Just like the Lingbo dance of the Internet of Things (IoT) must be lower and lower, a startup company has recently jumped away from the “hidden mode†and pushed cellular networks to new lows in power consumption and price.
The startup Riot Micro is now sampling a modem chip tailored for the latest 4G IoT standard. The RM1000 chip is said to require only a few milliamps (mA) to a few microamps (uA) of current, and can be sold at a price well below the industry target of $5 per module.
Operators around the world have just launched various LTE-based cellular IoT networks. Their goal is to go beyond this emerging variety of low-power wide area networks (LPWANs) such as LoRa, Sigfox, and 802.11ah Wi-Fi.
Riot Micro's chips are designed to handle the narrowband Internet of Things (NB-IoT) and LTE Cat M1 (or eMTC) standards. Peter Wong, CEO of Riot Micro, said, "The two standard modem chips are very similar and have a lot in common with each other, but they can't be executed at the same time, only one of them can be used at a time."
Instead of building the baseband function in software on the DSP, Riot splits the Fast Fourier Transform (FFT) and the baseband filter into several physical layer blocks. In addition, it also reduces the LTE protocol stack to the basic elements required for IoT specifications.
The chip is fabricated on TSMC's 55nm technology and processes NB-IoT and Cat M1 through a 26MHz ARM M0 controller, embedded SRAM and a new PLL. Competing chips typically use controllers that execute at frequencies greater than 100 MHz, and up to 16 MB of RAM, primarily from the outside.
Peter Wong, CEO of Riot Micro, presents its evaluation board (Source: Riot Micro)
The low-speed clock rate allows Riot to use a low-dropout regulator (LDO) for power management, replacing the more expensive DC/DC converters, eliminating the need to compensate for the noise of fast logic components.
The result is a current of approximately 20 mA drawn from a 3.7V battery when the fundamental frequency is being processed at 23 dBm. The complete chipset includes third-party power amplifiers (PAs) and RFICs that consume about 100mA.
In sleep mode, the component consumes less than 2uA. When most of the chips are in sleep mode, the program code will still monitor the paging channel of the signal. RioT claims that the chip has a lower latency to enter and exit sleep mode than competing products because it does not need to load DSP code.
Wong said: "We think it's enough to make the cost of cellular networks as low as Bluetooth, which helps drive the deployment of the Internet of Things."
The RM1000 evaluation board uses Skyworks PA and RFIC from Swiss ACP, but can also be used with Qorvo or other vendors' chips.
Actively seeking chip integration
The startup is currently facing two major challenges. Its highly customizable modem means it doesn't support traditional 2G/3G, and the LTE standard - competing chips are processed in software on the DSP core.
Riot believes that 2G needs to be supported a year ago, but Greg Wynans, vice president of marketing at Riot, said: "This demand seems to have disappeared now."
Now, operators are more interested in using NB-IoT to push to new lows in power and price. In addition, some believe that NB-IoT is part of its transition plan to shut down 2G networks because 2G network design does not support large-scale IoT nodes.
Another challenge for Riot is that it is a newcomer to the market, with chips and software not yet tested. As a result, the startup is testing its chips with base station and carrier software, and plans to mass-produce chips by June of this year.
Wong said: "The disadvantage of the hardware-centric approach is that it must be implemented correctly." He added that this available chip has been developed for four months. "We didn't change the firmware choice on the DSP, so before entering mass production. Many simulations were carried out."
Competitors such as Qualcomm and Sequans have developed M1 and NB-IoT chips and have been tested by operators. As the volume increases, they expect to further optimize the chip to meet specifications, while giants such as Intel and Qualcomm have already built the required PA and RFIC within their own companies.
Basic block diagram of RM1000
Wong said: "I don't know if anyone will do hardware-centric design like us, but they may use lower power and lower frequency DSPs... and some of them may not have their own protocol stack."
Next, Riot intends to integrate the PA or RFIC into the next generation of components. However, finding an independent IP source for these blocks is not easy; so far, Riot has not yet established its own simulation team.
Riot Micro has raised nearly $20 million in funding since its inception four years ago. The company's initial goal was to sell the LTE protocol stack until Wong, who was an LSI technology strategist three years ago, joined as CEO.
“It’s not easy to transition from IP and algorithm development, but we’re retuning to become a semiconductor company,†he said. Others have realigned LTE modems for NB-IoT.
Wong also hired the LTE protocol team from Blackberry and the former Newport Media Bluetooth and Wi-Fi chip experts acquired by Broadcom.
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