World’s smallest ARM chip has huge implications for implantable tech

28 Feb
Surya R Praveen Freescale KL0PA on keyboard

Freescale has just introduced the world’s smallest ARM Cortex-powered microcontroller unit (MCU), the Kinetis KL02. Compared with its nearest competitor, the Kinetis consumes 25% less board area yet provides 60% more general purpose input-output (GPIO).Freescale has not identified the customer driver for this chip but a quick look at the datasheet may give us rough idea — its end use may be closer to home than you might at first think.

For a chip of this size (1.9 x 2.0 millimeters), you might expect some essential features normally associated with a full-blown microcontroller to be missing, but that is clearly not the case. The Kinetis includes 12-bit analog to digital conversion, an analog comparator, a low power UART, and high speed inter-chip communications using either the SPI or I2C bus. It uses a 32-bit processor, 32k of flash memory, and has 4k of RAM. Also it incorporates several Pulse Width Modulation (PWM) modules, which can be used for effective but simple digital-to-analog conversion. PWM sometimes gets a bad rap as the poor man’s D-to-A, but for low-end systems it is often the best way to get a command voltage for motors, or convert to a current for electromagnets, heaters, or actuators.

Surya R Praveen Freescale tiny arm MCU

The size of the Kinetis makes it perfect for new applications including the Internet of Things or swallowable devices to image your internals. Going one step further on that theme (OK, possibly two or three), bloodborne nanobots controlled by magnetic resonance navigation is now new frontier with huge potential that could be better explored with chips like this. Freescale has already delivered devices used for wireless activity/sleep cycle trackers like the Fitbit They also have found application in tubing-free insulin pumps like the Omnipod.

Perhaps the most interesting detail on the Kinetis spec page is the Human-Machine Feature section. Interfaces like a brain-computer interface (BCI) not only require a lot of raw computing power, likely handled by other dedicated chips, but also a lot of GPIO. FPGAsare the go-to technology for high-speed and low power when you have a lot of inputs, but the smallest FPGA now available doesn’t come close to the Kinetis’ footprint. You also want to have direct memory access (DMA) and support for pin interrupts, both features also found in the Kinetis. Finally Freescale makes mention here of the capacitive touch interface which supports up to 16 electrodes with DMA transfer.

This is pretty exciting stuff for any brain-computer interface or implantable tech designer. As a miniature front-end to handle up to 16 channels of data collection, the Kinetis might even open up the possibility of putting the hardware inside the skull at the site of the electrodes, instead of burying it elsewhere in the body and threading leads under the skin. Proximity is critical for noise reduction, even after current amplification as you want your system as close to the recording site as possible.

Up until now most BCIs have mainly been stimulator devices, but for more complex controlfeedback from the neurons in the vicinity of stimulation will be mandatory. Chips like the Kinetis will be instrumental in making the next generation of implantable tech a reality.


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