**5. Conclusions**

This paper presents the wide locking range and low-power divide-by-two CR-ILFD. The fourth-order resonator is applied to extend the narrow operating range of the ILFD. In addition, the CR core decreases the power consumption. The input frequency locking range is from 18.8 to 33.8 GHz (57%) at an injection power of 0 dBm. The full-span spectrums at the maximum or minimum frequency are presented. The power difference between the output and harmonic signals is approximately 10 dB or more over the entire locking range. The proposed CR-ILFD dissipates 2.26 mW froma1V supply voltage and the die size is 0.75 mm × 0.45 mm. This CR-ILFD is implemented in a 65 nm CMOS technology.

**Author Contributions:** Conceptualization, K.-I.O. and D.B.; methodology, K.-I.O.; software, K.-I.O.; validation, K.-I.O., G.-H.K. and D.B.; formal analysis, K.-I.O.; investigation, K.-I.O. and G.-H.K.; resources, K.-I.O.; data curation, K.-I.O.; writing—original draft preparation, K.-I.O., J.-G.K. and D.B.; writing—review and editing, K.-I.O. and D.B.; visualization, K.-I.O. and D.B.; supervision, K.-I.O. and D.B.; project administration, K.-I.O., J.-G.K. and D.B.; funding acquisition, D.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the Institute for Information & Communications Technology Planning & Evaluation (IITP) gran<sup>t</sup> funded by the Korea governmen<sup>t</sup> (MSIT) (No. 2019-0-00138, Development of Intelligent Radar Platform Technology for Smart Environments) and by the Chung-Ang University Research Scholarship Grants in 2019.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** No new data were created in this study. Data sharing is not applicable to this article.

**Acknowledgments:** The authors would like to thank all authors of previous papers for approving the use of their published research results in this paper.

**Conflicts of Interest:** The authors declare no conflict of interest.
