This year's Consumer Electronics Show in Las Vegas focused on the "Internet of things," which is the idea that every object in the human environment (such as kitchen appliances and industrial equipment) could be outfitted with sensors that exchange data; a newly-designed transmitter could bring this idea one step closer to reality.
This type of information exchange would require transmitters that are powerful enough to broadcast to other devices yards away and are energy-efficient enough to last for extended periods of time, MIT reported.
"A key challenge is designing these circuits with extremely low standby power, because most of these devices are just sitting idling, waiting for some event to trigger a communication," said Anantha Chandrakasan, the Joseph F. and Nancy P. Keithley Professor in Electrical Engineering at MIT. "When it's on, you want to be as efficient as possible, and when it's off, you want to really cut off the off-state power, the leakage power."
At this week's Institute of Electrical and Electronics Engineers' International Solid-State Circuits Conference the researchers will present a new transmitter that reduces off-state leakage 100-fold. The transmitter also provides enough power to facilitate Bluetooth transmission, or even longer-range 802.15.4 wireless-communication protocol.
The researchers' secret was to borrow techniques already used to reduce the leakage power in digital circuits. The core of a digital circuit is a transistor, which connects two electrical leads through a semiconducting material. Semiconductors are not naturally good conductors or insulators, but in a transistor a second wire (known as a gate) draws in electrons and creates a bridge that can cross between the leads. Even when no charge is applied to the gate some current leak manages to slip through; this could make a significant impact on battery life over time.
The research team worked to combat this by applying a negative charge to the gate when the transmitter is idle. The charge drives away electrons from the electrical leads, causing the semiconductor to become a better insulator. To generate this negative charge the researchers used a circuit known as a "charge pump," which is composed of a network of capacitors (charge-storing electronic components) and switches. When the pump is exposed to voltage it builds up charge in one of the capacitors. Throwing a certain switch connects the positive end capacitor to the ground, creating a current; in this process the only true power drain occurs during the flipping of the switch.
