If some preventive measures are not taken in pcb design, interference, data loss and poor signal integrity may occur. We will outline many rules and guidelines to consider when choosing Bluetooth technology for a given application, more specifically, designing it into the circuit board.
A variety of applications use Bluetooth, including:
Beacons used in shopping malls
Eddystone Framework for Industrial Sensing Applications
And headphones and audio/stereo products.
Remote peripherals, such as video game controllers or computer mouse/keyboard
home automation
Wireless consumer electronics applications, including cameras, printers and telephones
Each application contains the same general Bluetooth technology, but it is used in different ways. According to the connection type, design engineers need to combine basic principles to optimize signal integrity and overall equipment efficiency.
Compared with Wi-Fi, Bluetooth is not a very fast wireless option, but it is becoming faster. It can’t pass through walls and other nearby obstacles well, and its range is poor.
It’s still a good choice, even though it’s under development (5.0 is the latest update, which is a good improvement over 4.2). In most cases, it is a fairly low power consumption, reliable, secure and widely supported option, which can be easily implemented on various small peripheral devices.
Bluetooth has existed for more than 20 years and is still developing. Although it has been improved in speed, power, range, security and other attributes for many years, it still seems to have some same problems since it was put forward in the mid-1990s, including its sensitivity to signal interference.
Then, from the point of view of PCB design, how to optimize signal integrity and minimize interference and packet loss?
The following are some precautions and general rules of thumb for Bluetooth circuit pcb design:
Use authentication module
1. If you integrate Bluetooth into your products and have limited resources, please consider using pre-certified, fully included modules to help speed up development and time to market. It may eventually increase some costs, but it can usually prevent some troubles caused by antenna placement/design and EMI sensitivity.
At present, there are several certified modules with reasonable prices on the market, most of which are integrated with small ARM processors, such as RN4020 or RN4870 of Microchip, or BT121 or BGM113 of Silicon Labs. On-board processor can provide greater flexibility and functions, such as controlling simple peripheral devices through GPIO, SPI, I2C, PWM, etc. in addition to Bluetooth stack.
Check your Bluetooth device selection.
2. Make sure that you choose the appropriate Bluetooth device for the application, and that the size and adjustment of the antenna are also appropriate.
If you are looking for a simple beacon application, you only need to advertise the location or data in a short time/interval, then you can use a cost-effective solution with low power consumption (Bluetooth low power consumption or BLE), minimal functions and peripherals to save on-board real estate and final cost.
If you are looking for a Bluetooth application with higher throughput, audio streaming or data exchange, then you may need something with higher Tx power, higher Rx sensitivity and faster data rate (although slowing down data transmission). The rate usually helps to minimize dropped data packets).
If you are looking for an all-in-one chip, please consider using a chipset that contains powerful or auxiliary processors, including available UART, SPI, I2C, PWM, ADC, DAC and GPIO pins.
If you are dealing with work that relies heavily on RSSI readings, please ensure that its RSSI monitor has sufficient dB resolution.
Or remove the copper signal and high-energy components.
3. When designing pcb circuit in Bluetooth chipset or module, keep the antenna area completely away from nearby copper signals or components carrying a lot of energy (especially the switched power supply path, such as boost or buck converter).
This also includes keeping the area (and ply) free of plane and polygon casting. Most Bluetooth chipset manufacturers will provide layout guidelines that should be closely followed during PCB design. If you manually arrange the antenna area, please use the ground plane as appropriate to keep a good bandwidth at the input and make sure to leave enough space for tuning elements (printed and ceramic antennas require a ground plane).
Use ground stitching vias to prevent harmful radiation from the edge of PCB, as it may penetrate the nearby Bluetooth signal. If you can, try to optimize the shape of the circuit board for the Bluetooth device and its antenna, so that it is located at the edge and away from nearby components and signals. If analog-based signals (such as audio) are used, make sure that the analog and digital ground planes are separate.
It is always a good idea to shield electronic devices (certainly not antennas) to prevent cross-coupling and minimize picked-up noise.
Matters needing attention in power supply
4. Make sure that the guide rail supplying power to Bluetooth module or chip is clean, and use bypass (1.0 uF) and decoupling capacitors (0.1uF and 10nF) when necessary. You can also arbitrarily use ferrite beads on the power rail entering the Bluetooth area of the circuit board to suppress high-frequency noise.
Tools and analysis
5. If you are designing the antenna area, please make sure that you have appropriate equipment (e.g. network analyzer) to analyze and adjust the matching network, or consider sending the design to a 3rd party RF testing laboratory.
Consider obstacles in the real world
6. During Bluetooth connection, there are many things that can cause blockage or detuning, including nearby water (so do humans … we are mainly composed of water), metallized objects, smart phones/tablets, computers, operating devices on the same ISM frequency band, such as microwave oven or WLAN technology, power supply, wireless radio frequency video, office lighting and home phone.
Even when paired at a close distance (1-2m), it is easily affected by signal loss. If the risk of such factors affecting the signal quality is high, choose the equipment with higher power and run at a slower speed to minimize the packet loss rate. Or, if the electronic device is inside the housing, make sure that the metallized 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 nonlinear and somewhat unpredictable according to the surrounding environment.
Whether you are designing a small, simple Beacon module or a Bluetooth hub with data flow and power consumption, following these considerations can save you a lot of trouble in the test/implementation phase of the design.
With the expansion of Bluetooth PCB assembly, it is an exciting time to integrate wireless communication and control into products. The future will only bring smaller, faster, cheaper and stronger Bluetooth components.
