236μW RF transmitter ditches PLL for ultra-low-power IoT
A tiny 236-microwatt transmitter uses oscillator-based phase synthesis for efficient multi-PSK modulation.
A team led by Meysam Sohani Darban at Virginia Tech has demonstrated a revolutionary ultra-low-power transmitter that sidesteps the traditional phase-locked loop (PLL) by performing phase modulation directly within a ring oscillator. Fabricated in a 22-nm FD-SOI process, the chip occupies just 23×17.6 μm² and consumes only 236 μW (excluding the output driver) while operating in the 2.4 GHz ISM band. The design uses synchronized charge extraction at the oscillator’s transition points to induce controlled phase shifts, ensuring constant amplitude and frequency. A time-domain multi-triggering technique allows reconfigurable multi-mode modulation—supporting 16-PSK, 8-PSK, QPSK, and BPSK—within a single hardware block.
Measured results show a symbol rate of 2 MSps with a maximum error vector magnitude (EVM) of 5.13% rms, and the output delivers -10 dBm over a 60 MHz bandwidth. By eliminating the power-hungry PLL and associated frequency synthesis circuitry, the design achieves a favorable trade-off between power, complexity, and modulation flexibility. This makes it highly suitable for energy-constrained applications such as IoT sensors, medical implants, and battery-free wearables where every microwatt matters. The work was published on arXiv (2605.11261) and represents a significant step toward truly low-power wireless communication.
- 236 μW total power consumption - 10-100x lower than traditional PLL-based transmitters at 2.4 GHz
- Supports 16-PSK, 8-PSK, QPSK, and BPSK in a unified 23×17.6 μm² core fabricated in 22-nm FD-SOI
- Achieves 2 MSps symbol rate with <5.13% rms EVM and -10 dBm output power over 60 MHz bandwidth
Why It Matters
Enables battery-free IoT and medical implants by slashing transmitter power while maintaining modulation flexibility.