Transmitter save power for latest WiFi protocol

At this week’s IEEE ISSCC (Internation Solid State Circuits Conference), research centre, imec and Holst Centre presented a 1.3nJ/b fully digital polar transmitterwith a 10-fold power reduction, compared with OFDM transmitters.

The HaLow designation was introduced by the Wi-Fi Alliance for the new low power, long range Wi-Fi IEEE802.11ah protocol, which is optimised for IoT applications, with sub-GHz carrier frequency and mandatory modes with 1MHz/2MHz channel bandwidths. This allows devices to operate in a longer range with scalable data rates from 150kbit/s to 2.1Mbit/s. The standard uses OFDM to improve the link robustness against fading (important in urban environments), and to achieve a high spectral efficiency.

The digital polar transmitter meets the tight spectral mask and error-vector-magnitude (EVM) requirements of conventional WiFi standards. The measured phase noise at 1.5MHz offset is -115dBc/Hz, which is 15dB lower than the spectral mask requirement for the IEEE 802.11ah standard. At 1MHz/2MHz with 64-QAM OFDM data packets, both the far-out and close-in spectrum pass the mask with at least 4.8dB margin. The EVM is below 4.4%.

The power consumption of the transmitter is as low as 7.1mW, when delivering 0dBm output power and operating from a 1V supply. This represents a factor of 10 power reduction compared to OFDM transceivers, meeting stringent requirements for IoT applications, says the research centre.