A number of challenges arise when designing Bluetooth wireless earbuds. Synchronizing the pair of earbuds is critical to acceptable operation. This can be difficult for a totally wireless solution, which is why many systems skip this task and run a wire between the earbuds. Power requirements also prove challenging, since increasing the battery capacity normally means enlarging the earbud. Finally, the overall audio quality will be limited if the wireless connection between the earbuds and the Bluetooth source, typically a smartphone or smart watch, is poor.
Cypress Semiconductor’s CYW20721 Bluetooth microcontroller and PSoC 4100S address all of these issues (Fig. 1). The CYW20721 supports Cypress’ Wireless Audio Stereo Synchronization (WASS) technology designed to deliver a robust wireless connection between earbuds. The two chips consume half the power of competing solutions, which can lead to double the playback time or reduce the size of the batteries. They’re designed to work with a range of third-party codecs.
1. Cypress Semiconductor’s CYW20721 and PSoC 4100S are designed for wireless earbud applications.
The CYW20721 sports a 96-MHz Arm Cortex-M4 with 512 kB of SRAM and 1 MB of flash storage (Fig. 2). The Bluetooth subsystem supports a 2-Mb/s proprietary Bluetooth Low Energy (BLE) system. The on-chip security engine and ROM support secure over-the-air (OTA) updates.
2. The CYW20721 integrates a dual-mode Bluetooth engine with a 96-MHz Arm Cortex-M4 microcontroller.
The system has an RF receive sensitivity of −95 dBm; the competition’s is approximately −88 dBm. A 6-dBm difference can double the range of a system. And the higher sensitivity doesn’t come at a power cost—the CYW20721 uses 20.7 mW for A2DP support.
The chip also supports single- and dual-microphone codec configurations. The microphones are used for voice calls. The wireless chip is supported by Cypress Semiconductor’s WICED development toolset.
PSoC 4100S is based on a 48-MHz Arm Cortex-M0+ (Fig. 3). It’s designed as a sensor hub manager that can be used for many other applications. The CapSense touch interface also handles in-ear detection. Pulse-width modulation (PWM) can be used to provide haptic feedback support. And its low power operation works well for the earbud application.
3. The PSoC 4100S provides CapSense support, including proximity detection, and acts as a sensor hub.
Cypress Semiconductor has a small-form-factor reference design for a pair of 15-mm earbuds designed to fit in a charging cradle. The design is suitable for rebranding and includes complete human-machine-interface (HMI) support with in-ear detection and touch controls.
The system delivers audio latency of less than 50 µs between the primary (PE) and secondary earbud (SE). The delay between the Bluetooth source and earbuds is configurable and depends on the audio play buffer size. The system can also switch between PE and SE to allow for better operation under poor RF conditions, such as in an area with many competing wireless devices.
The CYW20721 and PSoC 4100S can address other applications, such as Bluetooth speakers and wearable applications., thanks to their low power operation and the CYW20721’s wireless support. The CYW20721 is available in a 5- × 5-mm, 40-pin QFN package or a 3.2- × 3.1-mm, 134-ball WLCSP die.