AD620
Precision instrumentation amplifier with gain range of 1 to 1000, low noise, and excellent CMRR for sensor applications.
Product Overview
Description
The AD620 is a low cost, high accuracy instrumentation amplifier that requires only one external resistor to set gains of 1 to 1000. It features high accuracy with 40ppm maximum nonlinearity, low offset voltage (50μV max), and excellent offset drift (0.6μV/°C).
With low noise (0.28μV p-p, 0.1Hz to 10Hz) and high CMRR (100dB at gain=10), the AD620 is ideal for precision data acquisition systems. The input bias current is very low at 1nA max, minimizing errors with high source impedances.
The AD620 operates from ±2.3V to ±18V dual supplies or 4.6V to 36V single supply. It consumes only 1.3mA supply current, making it suitable for battery-powered portable applications. The device is available in 8-lead PDIP and SOIC packages.
Product Series
AD
Primary Application
Bridge signal conditioning
Key Features
- Gain set with single external resistor
- High accuracy (40ppm nonlinearity)
- Low offset voltage (50μV max)
- Excellent CMRR (100dB at gain=10)
- Low noise (0.28μV p-p)
- Low input bias current (1nA)
- Low power (1.3mA supply current)
- Wide supply range
Specifications
| Gain Range | 1 to 1000 |
|---|---|
| Offset Voltage | 50μV max |
| Offset Drift | 0.6μV/°C |
| Noise | 0.28μV p-p (0.1-10Hz) |
| CMRR | 100dB at gain=10 |
| Bandwidth | 120kHz at gain=100 |
| Slew Rate | 1.2V/μs |
| Supply Voltage | ±2.3V to ±18V |
| Supply Current | 1.3mA max |
| Input Bias Current | 1nA max |
| Package | PDIP-8, SOIC-8 |
| Temperature Range | -40°C to +85°C |
Applications
Bridge signal conditioning
Sensor signal conditioning
Industrial process control
Industrial automation and control
Medical instrumentation
Medical electronics
Data acquisition systems
Data acquisition and conversion
Portable battery-powered equipment
Battery and charging management
Sensor interfaces
Sensor signal conditioning
FAE Expert Insights
"The AD620 has been an industry standard for instrumentation amplifiers for decades, and for good reason. It offers an unbeatable combination of precision, ease of use, and cost-effectiveness. The single-resistor gain setting is incredibly convenient - just use a precision 0.1% resistor and you get accurate gain without trimming. I've used it in countless bridge sensor applications (load cells, pressure sensors) with excellent results. The 100dB CMRR at gain=10 effectively rejects common-mode noise in industrial environments. The 1nA input bias current is low enough for most sensor applications. One limitation is the bandwidth - 120kHz at gain=100 means it's not suitable for high-speed applications. For those, consider the AD8421. Also, the offset voltage (50μV) is higher than zero-drift alternatives, but adequate for many applications. Overall, a proven workhorse for precision sensor conditioning."
Industry standard for instrumentation amps; single-resistor gain setting; excellent CMRR for industrial noise rejection
— Sarah Johnson, BeiLuo
Frequently Asked Questions
How do I calculate the gain resistor for AD620?
The AD620 gain is set by a single external resistor (RG) connected between pins 1 and 8. The gain equation is: Gain = 49.4kΩ / RG + 1. To calculate RG for a desired gain: RG = 49.4kΩ / (Gain - 1). For example: For gain = 10: RG = 49.4kΩ / (10-1) = 5.49kΩ; For gain = 100: RG = 49.4kΩ / (100-1) = 499Ω; For gain = 1000: RG = 49.4kΩ / (1000-1) = 49.4Ω. Use precision resistors (0.1% or better) for accurate gain. The resistor should be placed close to the AD620 with short traces. Standard E96 values can be used - for non-standard values, combine two resistors in series. The gain accuracy is primarily determined by the RG resistor tolerance and the AD620's internal resistor matching (0.15% typical).
Use equation RG = 49.4kΩ / (Gain - 1); use 0.1% precision resistors; place RG close to device.
What is the input common-mode range of AD620?
The AD620 input common-mode range depends on the supply voltage and gain setting. With ±5V supplies and gain=1, the input range is approximately ±3.9V. As gain increases, the output swing requirements reduce, allowing wider input common-mode range. With ±15V supplies, the input range extends to approximately ±13V at low gains. The key constraint is that the internal nodes must not saturate - the common-mode voltage plus the differential signal must stay within the amplifier's linear range. For single-supply operation (e.g., +5V), the input common-mode range is approximately 1.2V to 3.8V at gain=1. For bridge sensors powered from 5V with 2.5V common-mode, this works well. Always consult the datasheet common-mode range graphs for your specific supply voltage and gain combination.
Input range depends on supply and gain; with ±5V supplies, range is ±3.9V at gain=1; verify with datasheet graphs.
How do I minimize noise in AD620 circuits?
To minimize noise in AD620 instrumentation amplifier circuits: 1) Use low source resistances - the AD620's voltage noise (9nV/√Hz) dominates for Rs < 1kΩ, but current noise (100pA/√Hz) becomes significant for high source impedances; 2) Add differential and common-mode filtering at the inputs - use 100Ω resistors with 100nF capacitors for 16kHz low-pass filtering; 3) Keep input traces short and symmetric to maintain CMRR; 4) Use star grounding to avoid ground loops; 5) For DC applications, add output filtering - a 10μF capacitor across the output reduces wideband noise; 6) Use the AD620's internal feedback - don't add external feedback components; 7) For ultimate noise performance, consider the AD8421 which has lower noise (3.2nV/√Hz). The total noise in a 1kHz bandwidth is approximately 280nV p-p (0.1-10Hz) plus broadband contribution.
Keep source impedance low; add input filtering; use star grounding; add output capacitor for DC apps.
Can AD620 operate from a single 5V supply?
Yes, the AD620 operates from single supplies from 4.6V to 36V. With a single 5V supply, the input common-mode range is approximately 1.2V to 3.8V, and the output can swing to within approximately 0.5V of either rail. This makes it suitable for many single-supply sensor applications. For a typical bridge sensor powered from 5V: the bridge common-mode is 2.5V (within the 1.2-3.8V range), and with gain=100, a 10mV differential signal produces 1V output (well within the 0.5V to 4.5V output range). For the best single-supply performance, use the AD620A or B grades which have better offset specifications. If you need rail-to-rail output for single-supply operation, consider the AD8221 or AD8421 which have improved output swing characteristics.
Operates from 4.6V-36V single supply; input range 1.2V-3.8V with 5V; output swings to within 0.5V of rails.
What is the difference between AD620 and AD621?
The AD621 is a variant of the AD620 with internal gain setting resistors for fixed gains of 10 or 100. Key differences: AD620 requires external resistor for any gain 1-1000; AD621 has no external gain resistor - gain is pin-selectable (10 or 100). The AD621 offers better gain accuracy (0.05% vs 0.7% for AD620) because the internal resistors are laser-trimmed. However, the AD621 is limited to gains of 10 or 100 only - no other gains are available. The AD620 offers more flexibility with any gain from 1 to 1000. Both have similar offset, CMRR, and noise specifications. Choose AD621 if you need exactly gain=10 or 100 with highest accuracy and don't want an external resistor. Choose AD620 if you need variable gain or gains other than 10/100. The AD621 is also slightly more expensive due to the internal trimmed resistors.
Use AD621 for fixed gain 10 or 100 with best accuracy; use AD620 for variable gains 1-1000.