An 80-GHz DCO utilizing improved SC ladder and promoted DCTL-based hybrid tuning banks

• Published in: Journal of semiconductors 2023-10, Vol.44 (10), p.102402-90
• Main Authors: Tang, Lu, Chen, Yi, Wang, Kui
• Format: Article
• Language: English
• Subjects: DCO; digitally controlled transmission lines; sub-MHz; switched-capacitor ladder; tuning bank
• ISSN: 1674-4926; 2058-6140
• DOI: 10.1088/1674-4926/44/10/102402

An 80-GHz DCO based on modified hybrid tuning banks is introduced in this paper. To achieve sub-MHz frequency resolution with reduced circuit complexity, the improved circuit topology replaces the conventional circuit topology with two binary-weighted SC cells, enabling eight SC-cell-based improved SC ladders to achieve the same fine-tuning steps as twelve SC-cell-based conventional SC ladders. To achieve lower phase noise and smaller chip size, the promoted binary-weighted digitally controlled transmission lines (DCTLs) are used to implement the coarse and medium tuning banks of the DCO. Compared to the conventional thermometer-coded DCTLs, control bits of the proposed DCTLs are reduced from 30 to 8, and the total length is reduced by 34.3% (from 122.76 to 80.66 μ m). Fabricated in 40-nm CMOS, the DCO demonstrated in this work features a small fine-tuning step (483 kHz), a high oscillation frequency (79–85 GHz), and a smaller chip size (0.017 mm 2 ). Compared to previous work, the modified DCO exhibits an excellent figure of merit with an area (FoM A ) of –198 dBc/Hz.