A Ultra-low-power Wake-up Wireless Transmitter for Bio-luminescence Detection in Ingestible Capsules

This paper presents a wake-up transmitter (WuTX) for bio-luminescence detection in ingestible capsules. The WuTX achieves long-term standby operation through sleep and work modes, with dual-mode switching implemented by a wake-up timer (WuTIM). In sleep mode, only the always-on LDO ($L D O_{A o B}$), reference circuits, and WuTIM are activated, the system operates at 0.4 V through $L D O_{A o B}$, leading to a power consumption of just 10 nW. In work mode, all modules are enabled by WuTIM, the system operates at 1.1 V through $L D O_{T X}$. A chirp injection is adopted to shorten the start-up time of the crystal oscillator (XCO), providing a 26 MHz reference frequency within 1.8 ms while consuming only $25.8 \mu \mathrm{~W}$. Then, a narrow pulse injection signal drives the injection-locked ring oscillator (ILRO) to produce a 130 MHz signal. This signal further generates a 910 MHz carrier frequency by an edge combiner (EC). Finally, a switched capacitor power amplifier (SCPA) is adopted to provide a wide output power range. Fabricated in a 40 nm CMOS process, the WuTX can achieve ${- 1 6} \mathrm{d B m}$ output power with a power consumption of 830 $\mu \mathrm{W}$, leading to an energy efficiency up to $15.9 \mathrm{pJ} / \mathrm{bit}$.