Renesas has announced that Casio Computer Co. has chosen Renesas’ RE01 controller as the primary controller for Casio’s new shock resistant smartwatch. The GBD-H1000, a new member of Casio’s G-SHOCK line of smart watches, is said to run on harvested power. It also features a heart rate monitor and GPS functionality.The GBD-H1000 measures its wearer’s heart rate using an optical sensor. Other sensors measure temperature, compass bearing, and barometric pressure. The watch also contains technology that measures distance traveled.
Casio’s G-SHOCK watch and Renesas’ RE family controller. Image used courtesy of Renesas
Even with all these capabilities, Casio claims that the new watch does not need a battery as it can be powered entirely from solar energy. The secret to this feat of energy efficiency? Renesas says it’s their SOTB processing technology.
What is SOTB process technology?
The products from Renesas’ RE01 Group, the “brains” that power Casio’s new watch, are very low-power devices based on Silicon on Thin Oxide Buried (SOTB) process technology. In semiconductors, large geometries they serve to reduce the leakage current; less power is wasted when the device is on standby. But, larger geometries mean more power is consumed when the device is active. The compensation is illustrated below.
Low active current vs. low standby current – the usual trade-off. Image used courtesy of Renesas
Renesas’ SOTB process technology allows designers to “have your cake and eat it too”, benefiting from the low leakage currents of a larger geometry node size while having the low active current typical of smaller silicon geometries. .
Silicon on thin oxide buried (SOTB) process technology. Image used courtesy of Renesas
As illustrated above, the “secret sauce” is a thin film of insulating oxide (“BOX” or buried oxide) deposited on top of the base silicon substrate. An extremely thin silicon layer without impurities is then deposited on top of the BOX layer that forms a doping-free channel transistor under the gate, allowing for a very low operating voltage. Small geometries, as expected , they also tend to allow SOTB-based devices to operate at high frequencies. IC designers will also be happy to learn that they can combine SOTBs on the same substrate as standard silicon processes.
Renesas RE01 Product Family
In addition to watches, Renesas’ RE01 family of products is applicable anywhere high performance and low power consumption are a must. These applications can include healthcare, security, home appliances, metering, building automation, IoT, and of course, wearables, because the glory of these devices is the ability to operate without a battery. Instead, they are equipped with an on-board energy harvesting control circuit. RE01 Group devices can operate at 64Mhz with a 1.62V power supply and require as little as 4 µA. All are based on the ubiquitous Arm Cortex M0 + core. They include a parallel MIP-LCD interface, 2D graphics, 1.5 MB flash and 256 KB SRAM. Units can handle data logging and firmware updates with security features including trusted secure IP.
RE01 block diagram. Image used courtesy of Renesas
Three members of the family are now available with three more in development, the three currently available are the R7F0E017D2DBN, the R7F0E015D2CFB and the R7F0E011D2CFP. The R7F0E017D2DBN measures 4.47mm by 4.27mm, while the others are significantly larger. It must be assumed, then, that the R7F0E017D2DBN is the one used in the Casio watch – Renesas offers a wonderfully detailed data sheet. There are some naming inconsistencies in the document, but they should have no consequences for designers.
With or without batteries
Renesas offers a guide on how your RE01 devices can form the basis of a smartwatch or wearable device.
Example of a portable or hybrid watch with RE01. Image used courtesy of Renesas
As you can see, an optional battery is foreseen.
According to the product brochure, Renesas offers a host of software and hardware tools to assist designers. Included in this set is an evaluation kit, the RE01 1500KB.
The RE01 1500KB Evaluation Kit. Image used courtesy of Renesas
Included in this kit is a motherboard, a solar panel, a USB cable, and an expansion board.
Solar powered wearables on board, really?
The promise has been made by others before, and sometimes it has failed. Engineers, do you think SOTB technology will make this technological feat come true this time?
Do you have experience with solar powered wearables? If you can share your experience, let us know about the ins and outs of the design of such a device in the comments below.