Researchers at MIT have unveiled a new compact, wireless receiver chip designed for 5G-compatible smart devices, boasting a remarkable resistance to interference—approximately 30 times greater than conventional wireless receivers. This innovative, low-cost receiver is particularly suitable for battery-operated Internet of Things (IoT) applications, such as environmental sensors, smart thermostats, and health wearables, which require extended operational longevity.
The chip employs a unique passive filtering system that utilizes less than one milliwatt of static power. It effectively shields both the input and output of the receiver’s amplifier from disruptive wireless signals that could hinder device performance. Central to this technology is an advanced configuration of precharged, stacked capacitors interconnected by a network of tiny switches. These miniature switches consume significantly less power during operation compared to traditional IoT receiver switches.
The arrangement of the receiver’s capacitor network and amplifier is meticulously designed to exploit a phenomenon in amplification, allowing the use of smaller capacitors than typically necessary. “This receiver could enhance the functionality of IoT devices. Health monitors or industrial sensors could become more compact and enjoy extended battery life, while also improving reliability in environments with heavy radio traffic, like factory floors or smart city setups,” stated Soroush Araei, an electrical engineering and computer science graduate student at MIT, who is the lead author of a paper detailing the receiver’s development.
Araei collaborated on the research with Mohammad Barzgari, a postdoctoral researcher at the MIT Research Laboratory of Electronics; Haibo Yang, another EECS graduate student; and Negar Reiskarimian, a senior author and assistant professor in EECS at MIT. The findings were shared at the IEEE Radio Frequency Integrated Circuits Symposium.
A New Standard for IoT Receivers
The receiver functions as a crucial link between an IoT device and its surroundings, tasked with detecting and amplifying wireless signals, eliminating interference, and converting the signals into digital data for further processing. Traditionally, IoT receivers have relied on fixed frequencies and utilized a single narrow-band filter to suppress interference, making them straightforward and cost-effective. However, the introduction of 5G mobile network specifications allows for the development of more affordable and energy-efficient devices, paving the way for a broader array of IoT applications that can take advantage of faster data speeds and enhanced network capabilities.
Next-generation IoT devices necessitate receivers capable of tuning across a wider frequency spectrum while remaining cost-effective and energy-efficient. “This presents a significant challenge, as we must now consider not only the power and cost of the receiver but also its adaptability to multiple sources of interference present in the environment,” Araei explained.
To minimize the size, cost, and energy consumption of IoT devices, engineers cannot depend on the large, off-chip filters commonly utilized in devices operating across broad frequency ranges. One proposed solution involves a network of on-chip capacitors designed to filter out undesired signals. However, these capacitor networks often face a specific type of signal noise known as harmonic interference. In prior research, MIT scientists created a novel switch-capacitor network that effectively targets these harmonic signals early in the receiver’s processing chain, filtering them out before they are amplified and transformed into digital data.
Minimizing Circuit Size
This research has been expanded by employing the innovative switch-capacitor network as a feedback path within an amplifier that features negative gain. This setup makes use of the Miller effect, a principle that allows small capacitors to mimic the behavior of larger ones. “This technique enables us to satisfy the filtering requirements for narrow-band IoT without the need for physically larger components, resulting in a significant reduction in circuit size,” Araei noted. The receiver’s active area is less than 0.05 square millimeters.
A challenge faced by the researchers was figuring out how to generate sufficient voltage to operate the switches while maintaining an overall power supply of only 0.6 volts. In the presence of interfering signals, these diminutive switches can inadvertently turn on and off, particularly when the necessary switching voltage is exceedingly low. To counter this issue, the team devised a unique method utilizing bootstrap clocking, which raises the control voltage just enough to ensure reliable switch operation, all while consuming less power and utilizing fewer components than conventional clock-boosting techniques.
Together, these advancements allow the new receiver to operate with less than one milliwatt of power, effectively blocking approximately 30 times more harmonic interference compared to standard IoT receivers. “Our chip is also exceptionally quiet, minimizing airwave pollution. This is largely due to the small size of our switches, which results in minimal signal leakage from the antenna,” Araei added.
Due to its compact design and reliance on switches and precharged capacitors instead of more complex electronics, the receiver could be more economically feasible for manufacturing. Furthermore, its ability to accommodate a wide range of signal frequencies makes it suitable for a diverse array of current and future IoT devices. Following the successful prototype development, the researchers aim to enable the receiver to function without a dedicated power supply, potentially harnessing ambient Wi-Fi or Bluetooth signals to power the chip.
