Distortion produced by RF MEMS varactors on digital communication signals

This paper presents a study of the nonlinear effects introduced by MEMS varactors when excited with digitally modulated RF signals (QPSK and 16 QAM). The study is based on simulating a nonlinear model of the MEMS device using harmonic-balance and envelope solvers, and on experimental measurements of the wave reflected by the on-wafer MEMS device. It is shown that the adjacent-channel power ratio (ACPR) and error-vector magnitude (EVM) of the digital signal suffer a degradation due to the device nonlinear distortion.Peer Reviewe

Characterization of dynamics and power handling of RF MEMS using vector measurement techniques

This paper proposes a new method to measure dynamics and power handling of RF microelectromechanical systems (MEMS) devices based on a mobile membrane. The method uses in-phase/quadrature demodulation of an RF signal proportional to the reflection coefficient of the measured device, which contains information of its mechanical properties, such as actuation and release times and instantaneous position of the mobile membrane. Both one-port (capacitors) and two-port devices (switches and extended tuning-range capacitors) can be measured. Its main advantage is the capability of obtaining information from both magnitude and phase variations of the device reflection coefficient to characterize its dynamics and power handling. It is shown that detecting phase is advantageous in high quality factor capacitors, where the magnitude of the reflection coefficient is nearly constant for any position of the mobile membrane. Open-short-load calibration of the system is provided in order to obtain absolute measurements, which are necessary for power-handling characterization. The performances of the proposed method are demonstrated by comparison to systems based on detection of the magnitude of the reflection coefficient. A MEMS capacitor is characterized in terms of dynamics-actuation and release times, and mechanical resonance frequency and in terms of power handling-membrane instantaneous position and phase and tuning range variation.Peer Reviewe

Noise model of a reverse-biased Cold-FET applied to the characterization of its ENR

This paper presents a broadband-noise circuit model for a cold-FET (Vds = 0 V) with a reverse-biased gate. The noise model includes two intrinsic uncorrelated noise-current sources whose spectral densities are determined from measurement of the device's S parameters and noise powers. The model is used to characterize the device's excess noise ratio (ENR) for application to full receiver-noise calibration. Experimental results up to 40 GHz are given.Peer Reviewe

A Method for the Determination of a Distributed FET Noise-Model Based on Matched-Source Noise-Figure Measurements

A new method for the determination of a distributed FET noise model is presented. It is based on the extraction of the intrinsic noise-correlation matrix of an elemental section of the device from the device's noise figure, measured for only one source-impedance state at a number of frequency points. Experimental results up to 40 GHz are given.Peer Reviewe

Application of CAD load-pull techniques in mixer design

This work describes the application of a commercial CAD software to implement load-pull techniques in the design of microwave mixers. This method is used to generate conversion-loss regions when a diode is pumped and operated as a mixer circuit. Emphasis is placed on the inclusion of image and out-of-band terminations to optimize the operating conditions required to obtain low conversion loss. An X-band 5-dB conversion-loss mixer is designed and tested using this methodPostprint (published version

A Method to Simultaneously Extract the Small-Signal Equivalent Circuit and Noise Parameters of Heterojunction Bipolar Transistors

A method to extract the elements of the small-signal equivalent circuit and the noise parameters (NPs) of heterojunction bipolar transistors (HBTs) is presented. The extraction is done by simultaneous fitting of the measured S-parameters, noise figure (for a well-matched impedance), and NPs (estimated using the so-called F50 method). An additional error term, given by the root square sum of the differences between the NPs estimated from the F50 method and the NPs directly computed using the Hawkins model, is considered in order to avoid nonphysical results in the extraction of the intrinsic noise sources. To obtain the initial values of the equivalent-circuit elements, analytical expressions are applied under a number of bias conditions, namely, reverse bias, forward bias, and active bias. Experimental verification of the extraction of the equivalent-circuit elements and NPs of an HBT, up to 8 GHz, are presented, and the NPs are compared to those measured with an independent (tuner-based) method. The behavior of Fmin, extracted using the proposed method, as a function of the HBT collector current, is also presented.Peer Reviewe

Measurement of on-wafer transistor noise parameters without a tuner using unrestricted noise sources

The authors present a method for calibrating the four noise parameters of a noise receiver which does not require a tuner The method permits using general (mismatched) noise sources, which may present very different source reflection coefficients between their hot and cold states. The method is applied to the calibration of a noise set-up using on-wafer noise sources (a reverse-biased cold-FET and an avalanche noise diode). Experimental validation of the receiver calibration and its application to the determination Of on-wafer FET noise parameters to 40 GHz is presented.Peer Reviewe

Bias-dependence of FET intrinsic noise sources, determined with a quasi-2D model

The bias-dependence of microwave-FET intrinsic noise sources in their hybrid configuration is theoretically determined, using a new quasi-2D (Q-2D) physical model based on Thornber's current equation [8]. It is shown that the correlation coefficient cannot be neglected, in agreement with empirical work in the literature. Experimental verification using noise-parameter measurements up to 26 GHz is presented.Peer Reviewe

Application of CAD load_pull techniques in mixer design

This work describes the application of a commercial CAD software to implement load-pull techniques in the design of microwave mixers. This method is used to generate conversion-loss regions when a diode is pumped and operated as a mixer circuit. Emphasis is placed on the inclusion of image and out-of-band terminations to optimize the operating conditions required to obtain low conversion loss. An X-band 5-dB conversion-loss mixer is designed and tested using this method.Peer Reviewe

Study of intermodulation in RF MEMS variable capacitors

This paper provides a rigorous study of the causes and physical origins of intermodulation distortion (IMD) in RF microelectromechanical systems (MEMS) capacitors, its analytical dependence on the MEMS device design parameters, and its effects in RF systems. It is shown that not only third-order products exist, but also fifth order and higher. The high-order terms are mainly originated by the nonlinear membrane displacement versus applied voltage and, in the case considered in this study, with an additional contribution from the nonlinear dependence of the reflection coefficient phase on the displacement. It is also shown that the displacement nonlinear behavior also contributes to the total mean position of the membrane. In order to study these effects in depth, an analytical frequency-dependent IMD model for RF MEMS based on a mobile membrane is proposed and particularized to the case of a MEMS varactor-a device for which IMD can be significant. The model is validated, up to the fifth order, theoretically (using harmonic balance) and empirically (the IMD of a MEMS varactor is measured). To this end, a two-tone IMD reflection measurement system for MEMS is proposed.Peer Reviewe