All-digital PLL ups performance for IoT radio transceivers

Whereas a PLL is traditionally oneof the major power consumers in a radio and can take up to 30% of the radio area, this new ADPLL features a small area (0.18mm² in 40nm CMOS), low power consumption (0.67mW) and excellent performance. With all spurs lower than -56dBc and jitter below 2ps, which is beyond state-of-the-art digital PLLs, the new ADPLL shows an excellent 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’s all-digital PLL is an industry-first, combining record-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 below any of today’s solutions. 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 excellent performance.

“We are proud that we have developed the world-class low power ADPLL with imec. We develop the RF transceiver with this ADPLL and integrate ROHM’s ultra-low power sensors and micro controllers into the “sensor edge” module. We hope they will be leaders of IoT market.“ commented Isao Matsumoto, Director, LSI Production Headquarters/LSI Product Development Headquarters at ROHM.

“We are pleased of our collaboration with ROHM to solve yet another challenge and deliver an ADPLL that adds to imec’s world-class record low power radio design portfolio. With this performance, this all-digital PLL has become a mature and superior alternative to the widespread analog PLLs,” commented Kathleen Philips, Program Director at imec/Holst Centre for Perceptive Systems for an Intuitive IoT. “The ADPLL is ready for industrial mass production and is currently being transferred to our industrial partners for product integration.”

At ISSCC2017, imec presents 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.