One input grounded. G = 1.
4
See Typical Performance Characteristics for expected operation between 85°C to 125°C.
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, e
NI
Output Voltage Noise, e
NO
RTI
G=1
G = 10
G = 100 to 1000
Current Noise
VOLTAGE OFFSET
1
Input Offset, V
OSI
Over Temperature
Average TC
Output Offset, V
OSO
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
V
CM
= −10 V to +10 V
80
100
120
130
V
CM
= –10 V to +10 V
80
90
100
100
RTI noise = √e
NI2
+ (e
NO
/G)
2
V
IN+
, V
IN−
, V
REF
= 0
f = 0.1 Hz to 10 Hz
2
0.5
0.25
40
6
70
135
0.9
600
1.00
9
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. C | Page 5 of 24
Min
ARM Grade
Typ
Max
Unit
dB
dB
dB
dB
dB
dB
dB
dB
8
75
nV/√Hz
nV/√Hz
µV p-p
µV p-p
µV p-p
fA/√Hz
pA p-p
µV
µV
µV/°C
µV
mV
µV/°C
dB
dB
dB
dB
f = 1 kHz
f = 0.1 Hz to 10 Hz
V
S
= ±5 V to ±15 V
T = −40°C to +85°C
V
S
= ±5 V to ±15 V
T = −40°C to +85°C
V
S
= ±2.3 V to ±18 V
2
3
1
1.5
nA
nA
pA/°C
nA
nA
pA/°C
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