Frequency

2.4GHz radio chip features reduced supply voltage & power consumption

25th February 2015
Barney Scott
0

At the 2015 International Solid State Circuits Conference (ISSCC), Imec, Holst Centre and Renesas presented an ultra-low power 2.4GHz short range radio compliant with BLE and IEEE802.15.4 (ZigBee). Implemented in 40nm CMOS, the radio achieves a supply voltage reduced by 20%, power consumption reduced by 25% and chip area reduced by 35%, as compared to the previous 90nm RF front-end design.

Imec, Holst Centre and Renesas’ 2.4GHz radio achieves world-class energy efficiency by employing a digital-intensive RF architecture tightly integrated with the Digital BaseBand (DBB) and a MCU. Additionally, several low-voltage techniques are adopted to ensure sub-1V operation, achieving 3.7mW receiver (RX) and 4.4mW transmitter (TX) power consumption. Furthermore, the digital-intensive RF design reduces the analogue core area to 1.3mm2, and the DBB/MCU/SRAM occupies an area of 1.1mm2.

Fabricated in a 40nm CMOS process, the radio supports the most common standards for mobile sensor networks (BLE, IEEE802.15.4).  A mixed-mode fast Carrier Frequency Offset (CFO) compensation through a 2-point injection All-Digital Phase-Locked Loop (AD-PLL) expands the receiver’s tolerance to Carrier Frequency Offset (CFO) from ±20 to ±60ppm.

An All-Digital PLL is used because of its small area and extensive self-calibration.  An excellent RX sensitivity of -93.5dBm (BLE spec under -70dBm) for BLE was measured, with a packet error rate of 30.8%. The RX with fast Automatic Gain Control (AGC) has a dynamic range from the sensitivity level up to -5dBm (BLE spec over -10dBm), and fulfills BLE requirement on adjacent channel rejection with sufficient margin.

“From healthcare to smart buildings, ubiquitous wireless sensors connected through cellular devices are becoming widely used in everyday life,” said Harmke De Groot, Department Director, imec. “The radio consumes the majority of the power of the total system and is one of the most critical components to enable these emerging applications. Moreover, a low-cost area-efficient radio design is an important catalyst for developing small sensor applications, seamlessly integrated into the environment. Implementing an ultralow power radio will increase the autonomy of the sensor device, increase its quality, functionality and performance and enable the reduction of the battery size, resulting in a smaller device, which in case of wearable systems, adds to user’s comfort.”

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