AD8421BRZ
AD8421BRZ - 3nV/√Hz Low Power Instr Amp | Analog Devices
The Analog Devices AD8421BRZ is a low cost, low power, extremely low noise, ultralow bias current, high speed instrumentation amplifier in an 8-lead SOIC package. It is a single-circuit instrumentation amplifier that provides precision differential signal conditioning for a broad range of data acquisition, medical instrumentation, industrial process control, and sensor interface applications. The device combines a 3 nV/√Hz voltage noise density, 10 MHz bandwidth at G=1, and a low 2.3 mA quiescent current, making it suitable for both high-performance and power-sensitive precision systems.
An instrumentation amplifier is a precision differential voltage gain stage with high input impedance, low offset voltage, and high common-mode rejection. It is the front-end building block used to amplify small differential signals that sit on large common-mode voltages, such as bridge outputs, thermocouple signals, and medical biopotentials. In the signal-chain hierarchy, an instrumentation amplifier sits between the sensor and the ADC, pairing with data converters and precision amplifiers to form complete measurement systems. Its ability to set the gain with one external resistor and reject common-mode interference makes it indispensable in precision analog applications.
Key features of the AD8421BRZ include a 3 nV/√Hz voltage noise density at 1 kHz, 10 MHz bandwidth at unity gain, and an input bias current of 250 pA max. The device operates from a single supply of 5 V to 36 V or from dual supplies of ±2.5 V to ±18 V. The gain range is from 1 to 10,000 set by a single external resistor. The high CMRR of 126 dB at G=100 and low offset drift provide accurate measurement over temperature, while the −40°C to +85°C industrial temperature range supports robust system designs.
From a technical standpoint, the AD8421 uses a precision three-op-amp topology with laser-trimmed resistors, enabling low offset, low drift, and excellent AC performance. The very low bias current reduces errors from high source impedances, while the high bandwidth supports high-speed sampling and control loops. The device is specified over the industrial temperature range for the 8-lead SOIC package. The reference pin allows precise offset adjustment, which is essential for unipolar ADC interfaces and bridge-sensor nulling.
Typical applications include high-speed data acquisition systems, medical ECG and patient monitoring, precision weigh scales, current-sense amplification in motor controls, and sensor signal conditioning for industrial automation. The AD8421BRZ is also a favorable choice for test and measurement equipment where low noise and high CMRR directly affect measurement accuracy.
When laying out the printed circuit board, place the gain-setting resistor as close as possible to the RG pins to minimize parasitic capacitance and gain errors. Decouple each supply pin with 0.1 µF ceramic capacitors to the ground plane. For best noise performance, keep the source impedances balanced and use guarded traces on high-impedance inputs.
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