Microwave Tech - Design scheme of very low power Bluetooth voice remote controller

Virtual assistants are integrated into more devices in the home. Amazon recently announced that it will launch a variety of new devices for Alexa, including earplugs, glasses and rings, to provide consumers with more ways to obtain information. The recurring themes in these new voice products are wireless and hands-free, which can easily connect to mobile phones or other hosts and listen to instructions. Its internal technology is a Bluetooth RF chipset supporting wireless connection and a special embedded processor running wake-up word engine (WWE) to recognize voice commands.

Another example of this trend is that every new flat-panel TV, set-top box and media player is equipped with a remote control, and they will soon be completely wireless and hands-free. Of course, when you want voice control, many people still use the old infrared line of sight remote control mode or key dialogue, but these are soon out of date. Users need a device that can seamlessly respond to commands, rather than a device that must press and hold the call key like a walkie talkie. Similar to the wave of electronic products near Amazon, the next generation of TV remote control will be wireless and hands-free.

However, remote control design also brings some unique challenges. For example, the remote control is usually not rechargeable; They usually use standard AA batteries. The remote control not only needs to perform well in a noisy environment, but also needs to be 3 to 9 feet away from your body. It can also transmit information wirelessly to the host device (such as TV).

In addition, consumers prefer to use durable batteries that do not need to be replaced frequently. In essence, the performance of the remote controller must be the same as that of Amazon echo dot, but at the same time, the power consumption is less than that of in ear headphones.

Designing a powerful, energy-efficient remote control is a challenge. Innovative Bluetooth solutions and audio processing solutions are needed, because each improvement will prolong the battery life.

Using Bluetooth 5.0/le solves several problems of traditional infrared. Firstly, Bluetooth is a standard solution, so the device can easily communicate with existing Bluetooth devices. In addition, Bluetooth 5.0/le provides a transmission range equivalent to that of WiFi devices, which is very suitable for voice remote control. Traditional Bluetooth solutions have been optimized for mobile phones and laptops, which have larger battery capacity and less power consumption.

Atmosic's innovative solution can significantly reduce power consumption by 5x and extend battery life by 3 to 5x compared with competitive solutions.

In addition to the Bluetooth design with extremely low power consumption, a secondary wake-up receiver can also be used. The power consumption of the receiver can be lower (20 to 50 times lower than that of the standard receiver), so that the whole Bluetooth SOC can enter a deep sleep state; The device can wake up in a special mode of another host. We will not introduce this technology in detail here, because it is only applicable to a small number of special remote controls.

The third low-power technology uses energy collection to obtain RF wireless energy to prolong battery life. Many homes and buildings have a lot of RF energy (usually in the ISM band), which can be collected when the remote control is placed on the table. According to the energy level, a device can obtain tens of microwatts of energy. The ultimate goal is to replace the battery power supply when possible and extend the service life of the battery to a few years. At present, the service life of the remote controller is only 6 to 9 months. For industrial and special-purpose remote controls, other energy technologies can also be used, such as solar energy, thermal energy and sports energy collection.

As mentioned earlier, to achieve real hands-free operation, the remote control must work like a smart speaker at the same time, but it must also be as energy-saving as an in ear headset. Companies like QuickLogic have developed highly optimized and ultra-low power supporting devices to cope with this challenge with Bluetooth chipsets.

The voice remote controller connected with Bluetooth basically has three modes: standby mode, wake-up word detection mode and data transmission mode. The power consumption is also gradually increased.

In the standby mode, Bluetooth and the accompanying chip are in the sleep state, waiting for some wake-up words in the surrounding environment. One way to achieve this energy saving is to use vesper's microphone wake-up sound function, which consumes only 10? A. Wait for the ambient sound to exceed the pre configured threshold. In a typical living room use case, the system is in this mode 80% of the time.

Once the threshold level is reached, an interrupt will be triggered from the microphone and wake up the accompanying chip; At this time, the wake-up word detection mode is entered. The MCU accompanying the chip can start and run WWE for a period of time to detect whether the keyword is spoken. Third party solutions (such as voicespot WWE of retune DSP) can run on the cortex-m4, using only one microphone without using a computationally intensive solution of multi microphone adaptive beamforming, which is usually required for midfield (3 to 9 feet) speech recognition.

In addition to significantly saving processor resources, reducing each microphone from the system can also save 400 to 650? A (active power). If the wake-up word is detected, it will interrupt and wake up the Bluetooth chip to enter the data transmission mode. This is necessary because the user word after the wake-up word needs to be transmitted to the host (such as TV) in the form of pulse code modulation (PCM) or compressed data.

If no wake-up word is detected, the system will return to the initial standby mode. Some supporting chips, such as the chip of QuickLogic, have dedicated low-power sound detection (LPSD) hardware to reduce the average system power used in wake-up word detection mode. For example, some fan sounds have a high decibel sound pressure, but obviously not speech. LPSD hardware has enough intelligence to sense this and ignore sound to avoid unnecessary additional power consumption of WWE.

Bluetooth 5.0/le is very suitable for data transmission mode because it can transmit data in low-power on-demand packets. An ideal partner should have enough storage space and processing power to compress voice data before sending it to Bluetooth devices. A typical example is to run opus audio encoder.