Design of a feedback digitally controlled oscillator for linearity enhancement

This paper presents a novel feedback digitally controlled oscillator (DCO) to enhance a high linearity. Because of a negative feedback loop, the feedback DCO shows a linear relationship between an input digital control word and an output frequency. In addition, the feedback DCO has a low-pass and high-pass filtering effect on the input digital control word and a DCO noise, respectively. Hence, we are able to change and optimize the bandwidth of the feedback DCO according to the each noise sources. We designed the feedback DCO scheme in 130 nm CMOS technology. The peak-to-peak gain of the proposed feedback DCO is 17 MHz/LSB which is 96% smaller than a conventional DCO. The feedback DCO consumes 1.7 mW at 2.2 GHz output frequency.