3 nV/Hz, Low Power
Instrumentation Amplifier
Data Sheet
AD8421
FEATURES PIN CONNECTION DIAGRAM
Low power
AD8421
1 8
IN +V
S
2.3 mA maximum supply current
R 2 7 V
G OUT
Low noise
3 6
R REF
G
3.2 nV/Hz maximum input voltage noise at 1 kHz
+IN 4 5 V
S
200 fA/Hz current noise at 1 kHz
Excellent ac specifications
TOP VIEW
(Not to Scale)
10 MHz bandwidth (G = 1)
Figure 1.
2 MHz bandwidth (G = 100)
0.6 s settling time to 0.001% (G = 10)
80 dB CMRR at 20 kHz (G = 1)
35 V/s slew rate
High precision dc performance (AD8421BRZ)
10
94 dB CMRR minimum (G = 1)
G = 100
0.2 V/C maximum input offset voltage drift
BEST AVAILABLE
1 ppm/C maximum gain drift (G = 1)
7mA LOW NOISE IN-AMP
1
500 pA maximum input bias current
Inputs protected to 40 V from opposite supply
2.5 V to 18 V dual supply (5 V to 36 V single supply)
100n
Gain set with a single resistor (G = 1 to 10,000)
APPLICATIONS
BEST AVAILABLE
1mA LOW POWER IN-AMP
10n
Medical instrumentation
AD8421
Precision data acquisition
R NOISE ONLY
Microphone preamplification
S
1n
Vibration analysis
100 1k 10k 100k 1M
Multiplexed input applications
SOURCE RESISTANCE, R ()
S
ADC driver
Figure 2. Noise Density vs. Source Resistance
GENERAL DESCRIPTION
The AD8421 is a low cost, low power, extremely low noise, ultralow The AD8421 delivers 3 nV/Hz input voltage noise and
bias current, high speed instrumentation amplifier that is ideally 200 fA/Hz current noise with only 2 mA quiescent current,
suited for a broad spectrum of signal conditioning and data making it an ideal choice for measuring low level signals. For
acquisition applications. This product features extremely high applications with high source impedance, the AD8421 employs
CMRR, allowing it to extract low level signals in the presence of innovative process technology and design techniques to provide
high frequency common-mode noise over a wide temperature noise performance that is limited only by the sensor.
range.
The AD8421 uses unique protection methods to ensure robust
The 10 MHz bandwidth, 35 V/s slew rate, and 0.6 s settling inputs while still maintaining very low noise. This protection
time to 0.001% (G = 10) allow the AD8421 to amplify high speed allows input voltages up to 40 V from the opposite supply rail
without damage to the part.
signals and excel in applications that require high channel count,
multiplexed systems. Even at higher gains, the current feedback
A single resistor sets the gain from 1 to 10,000. The reference
architecture maintains high performance; for example, at G = 100,
pin can be used to apply a precise offset to the output voltage.
the bandwidth is 2 MHz and the settling time is 0.8 s. The
The AD8421 is specified from 40C to +85C and has typical
AD8421 has excellent distortion performance, making it suitable
performance curves to 125C. It is available in 8-lead MSOP
for use in demanding applications such as vibration analysis.
and SOIC packages.
Rev. 0
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TOTAL NOISE DENSITY AT 1kHz (V/ Hz)
10123-001
10123-078AD8421 Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1 Gain Selection............................................................................. 20
Applications....................................................................................... 1 Reference Terminal .................................................................... 21
Pin Connection Diagram ................................................................ 1 Input Voltage Range................................................................... 21
General Description ......................................................................... 1 Layout .......................................................................................... 21
Revision History ............................................................................... 2 Input Bias Current Return Path ............................................... 22
Specifications..................................................................................... 3 Input Voltages Beyond the Supply Rails.................................. 22
AR and BR Grades........................................................................ 3 Radio Frequency Interference (RFI)........................................ 23
ARM and BRM Grades................................................................ 5 Calculating the Noise of the Input Stage................................. 23
Absolute Maximum Ratings............................................................ 8 Applications Information .............................................................. 25
Thermal Resistance ...................................................................... 8 Differential Output Configuration .......................................... 25
ESD Caution.................................................................................. 8 Driving an ADC ......................................................................... 26
Pin Configuration and Function Descriptions............................. 9 Outline Dimensions....................................................................... 27
Typical Performance Characteristics ........................................... 10 Ordering Guide .......................................................................... 27
Theory of Operation ...................................................................... 20
Architecture................................................................................. 20
REVISION HISTORY
5/12Revision 0: Initial Version
Rev. 0 | Page 2 of 28