A Passive Telemetry Interface System with Closed-loop Power Control Function for Body-implanted Applications

In this paper, we propose a passive telemetry interface system for a body-implanted chip with a closed-loop power control function, which keeps the chip temperature at the allowable level for human body. The system is controlled by monitoring an excessive current at the implanted chip and limiting the power supply at the external interrogator unit. Power consumption of the current monitor circuit implemented in 0.18 mum standard CMOS technology is lower than 35 muW with a 1.8 V power supply. Experimental results of the closed-loop power control system confirm its expected features of a detecting current of 150 muA at a distance between the transponder and the interrogator less than 10 mm.