AD8244 Datasheet, PDF (1/20 Pages) Analog Devices – Single-Supply, Low Power, Precision FET Input Quad Buffer

Data Sheet
Single-Supply, Low Power,
Precision FET Input Quad Buffer
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
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
PIN CONFIGURATION
AD8244
IN A 1
OUT A 2
+V_S 3
OUT B 4
IN B 5
10 IN D
9 OUT D
8 –V_S
7 OUT C
6 IN C
Figure 1.
10
TYPICAL MISMATCH
BETWEEN ANY
TWO CHANNELS
1
IN-AMP
1/2
0.1
AD8244
0.01
0.001
10
100
1k
10k
FREQUENCY (Hz)
100k
Figure 2. Gain Matching vs. Frequency
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. 0
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