AD620BRZ : Common PCB Layout Mistakes That Affect Performance

Common PCB Layout Mistakes That Affect AD620 BRZ Performance and How to Fix Them

The AD620BRZ is a precision instrumentation amplifier commonly used in applications requiring accurate signal amplification. However, improper PCB layout design can significantly affect its performance, leading to issues such as noise, inaccurate readings, and instability. In this article, we will go through common PCB layout mistakes that impact the AD620BRZ and provide step-by-step solutions to resolve these issues.

1. Poor Grounding and Ground Plane Issues

Problem:

One of the most common mistakes in PCB layouts is improper grounding. The AD620BRZ is sensitive to ground noise, and if the ground plane is not designed properly, it can introduce unwanted noise and affect the accuracy of the signal.

Cause:

Ground loops or poor grounding connections lead to voltage differences across the ground plane, which can couple with the input signals, causing noise and performance degradation.

Solution: Create a Solid Ground Plane: Ensure that your PCB has a continuous, uninterrupted ground plane that covers the entire board. This will reduce ground loop problems and provide a low-impedance return path for current. Star Grounding Technique: If you need to connect multiple components to ground, use the star grounding technique, where all the ground connections converge to a single point to avoid noise coupling between components. Minimize Ground Bounce: Keep the ground traces as short as possible and ensure they are wide enough to carry the current without introducing significant voltage drops.

2. Inadequate Power Decoupling capacitor s

Problem:

Power supply fluctuations or noise can interfere with the AD620BRZ’s performance. Insufficient or incorrectly placed decoupling Capacitors can cause the amplifier to be unstable or produce noisy outputs.

Cause:

The absence of decoupling capacitors or poor placement of them can result in power supply noise coupling into the amplifier, leading to signal distortion and reduced accuracy.

Solution: Use Proper Decoupling Capacitors: Place both high-frequency and low-frequency decoupling capacitors close to the power supply pins of the AD620BRZ. Typically, a 0.1 µF ceramic capacitor for high frequencies and a 10 µF tantalum or electrolytic capacitor for low frequencies are good choices. Place Capacitors Close to the Pin: The capacitors should be as close as possible to the AD620BRZ power supply pins to effectively filter noise from the supply rails. Ensure Proper Trace Width: Make sure the traces connected to the power supply and ground are wide enough to handle the current without introducing too much resistance.

3. Long Signal Traces and Poor Signal Routing

Problem:

Long signal traces and improper routing can introduce noise and capacitance, leading to signal degradation. This is especially problematic for differential input signals, as the AD620BRZ is sensitive to both.

Cause:

Long and unshielded signal traces can act as antenna s, picking up external interference. Additionally, improper routing can result in mismatched trace lengths, causing timing mismatches and affecting differential signals.

Solution: Keep Signal Traces Short and Direct: Minimize the length of the signal traces between the input, the AD620BRZ, and the output. This will reduce the chances of noise coupling and signal degradation. Use Differential Traces for Input Signals: For differential signals, use tightly coupled traces to maintain equal impedance and minimize noise interference. Avoid Crossing Power or Ground Traces: Do not route sensitive signal traces over power or ground traces, as this can introduce unwanted noise.

4. Improper Placement of the AD620BRZ

Problem:

Placing the AD620BRZ too close to noisy components, such as high-speed digital circuits or power supplies, can result in excessive noise coupling into the amplifier, degrading its performance.

Cause:

Noise from nearby components can interfere with the low-level signals that the AD620BRZ is amplifying, leading to unwanted fluctuations or inaccuracies in the output.

Solution: Place the AD620BRZ Away from Noisy Components: Ensure that the AD620BRZ is placed as far away as possible from noisy components like power supplies, clocks, or high-speed digital circuits. This will reduce the chances of noise coupling. Use Shielding: If necessary, use ground shields or planes to physically separate the AD620BRZ from noisy components.

5. Incorrect Feedback Loop Design

Problem:

The AD620BRZ uses external resistors to set the gain, and if the feedback loop is improperly designed, it can lead to instability or incorrect amplification.

Cause:

Incorrect placement or values of resistors in the feedback loop can cause the amplifier to behave unpredictably, leading to issues like offset voltage, drift, or incorrect gain.

Solution: Choose Appropriate Feedback Resistor Values:

Carefully select the values of the feedback resistors based on the desired gain. The AD620BRZ’s gain is set by the formula:

[ G = 1 + \frac{50 k\Omega}{RG} ] where ( RG ) is the resistor connected between pins 1 and 8 of the amplifier. Place Feedback Components Close to the Amplifier: Ensure that the feedback resistors are placed as close as possible to the AD620BRZ to avoid introducing additional noise or unwanted parasitic effects.

6. Lack of Proper Thermal Management

Problem:

The AD620BRZ, like most precision components, can experience thermal drift. Poor thermal management on the PCB can cause the device to operate outside of its optimal temperature range, affecting its performance.

Cause:

Without sufficient heat dissipation, the AD620BRZ can overheat, leading to instability, inaccurate measurements, and potentially even damage to the component.

Solution: Use Thermal Vias and Heat Sinks: If the AD620BRZ is placed in a location where it might generate heat, make sure to use thermal vias to dissipate the heat to the backside of the PCB or include a heatsink if necessary. Keep the Device Cool: Ensure that the PCB has adequate airflow, or use passive cooling methods such as copper pour for thermal dissipation.

Conclusion

In summary, poor PCB layout can significantly affect the performance of the AD620BRZ precision instrumentation amplifier. By following these best practices — proper grounding, decoupling capacitors, careful signal routing, correct feedback loop design, and good thermal management — you can minimize noise, ensure stable performance, and get the most out of this versatile amplifier. Avoiding these common layout mistakes will help maintain the accuracy and reliability of your circuit.