A noise-insensitive high-resolution digitally controlled ring oscillator with multipoint-tuning technique

An eight-phase digitally controlled ring oscillator that employs a multipoint-tuning technique is presented. The DCO fine-tuning is realized by multi-variable RC loads to improve frequency resolution and coupled-noise rejection by reducing DCO gain. With a set of rotating control logic circuits and eight DACs, the DCO achieves a minimum frequency quantization step of 55 kHz and noise sensitivity of 22 MHz/V. Implemented in a 0.13-μm CMOS process with a 1.2-V supply, the proposed ring-DCO is tuned by 24-bit frequency control word and operates from 1.76 to 3.74 GHz.