A Novel Digitally-Controlled Varactor for Portable Delay Cell Design

Pao-Lung CHEN  Ching-Che CHUNG  Chen-Yi LEE  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E87-A   No.12   pp.3324-3326
Publication Date: 2004/12/01
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section LETTER (Special Section on VLSI Design and CAD Algorithms)
Category: Physical Design
portable delay element,  digitally-controlled varactor (DCV),  DLL,  DCO,  cell-based,  

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In this paper, a novel digitally-controlled varactor (DCV) for portable delay cell design is presented. The proposed varactor uses the gate capacitance differences of NAND/NOR gates under different digital control inputs to build up a digitally-controlled varactor. Then the proposed varactor is applied to design a high resolution delay cell and to achieve a fine delay resolution. Different types of NAND/NOR gates (2-input or 3-input) for DCV design are also investigated in this paper. The proposed DCV can be implemented with standard cells, thus it can be easily ported to different processes in a short time. A test chip fabricated on a standard 0.35 µm CMOS 2P4M process proves that the proposed delay cell has a fine delay resolution about 1.55 ps. As a result, the proposed DCV exhibits finer resolution, better linearity, and better portability than traditional delay elements, and is very suitable for portable delay cell design.