Rohm, Imec, a research and innovation hub in nanoelectronics and digital technologies, and Holst Centre (set up by Imec and TNO) presented an all-digital phase-locked loop (ADPLL) for Internet-of-Things (IoT) radio transceivers at the 2017 International Solid-State Circuits Conference in San Francisco (US). Whereas a PLL is traditionally one of the major power consumers in a radio and can take up to 30% of the radio area, this new ADPLL features a small area (0.18 mm² in 40 nm CMOS) and low power consumption (0.67 mW).
With all spurs lower than -56 dBc and jitter below 2ps, which is beyond state-of-the-art digital PLLs, the new ADPLL shows a robustness.
The intuitive IoT relies on tiny sensor nodes, invisibly embedded in our environment and wirelessly connected to the internet. As billions of IoT devices are set to be deployed, battery replacement becomes impossible and therefore, power consumption reduction, especially in wireless connectivity, is the leading concern and challenge to address.
The PLL is the radio component for frequency synthesis and has traditionally been an analog component, although the research community has been working on digital alternatives. All-digital PLLs enable a smaller footprint, better control and testability, and improved scaling to advanced CMOS nodes. However, to-date, they have lagged behind in terms of performance, compared to analog solutions.
Rohm and Imec say their all-digital PLL is an industry-first, combining low power consumption of only 0.67mW with state-of-the-art performance. It supports all specifications of Bluetooth Low Energy (BLE) radios while significantly reducing cost and power. This divider less fractional-N digital PLL features a power-efficient spur-mitigation technique and a digital phase unwrap technique. Both approaches contribute to its performance.
Rohm has developed the low-power ADPLL with Imec and now develops the RF transceiver with this ADPLL and integrates Rohm’s ultra-low-power sensors and micro controllers into the "sensor edge" module.
The ADPLL is ready for industrial mass production and is currently being transferred to industrial partners for product integration.
At ISSCC2017, Imec presented four papers addressing key building blocks for ultra-low power connectivity. The innovations serve power reduction in active, standby, sleep and transient operation of standard radios like Bluetooth, or newcomers in the sub-GHz communication space.