Proving the Business Case for the Internet of Things

Lapis dual-band wireless chip targets IoT use

Steve Rogerson
November 26, 2019



Rohm subsidiary Lapis Semiconductor has introduced a multiband (sub1GHz and 2.4GHz) wireless communication chip for applications requiring low power consumption over relatively long distances, such as smart meters, gas and fire alarms, smart agriculture, and home and building security systems.
 
In recent years, the worldwide increase of energy usage from natural resources has emphasised the need for improved energy efficiency to mitigate the effects of global warming. To address this need, the use of smart meters has increased dramatically in Japan since 2015 and the wireless M-bus system was launched in Europe.
 
At the same time, there is a trend to collect and manage sensor data using wireless networks not only to optimise energy consumption and lighting in buildings but also for crime and disaster prevention. Furthermore, these wireless sensor networks are becoming increasingly used to improve productivity in agriculture.
 
In response, Japan-based Lapis Semiconductor developed the ML7421wireless communication device. In addition to covering the sub-1GHz frequency band (400 to 960MHz), it also covers the 2.4GHz frequency band, providing universal compatibility. This LSI has stable wireless characteristics even under changing environmental parameters such as voltage and temperature fluctuations.
 
Fluctuations over temperature (-40 to +85˚C) are 0.5dB in transmit output power and 1.0dB in receive sensitivity. Furthermore, a DC-DC converter, class-E power amplifier and a high-speed radio wave check function allow the average current consumption to decrease by 15% compared with conventional Lapis products, leading to lower system power consumption and longer battery life.
 
Lapis expects that the LSI with low power consumption and worldwide compatibility will be adopted in smart meters and wireless networks around the world.
 
The ML7421 supports both sub-1GHz and 2.4GHz. Previously, it was necessary to select wireless LSIs for each country and develop devices for them. By supporting the 2.4GHz band available worldwide, a single device can be deployed globally.
 
Additionally, in environments where communications at 2.4GHz are unstable, long-distance sub-1GHz communications are available. For this reason, 2.4GHz and sub-1GHz can be used as bridged communications depending on the application or the environment.
 
The ML7421 can be used in radio stations compliant with Etsi EN 300200, FCC part 15, and Arib STD-T66, T67 and T108 with several packet-handling functions based on wireless M-Bus and IEEE802.15.4g.
 
In addition, improving delta-sigma ADCs makes it possible to achieve flexible data rate demodulation up to 300kbit/s for global usage, while improving receiver sensitivity. As a result, the ML7421 is suitable for equipment used outdoors such as smart meters and various IoT sensors. These stable characteristics make it possible to extend long-range communication further with a high power amplifier.
 
Low power design technology cultivated over many years allows Lapis to decrease average current consumption by 15% during the general sensor operation; in 5s intervals, sleep mode, transmitter mode and receiver mode are included. Improving the DC-DC converter and the class-E power amplifier reduces transmitter mode current consumption down to 27mA at 13dBm output.
 
In addition, a high-speed radio wave check function reduces the time required for start-up of reception, reducing the total time for receiver strength detection (around 1ms). As a result, power consumption of wireless nodes within a network are reduced, contributing to overall lower system power consumption and longer battery life.
 
Rohm Semiconductor is a Japanese company with nearly ¥400bn revenue and 23,000 employees. Manufacturing plants are in Japan, Korea, Malaysia, Thailand, Philippines, China and Europe. Lapis Semiconductor (former OKI Semiconductor), SiCrystal and Kionix are among its subsidiaries.