Design of voice remote control based on ultra-low power Bluetooth

Virtual assistants are being integrated into more devices in the home, and Amazon recently announced that it will launch a variety of new devices for Alexa, including earbuds, glasses, and rings, to provide consumers with more ways to access information. A recurring theme in these new voice products is wireless and hands-free, which can easily connect to a phone or other host and listen for commands. The internal technology is a Bluetooth RF chipset that supports wireless connectivity and a dedicated embedded processor running a wake-up word engine (WWE) to recognize voice commands.

Another example of this trend is that every new flat-screen TV, set-top box, and media player comes with a remote control, and they too will soon be completely wireless and hands-free. Sure, a lot of people still use the old infrared line-of-sight remote control model or push-to-talk when you want voice control, but these are quickly becoming obsolete. Users want a device that responds to commands seamlessly, not like a walkie-talkie where you have to hold down the talk button. Similar to the recent wave of Amazon gadgets, the next generation of TV remotes will be wireless and hands-free.

However, remote control design also presents some unique challenges. For example, remote controls are typically not rechargeable; they typically use standard AA batteries. Not only do remote controls need to perform well in noisy environments, but they also need to be able to stay 3 to 9 feet away from your body while also wirelessly and instantly transmitting information to a host device (such as a TV).

Additionally, consumers prefer long-lasting batteries that don’t need to be replaced frequently, so essentially the remote must perform like an Amazon Echo Dot but consume less power than an in-ear headset.

Designing a powerful, energy-efficient remote control is a challenge that requires innovative Bluetooth solutions and audio processing solutions, as each of these improvements extends battery life.

Using Bluetooth 5.0/LE solves several issues with traditional infrared. First, Bluetooth is a standards-compliant solution, so it is easy for the device to communicate with existing Bluetooth devices. In addition, Bluetooth 5.0/LE provides a transmission range comparable to WiFi devices, which is perfect for voice remote controls. Traditional Bluetooth solutions have been optimized for mobile phones and laptops, which have larger battery capacities and Bluetooth does not consume as much power.

Atmosic's innovative solution significantly reduces power consumption by 5 times and extends battery life by 3 to 5 times compared to competing solutions.

In addition to the extremely low-power Bluetooth design, a secondary wake-up receiver can be used that consumes even less power (20 to 50 times less than a standard receiver) to put the entire Bluetooth SoC into a deep sleep state; the device can be woken up by a special mode from another host. We will not go into detail about this technology here, as it is only applicable to a small number of dedicated remote controls.

A third low-power technology is to use energy harvesting to harvest RF wireless energy to extend battery life. Many homes and buildings have a lot of RF energy (usually in the ISM band) that can be harvested when the remote control is placed on a table. Depending on the energy level, a device can harvest tens of microwatts of energy. The ultimate goal is to replace battery power when possible, extending the life of the battery to several years, compared to the current life of only 6 to 9 months for remote controls. For industrial and special-purpose remote controls, other energy technologies such as solar, thermal and motion energy harvesting can also be used.

As mentioned earlier, to achieve true hands-free operation, the remote control must simultaneously work like a smart speaker but also be as power-efficient as an in-ear headset. Companies like QuickLogic have developed highly optimized, ultra-low-power companion devices to accompany Bluetooth chipsets to meet this challenge.

There are basically three modes for Bluetooth-connected voice remote controls: standby mode, wake-up word detection mode, and data transmission mode, and the power consumption also gradually increases.

In standby mode, Bluetooth and the companion chip are dormant, waiting for some wake word from the surrounding environment. One of the most power-efficient ways to achieve this is to use Vesper's microphone wake-up sound feature, which consumes only 10µA, waiting for ambient sound to exceed a 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 is triggered from the microphone and the companion chip wakes up; at this point it enters wake-word detection mode. The companion chip’s MCU can start and run WWE for a period of time to detect if the keyword is spoken. Third-party solutions such as Retune DSP’s VoiceSpot WWE can run on the Cortex-M4 and use only one microphone, eliminating the need for computationally intensive solutions with multi-microphone adaptive beamforming, which is typically required for mid-field (3 to 9 feet) speech recognition.

In addition to the obvious savings in processor resources, removing each microphone from the system saves 400 to 650µA (active power). If a wake-up word is detected, it interrupts and wakes up the Bluetooth chip into data transmission mode. This is necessary because the user word following the wake-up word needs to be transmitted to the host (such as a TV) in the form of pulse code modulation (PCM) or compressed data.

If no wake word is detected, the system reverts to initial standby mode. Some companion chips, such as those from QuickLogic, have dedicated low-power sound detection (LPSD) hardware to reduce the average system power used in wake word detection mode. For example, some fan sounds have a high decibel sound pressure but are clearly not speech. The LPSD hardware is smart enough to sense this and ignore the sound to avoid running WWE unnecessarily with additional power consumption.

Bluetooth 5.0/LE is well suited for data transmission mode because it can transmit data in low-power on-demand packets. An ideal companion should have enough storage space and processing power to compress voice data before sending it to the Bluetooth device, a typical example is running the Opus audio encoder.