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Dealing with AD620BRZ Gain Error: Causes and Remedies

Dealing with AD620 BRZ Gain Error: Causes and Remedies

When using the AD620BRZ instrumentation amplifier, you may encounter issues related to gain error, which can significantly affect the accuracy of your measurements. In this article, we will analyze the causes of gain error in the AD620BRZ and provide step-by-step solutions to help you fix the problem. Let’s break it down clearly and simply:

What is Gain Error?

Gain error occurs when the output of the amplifier doesn’t scale as expected according to the input signal. For the AD620BRZ, this could mean the output gain is either too high or too low compared to what was calculated based on the input and the configured gain resistor. This error affects the precision of the readings and could lead to incorrect results in your application.

Causes of Gain Error

Incorrect Gain Resistor Value The AD620BRZ uses an external resistor to set the gain. If this resistor is not of the correct value or is incorrectly placed, it can lead to gain errors. For example, using a resistor with a tolerance that is too wide or is damaged can distort the desired gain.

Input Offset Voltage The AD620BRZ has a small input offset voltage, which can cause gain error if not properly accounted for. This is especially important when dealing with low-voltage signals. The offset voltage can alter the input-to-output relationship and lead to inaccuracies in the gain.

Power Supply Variations Power supply fluctuations or noise can affect the performance of the AD620BRZ, leading to variations in the gain. Instabilities in the power supply can cause fluctuations in the output, which manifest as gain errors.

Temperature Effects The AD620BRZ is sensitive to temperature variations. The amplifier’s gain can drift due to changes in ambient temperature, leading to a change in its performance over time. This temperature-related variation can cause gain error if the device is not thermally stabilized.

PCB Layout Issues Improper PCB layout can cause parasitic effects that influence the gain. Long leads, poor grounding, or improper routing of traces can introduce noise or inductance that affects the amplifier’s performance.

How to Solve Gain Error in AD620BRZ

Step 1: Check the Gain Resistor Value

Ensure that the gain resistor (Rg) is of the correct value as per the AD620BRZ datasheet. Double-check the resistor’s tolerance. It is recommended to use resistors with a low tolerance (1% or better) for precise control over the gain. Verify the resistor’s placement on the PCB to ensure there are no connection issues such as soldering mistakes or broken traces.

Step 2: Minimize Input Offset Voltage

If you are dealing with low-level signals, consider using a trimming capacitor or adjusting the reference pin to minimize the effect of input offset voltage. Use a low-offset version of the AD620 if your application requires extreme precision.

Step 3: Stable Power Supply

Make sure your power supply is stable, with low noise and ripple. Use decoupling capacitors close to the AD620BRZ to filter out power supply noise. If possible, use a regulated power supply to avoid fluctuations that could affect the amplifier’s gain.

Step 4: Temperature Compensation

Use temperature-compensated resistors to reduce the effect of temperature changes on the gain. If your application is sensitive to temperature, consider using a temperature sensor in conjunction with the AD620BRZ to monitor and adjust for gain changes due to temperature shifts.

Step 5: Improve PCB Layout

Ensure that the PCB layout minimizes noise and interference. Place sensitive signal traces away from high-current traces and ensure good grounding. Use short, direct paths for the gain-setting resistor and keep traces to the reference pin as short as possible.

Step 6: Calibration

If the gain error persists, perform a system calibration. Measure the output at different gain settings, and adjust the gain resistor or compensate for the error in software to correct the overall gain accuracy. Conclusion

Gain errors in the AD620BRZ are typically caused by issues with the gain resistor, input offset voltage, power supply noise, temperature variations, or PCB layout. By carefully following the steps above—checking the resistor value, minimizing offset voltage, ensuring power stability, compensating for temperature, optimizing PCB layout, and calibrating the system—you can solve gain-related issues and achieve accurate and reliable results from your AD620BRZ instrumentation amplifier.