AD620AN: Precision Instrumentation Amplifier for Low-Level Signal Conditioning

ElecSuppliers Part Number ComparisonAug 21, 2026

The AD620AN is a precision instrumentation amplifier designed for amplifying low-level differential signals in measurement and signal-conditioning circuits. It combines a compact three-op-amp instrumentation amplifier architecture with an integrated gain-setting network, allowing the gain to be established with a single external resistor.

The device is particularly relevant to sensor interfaces where the useful signal may be small compared with the common-mode voltage present at the amplifier inputs. Its combination of low input offset, low input bias current, low noise and high common-mode rejection makes the AD620 suitable for precision data acquisition and transducer applications.

The AD620AN is the 8-lead PDIP version of the AD620 and is intended for through-hole PCB designs.

AD620AN Key Specifications

The AD620 provides a gain range from 1 to 10,000. Gain is programmed using one external resistor according to:

G = 1 + 49.4 kΩ / RG

where RG is the external gain resistor.

The amplifier operates from supplies ranging from ±2.3V to ±18V and has a maximum supply current of approximately 1.3mA under the specified operating conditions.

The device provides a typical input voltage noise of 9 nV/√Hz at 1kHz and a maximum B-grade input offset voltage of 50µV.

At a gain of 10, the B-grade device has a minimum common-mode rejection ratio of 100dB under the specified conditions.

These specifications make the AD620 more suitable for precision low-level signal amplification than a general-purpose operational amplifier used without an instrumentation-amplifier configuration.

AD620AN Gain Setting

The single-resistor gain configuration is one of the most useful characteristics of the AD620.

Instead of requiring several precision resistors to establish differential gain, the designer can use one external resistor between the gain pins.

At unity gain, the external gain resistor is not required. Increasing the gain resistor value reduces the gain, while reducing its value increases the gain.

For example, a design requiring approximately 100× gain can select the gain resistor from the AD620 gain equation and then account for resistor tolerance and gain error in the overall accuracy calculation.

This makes the AD620 particularly convenient when different versions of the same sensor interface require different amplification levels.

AD620AN Differential Signal Amplification

The AD620 is designed to amplify the voltage difference between its two input terminals while rejecting voltage common to both inputs.

This is important in sensor systems where the desired signal is relatively small.

A bridge sensor, for example, may produce a millivolt-level differential output while both sensor terminals sit at a considerably higher common-mode voltage.

A conventional single-ended amplifier may have difficulty maintaining accurate amplification under these conditions. The instrumentation-amplifier structure of the AD620 is designed specifically for this type of measurement.

The actual performance still depends on the sensor impedance, wiring, PCB layout and common-mode voltage range.

AD620AN Common-Mode Rejection

Common-mode rejection is a major factor when selecting an instrumentation amplifier.

The AD620 provides a minimum CMRR of 100dB at a gain of 10 for the B grade under the specified test conditions.

This allows the amplifier to suppress voltage components that appear similarly on both inputs while amplifying the differential component.

In practical systems, achieving high common-mode rejection requires more than the amplifier specification alone. Unequal source impedances, cable resistance, PCB leakage and external interference can all reduce the effective system-level CMRR.

For precision sensor applications, matching the impedance seen by the two inputs is therefore an important part of the design.

AD620AN Offset Voltage and Accuracy

Input offset becomes increasingly important as the sensor signal becomes smaller.

The B-grade AD620 specifies a maximum input offset voltage of 50µV and maximum input offset drift of 0.6µV/°C.

At high gain, even a small input-referred offset can become significant at the amplifier output.

For this reason, the AD620 gain should be selected according to the actual sensor output range rather than simply using the highest possible gain.

A good design normally leaves sufficient output headroom so that sensor tolerance, offset and temperature variation do not cause the amplifier to saturate.

AD620AN Low-Noise Performance

The AD620 has a typical input voltage noise of 9 nV/√Hz at 1kHz.

Its low-frequency noise is also specified for the 0.1Hz to 10Hz region, which is particularly relevant to slowly changing sensor signals.

Low-frequency noise can become a significant limitation in weighing systems, strain measurement and other precision instrumentation applications where the useful signal changes slowly.

The final noise performance, however, depends on the entire signal chain. Sensor noise, resistor noise, electromagnetic interference and power-supply noise can all become larger than the amplifier's intrinsic noise if the surrounding circuit is not properly designed.

AD620AN Bandwidth and Gain Relationship

The AD620's bandwidth changes substantially with gain.

Its typical small-signal bandwidth is approximately 1MHz at gain 1, 800kHz at gain 10, 120kHz at gain 100, and 12kHz at gain 1000.

This relationship is important when using the device for both high gain and higher-frequency signals.

A design that requires a gain of 1000 should not assume that the amplifier retains its unity-gain bandwidth.

For low-frequency instrumentation, the available bandwidth at high gain is generally sufficient. Applications requiring high gain and wide bandwidth should evaluate the gain-bandwidth relationship as part of the initial amplifier selection.

AD620AN Settling Performance

The AD620 provides a typical settling time to 0.01% of approximately 15µs for gains from 1 to 100 under the specified test conditions.

At a gain of 1000, the specified settling time increases to approximately 150µs.

This becomes relevant when the AD620 is used ahead of a multiplexer or ADC.

If the input signal changes rapidly, the following ADC must allow sufficient time for the amplifier output to settle before conversion.

Therefore, the amplifier's gain, settling time and ADC acquisition period should be considered together when designing a sampled data-acquisition system.

AD620AN Supply Voltage

The AD620 supports a wide dual-supply range from ±2.3V to ±18V.

The relatively low supply current is useful for portable measurement equipment and other applications where analog circuitry must operate with limited power.

The supply voltage also affects the available input common-mode range and output swing.

Consequently, selecting ±2.3V supplies simply because they fall within the specified operating range does not guarantee that the circuit will operate correctly. The expected sensor voltage, programmed gain and output requirements must all remain within the amplifier's actual operating limits.

AD620AN Reference Pin

The AD620 includes a reference input that allows the output voltage to be shifted relative to the circuit's ground reference.

The output relationship can be considered as the amplified differential input voltage plus the voltage applied to the reference terminal.

This feature is useful in single-supply or ADC-driven systems where the amplifier output needs to be positioned around a particular voltage rather than centered at 0V.

For example, a bipolar sensor signal can be shifted into the usable input range of a unipolar ADC by applying an appropriate reference voltage.

The reference source should have sufficiently low impedance because the reference input participates directly in the output signal path.

AD620AN Applications

The AD620 is well suited to applications involving low-level differential measurements.

Typical applications include:

Weighing and load measurement

Strain-gauge instrumentation

Transducer interfaces

Industrial process measurement

Precision data acquisition

Medical instrumentation

Portable measurement equipment

The common requirement across these applications is accurate amplification of a small differential signal before further analog processing or analog-to-digital conversion.

AD620AN for Strain Gauge and Load Cell Circuits

Load cells and strain gauges are representative applications for the AD620.

A bridge-based sensor can generate a very small differential voltage that changes according to mechanical load.

The AD620 can amplify this signal before it reaches an ADC, allowing the available ADC input range to be used more effectively.

The gain should be calculated from the sensor's full-scale output rather than selected arbitrarily.

For example, if a sensor produces only a few millivolts at full scale, a relatively high gain may be appropriate. If the sensor output is already hundreds of millivolts, excessive gain could cause output saturation.

AD620AN in Precision Data Acquisition

The AD620 can function as the analog front end of a precision data-acquisition system.

The amplifier establishes the appropriate signal amplitude before the ADC performs conversion.

A complete design should consider the sensor output, AD620 gain, amplifier offset, noise, bandwidth, ADC input range and reference voltage as one signal chain.

This approach is particularly important when the ADC has substantially higher resolution than the raw sensor signal can use effectively.

Amplifying and conditioning the sensor signal before conversion can make better use of the available ADC resolution while also providing a controlled interface between the sensor and converter.

AD620AN Package and Ordering Information

The AD620AN is supplied in an 8-lead PDIP package with the N-8 package designation.

The through-hole package makes it suitable for prototypes, laboratory equipment and existing PCB designs based on an 8-lead DIP footprint.

Other AD620 ordering variants use different package configurations. For example, the AD620AR and AD620ARZ are associated with 8-lead SOIC packages.

This means the complete Part Number should be checked when sourcing a replacement. The base name AD620 alone does not identify the physical package.

AD620AN Replacement Considerations

A suitable replacement for AD620AN needs to match more than the instrumentation-amplifier function.

Important parameters include gain range, gain-setting method, input offset, offset drift, input bias current, common-mode rejection, noise, bandwidth, supply range and output swing.

The package is also critical for direct PCB replacement.

A newer instrumentation amplifier may provide improved specifications but still require PCB changes if it uses a different pinout or package.

For an existing through-hole design, the 8-lead PDIP configuration of AD620AN should therefore be included in the replacement criteria.

AD620AN Selection for New Designs

The AD620AN is a practical choice when a design needs precision differential amplification, externally programmable gain and a through-hole package.

Its wide gain range allows the same amplifier architecture to accommodate very small sensor outputs as well as higher-level differential signals.

The combination of low input offset, low noise, low bias current and high common-mode rejection makes it particularly useful at the front end of measurement systems.

For new designs, the key selection factors are the required gain, sensor output level, common-mode voltage, bandwidth, power supply, output range and PCB package requirements.

When these conditions match the application, AD620AN can provide a compact and straightforward instrumentation-amplifier stage for precision analog signal conditioning.