A Process-Voltage-Temperature insensitive hybrid Voltage controlled ring oscillator for Biomedical IoT node

This work presents a PVT insensitive ring oscillator (RO) for IoT applications. A five-stage RO is designed by integrating diverse delay cells having contradictory temperature characteristics, complementary to absolute temperature (CTAT) and proportional to absolute temperature (PTAT) delay cells to reduce the temperature coefficient. In addition, auxiliary circuit is employed to compensate for process and supply variations. The RO implemented with a 180 nm standard CMOS process reliably produces a 6.8 MHz reference frequency with a temperature drift of 0.9 % at the supply voltage of 1.2 V. Also, it operates at a low power dissipation of 362 µW with an compact area of 4080 µm2.