Low-voltage transformer-based CMOS VCOS and frequency dividers

Transformer feedback and coupling have been recently proposed in realizing low-voltage CMOS voltage-controlled oscillators and frequency dividers with high performance in terms of high frequency, low power, low phase noise, and good figure of merits. This paper reviews reported transformer-feedback and transformer-coupled circuit techniques and presents several designs with state-of-the-art measured performance as case studies. The key advantages as well as limitations of the techniques will also be summarized.