3 nV/√Hz, Low Power

Instrumentation Amplifier

Data Sheet

AD8421

Rev. 0

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FEATURES

Low power

2.3 mA maximum supply current

Low noise

3.2 nV/√Hz maximum input voltage noise at 1 kHz

200 fA/√Hz current noise at 1 kHz

Excellent ac specifications

10 MHz bandwidth (G = 1)

2 MHz bandwidth (G = 100)

0.6 μs settling time to 0.001% (G = 10)

80 dB CMRR at 20 kHz (G = 1)

35 V/μs slew rate

High precision dc performance (AD8421BRZ)

94 dB CMRR minimum (G = 1)

0.2 μV/°C maximum input offset voltage drift

1 ppm/°C maximum gain drift (G = 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)

Gain set with a single resistor (G = 1 to 10,000)

APPLICATIONS

Medical instrumentation

Precision data acquisition

Microphone preamplification

Vibration analysis

Multiplexed input applications

ADC driver

PIN CONNECTION DIAGRAM

TOP VIEW

(Not to Scale)

–IN

1

+IN

4

8

7

REF

6

5

AD8421

Figure 1.

10µ

1n

100

1M

1µ

100n

10n

1k

10k

100k

G = 100

AD8421

BEST AVAILABLE

1mA LOW POWER IN-AMP

BEST AVAILABLE

7mA LOW NOISE IN-AMP

Figure 2. Noise Density vs. Source Resistance

GENERAL DESCRIPTION

The AD8421 is a low cost, low power, extremely low noise, ultralow

bias current, high speed instrumentation amplifier that is ideally

suited for a broad spectrum of signal conditioning and data

acquisition applications. This product features extremely high

CMRR, allowing it to extract low level signals in the presence of

high frequency common-mode noise over a wide temperature

range.

The 10 MHz bandwidth, 35 V/μs slew rate, and 0.6 μs settling

time to 0.001% (G = 10) allow the AD8421 to amplify high speed

signals and excel in applications that require high channel count,

multiplexed systems. Even at higher gains, the current feedback

architecture maintains high performance; for example, at G = 100,

the bandwidth is 2 MHz and the settling time is 0.8 μs. The

AD8421 has excellent distortion performance, making it suitable

for use in demanding applications such as vibration analysis.

The AD8421 delivers 3 nV/√Hz input voltage noise and

200 fA/√Hz current noise with only 2 mA quiescent current,

making it an ideal choice for measuring low level signals. For

applications with high source impedance, the AD8421 employs

innovative process technology and design techniques to provide

noise performance that is limited only by the sensor.

The AD8421 uses unique protection methods to ensure robust

inputs while still maintaining very low noise. This protection

allows input voltages up to 40 V from the opposite supply rail

without damage to the part.

A single resistor sets the gain from 1 to 10,000. The reference

pin can be used to apply a precise offset to the output voltage.

The AD8421 is specified from −40°C to +85°C and has typical

performance curves to 125°C. It is available in 8-lead MSOP

and SOIC packages.