The AD8244BRMZ is a low power FET input quad Unity-gain Buffer designed to isolate very large source impedances from the rest of the signal chain. The 2pA 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 non-inverting 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. The AD8244 solves this problem with unique pinout that physically separates the high impedance inputs from the low impedance supplies and outputs of the other buffers. 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.

• Extremely high input impedance
• Low noise
• High DC precision – 3μV/°C maximum offset drift (B grade)
• No leakage from inputs to supply pins
• Provides guarding capability
• Rail-to-rail output
• Single-supply operation – Input range extends to ground
• 250μA Maximum supply current per amplifier
• 2pA Maximum input bias current at 25°C

The AD824 is a quad, FET input, single supply amplifier, featuring rail-to-rail outputs. The combination of FET inputs and rail-to-rail outputs makes the AD824 useful in a wide variety of low voltage applications where low input current is a primary consideration. The AD824 is guaranteed to operate from a 3 V single supply up to ±15 V dual supplies. AD824AR-3V parametric performance at 3 V is fully guaranteed. Fabricated on Analog Devices, Inc., complementary bipolar process, the AD824 has a unique input stage that allows the input voltage to safely extend beyond the negative supply and to the positive supply without any phase inversion or latch-up. The output voltage swings to within 15 mV of the supplies. Capacitive loads to 350 pF can be handled without oscillation.

The FET input combined with laser trimming provides an input that has extremely low bias currents with guaranteed offsets below 1 mV. This enables high accuracy designs even with high source impedances. Precision is combined with low noise, making the AD824 ideal for use in battery powered medical equipment. Applications for the AD824 include portable medical equipment, photo diode preamplifiers, and high impedance transducer amplifiers. The ability of the output to swing rail-to-rail enables designers to build multistage filters in single supply systems and maintain high signal-to-noise ratios. The AD824 is specified over the extended industrial (−40°C to +85°C) temperature range and is available in narrow 14-lead SOIC package.