Hanson, a graduate from the University of Michigan, founded Ambiq Micro Inc. (Austin, Texas) back in 2010 on the simple premise that as power consumption scales with the square of voltage: the lower the operational voltage, the lower the power consumption of any given circuit.
So here is a little background: conventionally MOS transistors are designed to operate in the strong inversion zone where voltage and current scale linearly. This allows transistors to switch faster but it is possible to take transistor operation close to and even below the threshold voltage. So, for manufacturing processes at around 40nm or 28nm this would mean operating circuits at around 0.3V to 0.5V rather than the conventional case of 1.0V or more.
But this simple idea is not so simple to implement because different types of circuit are more or less tolerant of voltage scaling and may need significant modification. Also, the digital circuit clock frequency must be scaled back with voltage, which reduces the peak performance. But, generally, for energy efficiency sub- or near-threshold operation has been recognized to be good thing and Ambiq was one of a few companies that started to consider it in the early part of the previous decade.
We asked Hanson, if sub-threshold operation is a good idea, why is it still an outlier activity and most MCUs sold operate at higher voltages with inferior power efficiency.
"Most of our competition would rather have the foundry solve their problems for them," said Hanson. While it is the case that foundries have been characterizing manufacturing processes for lower voltages than they conventionally did, they are not going sub- or even near-threshold because they want to offer a relatively unified support in terms of foundational intellectual property cores.
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