3.5 A 34µW 32MHz RC Oscillator with ±530ppm Inaccuracy from −40°C to 85°C and 80ppm/V Supply Sensitivity Enabled by Pulse-Density Modulated Resistors

This paper presents a method for precise and robust cancellation of the resistor TC across process using a parallel combination of two switched -resistors [5] that are digitally -controlled by pulse -density modulated sequences. Using the proposed composite resistor and trimming at only two temperature -insertion points, a prototype FLL-based 32MHz oscillator fabricated in a 65nm CMOS process achieves an inaccuracy of ±530ppm (8.4ppmPC), 8OppmN voltage sensitivity, and 2.5ppm Allan deviation with an excellent power efficiency of 1μW/MHz.