Smallest and most frugal Bluetooth chip

April 11, 2019 | 07:39
Smallest and most frugal Bluetooth chip
Smallest and most frugal Bluetooth chip
Researchers in the United States have built a Bluetooth chip that is extremely small and very low power. It would operate for 11 years (!) from a single button cell. This is very convenient for all kinds of Internet of Things applications.
Bluetooth is a wireless short-distance connection between devices. Many devices have a Bluetooth connection, but the smallest – for example 'smart' light bulbs – cannot have Bluetooth. This consumes too much power and the chips are often too large to fit inside small devices.

Antenna and oscillator in one

Researchers from the University of Michigan have now found a solution for that. They reduced the size of the chip by combining two important components into one – the oscillator and the antenna.
A ‘normal’ transmitter requires a tunable RF oscillator in order to generate the desired frequency, plus a power amplifier to increase its amplitude, and finally an antenna to radiate the signal. The team of researchers have combined the oscillator and antenna in such a way that the amplifier is no longer necessary. This invention is called the ‘power oscillator’.


The heart of the oscillator is formed by a resonant tank circuit: an inductor and a capacitor. The energy moves between the magnetic field of the inductor and the electric field of the capacitor at a resonant frequency that is determined by the capacitance and self inductance. In the new circuit the researchers even used the antenna itself as the inductor in the resonant tank. Because the antenna now functions as an inductor, it radiates through a varying magnetic field and not through an electric field; this means that the antenna can be made smaller.


The antenna now has a length of only 1.4 cm and, moreover, it functions better. The antenna is also circular in shape so that it occupies even less space. This makes the chip not only smaller but also lower power: during transmission the power consumption is a mere 0.6 mW. This is for Bluetooth Low Energy, a low-power Bluetooth variant. With this, only small amounts of data can be transmitted, but that is often sufficient. Consider devices that are worn on the body, such as heart beat and glucose monitors. After all, these need to send a value to a smartphone only periodically.
The transformer (the octagon at bottom left) that is it integrated in the power supply, increases the efficiency. The active part of the chip measures only 0.5 mm² (photo: University of Michigan).


With this low power consumption, a button cell will last for 11 years. And this is just as well, because if in the near future IoT becomes a fact, everyone will have hundreds of devices in the home that are all connected to each other. And if the batteries have to be replaced frequently, then you will never get an opportunity to do anything else. With this new chip, devices can be frugally connected to other, larger devices, which can then send the information to the web.

Source: IEEE Spectrum
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