ADI AD8221

AD8221 General Description

The AD8221 is a versatile and high-performance instrumentation amplifier renowned for its exceptional performance, particularly in terms of common-mode rejection ratio (CMRR) over a wide frequency range. While many instrumentation amplifiers in the market experience a decline in CMRR beyond 200 Hz, the AD8221 stands out by maintaining a minimum CMRR of 80 dB up to 10 kHz across all gain settings, even at unity gain (G = 1). This remarkable feature makes the AD8221 capable of effectively rejecting wideband interference and line harmonics, thereby simplifying the overall filter requirements in various applications.

Connection Diagram

AD8221 Manufacturer

The AD8221 precision instrumentation amplifier is manufactured by Analog Devices, Inc., commonly referred to as ADI. Analog Devices, Inc. (ADI) is a leading global semiconductor company specializing in the design and manufacturing of a wide range of analog and mixed-signal integrated circuits (ICs), sensors, data converters, and other semiconductor devices. Founded in 1965 by Ray Stata and Matthew Lorber, Analog Devices has grown to become a prominent player in the electronics industry. The company is headquartered in Norwood, Massachusetts, USA, and operates globally with offices, manufacturing facilities, and research centers around the world.

AD8221 Specification

Features

Easy to Use: The AD8221 is designed for user convenience. It offers straightforward configuration and can be easily integrated into various circuit designs.

Space-Saving MSOP Package: The AD8221 is available in a compact MSOP (Mini Small Outline Package) form factor, which is ideal for applications with limited board space, ensuring efficient use of PCB real estate.

Gain Programmability with a Single External Resistor: One of the standout features of the AD8221 is its gain adjustability. Users can set the desired gain by simply connecting an external resistor. This flexibility allows for a wide range of gain settings, from 1 to 1000, catering to diverse signal amplification requirements.

Wide Power Supply Range: The AD8221 can operate within a broad power supply voltage range, spanning from ±2.3 V to ±18 V. This versatility in power supply voltage makes it suitable for various voltage environments.

Extended Temperature Range: The AD8221 maintains specified performance even in challenging temperature conditions. It can operate reliably within a temperature range of -40°C to +85°C, making it suitable for both industrial and extreme temperature environments. It can even operate up to 125°C in certain conditions.

High CMRR: The AD8221 boasts a minimum CMRR of 80 dB up to 10 kHz at unity gain (G = 1). This means it effectively rejects common-mode noise, ensuring that the amplified signal remains clean and accurate.
Wide Bandwidth: With a bandwidth of 825 kHz at unity gain (G = 1), the AD8221 is capable of handling a broad range of frequencies, making it suitable for applications where signal fidelity is crucial.
Fast Slew Rate: The amplifier features a 2 V/µs slew rate, enabling it to rapidly respond to input changes.

Low Input Voltage Noise: The AD8221 maintains a maximum input voltage noise of 8 nV/√Hz at 1 kHz. This ensures that the amplifier itself does not introduce significant noise into the signal.
Low Input Noise: The amplifier exhibits minimal input noise of 0.25 µV p-p in the 0.1 Hz to 10 Hz range, making it suitable for applications requiring high signal clarity in low-frequency bands.

Exceptional CMRR: The AD8221BR variant offers an impressive minimum CMRR of 90 dB at unity gain (G = 1), enhancing its common-mode noise rejection capabilities.
Low Input Offset Voltage: It features a maximum input offset voltage of 25 µV, ensuring precise signal amplification with minimal offset error.
Stable Offset Drift: The AD8221BR boasts a maximum input offset drift of 0.3 µV/°C, ensuring that the offset voltage remains stable over varying temperatures.
Low Input Bias Current: With a maximum input bias current of 0.4 nA, the AD8221BR minimizes the impact of input current on the measured signal.

 CMRR vs. Frequency for G = 1

AD8221 Application Note

https://www.aipcba.com/datasheet/ad8221-application-note.html

AD8221 Equivalent Parts

AD8221 Absolute Maximum Ratings

Supply Voltage (±18 V): This rating specifies the maximum allowable supply voltage that can be applied to the AD8221 without causing damage to the device. Operating the amplifier beyond this voltage range may lead to permanent damage.

Internal Power Dissipation (200 mW): The internal power dissipation rating indicates the maximum amount of power that the device can safely dissipate as heat while operating. Exceeding this value may result in overheating and potential damage.

Output Short-Circuit Current (Indefinite): This rating indicates that the AD8221 can withstand a continuous short-circuit condition at its output without sustaining damage. However, it's important to note that this is not a recommended operating condition, and short-circuits should be avoided to prevent excessive current flow and potential overheating.

Input Voltage (Common-Mode) (±VS): The common-mode input voltage rating specifies the maximum voltage that can be applied to the inputs while maintaining proper amplifier operation. Operating the inputs beyond this range can result in distortion or damage to the device.

Differential Input Voltage (±VS): This rating indicates the maximum voltage difference that can be applied between the non-inverting and inverting inputs of the AD8221 without causing damage. Exceeding this voltage difference can lead to device failure.

Storage Temperature Range (−65°C to +150°C): The storage temperature range defines the temperature limits within which the AD8221 can be safely stored when not in operation. Storing the device outside this range may affect its long-term reliability.

Operating Temperature Range (−40°C to +125°C): This rating specifies the recommended temperature range for normal operation of the AD8221. The device is designed to operate within this temperature range while maintaining its specified performance characteristics. Operating the device outside this range may result in performance degradation or damage.

Pin configuration and function description

Application

Weigh Scales: The AD8221 is frequently used in precision weigh scale systems to accurately measure weight and force. Its high input impedance and low noise characteristics are well-suited for such applications.

Industrial Process Controls: In industrial settings, the AD8221 can be found in various process control systems where accurate measurement and control of variables such as pressure, temperature, and flow rate are critical.

Bridge Amplifiers: The AD8221 is often employed as a bridge amplifier, where it amplifies small differential voltage signals from Wheatstone bridge sensors, strain gauges, or load cells. This is commonly used in load cell interfaces for weighing systems.

Precision Data Acquisition Systems: The AD8221 plays a crucial role in precision data acquisition systems where the accuracy and fidelity of signal measurement are paramount. It is used to amplify weak sensor signals before digitization.

Medical Instrumentation: Medical devices, such as patient monitoring equipment, use the AD8221 for its ability to accurately amplify biopotential signals, including ECG (electrocardiogram) and EEG (electroencephalogram) signals.

Strain Gauges: Strain gauge applications often require accurate measurement of minute changes in resistance due to mechanical strain. The AD8221 is employed to amplify these small changes in resistance.

Transducer Interfaces: The AD8221 serves as an excellent interface between various sensors and data acquisition systems. It amplifies and conditions sensor signals, ensuring precise measurements.

Sensor Signal Conditioning: The AD8221 can be used for conditioning signals from a wide range of sensors, including pressure sensors, temperature sensors, and level sensors, to provide accurate readings.

Industrial Automation: In industrial automation and control systems, the AD8221 assists in acquiring and processing analog signals for control and monitoring purposes.

Test and Measurement Equipment: Precision test and measurement instruments, such as multimeters, spectrum analyzers, and oscilloscopes, may incorporate the AD8221 for accurate signal measurements.

Bridge-Based Sensors: Any sensor that utilizes a Wheatstone bridge configuration can benefit from the AD8221's high-precision amplification and common-mode rejection capabilities.

Theory of Operation

AD8221 Related Parts

Dimensions

Gain of Instrumentation Amplifier

The gain of an instrumentation amplifier (in-amp) is determined by the ratio of two resistors, typically labeled Rg (gain resistor) and Rf (feedback resistor). The gain equation for an instrumentation amplifier is as follows:

Gain (A) = 1 + (2 * Rf / Rg)

In this equation, A represents the gain, Rf is the feedback resistor, and Rg is the gain resistor. The gain resistor, Rg, is often external and can be set to a specific value based on your application requirements. The feedback resistor, Rf, is usually internal to the instrumentation amplifier and is fixed.

To change the gain of the instrumentation amplifier, you can adjust the value of the external gain resistor, Rg. Increasing Rg will increase the gain, while decreasing Rg will decrease the gain.

Instrumentation Amplifier Application

Strain Gauge Amplification: In industrial and structural engineering, strain gauges are used to measure physical deformation in materials. Instrumentation amplifiers are used to amplify the small changes in resistance produced by the strain gauges, providing accurate strain measurements.

Temperature Measurement: Instrumentation amplifiers can be used with temperature sensors like thermocouples or RTDs (resistance temperature detectors) to accurately measure temperature changes in a wide range of applications, including industrial process control and environmental monitoring.

Biomedical Applications: In medical instrumentation, in-amps are used for tasks such as amplifying bioelectric signals from ECG (electrocardiogram) electrodes or EEG (electroencephalogram) sensors, as well as for blood pressure monitoring.

Bridge Sensor Amplification: Many sensor types, such as pressure sensors and load cells, are based on the Wheatstone bridge configuration. Instrumentation amplifiers can be used to amplify the differential voltage output of such sensors.

Industrial Process Control: In manufacturing and process control systems, in-amps can amplify sensor signals from various transducers to monitor and control physical processes, ensuring quality control and efficiency.

Data Acquisition Systems: Instrumentation amplifiers are often a crucial part of data acquisition systems, used to condition and amplify low-level sensor signals before digitizing and processing the data.

Weighing Scales: Precision weighing scales and balances utilize load cells for measuring weight. In-amps are commonly used to amplify the load cell's output to obtain accurate weight measurements.

Audio Amplification: In-amps are used in high-fidelity audio applications to amplify very low-level audio signals, providing clean and high-quality sound reproduction.

Pressure and Force Measurement: In applications such as automotive testing, aerospace, and materials testing, in-amps are used to amplify signals from pressure sensors and force transducers for measuring stress and force.

Voltage Measurement: In some cases, in-amps are used for general-purpose voltage amplification in precision measurement and control systems.

Instrumentation Amplifier Circuit

Read More:

https://www.ti.com/lit/an/sboa282a/sboa282a.pdf?ts=1697360463974

AD8221 Evaluation Board

The EVAL-AD8221EB is an evaluation board designed to facilitate the evaluation and experimentation with the AD8221 instrumentation amplifier manufactured by Analog Devices. 

Evaluation of AD8221: The primary purpose of this evaluation board is to allow users to evaluate the performance and characteristics of the AD8221 instrumentation amplifier.

Adjustable Gain and Reference Jumper: The board is designed to enable users to easily adjust the gain resistor and reference jumper settings. This flexibility is important for various applications where signal amplification and reference configurations need to be customized.

Output Interface: The board provides an SMA/SMB outline at the output, allowing users to connect the output signal to external measurement or analysis equipment.

Integration with Complementary Tools: Users have the option to add their own connector to interface the evaluation board with other tools or evaluation boards, such as analog-to-digital converter (ADC) evaluation boards provided by Analog Devices. This integration allows for a broader range of testing and measurements.

Breadboard Space: The inclusion of breadboard space on the evaluation board encourages experimentation and prototyping. Users can extend the functionality of the evaluation board by adding additional components like active filters, line drivers, or other signal conditioning elements. This makes the board a versatile development tool.

Development and Experimentation: The board's design promotes experimentation with the AD8221 and offers a platform for developing and testing different signal processing and conditioning circuits in addition to the primary application of instrumentation amplification.

AD8221 Spice Model

https://www.analog.com/en/design-center/simulation-models/spice-models.html

Related Articles:

Gain of an Instrumentation Amplifier
AD8221 Application Circuit

Specifications