A Portable Digitally Controlled Oscillator Using Novel Varactors

Pao Lung Chen, Ching Che Chung, Chen-Yi Lee

Research output: Contribution to journalArticlepeer-review

87 Scopus citations


This work presents a portable digitally controlled oscillator (DCO) by using two-input NOR gates as a digitally controlled varactor (DCV) in fine-tuning delay cell design. This novel varactor uses the gate capacitance difference of NOR gates under different digital control inputs to establish a DCV. Thus proposed DCO can improve delay resolution 256 times better than a single buffer design. This study also examines different types of NOR/NAND gates (2-input or 3-input) for DCV. The proposed DCO with novel DCV can be implemented with standard cells, and thus it can be ported to different processes in short time. Furthermore, the final circuit layout can be generated using an auto placement and routing (APR) tools. A test chip demonstrates that LSB resolution of the DCO can be improved to 1.55 ps with standard 0.35-μm 2P4M CMOS digital cell library. The proposed DCO has good performance in terms of fine resolution, high portability, and short design turnaround cycle compared with conventional DCO designs.

Original languageEnglish
Pages (from-to)233-237
Number of pages5
JournalIEEE Transactions on Circuits and Systems I: Regular Papers
Issue number5
StatePublished - 5 May 2005


  • All-digital phase-locked loop (ADPLL)
  • PLL
  • cell-based hardware-description language
  • digitally controlled oscillator (DCO)
  • digitally controlled varactor (DCV)

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