A 16.6μW 32.8MHz monolithic CMOS relaxation oscillator

This paper presents a 32.8MHz low power, supply insensitive monolithic CMOS relaxation oscillator. Instead of using voltage-mode comparators for cycle-to-cycle capacitor voltage swing (CVS) threshold voltage comparison, the CVS is regulated by a low-power closed-loop control which consists of a current-controlled delay cell (CCDC), a Gm-C error integrator and a comparator-free switch logic block. The CCDC and switching logics are powered by a logic supply regulator for reducing switching-losses and line sensitivity. The oscillator consumes 16.6μW from a 1.5V supply voltage at room temperature, achieving a FOM of 0.51μW/MHz. The measured output frequency variation is <;±0.13%/V @ 32.8MHz, for a supply range of 1.5V to 3.6V It occupies 0.013mm² in a 0.18μm CMOS process.