How to Improve PCB Design of Bluetooth Printed Circuit Boards

How to Improve PCB Design of Bluetooth Printed Circuit Boards

If certain precautions are not taken, printed circuit boards with Bluetooth technology may experience interference, data loss, and poor signal integrity. We will outline many of the rules and guidelines to consider when choosing Bluetooth technology for a specific application, especially when designing it into a circuit board.

Various applications utilize Bluetooth, including:

l Beacons used in large shopping malls

l Eddy current frame for industrial sensing applications

l Headphones and audio/stereo products

l Remote peripherals such as video game controllers or computer mouse/keyboard

l Home automation system

l Wireless consumer electronics applications including cameras, printers and phones

Each application uses the same general Bluetooth technology, but is used differently and depending on the type of connection, design engineers need to incorporate fundamentals to optimize signal integrity and overall device efficiency.

Bluetooth isn't a very fast wireless option compared to Wi-Fi, but it's getting faster. It also doesn't penetrate walls and other nearby obstacles well, and has poor range.

Although still a work in progress, it's still a good option (5.0 is the latest update, a nice improvement over 4.2). In most cases, it is a low power, reliable, secure, widely supported option that can be easily implemented on a variety of small peripherals.

Bluetooth technology is over 20 years old and is still evolving, and while Bluetooth technology has improved in speed, power, range, security and other attributes over the years, it still seems to have remained since the concept came out in the mid-90s There are some of the same issues, including its susceptibility to signal interference.

So, from a PCB design perspective, what can be done to optimize signal integrity and minimize interference and lost packets?

Here are some Bluetooth circuit design considerations and general rules of thumb:

Use certified modules

1. If you are integrating Bluetooth into a product and have limited resources, consider using a pre-certified, fully contained module to help speed development and time-to-market. There may be a little extra cost in the end, but some headaches from antenna placement/design and EMI susceptibility are usually avoided.

There are several affordable certified modules on the market today, most of which integrate a small ARM processor such as Microchip's RN4020 or RN4870 or Silicon Labs' BT121 or BGM113. Mounting the processor on the board allows it to have more flexibility and functionality, for example, simple peripherals can be controlled via GPIO, SPI, I2C, PWM, etc. in addition to its Bluetooth stack.

Check your bluetooth device selection

2. Make sure you have the right Bluetooth device selected for the app and the antenna is properly sized and adjusted.

If you are going to use a simple beacon application that only needs short bursts/intervals to announce location or data, you can use low energy (Bluetooth Low Energy or BLE) with minimal functionality and peripherals Cost-effective solution for equipment to save onboard real estate and final cost.

If you are looking for more products for higher throughput, audio streaming or data exchange Bluetooth applications, then you may want a product with higher transmit power, higher receive sensitivity and faster data rates (albeit at a reduced data transfer speed) ) rate usually helps to minimize packet loss).

If you're looking for an all-in-one chip, consider a chipset that includes a powerful or auxiliary processor with available UART, SPI, I2C, PWM, ADC, DAC, and GPIO pins.

If you're working on something that relies heavily on RSSI readings, make sure its RSSI monitor has adequate dB resolution.

Separation or removal of copper signals and high-energy components

3. When designing in a Bluetooth chipset or module, keep the antenna area completely away from nearby copper signals or components that carry a lot of energy (especially power paths switched by boost or buck converters).

This also includes keeping areas (and slabs) free of plane and polygon dumps. Most Bluetooth chipset manufacturers will provide layout guidelines that should be strictly followed during PCB design. If you are laying out the antenna area manually, use the ground plane appropriately to maintain good bandwidth at the input, and be sure to leave enough space for the tuning elements (printed and ceramic antennas require a ground plane).

Use ground trace vias to prevent unwanted radiation from the edge of the PCB as it may penetrate nearby Bluetooth signals. If you can, try to optimize the shape of the board for the location of the Bluetooth device and its antenna, placing it on the edge and away from nearby components and signals. If using analog-based signals such as audio, make sure the analog and digital ground planes are separated.

It's always a good idea to shield the electronics (not the antenna, of course) to prevent cross-coupling and minimize noise.

Power Considerations

4. Make sure the rails powering the Bluetooth module or chip are clean and use bypass (1.0 uF) and decoupling capacitors (0.1uF and 10nF) if needed. It is also possible to use ferrite beads on the power rails into the Bluetooth area of the board to suppress high frequency noise.

Tools and Analysis

5. If you are designing an antenna area, make sure you have the proper equipment (such as a network analyzer) to analyze and tune the matching network, or consider sending the design to a third-party RF test lab.

Consider real-world obstacles

6. There are many factors that can cause blocking or detuning during a Bluetooth connection, including nearby water (humans too...we are mostly water), metallized objects, smartphones/tablets, computers, operating equipment in On the same ISM band, for example microwave oven or WLAN technology, power supply, wireless RF video, office lighting and home telephone.

It is extremely susceptible to signal loss even when paired at close range (1-2 meters). If such conditions have a higher risk of affecting signal quality, choose a higher powered device and operate at a lower speed to minimize packet loss. Alternatively, if the electronics are inside the case, make sure the metallization is minimized and away from the BLE module. The relationship between Bluetooth signal strength and distance is not linear. Actually, it is very nonlinear and somewhat unpredictable depending on the surrounding environment,

Whether you're designing a small, simple Beacon module, or a data-flowing, power-hungry Bluetooth hub, following these considerations can save you a lot of trouble during the testing/implementation phase of your design.

With the expansion of Bluetooth PCB assemblies, now is an exciting time to integrate wireless communication and control into products, and the future will only bring smaller, faster, cheaper and more powerful Bluetooth assemblies.