Instrumentation Amplifier
AD8237
Rev. 0
on furnished by Analog Devices is believed to be accurate and reliable. However, no
Trademarks and registered trademarks are the property of their respective owners.
Fax: 781.461.3113 ©2012 Analog Devices, Inc. All rights reserved.
BW
1
+IN
2
–IN
3
–V
S
4
V
OUT
8
FB
7
REF
6
+V
S
5
AD8237
TOP VIEW
(Not to S cale)
+
–
–
+
10289-001
6
5
4
3
2
1
–1
0
0 1 2 3 4 5
INPUT COMMON-MODE VOLTAGE (V)
OUTPUT VOLTAGE (V)
TRADITI ONAL IN-AMP
(RAIL-TO-RAIL OUT)
AD8237
10289-002
G = 100
V
S
= 5V
V
REF
= 2.5V
Data Sheet
FEATURES
Gain set with 2 external resistors
Can achieve low gain drift at all gains
Ideal for battery powered instruments
Supply current: 115 µA
Rail-to-rail input and output
Zero input crossover distortion
Designed for excellent dc performance
Minimum CMRR: 106 dB
Maximum offset voltage drift: 0.3 µV/°C
Maximum gain error: 0.005% (all gains)
Maximum gain drift: 0.5 ppm/°C (all gains)
Input bias current: 1 nA guaranteed to 125°C
Bandwidth mode pin (BW) to adjust compensation
8 kV HBM ESD rating
RFI filter on-chip
Single-supply operation: 1.8 V to 5.5 V
8-lead MSOP package
APPLICATIONS
Bridge amplification
Pressure measurement
Medical instrumentation
Thermocouple interface
Portable systems
Current measurement
GENERAL DESCRIPTION
The AD8237 is a micropower, zero drift, rail-to-rail input and
output instrumentation amplifier. The relative match of two
resistors sets any gain from 1 to 1000. The AD8237 has excellent
gain accuracy performance that can be preserved at any gain
with two ratio-matched resistors.
The AD8237 employs the indirect current feedback architecture to
achieve a true rail-to-rail capability. Unlike conventional in-amps,
the AD8237 can fully amplify signals with common-mode voltage
at or even slightly beyond its supplies. This enables applications
with high common-mode voltages to use smaller supplies and
save power.
The AD8237 is an excellent choice for portable systems. With a
minimum supply voltage of 1.8 V, a 115 µA typical supply current,
and wide input range, the AD8237 makes full use of a limited
power budget, yet offers bandwidth and drift performance suitable
for bench-top systems.
Infor mati
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.
Micropower, Zero Drift, True Rail-to-Rail
PIN CONFIGURATION
Figure 1.
Table 1. Instrumentation Amplifiers by Category
General
Purpose
AD8421 AD8237 AD620 AD8237 AD8250
AD8221/AD8222 AD8231 AD621 AD8420 AD8251
AD8220/AD8224 AD8293 AD524 AD8235/AD8236 AD8253
AD8228 AD8553 AD526 AD627 AD8231
AD8295 AD8556 AD624
AD8226 AD8557
1
See www.analog.com for the latest instrumentation amplifiers.
Zero
Drift
Military
Grade
Micropower
The AD8237 is available in an 8-lead MSOP package. Performance
is specified over the full temperature range of −40°C to +125°C.
Figure 2. Input Common-Mode Voltage vs. Output Vo ltage, +V
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
1
Digital
Gain
= 5 V, G = 100
S
www.analog.com
AD8237 Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
Pin Configuration ............................................................................. 1
General Description ......................................................................... 1
Revision History ............................................................................... 2
Specifications ..................................................................................... 3
Absolute Maximum Ratings ............................................................ 7
Thermal Resistance ...................................................................... 7
ESD Caution .................................................................................. 7
Pin Configuration and Function Descriptions ............................. 8
Typical Performance Characteristics ............................................. 9
Theory of Operation ...................................................................... 20
Architecture ................................................................................. 20
Setting the Gain .......................................................................... 20
Gain Accuracy............................................................................. 21
Clock Feedthrough ..................................................................... 21
Input Voltage Range ................................................................... 21
Input Protection ......................................................................... 22
Filtering Radio Frequency Interference .................................. 22
Using the Reference Pin ............................................................ 22
Layout .......................................................................................... 23
Input Bias Current Return Path ............................................... 23
Applications Information .............................................................. 25
Battery Current Monitor ........................................................... 25
Programmable Gain In-Amp.................................................... 25
AD8237 in an Electrocardiogram (ECG) Front End............. 26
Outline Dimensions ....................................................................... 27
Ordering Guide .......................................................................... 27
REVISION HISTORY
8/12—Revision 0: Initial Version
Rev. 0 | Page 2 of 28
Data Sheet AD8237
COMMON-MODE REJECTION RATIO (CMRR)
VCM = 0.1 V to 4.9 V
CMRR at 1 kHz
80 dB
Input Bias Current
TA = +25°C
250
650
pA
Low Bandwidth Mode
Pin 1 connected to −VS
SPECIFICATIONS
+VS = +5 V, − VS = 0 V, V
otherwise noted.
Table 2.
Parameter Test Conditions/Comments Min Typ Max Unit
CMRR at DC
G = 1, G = 10 106 120 dB
G = 100, G = 1000 114 140 dB
Over Temperature (G = 1) TA = −40°C to +125°C 104 dB
NOISE
Voltage Noise
Spectral Density f = 1 kHz 68 nV/√Hz
Peak to Peak f = 0.1 Hz to 10 Hz 1.5 µV p-p
Current Noise
Spectral Density f = 1 kHz 70 fA/√Hz
Peak to Peak f = 0.1 Hz to 10 Hz 3 pA p-p
VOLTAGE OFFSET
Offset 30 75 µV
Average Temperature Coefficient TA = −40°C to +125°C 0.3 µV/°C
Offset RTI vs. Supply (PSR) 100 dB
INPUTS1 Valid for REF and FB pair, as well as +IN and −IN
= 2.5 V, VCM = 2.5 V, TA = 25°C, G = 1 to 1000, RL = 10 kΩ to ground, specifications referred to input, unless
REF
Over Temperature TA = −40°C to +125°C 1 nA
Average Temperature Coefficient 0.5 pA/°C
Input Offset Current TA = +25°C 250 650 pA
Over Temperature TA = −40°C to +125°C 1 nA
Average Temperature Coefficient 0.5 pA/°C
Input Impedance
Differential 100||5 MΩ||pF
Common Mode 800||10 MΩ||pF
Differential Input Operating Voltage TA = −40°C to +125°C ±3.85 V
Input Operating Voltage (+IN, −IN, or REF) TA = +25°C −VS − 0.3 +VS + 0.3 V
TA = −40°C to +125°C −VS − 0.2 +VS + 0.2 V
DYNAMIC RESPONSE
Small Signal Bandwidth −3 dB
G = 1 200 kHz
G = 10 20 kHz
G = 100 2 kHz
G = 1000 0.2 kHz
High Bandwidth Mode Pin 1 connected to +VS
G = 10 100 kHz
G = 100 10 kHz
G = 1000 1 kHz
Rev. 0 | Page 3 of 28
AD8237 Data Sheet
G = 100
440 µs
OUT
CM
Gain vs. Temperature
TA = −40°C to +125°C
0.5
ppm/°C
OUT
Parameter Test Conditions/Comments Min Typ Max Unit
Settling Time 0.01% 4 V output step
Low Bandwidth Mode Pin 1 connected to −VS
G = 1 80 µs
G = 10 100 µs
G = 1000 4 ms
High Bandwidth Mode Pin 1 connected to +VS
G = 10 80 µs
G = 100 100 µs
G = 1000 820 µs
Slew Rate
Low Bandwidth Mode 0.05 V/µs
High Bandwidth Mode 0.15 V/µs
EMI Filter Frequency 6 MHz
GAIN2 G = 1 + (R2/R1)
Gain Range3 1 1000 V/V
Gain Error V
Gain Error vs. V
= 0.1 V to 4.9 V, G = 1 to G = 1000 0.005 %
15 ppm/V
Gain Nonlinearity V
= 0.2 V to 4.8 V, RL = 10 kΩ to ground
G = 1, G = 10 3 ppm
G = 100 6 ppm
G = 1000 10 ppm
OUTPUT
Output Swing
RL = 10 kΩ to Midsupply TA = +25°C −VS + 0.05 +VS − 0.05 V
TA = −40°C to 125°C −VS + 0.07 +VS − 0.07 V
RL = 100 kΩ to Midsupply TA = +25°C −VS + 0.02 +VS − 0.02 V
TA = −40°C to 125°C −VS + 0.03 +VS − 0.03 V
Short-Circuit Current 4 mA
POWER SUPPLY
Operating Range 1.8 5.5 V
Quiescent Current TA = +25°C 115 130 µA
TA = −40°C to +125°C 150 µA
TEMPERATURE RANGE
Specified −40 +125 °C
1
Specifications apply to input voltages between 0 V and 5 V. When measuring voltages beyond the supplies, there is additional offset error, bias currents increase, and
input impedance decreases, especially at higher temperatures.
2
For G > 1, errors from the external resistors, R1 and R2, must be added to these specifications, including error from the FB pin bias current.
3
The AD8237 has only been characterized for gains of 1 to 1000; however, higher gains are possible.
Rev. 0 | Page 4 of 28
Data Sheet AD8237
G = 1, G = 10
100
120 dB
DIFF
DIFF
VOLTAGE OFFSET
Average Temperature Coefficient
0.5 pA/°C
G = 10
20 kHz
+VS = 1.8 V, −VS = 0 V, V
otherwise noted.
Table 3.
Parameter Test Conditions/Comments Min Typ Max Unit
COMMON-MODE REJECTION RATIO (CMRR) VCM = 0.2 V to 1.6 V
CMRR at DC
G = 100, G = 1000 114 140 dB
Over Temperature (G = 1) TA = −40°C to +125°C 94 dB
CMRR at 1 kHz 80 dB
NOISE
Voltage Noise
Spectral Density f = 1 kHz, V
Peak to Peak f = 0.1 Hz to 10 Hz, V
Current Noise
Spectral Density f = 1 kHz 70 fA/√Hz
Peak to Peak f = 0.1 Hz to 10 Hz 3 pA p-p
Offset 25 75 µV
Average Temperature Coefficient TA = −40°C to +125°C 0.3 µV/°C
Offset RTI vs. Supply (PSR) 100 dB
INPUTS1 Valid for REF and FB pair, as well as +IN and −IN
Input Bias Current TA = +25°C 250 650 pA
Over Temperature TA = −40°C to +125°C 1 nA
= 0.9 V, VCM = 0.9 V, TA = 25°C, G = 1 to 1000, RL = 10 kΩ to ground, specifications referred to input, unless
REF
≤ 100 mV 68 nV/√Hz
≤ 100 mV 1.5 µV p-p
Input Offset Current TA = +25°C 250 650 pA
Over Temperature TA = −40°C to +125°C 1 nA
Average Temperature Coefficient 0.5 pA/°C
Input Impedance
Differential 100||5 MΩ||pF
Common Mode 800||10 MΩ||pF
Differential Input Operating Voltage TA = −40°C to +125°C ± 0.75 V
Input Operating Voltage (+IN, −IN, REF, or FB) TA = +25°C −VS − 0.3 +VS + 0.3 V
TA = −40°C to +125°C −VS − 0.2 +VS + 0.2 V
DYNAMIC RESPONSE
Small Signal Bandwidth −3 dB
Low Bandwidth Mode Pin 1 connected to −VS
G = 1 200 kHz
G = 100 2 kHz
G = 1000 0.2 kHz
High Bandwidth Mode Pin 1 connected to +VS
G = 10 100 kHz
G = 100 10 kHz
G = 1000 1 kHz
Slew Rate
Low Bandwidth Mode 0.05 V/µs
High Bandwidth Mode 0.15 V/µs
EMI Filter Frequency 6 MHz
Rev. 0 | Page 5 of 28
AD8237 Data Sheet
OUT
CM
Gain vs. Temperature
TA = −40°C to +125°C
0.5
ppm/°C
OUT
RL = 100 kΩ to Midsupply
TA = +25°C
−VS + 0.02
+VS − 0.02
V
Parameter Test Conditions/Comments Min Typ Max Unit
GAIN2 G = 1 + (R2/R1)
Gain Range3 1 1000 V/V
Gain Error V
Gain Error vs. V
= 0.2 V to 1.6 V, G = 1 to G = 1000 0.005 %
15 ppm/V
Gain Nonlinearity V
= 0.2 V to 1.6 V
G = 1, G = 10 3 ppm
G = 100 6 ppm
G = 1000 10 ppm
OUTPUT
Output Swing
RL = 10 kΩ to Midsupply TA = +25°C −VS + 0.05 +VS − 0.05 V
TA = −40°C to 125°C −VS + 0.07 +VS − 0.07 V
TA = −40°C to 125°C −VS + 0.03 +VS − 0.03 V
Short-Circuit Current 4 mA
POWER SUPPLY
Operating Range 1.8 5.5 V
Quiescent Current TA = +25°C 115 130 µA
TA = −40°C to +125°C 150 µA
TEMPERATURE RANGE
Specified −40 +125 °C
1
Specifications apply to input voltages between 0 V and 1.8 V. When measuring voltages beyond the supplies, there is additional offset error, bias currents increase,
and input impedance decreases, especially at higher temperatures.
2
For G > 1, errors from the external resistors, R1 and R2, must be added to these specifications, including error from the FB pin bias current.
3
The AD8237 has only been characterized for gains of 1 to 1000; however, higher gains are possible.
Rev. 0 | Page 6 of 28
Data Sheet AD8237
Human Body Model
8 kV
ABSOLUTE MAXIMUM RATINGS
Table 4.
Parameter Rating
Supply Voltage 6 V
Output Short-Circuit Current Duration Indefinite
Maximum Voltage at −IN, +IN, FB, or REF1 +VS + 0.5 V
Minimum Voltage at −IN, +IN, FB, or REF1 −VS − 0.5 V
Storage Temperature Range −65°C to +150°C
Junction Temperature Range −65°C to +150°C
ESD
Charge Device Model 1.25 kV
Machine Model 0.2 kV
1
If input voltages beyond the specified minimum or maximum voltages are
expected, place resistors in series with the inputs to limit the current to 5 mA.
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.
THERMAL RESISTANCE
θJA is specified for a device in free air.
Table 5.
Package θJA Unit
8-Lead MSOP, 4-Layer JEDEC Board 145.7 °C/W
ESD CAUTION
Rev. 0 | Page 7 of 28
AD8237 Data Sheet
BW
1
+IN
2
–IN
3
–V
S
4
V
OUT
8
FB
7
REF
6
+V
S
5
AD8237
TOP VIEW
(Not to S cale)
+
–
–
+
10289-003
7
FB
Feedback Input.
OUT
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
Figure 3. Pin Configuration
Table 6. Pin Function Descriptions
Pin No. Mnemonic Description
1 BW For high bandwidth mode, connect this pin to +VS, or for low bandwidth mode, connect this pin to −VS. Do not
leave this pin floating.
2 +IN Positive Input.
3 −IN Negative Input.
4 −VS Negative Supply.
5 +VS Positive Supply.
6 REF Reference Input.
8 V
Output.
Rev. 0 | Page 8 of 28
Data Sheet AD8237
16
14
12
8
10
6
4
2
0
–60 –20–40 0 20 40 60
UNITS
OFFSET VOLTAGE (µV)
10289-004
18
21
15
12
9
6
3
0
–0.6 –0.4 –0.2 0 0.2 0.4 0.6
UNITS
POSIT IVE INPUT BIAS CURRENT (n A)
10289-005
35
30
20
25
15
10
5
0
–60 –20–40 0 20 40 60
UNITS
GAIN ERROR ( µ V /V)
10289-006
30
35
40
25
20
15
10
5
0
–6 –4 –2 0 2 4 6
UNITS
CMRR (µV/V)
10289-007
18
15
12
9
6
3
0
–0.6 –0.4 –0.2 0 0.2 0.4 0.6
UNITS
INPUT OFFSET CURRENT (nA)
10289-008
24
18
21
12
15
9
6
3
0
100 110105 115 120 125 130
UNITS
SUPPLY CURRENT (µA)
10289-009
TYPICAL PERFORMANCE CHARACTERISTICS
+VS = +5 V, −VS = 0 V, V
= 2.5 V, TA = 25°C, RL = 10 kΩ to ground, unless otherwise noted.
REF
Figure 4. Typical Distribution of Offset Voltage
Figure 5. Typical Distribution of Input Bias Current
Figure 7. Typical Distribution of CMRR
Figure 8. Typical Distribution of Input Offset Current
Figure 6. Typical Distribution of Gain Error (G = 1)
Rev. 0 | Page 9 of 28
Figure 9. Typical Distribution of Supply Current
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