Researching Ultra-Low Power Interface Circuits Driven by Compact Energy Harvesting Elements

The Ishikuro Laboratory of the Department of Electronics and Electrical Engineering of the Keio University Faculty of Science and Technology is researching interface circuits that operate on a nanowatt level and can be driven with compact, energy harvesting elements.
“My lab is researching integrated circuits, and regarding applications, put simply, we’re researching integrated circuits for interfaces. For example, the natural world contains a variety of signals including the ability to sense light, and as is the case with this microphone as well, there are a variety of devices that can sense those signals. When a signal becomes an electric signal and is picked up, it can then be amplified and ultimately converted to a form that enables processing with a digital circuit. That’s the type of circuit that we’re researching.”
Today, smartphones have become mainstream devices for gathering information, and the data that is input by human hands is collected by search engines. However, in the future when practical applications of even more compact sensor based terminals become a reality, devices will be capable of gathering large amounts of signals on an even greater magnitude without relying on input by human hands. The key to making this a reality is ultra-compact interface circuitry that consumes very little power.
“For example, we’ve already developed an analog to digital converter that can operate with 1 nanowatt of power or less as the AD converter used by this microphone to pick up audio signals. In fact, it can operate with just 560 picowatts and with a power supply voltage of 0.4 volts. As far as the performance that can be achieved, well, for example, a one millimeter square solar cell can operate with energy that is generated by the light in a room. That’s the type of circuitry that we’re developing. With this type of circuit, we can achieve a microphone of this size, but we can also consider developing a microphone that is just one millimeter square in size. When that type of microphone is attached to a pair of eyeglasses, it can automatically recognize voice data, and the eyeglasses can then interpret what you’re thinking, and access a data center via a network. That’s the type of capabilities that we’ll be able to achieve.”
The Ishikuro Lab is also researching technology to wirelessly transmit power and data to ultra-compact systems that cannot be equipped with a battery.
“As one method for example, we’re using solar cells to convert light energy, and then using that energy to operate circuits. Another method is to wirelessly send power to a sensor chip. If we can realize these two methods, we’ll be able to wirelessly access information and energy using a sensor chip that is the size of a grain of rice or an extremely high capacity memory device that is the size of a card without having to connect cables.”
In the near future, society will be able to utilize information accessed from our everyday environment in a variety of services, and the Ishikuro Lab is dedicated to conducting research each day in order to achieve those possibilities.