A 1.66-nW/kHz, 32.7-kHz, 99.5ppm/°C fully integrated current-mode RC oscillator for real-time clock applications with PVT stability

A compact and low-power current-mode RC oscillator (RCO) with process, voltage, and temperature (PVT) stability has been developed. The circuit employs a current-mode RCO architecture without using a conventional comparator based voltage-mode architecture. The current-mode architecture enables a compact RCO and faster switching speed to be achieved. By designing transistor sizes equally between one in a bias circuit and another in a voltage to current converter, the effect of process variation can be minimized. A prototype chip in a 0.18-μm CMOS process demonstrated that the RCO generates a stable clock frequency of 32.7 kHz with a small area of 0.19 mm
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and low-power dissipation of 54.2 nW at 0.85-V power supply, which achieves a figure of merit (FoM) of 1.66 nW/kHz. The measured temperature coefficient and line regulation were 99.5ppm/°C and 8.9ppm/mV, respectively.