Extreme low power sensors

The Psikick chip. An incredibly low power chip ideal for IoT applications. Credit: Psikick

As sensors will become widespread in the environment, and in wearable, a crucial issue will be power consumption. Energy scavenging, I posted some ingenious ways of doing it, is a possibile way to supply energy: some kind of energy scavenging can harvest in the mW area when using radiation frequency but this requires capturing antennae of several cm, motion scavenging is more likely to be in the µW range.

Hence, scavenging is feasible only if the power consumption is very low, in the order of µW, better if we can go down to nW.

This is what a start up, PsiKick, is offering, sensors chips that requires 1/1000 of the power required by today's chips.  The chip's CPU requires just 400nW and has an RX power requirement (power needed for receiving data) as low as 100 nW with a Tx power (transmission power) up to 10µW at a transmission speed of 1Mbps. These numbers are quite impressive!

To make this possible PsiKick engineers are using sub thresholds voltage to power the chip. Sub-thresholds is a voltage that does not activate a transistor, so the transistor is normally considered to be off. If you want a transistor to perform as it should you better make sure that the voltage applied is over thresholds.

However, sometimes a transistor is not well behaving and even when you are under the thresholds some drain current still run and this may adversely affecting other transistors that would be made to believe that this current relates to an "on" transistor. Hence, engineers started to study sub-thresholds characteristics in the 70ies to avoid this type of malfunction.

Engineers at PsiKick have turned the table upside down. Since there is a drain current when a transistor is subjected to a sub thresholds voltage one can detect it and operate the other transistor on that drain current. In practice this means to find a way to lower the sub-thresholds limit, using the present one as a normal level for operating the chip.

Lowering the voltage has tremendous effect on the power consumption since energy is proportional to the square of the voltage.

With this ingenious approach of moving into an area where all the others engineering are careful to stay clear at Psikick they have managed to open the door to a dissemination of sensors since they can now be powered by ambient energy. A further enabling steps towards ubiquitous IoT!

Author - Roberto Saracco

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