Judith Maget

Influence of novel MOS varactors on the performance of a fully integrated UMTS VCO in standard 0.25-/spl mu/m CMOS technology

A novel MOS varactor design is compared to standard MOS varactors and its influence on the tuning range, phase noise, and pushing of a CMOS voltage-controlled oscillator (VCO) for UMTS is presented. Three fully integrated CMOS VCOs have been fabricated in standard 0.25-/spl mu/m technology, two with different versions of a novel device, and one with a conventional nMOSFET as the tuning element. All of the fully integrated VCOs fulfill UNITS tuning and phase noise specifications with a power consumption of only 7.5 mW at a 2.5-V power supply. The new varactors outperform the nMOSFET by increasing the frequency tuning from /spl plusmn/7% to /spl plusmn/11% or /spl plusmn/13%, while the measured phase noise of all three VCOs is -117 dBc/Hz at a 1 MHz offset from a 4-GHz carrier.

MOS varactors with n- and p-type gates and their influence on an LC-VCO in digital CMOS

The influence of the gate doping type of the MOS varactor on frequency tuning, phase noise, and frequency sensitivity to supply-voltage variations of a fully integrated inductance-capacitance voltage-controlled oscillator (LC-VCO) is presented. Three varactors in multifinger layout with shallow trench isolation (STI) are compared. The polysilicon gate is either entirely n- or p-doped or the fingers have alternating n and p doping. Differences in capacitance and quality factor are shown. Two identical VCOs with the varactors having n gates or np gates are realized. Homogenous doping increases the VCO tuning range to 1.31 GHz (/spl plusmn/20%) in comparison to 1.06 GHz (/spl plusmn/15%) obtained by mixed doping. However, mixed doping has the advantages of more linear VCO frequency tuning, lower close-in phase noise, and reduced maximum sensitivity to variations in supply voltage. Several varactor parameters are introduced. They allow prediction of the influence of varactors on the performance of a given VCO. With a current consumption of only 1 mA from a supply voltage of 1.5 V, both VCOs show a phase noise of -115 dBc/Hz at 1-MHz offset from a 4-GHz carrier and a VCO figure of merit of -185.3 dBc/Hz.

A physical model of a CMOS varactor with high capacitance tuning range and its application to simulate a voltage controlled oscillator

A physical model of a CMOS varactor with high capacitance tuning range in multi-finger layout is presented. The model describes the voltage dependent capacitances and resistances and the parasitics due to connecting wires. Simulations of frequency tuning of a LC-oscillator employing the varactor are verified against measurements.

Voltage-controlled Substrate Structure for Integrated Inductors in Standard Digital CMOS Technologies

A new substrate structure for integrated inductors in standard CMOS technology is presented. It is comprised of alternating n � -well and p � -substrate regions. Through applying a voltage to the structure the semiconductor region below the inductor is depleted from mobile charge carriers up to a certain depth. Substrate losses due to parasitic capacitances and eddy currents are reduced. Without applied voltage the peak quality factor and the corresponding frequency is increased by 34% compared to an inductor without substrate structure. Through applying a voltage a total increase of quality factor by more than 41% and of resonance frequency by up to 56% is achieved.

A physical model of a CMOS varactor with high capacitance tuning range and its application to simulate integrated VCOs

Abstract A physical model of a novel MOS varactor design is presented. The voltage and frequency dependent results for the varactors small-signal capacitance and resistance agree well with measured values for different device geometries. The model is further tested through simulating a fully integrated voltage controlled oscillator (VCO) for UMTS applications. Measured frequency tuning and phase noise of the VCO are accurately reproduced.

A Varactor with High Capacitance Tuning Range in Standard 0.25um CMOS Technology

This paper presents a novel MOS varactor with outstanding capacitance tuning capabilities. Several test structures have been fabricated in standard digital 0.25μm CMOS technology. The novel varactor features a Cmax/Cmin ratio of 5.3:1. Quality factors range from 16 to 190 with an average Q of 86 at 2GHz. Thus it is outperforming all standard CMOS varactors reported up to now.