An Ultra-Low Power Timing Based OOK Modulation CMOS Transmitter Applied in RF-Powered Temperature Sensor Node

This paper presents an energy-efficient CMOS transmitter (TX) for autonomous temperature sensor nodes. The TX structure is simplified using a frequency divider and power amplifier (PA) with on-off keying (OOK) modulation. A two-stage duty cycle modulator is introduced to significantly reduce power consumption. The $1^{\text {st }}$ stage controls TX operation between active and inactive modes based on energy availability, while the $2^{\text {nd }}$ stage compresses the duty ratio during active mode to further reduce operating time. Finally, a 305 MHz TX system is implemented with a standard $0.18 \mu \mathrm{~m}$ CMOS process. The active area of chip is $0.01 \mathrm{~mm}^{2}$. The supply voltage is 1.2 V. Post simulation results indicate that the power consumption of $862 \mu \mathrm{~W}$ is obtained during data transmission at room temperature. After $1^{\text {st }}$-stage modulation (1 active per 63 dis-active), the average power consumption is reduced to $13.7 \mu \mathrm{~W}$. After both $1^{\text {st }}$ and $2^{\text {nd}}$-stages modulation (277 pulses with pulse width of $1.5 \mu \mathrm{~s}$ in 1 s), the ultimate average power consumption reduces to only 5.9 nW. This ultra-low power performance demonstrates good applicability for wireless sensor network (WSN) applications.