Ken Suyama

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.

Noise analysis of ideal switched-capacitor networks

This paper presents a method for computing the noise power spectral density (PSD) in switched-capacitor networks, Explicit formulas are developed for both white and 1/f noise sources. The 1/f noise is handled directly in the formulation without having to approximate its PSD by using a noise shaping filter. The technique eliminates the need for computing eigenvalues or matrix exponentials as well as solving bilateral matrix equations, and thereby leads to a numerically efficient algorithm. The noise sources considered here are the ON-resistances of MOS switches and the input referred noise PSDs of operational amplifiers (opamps). Experiments are carried out to demonstrate the validity of the formulation for both white and 1/f input noise.

Experimental verification of signal transmission using synchronized SC chaotic neural networks

The authors report experimental results of bidirectional signal transmission via chaotic signal using switched-capacitor chaotic neural networks whose neurons were fabricated in a 2-/spl mu/m CMOS process. >

Switched-capacitor chaotic neuron for chaotic neural networks

A switched capacitor implementation of a neuron model which exhibits chaotic behavior is presented. The model is based on the experimentally observed characteristics of a squid neuron. It is shown that the proposed circuit qualitatively replicates the response of the real neuron by extensive simulations using SWITCAP2 and simulated program with IC emphasis (SPICE). Various nonideal effects such as DC gain, input offset voltage, and parasitic capacitances associated with SC implementation are investigated and the operational amplifier offset voltage is identified as a major problem. An existing offset voltage compensation scheme is adopted to alleviate the problem.<<ETX>>

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.

Strange ways to use the MOSFET

This paper discusses uses of the MOSFET other than as a transconductor or switch. Several possibilities are reviewed, and new ones are described. The techniques discussed include the use of the MOSFET as a capacitor, as a linearized resistor, as a tunable distributed RC filter element, as a passive voltage amplifier, and as a discrete-time parametric amplifier; also described are resistive-gate MOSFETs and resistive gate/resistive body MOSFETs.

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.