PowerDown: Power Efficiency

Recycling power used in one chip cycle to run the other can save 90% over pulling straight from the battery.


Power Down Semiconductor wants to make the batteries in smartphones and IoT devices last 10 times longer by not wasting power they’ve already used.

Every time an intelligent device has a thought, it pulls power from a battery and sends it through its maze of wires and millions of gates to create a O or a 1 at key points in the control and logic circuits.

“Think about how much energy just using the GPS in your phone uses, how hot it gets,” said David Huffman, founder and CEO of the company. “Think how long your smartphone battery would last if you could get the same performance but use energy harvesting to get it with 10x less power use.”

Huffman has designed circuits to save power using a technique called Multi-Level Charge Recycling (MLCR) which breaks up the supply into several equally spaced rails in order to re-use charge in various digital circuits. Most digital circuits move data by charging up to its supply voltage to represent “1” and then discharge that node to ground to signify “0.” The energy used to charge and discharge that node is dissipated as heat.

The PDSemi approach relies on an external resonating oscillator to charge and discharge nodes within the IC to conserve the energy that it would otherwise lose as heat. The resonant element sees only a fixed capacitance for each node, however, to reduce noise caused by variation in the timing or levels of charge in each node.

For an SRAM cell, for instance, the MLCR technique drives the bit lines with selected sinewaves based on the data. The bit cell will sample the peak or valley of the resonant waveform to distinguish between a “1” or a “0” respectively.

All of the capacitance of the bit lines is effectively cancelled by resonance and the only resistive losses are in the selection switch and the resonant element itself.

The MLCR is designed to process data at clock rates that are normal for the system involved, dampening performance while trying to save power by reducing the supply rail to just a few hundred millivolts, according to Huffman, who filed two patents for the technology. One is for a low-power decoder with resonant drive circuits. The other for a low-power SRAM bitcell with resonant drive circuits.

The IC is designed to be packaged with other chips. The prototype uses the technology within an SRAM cell, but, within a single smartphone it could be mounted with the GPS, an external SRAM die or connected to the LCD display controllers.

It creates with a 15% overhead in die area but only affects the function of subsystems to which it is attached. No special production processes are required to integrate the system, which can be produced using a relatively inexpensive 0.18um CMOS digital process and tested using existing EDA tools, according to Huffman.

The PDSemi roadmap indicates future versions will include a pin-compatible, energy harvesting IoT MCU as well as IC for custom IoT devices for ULP applications on wearable devices.

“There are a lot of different ways to power IoT or medical devices using power harvesting and low-power approaches,” he said. “The battery issue is a big deal, but all the other things people have tried have a big impact on performance; this doesn’t, so you can reduce the battery size by a factor of 10, or leave it the same and just have that much more capacity.”

PDSemi executives have been pitching the technology to OEMs and potential investors along the Pacific Rim, looking first at the and as both a microcontroller and a boost for display units to reduce energy use to potential OEM partners and investors along the Pacific Rim.

Source: Power Down Semiconductor

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