A fully on-chip 25MHz PVT-compensation CMOS Relaxation Oscillator

A fully on-chip, low-power and small area CMOS Relaxation Oscillator (ROSC) with voltage integral feedback structure and a new Bandgap Reference voltage (BGR) for accurate oscillation frequency independent of the PVT and comparator´s delay variations is presented. The designed circuit uses a new bandgap reference to generate the reference voltage required by relaxation oscillator which allow variations due to voltage and temperature to be compensated. Another merit of this oscillator is that the phase noise at low-offset frequency is suppressed by the voltage integral feedback circuit. The frequency of the relaxation oscillator is determined by the RC response time. Thus, the current and capacitance are controlled by temperature and process compensation circuits to compensate for the frequency variation. The ROSC is implemented in a 0.18μm CMOS technology and its active area is 0.14mm². The target frequency is 25MHz and current consumption is 22μA, where V_DD is 1.8V. The oscillation frequency variation for V_DD ranges from 1.4 to 1.9V is 0.2% and for temperature ranges from -40 to 125°C is 0.18%.