Nonlinear Shaping SC Oscillator With Enhanced Linearity

A nonlinear shaping technique for a switched-capacitor (SC) bandpass filter (BPF) based oscillator yielding enhanced linearity is presented. Usually, for an SC oscillator consisting of a BPF and a two-level comparator, the linearity can only be improved by increasing the quality factor (-factor) of the BPF. This paper proposes an efficient way to improve the linearity of SC BPF-based oscillators. In particular, by replacing the conventional two-level comparator by a sound multilevel comparator, a nonlinear shaping of the signal at the output of the comparator causes a significant improvement in linearity. To illustrate the effectiveness of the proposed technique, one conventional SC BPF-based oscillator and the proposed oscillator have been designed and fabricated in a standard 0.35- CMOS technology. Each oscillator was designed to operate from a 1.65 V supply voltage and a master clock frequency of 80 MHz. The oscillation frequency is 10 MHz and the -factor of the BPF is 10. Experimental results demonstrate that the proposed scheme improves the third-order harmonic distortion by 20 dB with respect to the conventional SC BPF-based oscillator.