PCB Tech - How to improve the PCB design of the Bluetooth circuit board

Bluetooth circuit board design guide

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

Various applications utilize Bluetooth, including:

Beacons used in shopping malls

Eddy current frame for industrial sensing applications

Headphones and audio/stereo products

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

Home automation system

Wireless consumer electronics applications, including cameras, printers and phones

Each application uses the same general Bluetooth technology, but in different ways and depending on the connection type, design engineers need to combine basic principles to optimize signal integrity and overall device efficiency.

Huaqiu DFM

Compared with Wi-Fi, Bluetooth is not a very fast wireless option, but it is getting faster and faster. It also cannot penetrate walls and other nearby obstacles well, and has a poor range.

Although still in progress, it is still a good choice (5.0 is the latest update, a good improvement over 4.2). In most cases, it is a low power consumption, reliable, safe, widely supported option, and can be easily implemented on various small peripheral devices.

Bluetooth technology has a history of more than 20 years and is still evolving. Although Bluetooth technology has improved in terms of speed, power, range, security and other properties over the years, it still seems to be still There are some of the same problems, including its susceptibility to signal interference.

So, from the perspective of PCB design, what measures can be taken to optimize signal integrity and minimize interference and packet loss?

The following are some bluetooth circuit design considerations and general rules of thumb:

Use certified modules

1. If you want to integrate Bluetooth into your product and have limited resources, please consider using pre-certified, fully contained modules to help speed up development and time to market. In the end, it may increase a little cost, but it can usually avoid some troubles caused by antenna placement/design and EMI susceptibility.

There are several certified modules at reasonable prices 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 greater flexibility and functions. For example, in addition to its Bluetooth stack, simple peripherals can be controlled through GPIO, SPI, I2C, PWM, etc.

Check your Bluetooth device selection

2. Make sure you have selected the appropriate Bluetooth device for the application, and the antenna size and adjustment are also appropriate.

If you want to use a simple beacon application, and the application only needs short bursts/intervals to announce location or data, you can use low energy (Bluetooth Low Energy or BLE) with minimal features and peripherals A cost-effective solution for equipment to save on-board real estate and final costs.

If you are looking for more products with higher throughput, audio streaming or data exchange Bluetooth applications, then you may need products with higher transmit power, higher receiving sensitivity and faster data rate (although it will reduce the data transmission speed ) Rate usually helps to minimize packet loss).

If you are looking for an all-in-one chip, consider using a chipset that contains powerful or auxiliary processors that include available UART, SPI, I2C, PWM, ADC, DAC, and GPIO pins.

If you are dealing with content that relies heavily on RSSI readings, please make sure that its RSSI monitor has sufficient dB resolution.

Separate or remove copper signals and high-energy components

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

This also includes making areas (and slabs) free of flat and polygonal dumping. Most Bluetooth chipset manufacturers will provide layout guidelines that should be strictly followed during PCB design. If you want to manually arrange the antenna area, please use a ground plane appropriately to maintain a good bandwidth at the input and make sure to leave enough space for the tuning element (printed and ceramic antennas require a ground plane).

Use ground trace vias to prevent unnecessary radiation from the edge of the PCB, as it may penetrate nearby Bluetooth signals. If possible, 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 you use analog-based signals such as audio, make sure that the analog and digital ground planes are separated.

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

Power precautions

4. Make sure that the rails that power the Bluetooth module or chip are clean, and use bypass (1.0 uF) and decoupling capacitors (0.1uF and 10nF) when needed. You can also use ferrite beads on the power rail to enter the Bluetooth area of the circuit board to suppress high-frequency noise.

Tools and analysis

5. If you want to design the antenna area, please make sure you have the appropriate equipment (such as a network analyzer) to analyze and adjust the matching network, or consider sending the design to a third-party RF test laboratory.

Consider the obstacles of the real world

6. During the Bluetooth connection process, there are many factors that can cause blocking or detuning, including nearby water (human beings are also...we are mainly water), metalized objects, smartphones/tablets, computers, and operating devices. On the same ISM frequency band, such as microwave oven or WLAN technology, power supply, wireless RF video, office lighting and home phone.

Even when paired at a close distance (1-2 meters), it is extremely susceptible to signal loss. If such conditions have a higher risk of affecting signal quality, choose a device with higher power and run it at a lower speed to minimize packet loss. Or, if the electronic device is inside the case, make sure that the metallization material is minimized and kept away from the BLE module. The relationship between Bluetooth signal strength and distance is not linear. In fact, it is very non-linear and somewhat unpredictable according to the surrounding environment, but it does follow a general pattern.

Whether you are designing a small, simple Beacon module, or designing a data stream, power-consuming Bluetooth hub, following these precautions can save you a lot of trouble in the test/implementation phase of the design.

With the expansion of Bluetooth PCB components, 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 components.