To realize the "Internet of things” — the idea that all parts of the human environment, from kitchen appliances to industrial equipment, could be equipped with sensors and processors that exchange data — transmitters must be energy-efficient enough to last for months.
A group researchers at the Massachusetts Institute of Technology (MIT) have developed a new transmitter design that reduces off-state leakage 100-fold. The design provides adequate power for Bluetooth transmission, or for the longer-range 802.15.4 wireless-communication protocol.
While semiconductors are not naturally very good conductors, neither are they perfect insulators. Even when no charge is applied to the gate, some current still leaks across the transistor.
The leakage is reduced by applying a negative charge to the gate when the transmitter is idle. The charge drives electrons away from the electrical leads, making the semiconductor a much better insulator.
In tests conducted on a prototype chip fabricated through the Taiwan Semiconductor Manufacturing Company’s research program, the MIT researchers found that their circuit spent only 20 picowatts of power to save 10,000 picowatts in leakage.
To generate the negative charge efficiently, the MIT researchers use a circuit known as a charge pump, which is a small network of capacitors — electronic components that can store charge — and switches. When the charge pump is exposed to the voltage that drives the chip, charge builds up in one of the capacitors. Throwing one of the switches connects the positive end of the capacitor to the ground, causing a current to flow out the other end.
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