Effect of separation and depth of N ⁺ diffusions in the quality factor and tuning range of PN varactors

Abstract

This article presents a wide range inductance-capacitance voltage controlled oscillator (VCO) with a unit cells-based varactor. The unit cell represents the minimum possible integrated varactor based on p-n junction diodes, where N þ diffusions are central rectangles, surrounded by doughnut shaped P þ diffusions, with their respective contacts. The varactors are designed using the AMS 0.35 mm BiCMOS process. A physical model has been derived from the measurement of a set of eight fabricated varactors. Measurements indicate that the VCO, which is intended to be used in DVB-H, oscillates from 1.087 to 2.032 GHz, with a 61% tuning range. The phase noises of À124 dBc/Hz at 1 MHz offset and À108 dBc/Hz at 100 kHz offset are obtained.