TWS Bluetooth headset: Working, and Core Components

What is a TWS Bluetooth headset?

TWS (True Wireless Stereo, True Wireless Stereo) Bluetooth headset is an extremely hot audio product in recent years. With the help of the Bluetooth chip, it first establishes a wireless connection between the mobile phone and the main earphone, and then establishes the wireless communication between the main earphone and the auxiliary earphone, thus completely abandoning the wire connection between the traditional earphones, which greatly facilitates the use of users. In addition, the main earphone can be used alone, which is fully capable of meeting the application requirements of a single bluetooth earphone in the existing market, and the use function is very powerful. Therefore, since Apple released the first TWS headset - Airpods in September 2016, the market response has been very enthusiastic. Subsequent audio manufacturers have followed up quickly after seeing this, and gathered together to deploy TWS Bluetooth headsets, making the TWS headset market colorful. Next, Bluetooth 5 will bring a more exciting user experience, and the new charging box design will make it more convenient for consumers.

What is TWS?

To talk about TWS Bluetooth headsets, let's start with TWS technology. TWS: It is the abbreviation of TrueWirelessStereo, which means true wireless stereo. The realization of this technology is based on the development of chip technology. Technically speaking, it means that the mobile phone is connected to the main speaker, and then the main speaker is connected to the slave speaker through Bluetooth wireless, so as to realize the real wireless separation of the left and right channels of Bluetooth. When the slave speaker is not connected, the master speaker returns to mono sound quality. TWS technology has been applied to the field of Bluetooth headsets, so it has also given birth to a new product - TWS Bluetooth headsets.

TWS earphone charging box system introduction

The detailed charging box system block diagram is as follows:

In the signal chain part, the sensors mainly include Hall sensors to realize the opening and closing detection of the box. The LED light realizes a cool display effect, and the Bluetooth chip can transmit the box information to the mobile phone, which is convenient for the mobile phone to check the power information of the box. Key detection may require some logic devices, such as the D flip-flop SN74LVC1G74, which can convert the pulse edge of the key into a level inversion, which is convenient for the MCU to record the key information.

For the power rail part, the general input port is made into a 5V micro USB interface (Apple’s Airpods have a lightning interface, which is also 5V). Considering that there are currently many adapters that support high-voltage fast charging, the charging box needs an overvoltage protection chip for mis-insertion protection, and a charger to charge the lithium battery. At present, many chargers integrate the function of overvoltage protection, but the overvoltage response time is mostly at the us level. It is recommended to add an additional overvoltage protection chip for fast protection. In terms of Charger, it is recommended to use a charger with power-path (path management). On the one hand, when the battery power of the box is low, you can immediately get a higher system voltage by plugging in the adapter to ensure that the box can immediately supply power to low-battery earphones; On the other hand, when the fast charging current is set to be small, if the load requires a constant load (such as driving LED lights), this part of the load is likely to be near the cut-off current of the charger, and the charger may not be able to Judging that the battery is fully charged, the user experience will be worse.

The battery is generally a single-cell lithium battery, which is usually provided by the battery pack manufacturer, and the fuel gauge and the secondary protection IC have been packaged to ensure that the battery works more reliably. The power supply of a single-cell lithium battery is mainly supplied to two parts: one part is boosted to 5V to power the earphone, and the other part is stepped down to 3V or below for the MCU/Sensor in the box.

TI's products are very rich and can cover most of the needs of the charging box. Here are the following ICs briefly recommended, which are suitable for use in the charging box. The recommended indicators are mainly packaging and power consumption, and the power consumption is mainly the quiescent current of the IC under enable. What needs to be mentioned is that since the overvoltage protection and the charger only work when charging, the adapter is plugged in at this time and the power supply is sufficient, so these two parts do not require Iq to be small, but the leakage current of the charger should be paid attention to.

TWS headphone system introduction

In the signal chain part, the Bluetooth chip is responsible for receiving the data sent by the mobile phone, and then pushes the earphone through the amp. The sensor is mainly a gravity sensor, which detects signals such as earphone shaking. At present, the integration level of the Bluetooth chip is very high, and it can also perform some tuning functions.

The power rail part is limited by the very small headphone space, and the headphone end can no longer be used as a power supply port for the micro USB interface, and it is usually changed to a specific metal contact piece. The input power of the earphones comes from the 5V after the charging box has been boosted and stabilized, so there is no risk of overvoltage at the input of the earphones, and there is no need to add overvoltage protection, and the single-cell lithium battery can be charged directly after passing through the charger. Similarly, the battery is also provided by the battery pack manufacturer, with integrated fuel gauge and secondary protection. The battery provides 2.5V or 1.8V power to the system through the LDO.

Advantages of wireless bluetooth headset

Compared with ordinary Bluetooth headsets, TWS true wireless Bluetooth headsets have the following advantages:

1. No wired connection is required, the left and right earphones form a stereo system through Bluetooth, which improves listening to music, talking, and wearing;

2. The outside of the true wireless Bluetooth headset completely abandons the way of wire connection, and the host can work alone, and the hands-free call is under control;

3. In line with human ear engineering, it is natural and comfortable to wear, and there will be no problem of entangled earphone wires in the past.

Basic technical features of TWS Bluetooth headset:

1. Adopt high-quality Bluetooth 5.0 chip, enhance the signal source, the signal is more stable, continuous connection

2. Compatible with smartphones and smart devices with built-in Bluetooth function

3. Single and double ears can be switched at will, can be used alone or together

4. Touch to switch, touch to switch songs, pause/play, answer and hang up the phone.

5. Lightweight and mini, low power consumption, long battery life

Although this headset has some disadvantages, the convenience it brings to everyone is worth betting on. I believe that the future market potential will be huge. However, in order to gain a share in this industry, for Bluetooth headset manufacturers, only by continuously enhancing product performance, improving product quality, beautifying product design, and reducing product prices can more users accept it.