Analog Devices Inc. AD8221AR

Overview

AD8221AR from Analog Devices is a precision instrumentation amplifier with gain programmability (1–1000) via a single external resistor, 825 kHz –3 dB bandwidth at G = 1, 8 nV/√Hz input voltage noise, and 80 dB minimum CMRR to 10 kHz - deployed in bridge amplifier and strain gage signal conditioning for industrial process controls.

For engineers reviewing the AD8221AR datasheet, AD8221AR pinout, AD8221AR application, or AD8221AR equivalent, key selection criteria include its high-frequency CMRR stability, low RTI noise floor, ±2.3 V to ±18 V dual-supply operation, and guaranteed performance across −40°C to +85°C industrial temperature range.

Technical Context

The AD8221AR implements a monolithic 3-op-amp topology with superbeta input transistors and laser-trimmed resistors, enabling 90 dB CMRR (G = 1) and <25 µV input offset voltage in BR-grade variants. Its current-feedback architecture preserves bandwidth as gain increases - delivering 14.7 kHz at G = 1000 versus 825 kHz at G = 1.

CMRR remains ≥80 dB up to 10 kHz (G = 1), outperforming conventional in-amps whose CMRR rolls off above 200 Hz. The balanced pinout (RG pins adjacent to inputs, REF next to VOUT) minimizes parasitic coupling and supports robust layout for high common-mode rejection.

Key Specifications

Pinout & Package

AD8221AR is housed in an 8-lead SOIC package (JEDEC MS-012AA), with thermal resistance θ_JA = 121°C/W on a 4-layer board.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar instrumentation amplifier applications.

Compared with AD8221AR, AD8421ARMZ delivers superior high-frequency CMRR and input bias performance but sacrifices single-supply flexibility; INA128UA offers cost advantage and pin compatibility at the expense of bandwidth, noise, and temperature stability.

Availability

AD8221AR is available at Aetrix Electronics and suitable for industrial process controls, precision data acquisition systems, and medical instrumentation requiring stable component supply and long-term manufacturability.

Supply support for AD8221AR includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, headquartered in Norwood, MA.

The AD8221 belongs to Analog Devices' precision instrumentation amplifier product line, engineered specifically for demanding sensor signal conditioning in industrial, medical, and test equipment where DC accuracy and AC common-mode rejection are critical.

FAQ

What is the maximum gain achievable with AD8221AR, and how is it set?

The AD8221AR supports a gain range of 1 to 1000, set using a single external resistor connected between Pins 2 and 3 (RG terminals). The gain equation is G = 1 + (49.4 kΩ / RG). For example, a 49.9 Ω resistor yields G ≈ 1000. The AD8221AR defaults to G = 1 when no resistor is installed. Gain accuracy depends on the tolerance and temperature coefficient of the external RG resistor.

Does AD8221AR support single-supply operation?

No, AD8221AR does not support true single-supply operation. It requires dual symmetric supplies ranging from ±2.3 V to ±18 V. The input common-mode voltage range is limited to (−VS + 1.9 V) to (+VS − 1.2 V), and the output swing is similarly rail-referenced. For single-supply applications, consider the AD8237 or AD8420 as alternatives explicitly rated for 3 V to 36 V single-rail use.

What is the purpose of the REF pin on AD8221AR, and how should it be used?

The REF pin on AD8221AR sets the output common-mode voltage level. The output is VOUT = G × (V+IN − V−IN) + VREF. To interface with a unipolar ADC, drive REF with a stable mid-supply voltage (e.g., +7.5 V for ±15 V supplies). The REF pin must be driven by a low-impedance source (<10 Ω), and its voltage must remain within −VS to +VS. Do not leave REF floating or connect it directly to high-impedance dividers.

How does AD8221AR's CMRR performance compare to standard instrumentation amplifiers at 10 kHz?

AD8221AR maintains a minimum CMRR of 80 dB at 10 kHz (G = 1), whereas most conventional instrumentation amplifiers exhibit CMRR roll-off starting at ~200 Hz. This extended high-frequency CMRR allows AD8221AR to reject 50/60 Hz harmonics and switching noise without external filtering - a key differentiator in electrically noisy industrial environments where competing in-amps typically fall below 60 dB at 10 kHz.

Can AD8221AR be used with ±10 V input signals, and what are the input voltage limits?

Yes, AD8221AR is explicitly designed for ±10 V input signals. With ±15 V supplies, the input common-mode range extends from −13.1 V to +13.8 V (G = 1), comfortably accommodating ±10 V differential inputs. At ±5 V supplies, the usable common-mode range is −3.1 V to +3.8 V. Input differential voltage must not exceed ±VS, and absolute input voltages must stay within −VS + 1.9 V to +VS − 1.2 V to avoid phase reversal or damage.