Single-Supply, Low Power,

Precision FET Input Quad Buffer

Data Sheet

AD8244

FEATURES

Low power

250 µA maximum supply current per amplifier

FET input

2 pA maximum input bias current at 25°C

Extremely high input impedance

Low noise

13 nV/√Hz voltage noise at 1 kHz

0.4 µV p-p voltage noise (0.1 Hz to 10 Hz)

0.8 fA/√Hz current noise at 1 kHz

High dc precision

3 µV/°C maximum offset drift (B grade)

3 MHz bandwidth

Unique pinout

No leakage from inputs to supply pins

Provides guarding capability

Rail-to-rail output

Single-supply operation

Input range extends to ground

Wide supply range

Single-supply: 3 V to 36 V

Dual-supply: ±1.5 V to ±18 V

Available in a compact 10-lead MSOP

APPLICATIONS

Biopotential electrodes

Medical instrumentation

High impedance sensor conditioning

Filters

Photodiode amplifiers

PIN CONFIGURATION

IN A 1

OUT A 2

+VS 3

OUT B 4

IN B

5

IN D

10

OUT D

9

–VS

8

OUT C

7

IN C

6

AD8244

Figure 1. Pinout Isolates Inputs from

Low-Impedance Leakage Sources

200nV/DIV

1s/DIV

Figure 2. 0.1 Hz to 10 Hz Voltage Noise

GENERAL DESCRIPTION

The AD8244 is a precision, low power, FET input, quad unity-gain

buffer that is designed to isolate very large source impedances

from the rest of the signal chain. The 2 pA maximum bias

current, near zero current noise, and 10 TΩ input impedance

introduce almost no error, even with source impedance well

into the megaohms.

Many traditional operational amplifier pinouts have a supply

pin that is next to the noninverting input. A guard trace must be

routed between these pins to avoid leakage currents much larger

than the bias current of a FET input op amp. Guard traces can

be routed between pins for large packages, such as DIP or even

SOIC; however, the board area consumed by these packages is

prohibitive for many modern applications. The AD8244 solves

this problem with a unique pinout that physically separates the

high impedance inputs from the low impedance supplies and

outputs of the other buffers. This configuration simplifies

guarding while reducing board space, allowing high performance

and high density in the same design.

The AD8244 design is focused on solving problems specific to

buffers. This includes close channel-to-channel matching which

allows channels of the AD8244 to be used in differential signal

chains with minimal error. With its low voltage noise, wide

supply range, and high precision, the AD8244 is also flexible

enough to provide high performance anywhere a unity-gain

buffer is needed, even with low source resistance.

The AD8244 is specified over the industrial temperature range

of −40°C to +85°C. It is available in a 10-lead MSOP package.

Rev. A

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