A team of MIT engineers have designed a low-power radio chip that could help extend battery life for smart objects. The team made the transmitter as efficient as possible in its active state, but the main focus was on minimizing leakage power. The new design reduces off-state leakage 100-fold, while also providing enough power for Bluetooth transmission, or even the 802.15.4 wireless-communication protocol.
The new transistor borrows techniques that are commonly used to reduce leakage power in digital circuits, by applying a negative charge to the gate when the transmitter is idle.
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. This process is repeated over and over. The only real power drain comes from throwing the switch, which happens about 15 times a second.
