Datasheet AD8244 (Analog Devices)

Single-Supply, Low Power, Precision FET Input Quad Buffer Data Sheet AD8244 FEATURES PIN CONFIGURATION Low power AD8244 250 µA maximum supply current per amplifier IN A 1 10 IN D FET input OUT A 2 9 OUT D 2 pA maximum input bias current at 25°C +VS 3 8 –VS OUT B 4 7 OUT C Extremely high input impedance
001
IN B 5 6 IN C Low noise
1689- 1
13 nV/√Hz voltage noise at 1 kHz
Figure 1. Pinout Isolates Inputs from Low-Impedance Leakage Sources
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
002
High impedance sensor conditioning 200nV/DIV 1s/DIV
11689-
Filters
Figure 2. 0.1 Hz to 10 Hz Voltage Noise
Photodiode amplifiers GENERAL DESCRIPTION
The AD8244 is a precision, low power, FET input, quad unity-gain high impedance inputs from the low impedance supplies and buffer that is designed to isolate very large source impedances outputs of the other buffers. This configuration simplifies from the rest of the signal chain. The 2 pA maximum bias guarding while reducing board space, al owing high performance current, near zero current noise, and 10 TΩ input impedance and high density in the same design. introduce almost no error, even with source impedance well The AD8244 design is focused on solving problems specific to into the megaohms. buffers. This includes close channel-to-channel matching which Many traditional operational amplifier pinouts have a supply allows channels of the AD8244 to be used in differential signal pin that is next to the noninverting input. A guard trace must be chains with minimal error. With its low voltage noise, wide routed between these pins to avoid leakage currents much larger supply range, and high precision, the AD8244 is also flexible than the bias current of a FET input op amp. Guard traces can enough to provide high performance anywhere a unity-gain be routed between pins for large packages, such as DIP or even buffer is needed, even with low source resistance. SOIC; however, the board area consumed by these packages is The AD8244 is specified over the industrial temperature range prohibitive for many modern applications. The AD8244 solves of −40°C to +85°C. It is available in a 10-lead MSOP package. this problem with a unique pinout that physically separates the
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Document Outline FEATURES APPLICATIONS PIN CONFIGURATION GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION OVERVIEW GUARDING INPUT PROTECTION LAYOUT CONSIDERATIONS DIFFERENTIAL SIGNAL CHAINS LOW OUTPUT IMPEDANCE vs. FREQUENCY APPLICATIONS INFORMATION ELECTROCARDIOGRAM (ECG) FILTERING Sallen-Key Low-Pass Filter Sallen-Key High-Pass Filter Twin-T Notch Filter PHOTODIODE AMPLIFIER LOW NOISE, JFET INPUT BUFFER OUTLINE DIMENSIONS ORDERING GUIDE