AD8421BRZ - 3nV/√Hz Low Power Instr Amp | Analog Devices
MPN： AD8421BRZ ✓ 啟用中AD8421BRZ 概覽
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.
直接替換替代品，適用於 AD8421BRZ — 相同封裝，腳位對腳位相容。需重新設計 PCB 的不同封裝零件不列入。
此系列的變體
與下列產品可直接替換的同系列型號： AD8421BRZ （相同外形與佔位） — 差異在於 Gain Range, Package, Input Offset Voltage, Amplifier Type, Bandwidth.
AD8421ARZ
✅ 直接替換 ⚠️ 規格未經驗證聯絡詢價
查看資料表 →AD8221ARZ
✅ 直接替換 ⚠️ 規格未經驗證聯絡詢價
查看資料表 →AD620ARZ
✅ 直接替換 ⚠️ 規格未經驗證聯絡詢價
查看資料表 →AD8223ARZ
✅ 直接替換 ⚠️ 規格未經驗證聯絡詢價
查看資料表 →INA128UA
✅ 直接替換 ⚠️ 規格未經驗證聯絡詢價
查看資料表 →INA129UA
✅ 直接替換 ⚠️ 規格未經驗證聯絡詢價
查看資料表 →LT1167CS8
✅ 直接替換 ⚠️ 規格未經驗證📋 參考替代品（不在目錄中）
AD8422BRZ
✅ 直接替換 ⚠️ 規格未經驗證📋 參考替代品（不在目錄中）
AD8421BRZ 最大額定值與電氣特性
| Amplifier Type | Instrumentation Amplifier |
| Number of Circuits | 1 |
| Voltage Noise Density | 3 nV/√Hz typ |
| Bandwidth | 10 MHz (G=1) |
| Supply Voltage - Single | 5 V to 36 V |
| Supply Voltage - Dual | ±2.5 V to ±18 V |
| 靜態電流 | 2.3 mA typ |
| Input Bias Current | 250 pA max |
| Input Offset Voltage | 60 µV max (B grade) |
| CMRR | 126 dB min (G=100) |
| Gain Range | 1 to 10000 |
| 工作溫度 | -40°C to +85°C |
| 封裝 | 8-Lead SOIC |
| 安裝類型 | Surface Mount |
| RoHS 狀態 | Compliant |
| REACH Status | Compliant |
AD8421BRZ 腳位配置
| 腳位 1 | RG- — Gain setting resistor negative terminal |
| 腳位 2 | -IN — Inverting differential input |
| 腳位 3 | +IN — Non-inverting differential input |
| 腳位 4 | -VS — Negative supply or ground for single-supply operation |
| 腳位 5 | REF — Reference voltage pin for output offset |
| 腳位 6 | OUT — Instrumentation amplifier output |
| 腳位 7 | +VS — Positive supply |
| 腳位 8 | RG+ — Gain setting resistor positive terminal |
典型應用
AD8421BRZ 適用於 6 應用s: Medical ECG and Patient Monitoring, High-Speed Data Acquisition Systems, Industrial Process Control and Bridge Sensing, Precision Sensor Signal Conditioning, Motor Control Current Sensing, Test and Measurement Instrumentation.
Medical ECG and Patient Monitoring
The AD8421BRZ is ideal for ECG front ends because its 3 nV/√Hz voltage noise and 126 dB CMRR preserve weak biopotential signals in the presence of 50/60 Hz interference. Its ultralow 250 pA input bias current minimizes errors from high-impedance electrodes, and the 2.3 mA quiescent current supports portable monitors. Differential signal amplification into a high-resolution ADC such as the AD7175-2BRUZ or AD7988-5BCPZ provides excellent system accuracy.
推薦
High-Speed Data Acquisition Systems
With a 10 MHz bandwidth at G=1, the AD8421BRZ is suited for high-speed DAQ systems that must capture fast transients and dynamic sensor signals. The low noise density supports high dynamic range, while the reference pin allows easy offset adjustment for unipolar ADC interfaces. In a typical channel, the AD8421BRZ output is connected to a SAR ADC such as the AD7988-5BCPZ or AD7172-2BRUZ, enabling simultaneous high-speed and high-precision measurement.
推薦
Industrial Process Control and Bridge Sensing
The AD8421BRZ can interface directly with strain-gauge bridges and pressure sensors in industrial automation. Its high CMRR rejects common-mode noise from long cable runs, while the low offset drift minimizes measurement error over temperature. The wide supply range of ±2.5 V to ±18 V or 5 V to 36 V simplifies powering from industrial 24 V rails. The output can drive an external ADC or a precision comparator for control-loop monitoring.
推薦
Precision Sensor Signal Conditioning
The AD8421BRZ provides the low noise and high input impedance needed for a wide variety of sensors, including thermocouples, RTDs, and photodetectors. Its ultralow input bias current minimizes loading on high-impedance sources, while the 10 MHz gain-bandwidth product supports real-time processing. Used together with precision amplifiers such as the ADA4522-2ARZ, the signal chain can achieve very low offset and drift suitable for laboratory-grade instrumentation.
推薦
Motor Control Current Sensing
The AD8421BRZ can be used in motor control applications to amplify the small differential voltage across a current-sense resistor. Its high bandwidth of 10 MHz at G=1 supports fast current-control loops, while the low noise and high CMRR reject motor-drive switching noise. The wide common-mode input range and supply flexibility allow direct connection to shunt resistors in both low-side and high-side current-sense configurations.
推薦
Test and Measurement Instrumentation
For bench instruments, low noise and high CMRR are essential to make accurate voltage and sensor measurements. The AD8421BRZ offers a compact 8-lead SOIC solution with 3 nV/√Hz noise, 10 MHz bandwidth, and a reference pin for output offset trimming. It can be used as the analog front end for multimeters, thermocouple meters, or precision source-measure units, feeding digitizers such as the AD7606BSTZ-4RL or AD7172-2BRUZ.
推薦
推薦產品摘要
工程參考資料，適用於 AD8421BRZ — 比較、設計指引及合規資訊。
選型指南
與替代品比較
| 參數 | 本產品 | AD8421ARZ | AD8221ARZ | INA128UA |
|---|---|---|---|---|
| Package | 8-SOIC | 8-SOIC | 8-SOIC | 8-SOIC |
| Brand | Analog Devices | Analog Devices | Analog Devices | Texas Instruments |
| Voltage Noise Density | 3 nV/√Hz | 3 nV/√Hz | 8 nV/√Hz | 8 nV/√Hz |
| Bandwidth at G=1 | 10 MHz | 10 MHz | 1 MHz | 1.3 MHz |
| Supply Voltage Range | ±2.5 V to ±18 V or 5 V to 36 V | ±2.5 V to ±18 V or 5 V to 36 V | ±2.5 V to ±18 V or 5 V to 36 V | ±2.25 V to ±18 V or 4.5 V to 36 V |
| Input Bias Current | 250 pA max | 250 pA max | 250 pA max | 5 nA max |
| CMRR at G=100 | 126 dB min | 126 dB min | 120 dB min | 120 dB min |
| Quiescent Current | 2.3 mA | 2.3 mA | 0.9 mA | 0.7 mA |
| Grade | B grade, industrial temperature | A grade, industrial temperature | Precision grade, industrial temperature | Standard grade, industrial temperature |
主要差異化特點
- Lowest voltage noise in the AD8421/AD8221 comparison (對比AD8221ARZ)
- 10 MHz unity-gain bandwidth supports high-speed DAQ (對比INA128UA)
- Ultralow input bias current preserves sensor accuracy (對比AD620ARZ)
- Grade selection for precision systems (對比AD8421ARZ)
設計說明
Place the gain-setting resistor (RG) directly between pins 1 and 8 to minimize parasitic inductance and capacitance. Stray capacitance at these pins can reduce bandwidth and cause gain peaking. Use a precision metal-film resistor with 0.1% tolerance or better when the gain accuracy is critical. For high-gain configurations, keep traces short and the resistor body close to the IC body.
Filter the reference pin with a low-impedance source. The reference pin (pin 5) sets the output common-mode voltage and must be driven from a low-impedance reference or buffer. For single-supply circuits, set the reference to mid-supply to maximize output swing. If using an external reference, place a 0.1 µF and 1 µF capacitor directly at the pin for noise bypass.
Do not exceed the input common-mode voltage range. Although the AD8421 has excellent CMRR, exceeding the specified input voltage range will degrade linearity and can damage the device. Add series protection resistors and clamp diodes for harsh industrial environments. Also ensure the power supply is clean and decoupled with 0.1 µF ceramic capacitors close to each supply pin.
合規資訊
Compliance values based on distributor and product page data for AD8421BRZ. AEC-Q100 not applicable for this standard instrumentation amplifier.
