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An on-chip CMOS relaxation oscillator with voltage averaging feedback using a reference proportional to supply voltage is presented. A voltage-averaging feedback (VAF) concept is proposed to overcome conventional relaxation oscillator problems such as sensitivity to comparator delay, aging, and flicker noise of current sources. A test-chip with typical frequency of 14.0 MHz was fabricated in a 0.18 μm standard CMOS process and measured frequency variations of ±0.16 % for supply changes from 1.7 to 1.9 V and ±0.19% for temperature changes from -40 to 125°C. The prototype draws 25 μA from a 1.8 V supply, occupies 0.04 mm2, and achieves 7x reduction in accumulated jitter (at 1500th cycle) as compared to a oscillator without VAF.
Date of Publication: June 2010