Aleksander Dec

Micromachined electro-mechanically tunable capacitors and their applications to RF IC's

Micromachined electro-mechanically tunable capacitors with two and three parallel plates are presented. Experimental devices have been fabricated using a standard polysilicon surface micromachining process. The two-plate tunable capacitor has a measured nominal capacitance of 2.05 pF, a Q-factor of 20 at 1 GHz, and achieves a tuning range of 1.5:1, The three-plate version has a nominal capacitance of 4.0 pF, a Q-factor of 15.4 at 1 GHz, and a tuning range of 1.87:1. The tuning ranges achieved here are near theoretical limits. Effects due to various physical phenomena such as temperature, gravity, and shock are examined in detail. An RF voltage-controlled oscillator with an integrated inductor and a micromachined tunable capacitor is also demonstrated. The active circuit and the inductor have been fabricated in a 0.5 /spl mu/m CMOS process. The voltage-controlled oscillator has been assembled by bonding together the CMOS and the micromachined parts. The 1.35 GHz voltage-controlled oscillator has a phase noise of -98.5 dBc/Hz at a 100 kHz offset from the carrier.

Microwave MEMS-based voltage-controlled oscillators

A microwave voltage-controlled oscillator (VCO) based on coupled bonding wire inductors and microelectromechanical system (MEMS)-based variable capacitors for frequency tuning is demonstrated in this paper. The MEMS-based variable capacitors were fabricated in a standard polysilicon surface micromachining technology. The variable capacitors have a nominal capacitance of 1.4 pF and have a Q factor of 23 at 1 GHz and 14 at 2 GHz. The capacitance is variable from 1.4 to 1.9 pF as the tuning voltage is swept from 0 to 5 V. The VCO, fabricated in a 0.5 /spl mu/m CMOS technology, was assembled in a ceramic package where MEMS and CMOS dice were bonded together. The oscillator operates at 2.4 GHz, achieves a phase noise of -122 dBc/Hz at 1 MHz offset from the carrier, and exhibits a tuning range of 3.4%.

RF micromachined varactors with wide tuning range

Polysilicon surface micromachined varactors using two- and three-plate structures with 1.5:1 and 1.87:1 tuning ranges, respectively, are presented. The tuning ranges are near-theoretical limits and can be obtained within 4.4 V control voltage. The two-plate varactor has a nominal capacitance of 2.05 pF and a Q-factor of 20 at 1 GHz.

Noise analysis of a class of oscillators

This paper presents noise analysis of a class of oscillators, which can be modeled by a positive feedback system with a frequency-selective Mth-order filter, an ideal comparator, and a white noise source. An explicit analytical expression for the output power spectral density is derived. A simplified expression is obtained for a special case when the Mth-order filter is replaced by a second-order bandpass filter. The general expression is shown to reduce to a well-known result if a high and-factor filter is further assumed. Theoretical results presented here are verified by experiment.

A zipper-action differential micro-mechanical tunable capacitor

We present a differential multi-fingered micro-electro-mechanical tunable capacitor. This device is intended to be used in RF IC applications such as filters and VCOs. The device is based on the zipper actuation principle, which allows for potentially wide tuning range. Differential structure is used to improve the quality factor. This capacitor was fabricated in MUMPs polysilicon surface micromachining process and achieves 46% tuning range with tuning voltage of 35 V. A CMOS VCO with this capacitor exhibited tuning range of 4.8% with the center frequency of 1.5 GHz. The phase noise was -131 dBc/Hz at 600 kHz offset from carrier with the output power of 1.6 dBm.

Differential multi-finger MEMS tunable capacitors for RF integrated circuits

Several micro-electro-mechanical tunable capacitors fabricated in polysilicon surface micro-machining process are presented. These devices are based on parallel-plate and zipper actuation principles. Differential and multi-finger techniques are used to achieve higher quality factors. These devices are evaluated by direct measurements and by measuring phase noise of voltage-controlled oscillators that use these devices. A voltage-controlled oscillator with a two-finger parallel-plate variable capacitor shows the phase noise of -129 dBc/Hz at 600 kHz offset from the carrier while outputting 1.3 dBm and tuning between 1.81 GHz and 1.85 GHz. An experimental fractal capacitor with quality factor better than 17 at 1.5 GHz and capacitance varying from 1.9 pF to 6.7 pF is also presented.

A 10 GHz frequency-drift temperature compensated LC VCO with fast-settling low-noise voltage regulator in 0.13 µm CMOS

This paper presents an LC voltage controlled oscillator (VCO) with an integrated compensation circuit that reduces oscillation frequency drift due to temperature variations. The temperature compensation circuit consists of MOS inversion varactor as a compensation capacitor, and BJTs and resistors for temperature dependent voltage bias generation, and noise contribution suppression of a bias noise. The effectiveness of this technique is demonstrated in a 10 GHz LC VCO with a frequency divider (divide-by-2), output measurement buffer, and integrated fast-settling low-noise voltage regulator. The VCO achieves current consumption of 21.0 mA, tuning range of 10.68 GHz to 12.40 GHz, phase noise of − 109.9 dBc / Hz at 1 MHz offset from 6.12 GHz carrier. The VCO frequency-drift due to temperature is improved by 82 % with the compensation circuit.

A 1.9 GHz micromachined-based low-phase-noise CMOS VCO

Low-phase-noise microwave oscillators require capacitors and inductors with high Q-factors, since the phase noise of an oscillator is inversely proportional to the Q-factor of the resonant circuit. Often the frequency of oscillations must be electronically tunable, and hence, at least one of these reactive elements must be tunable. In practice, it is difficult to realize a high-quality electronically tunable inductor, and an electronically tunable capacitor is generally used. The CMOS inverter VCO takes advantage of the large voltage swing property of the micromachined tunable capacitor. The cross-coupled CMOS inverters realize the negative resistance and form the core of the oscillator.

Electro-mechanical properties of a micromachined varactor with a wide tuning range [for VCO]

This paper discusses the electro-mechanical properties of a new micromachined varactor structure that can achieve a wide tuning range. An experimental device was fabricated in a polysilicon surface micromachining process. The varactor achieves a tuning range of 40 percent and a quality factor of 9.75 at 1 GHz when the capacitance is set to 3.62 pF.

A 5GHz LC VCO with extended linear-range varactor in purely digital 0.15um CMOS Process

MOSFET varactors with two different threshold voltages are used for extending linear tuning range of a voltage controlled oscillator (VCO). This method is suitable for VCOs implemented in purely digital CMOS processes where MIM-capacitors are not available and only MOS transistors can be used for tuning element. The effectiveness of this technique is demonstrated in a 5GHz LC VCO with divide-by-2, output buffer, and integrated low-dropout voltage regulator. The VCO consumes 4mA of current and achieves a tuning range of 4.18–4.94GHz as well as phase noise of −109dBc/Hz at 1MHz from 4.5GHz carrier. The effective linear range has been extended by 38 percent.