A comprehensive review: ultra-low power all-digital phase-locked loop RF transceivers for biomedical monitoring applications

This paper comprehensively reviews the evolution and latest advancement of ultra-low All-Digital Phase Locked Loop (ADPLL) RF transceivers designed specifically for biomedical monitoring devices. With CMOS technology, these transceivers provide efficiency and simplicity, which are essential in the medical industry. As the size and power needs of these devices decrease due to CMOS scaling, they become more suitable for small and low-energy applications. In addition, this review also provides an insight into the ADPLL applications, Digital Controlled Oscillator (DCO), and Phase Frequency Detectors. The review highlights notable differences in performance between time-to-digital converters (TDC) and TDC-less designs. TDC-less design, like Digital Phase Frequency Detectors (DPFD), offers improvements in phase noise, small size, fast phase and frequency acquisition, and power efficiency at the expense of resolution. Comparing LC-DCO and ring-DCO revealed that at high operating frequencies, the ring-DCO consumes more power but has a simpler design and a smaller circuit area than LC-DCO. Future research should focus on enhancing the performance of the ADPLL RF transceiver for biomedical devices, specifically by using a low-voltage supply and implementing DPFD to achieve low power consumption, compact design and fast locking. The significant challenges remain in maintaining low power consumption at higher frequencies with Ring-DCO design. Using the Verilog HDL for ADPLL design and implementation provides modularity, simulation, synthesis, and flexibility, which makes it an excellent alternative to designing RF transceivers in biomedical applications which are efficient and reliable.