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Carbon-based nanoelectromechanical devices are approaching applications in electronics. Switches based on individual carbon nanotubes deliver record low off-state leakage currents. Arrays of vertically aligned carbon nanotubes or nanofibers can be fabricated to constitute varactors. Very porous, low density arrays of quasi-vertically aligned arrays of carbon nanotubes behave mechanically as a single unit with very unusual material properties. [ABSTRACT FROM AUTHOR]

A varactor and FMR-tuned wideband band-pass filter (BPF) module with versatile frequency tunablity has been devised and realized on RT/Duroid substrate. By connecting four variable capacitance diodes (varactors) to the four open-circuited stubs of an X-band passive composite-BPF and adjusting the reverse bias voltage from 2 to 22 V, the 3 dB passband of the passive composite-BPF was continuously tuned from 7.7–12.4 GHz to 11.4–17.5 GHz. The corresponding bandwidth (BW) was enlarged from 4.7 to 6.1 GHz and the upper frequency of the passband was extended from 12.4 to 17.5 GHz, namely, a total frequency span of 9.8 GHz. The BW of the passive composite-BPF was further FMR-tuned using a pair of Band-Stop Filter (BSF). By setting the reverse bias voltage at 22 V together with the bias magnetic fields at 3250 and 4200 Oe, respectively, to the two BSFs, the 6.1 GHz BW and 9.8 GHz frequency span were compressed to 1.4 GHz toward the high-end frequency. The 4.7 GHz BW and 9.8 GHz frequency span were also compressed to 1.0 GHz toward the low-end frequency with 2650 and 3500 Oe bias magnetic fields and 2 V reverse bias voltage. Thus, the combination of the varactor and FMR-tuning has facilitated versatile passband and its BW tuning covering the X-and Ku-bands with both large frequency tunability and greatly improved frequency selectivity. [ABSTRACT FROM AUTHOR]

In this paper, an X-band low phase-noise voltage-controlled oscillator (VCO) using a novel electronically tunable substrate integrated waveguide (SIW) resonator is proposed and developed for RF/microwave applications on the basis of the substrate integrated circuits concept. In this case, the resonant frequency of the SIW cavity resonator is tuned by different dc-biasing voltages applied over a varactor coupled to the cavity. Measured results show that the tuning range of the resonator is about 630 MHz with an unloaded Q U of 138. Subsequently, a novel reflection-type low phase noise VCO is developed by taking advantage of the proposed tunable resonator. Measured results demonstrate a frequency tuning range of 460 MHz and a phase noise of 88 dBc/Hz at a 100-kHz offset over all oscillation frequencies. The VCO is also able to deliver an output power from 6.5 to 10 dBm. This type of VCO is very suitable for low-cost microwave and millimeter-wave applications. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the paper below is to present the design approach, manufacture process and measurement results of a complete phase shifter for Ku band controlled electronically. The phase shifter is based on microstrip technology and tunable reflective lines with varactor technology. This device allows to establish more than 360°phase variation with low insertion losses (2dB in average), compared with devices found in literature. In this paper, a 12GHz tunable phase shifter is analyzed, designed, simulated and prototyped. Eventually, prototype measurements are shown. [ABSTRACT FROM AUTHOR]

A reconfigurable planar inverted-F antenna using a switchable PIN-diode and a fine-tuning varactor is presented for mobile communication applications. Selection of operating modes is achieved by switching the PIN-diode between radiators and tuning the varactor on an antenna's shorting line. Mode I, with the PIN-diode off and tuning the varactor, operates for USPCS (1.85-1.99 GHz), WCDMA (1.92-2.18 GHz), and WLAN (5.15-5.825 GHz). As a result, the varactor used to achieve frequency fine-tuning does not need a DC bias circuit and can expand the bandwidth without increasing the physical size. Mode II, with the PIN diode on and the fixed 0-V varactor, operates for USPCS and m-WiMAX (3.4-3.6 GHz). To optimize the antenna structure, a parametric analysis is performed by sweeping the length and width of the radiators. Furthermore, equivalent models of a PIN diode and a varactor are presented for accurate prediction of antenna performances which are also analyzed by varying diode parameters. All simulated results are confirmed with measured data. The peak gains show 2.84, 2.81, 1.25, and 1.49 dBi at USPCS, WCDMA, m-WiMAX, and WLAN, respectively. [ABSTRACT FROM AUTHOR]

We report on the design, fabrication, and characterization of an 840-900-GHz frequency multiplier chain that delivers more than 1 mW across the band at room temperature with a record peak power of 1.4 mW at 875 GHz. When cooled to 120 K, the chain delivers up to 2 mW at 882 GHz. The chain consists of a power amplifier module that drives two cascaded frequency triplers. This unprecedented output power from an electronic source is achieved by utilizing in-phase power-combining techniques. The first stage tripler uses four power-combined chips while the last stage tripler utilizes two power-combined chips. The source output was analyzed with a Fourrer transform spectrometer to verify signal purity. [ABSTRACT FROM AUTHOR]

Abstract: This paper focuses on design of high-performance MEMS LC-tank circuit for use in CMOS voltage controlled oscillators (VCO) operating at 2.4GHz. The high-Q air suspended inductor has been designed by inductance of 2.87nH using MEMS technology to reduce the resistive loss and the substrate loss. A MEMS two-gap tunable capacitor has been designed. The DC voltage is 2.5V which is applied to the plates and the results of 2.04pF could be achieved. The pull-in voltage has been optimized to achieve low phase noise, low power consumption VCO. Through this optimization, less phase noise (−117.7dBc/Hz at 100KHz) and lower power consumption (11mW) have been obtained. [Copyright &y& Elsevier]

In this paper a novel quadrature generator is presented that exhibits a 110% operating frequency bandwidth. Existing circuits are unable to provide a quadrature signal over such a large fractional bandwidth. They are also highly susceptible to component tolerances that can often shift the center operating frequency rendering the circuit unusable. In this work, this issue is mitigated with the use of a negative feedback network that is able to actively compensate the circuit using varactors to match the operating frequency. In this manner, the bandwidth of the quadrature generator can be significantly increased. Simulation results show an operating frequency span from 1 to 6 GHz while maintaining a phase error below 5° and ±2 dB in amplitude error. The circuit, without bonding pads, uses an area of only 0.17 mm2. [ABSTRACT FROM AUTHOR]

A novel, tunable miniaturized-element frequency-selective surface that does not require additional bias networks is presented. This spatial filter is composed of two wire-grids printed on opposite sides of a substrate and connected to each other with an array of varactors using plated via holes. Varactor diodes are positioned between the grids. Via sections and metallic pads are fabricated and create a dc path for biasing the varactors with the grids themselves. This configuration eliminates the need for any additional network, and therefore resolves the design difficulties associated with the spurious response of the bias network. An equivalent circuit model is developed to facilitate the design procedure. Full-wave numerical simulations are used to validate the results based on the circuit model. Simulations show that by altering the capacitance of the varactors from 0.1 to 1 pF, a frequency tunability from 8 to 10 GHz with an almost constant bandwidth can be achieved. [ABSTRACT FROM AUTHOR]

This paper presents complete behavioral analysis of a surface micro-machined MEMS varactor for frequency tuning application in voltage controlled oscillators in RF applications with high Quality factor and tunability. The dimensions of the MEMS device have been optimized with Finite Element Method based CoventorWare analysis and verified through lumped parameter analysis in Saber platform. The MEMS varactor has been fabricated with the PolyMUMPs process. The paper also describes the Mechanical and electrical characterization of the MEMS varactor to meet the designed specification. [ABSTRACT FROM AUTHOR]

The application of varactor diodes as phase-shifting devices in reflectarrays has received considerable attention because it represents a low-cost and low-complexity solution for the creation of scanning antennas with continuous phase tuning. The main issues related to the design of varactor- loaded reflectarrays are the difficulty in the correct characterization of the unit cell, and the limited phase range achievable by changing the polarization voltage of the device. The contribution presented in this communication attempts to cover both these aspects. In particular, a simple model for the analysis of a varactor-loaded microstrip reflectarray cell is presented, and then employed to increase the patch's phase response to 360° . The result is then validated experimentally, with the results showing good agreement between simulated and measured data. [ABSTRACT FROM AUTHOR]

Abstract: A measurement method to measure biopotentials with a passive LC resonator is presented. The sensor consists of an LC resonance circuit where the capacitive component is a varactor and the biopotential electrodes are connected over the varactor ends. This induces a change in the varactor capacitance which can be measured over an inductive link as modified reflected impedance. The sensor itself dissipates virtually no energy at all but of course, some energy is lost in form of resistive losses in the sensor wires and components. The sensor is inexpensive to manufacture and since it is a totally passive device, it is very suitable for implantable applications. Two different measurement methods to sense the reflected impedance are also presented: a slope detector and a phase locked detector. Measurement results from human ECG are discussed that are measured with the both suggested measurement methods. The sensor is proven to be suitable for biopotential measurements with some limitations regarding the movements between the sensor and the receiver device. The properties and performance of the two different measurement devices are discussed. The measurement range, i.e. distance between the sensor and the measurement coils was approximately 5cm in air for the both measurement devices. However, it seems that the phase locked measurement device suits better to the measurements than the slope detector since its signal-to-noise ratio remains almost constant throughout the measurement range (distance). [Copyright &y& Elsevier]

The radio-frequency (RF) performance of a 65-nm RF technology is assessed. The RF CMOS was fabricated with a physical gate length of 60 nm. In addition to the deep-n-well and p+-guard-ring isolation, a multi-poly-finger layout and fabrication process is optimized to improve the CMOS device RF performance. A superior cutoff frequency fT of 250 GHz and a maximum oscillation frequency fmax of 220 GHz for the n-MOSFETs (NMOS) have been achieved. The minimum noise figures (A Fmin's) are around 0.2 and 0.3 dB at 2.4 and 5.8 GHz, respectively. n+/n-well accumulation-mode MOS varactors, inductors, and metal-oxide-metal (MOM) capacitors are integrated with CMOS devices in a single chip by a standard logic process without extra masks. The tuning ratio of the varactor can be up to 12 with a peak quality (Q) factor of 20. The polysilicon-patterned ground shield and 3.7-µm-thick Cu metal process are implemented to improve the Q factor of the inductors. The structure and performance of the MOM and metal-insulator-metal capacitors are benchmarked, and a mesh structure is proposed to reduce the mismatch of the MOM capacitors. [ABSTRACT FROM AUTHOR]

Abstract: Based on the understanding of the relation between the shape of the LC VCO tuning curve and the varactor characteristics, a technique using an array of unequal varactors with different bias was found to obtain a truly linear tuning curve. An LC VCO was designed using TSMC 0.13μm 1.2V/3.3V IO process, the VCO frequency varies from 1.9 to 2.7ghz as its control voltage varies from 0 to 1.2V. The tuning gain was KVCO =630MHz/V ±9.5%. [Copyright &y& Elsevier]

A reconfigurable tuner is demonstrated by using a low-loss shielded coplanar waveguide transmission line periodically loaded with CMOS transistor switches in series with capacitors. The switch-capacitor combination is used to change the local impedance of the transmission line in a binary fashion. It achieves a higher capacitance ratio (by 60%), less transmission loss (by 40%), higher quality factor (by 100%), and subsequently wider band- width and better Smith impedance chart coverage compared to optimized CMOS varactors realized in the same technology. The 5-16-GHz tuner demonstrated here is implemented in a standard 0.13-μm CMOS technology and can be configured to 220 different impedances through an integrated 20-bit shift register. [ABSTRACT FROM AUTHOR]

Main operating modes of varactor frequency doublers of microwave systems are considered. A closed system of equations and couplings are obtained that allows complete analysis and synthesis of doublers to be performed. [ABSTRACT FROM AUTHOR]

The design and implementation of an X-band phase shifter MMIC using the standard 0.18-μm CMOS process is presented. A transformed doublet varactor load is analyzed and applied to a 3-dB quadrature coupler to exhibit large phase shift tuning range and low insertion loss with minimal variation. By using the derived design equations, the implemented CMOS reflection-type phase shifter demonstrates a continuous phase shift tuning range greater than 185°, an average insertion loss of 5.2 dB with ±0.4 dB variation, and return losses better than 13 dB in 9–11 GHz. The total chip size including I/O pads is 0.76 × 0.79 mm2. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 645–648, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24131 [ABSTRACT FROM AUTHOR]

This paper highlights recent developments and challenges on beam steering characteristics of reconfigurable transmitarray antennas. It introduces the operating principle of beam forming/beam steering high gain transmitarray antennas to enable the user to opt for economical and high performance solutions. A transmitarray antenna typically consists of a source antenna and a phase transformation structure. The incident waves generated from the source antenna is tilted using the phase transformation structure in a desired direction to steer the beam. Moreover, the phase transformation structure alters the incident wavefront to a plane wavefront using phase change characteristics. In order to steer a beam to a specific desired angle, it can be divided into two methods. There is a method of applying a transmitarray with a variable transmission phase change or a method of changing the shape of the wavefront of the source antenna. This type of beam forming/beam steering high gain antenna has been mainly studied from the point of view of high efficiency, low profile, and low cost. Several solutions of transmitarray unit cells have been presented in the literature, using PIN diodes, varactors, MEMS switches, and microfluids enable electronics to realize reconfigurable characteristics of transmitarray antennas. This paper analyzes the characteristics of various beam steering high gain reconfigurable transmitarrays (RTA) and highlights the future opportunities and challenges of the structure design for transmitarray antennas. This paper also highlights the challenges and gaps in terahertz and optical frequencies related to future work due to the structure complexity and lack of components' availability. Moreover, the challenges and limitations related to multi-bit structures and dual-band requirements are presented. [ABSTRACT FROM AUTHOR]

A near-field direct antenna modulation (NFDAM) technique is introduced, where the radiated far-field signal is modulated by time-varying changes in the antenna near-field electromagnetic (EM) boundary conditions. This enables the transmitter to send data in a direction-dependent fashion producing a secure communication link. Near-field direct antenna modulation (NFDAM) can be performed by using either switches or varactors. Two fully-integrated proof-of-concept NFDAM transmitters operating at 60 GHz using switches and varactors are demonstrated in silicon proving the feasibility of this approach. [ABSTRACT FROM AUTHOR]

This article presents a novel tunable sharp notch filter using open stub structure with varactor for implementing detect-and-avoid method into ultrawideband radio system. On the basis of the experimental results on the open stub structure with lumped capacitor, we introduced two techniques in this work to realize a tunable sharp notch filter using open stub structure with varactor to perform narrow stopband and using resistors to build a DC bias circuit, so that no influence to the tunable notch filter over a wide band. The developed tunable notch filter has excellent performance: wide tuning range from 3.65 to 4.35 GHz with low tuning voltage from 0 to 6 V, narrow bandwidth less than 270 MHz of the notch filter (at 10 dB insertion loss at 0 V), and compact size of the developed filter: about 2.0 cm × 4.0 cm. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2712–2715, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23773 [ABSTRACT FROM AUTHOR]

CMOS reflection-type phase shifters with minimal insertion-loss variation over quadrants of phase-shift range are presented. Two performance enhancement techniques are proposed. First, the 3-dB quadrature hybrid is designed with a phase-compensated inductively coupled hybrid. Second, an impedance-transformed π-resonated varactor network is presented to provide a full 3600 phase range, using a MOSFET varactor with limited reactance variation range. The design considerations and simulation are described. Two experimental 2.45-GHz phase shifters were implemented in 0.18-µm CMOS technology. One has a measured phase-shift range of 120° with the insertion loss of 5.6 ± 1.2 dB in 2.33-2.60 GHz and the other has a phase range larger than 340° with the insertion loss of 10.6 ± 2 dB in 2.44-2.55 GHz. Both chips are extremely compact with sizes of 0.72 and 0.66 mm², respectively, and consume zero dc power. [ABSTRACT FROM AUTHOR]

Abstract: Parametric amplification of magneto-inductive (MI) waves propagating in magnetically coupled chains of nonlinear L–C resonators is studied. Analysis is first presented for a three-frequency travelling wave scheme in which the signal, idler and pump all propagate as MI waves. The effect of de-coupling the idlers is then considered and it is shown that this configuration relaxes the standard phase matching condition. Confirmation of the theory is provided using low-frequency PCB unit cells containing varactor diodes. The cells are characterised individually and then arranged as a 16-element ring resonator. Frequency matching and selective amplification of the primary resonance is demonstrated. The primary resonance can be excited using the field of a rotating magnetic dipole, and an application in magnetic resonance imaging is described. [Copyright &y& Elsevier]

This paper describes an analytic design procedure for microstrip tunable filters. Step-impedance resonators are employed and loaded with varactors for achieving agility in the filter response. Fixed lumped capacitors are utilized as admittance inverters in order to minimize the number of varactors in the filter. An analytic approach for filter design makes it possible to achieve a tunable filter showing the same frequency response when the center frequency is adjusted. A two-pole microstrip tunable filter whose center frequency can be adjusted from 1.1 to 1.5 GHz is designed to demonstrate the validity of design theory. A prototype tunable filter operating from 2.1 to 2.7 GHz is also designed and measured. A good agreement between the measured and simulated results is shown. Finally, three- and four-pole tunable filters are designed to show straightforward application of the presented design method to higher order tunable filter design. [ABSTRACT FROM AUTHOR]

Abstract: In this work we report on the small and large signal behaviour of advanced nMOS varactors fabricated in FinFET technology. This is the first paper showing large signal network analyzer (LSNA) measurements performed on FinFET varactors. These nonlinear measurements are modeled with a lookup table based model that is constructed using an accurate multi-bias small signal equivalent circuit. The validity of the extracted small and large signal models is verified through the very good agreement between measurements and simulations. [Copyright &y& Elsevier]

Low-loss tunable filters with three different fractional-bandwidth variations were designed and fabricated ϵr = 2.2,0.787 mm Duroid substrates for 850-1400-MHz applications. A detailed analysis for realizing predefined bandwidth characteristics is presented, and a design technique to take into account the source and load impedance loading is discussed. It is found that independent electric and magnetic coupling makes it possible to realize three different coupling coefficient variations with the same filter structure. The proposed topology is different from the comb-line design in that all three filters have identical electrical lengths, the same varactors, and the same filter Q values. Three different filters are built using Schottky varactor diodes with a tuning range from ∼ 850 to ∼ 1400 MHz. The constant fraction-bandwidth filter has a 1-dB bandwidth of 5.4% ± 0.3% and an insertion loss of 2.88-1.04 dB. The decreasing fractional-band- width filter shows a 1-dB bandwidth decrease from 5.2% to 2.9% with an insertion loss of 2.89-1.93 dB (this is effectively a 40-45-MHz constant absolute-bandwidth filter). The increasing fractional-bandwidth filter shows a 1-dB bandwidth increase from 4.3% to 6.5% with an insertion loss of 3.47-1.18 dB. The measured Q of the filters are between 53-152 from ∼ 850 to ∼ 1400 MHz. The measured third-order intermodulation intercept point ranges from 11.3 to 20.1 dBm depending on the bias voltage. To our knowledge, these planar tunable filters represent state-of-the art insertion-loss performance at this frequency range. [ABSTRACT FROM AUTHOR]

Microelectromechanical systems (MEMS) technology has been used for realizing G-band (140-220 GHz) distributed MEMS transmission line components. Novel dielectric-less MEMS components, as well as switched MEMS capacitors, have been fabricated with CMOS compatible surface micromachining, and experimental results are presented up to 220 GHz. [ABSTRACT FROM AUTHOR]

This study proposes the concept of frequency tuning for an electrically small antenna to be used in wideband applications in low frequencies. An electrically small antenna has too narrow bandwidth to be utilized for wideband systems. However, in such mobile TV services that the band is composed of each sub channel in VHF band, the narrow bandwidth can be appropriately utilized with wideband frequency tuning. That is, each service channel is covered by the narrow resonant band of a small sized radiator and the entire service band is satisfied by moving its frequency. To prove the idea of this study, a small helical antenna with the size of less than λ/10 is chosen as a sample and the T-DMB service, a kind of the mobile TV services allocated to 200-MHz band, is selected for testing. With the designed tuning circuit constituted of lumped elements and a varactor, a low impedance of the small radiator is matched to about 50 Ω and the wide bandwidth is satisfied by moving its narrow resonant frequency. The validity of the proposed antenna is also proved by the receiving measured result. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 244–247, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23049 [ABSTRACT FROM AUTHOR]

Abstract: We present here two examples of metamaterials for applications in the telecoms domain. The first concerns the realization of an ultra compact directive electronically reconfigurable antenna. The second deals with an infrared left-handed metamaterial working under normal incidence. For the first application, we use a composite phase varying metamaterial. An adjustable resonance radiating frequency between 7.9 and 8.2 GHz is obtained and a drastic enhancement in the directivity of the antenna is observed for a cavity thickness as small as (0.5 mm!). Concerning the second application we present simulations and measurements of a metamaterial made of gold wires and C-shaped nanostructures on silicon at infrared wavelengths. Both plasmonic resonances occur at 1.7 and 4.2 μm, corresponding to a simultaneously negative permittivity and permeability. A simplified version of this metamaterial is realized in the microwave domain. This new metamaterial is characterized and the left-handed behavior is experimentally demonstrated. To cite this article: B. Kante et al., C. R. Physique 9 (2008). [Copyright &y& Elsevier]

The engineering and tradeoffs for quality factor, capacitance tuning ratio, capacitance mismatch, and low-frequency noise for different varactor device structures, geometry sizes, and operations have been compared to provide a comprehensive guideline of an optimized structure for the advanced radio-frequency voltage-controlled oscillator (VCO). Compared with junction varactors, n+/n-well (NW) MOS varactors exhibit a higher capacitance tuning ratio (∼3) and a superior capacitance mismatch (< 0.1} % for a drawn size of 25 μm²). However, a noticeable low-frequency noise (∼10-18 A²/Hz) was observed in the accumulation-mode n+ /NW MOS varactors. A derived figure of merit in selecting a suitable varactor in terms of VCO's phase noise has been proposed for the first time. The measurement was performed by using the 0.18-μm 1P6M with AICu backend wafer. [ABSTRACT FROM AUTHOR]

A reflection-type phase shifter with constant insertion loss over a wide relative phase-shift range is presented. This important feature is attributed to the salient integration of an impedance-transforming quadrature coupler with equalized series-resonated varactors. The impedance-transforming quadrature coupler is used to increase the maximal relative phase shift for a given varactor with a limited capacitance range. When the phase is tuned, the typical large insertion-loss variation of the phase shifter due to the varactor parasitic effect is minimized by shunting the series-resonated varactor with a resistor Rp. A set of closed-form equations for predicting the relative phase shift, insertion loss, and insertion-loss variation with respect to the quadrature coupler and varactor parameters is derived. Three phase shifters were implemented with a silicon varactor of a restricted capacitance range of Cv,min = 1.4 pF and Cv,max = 8 pF, wherein the parasitic resistance is close to 2Ω. The measured insertion-loss variation is 0.1 dB over the relative phase-shift tuning range of 237° at 2 GHz and the return losses are better than 20 dB, excellently agreeing with the theoretical and simulated results. [ABSTRACT FROM AUTHOR]

We construct a synthetic left-handed transmission line with cascaded varactors and shunt inductors. By modulating dc bias, the capacitance of the varactors can be changed and modulation of the output phase state is possible. For frequencies from 4.7 to 6.4 GHz, a very linear phase variation versus voltages of over 2000 phase variation with low insertion-loss variation (±0.5 dB) is demonstrated. This circuit can also act as an efficient harmonic generator when a large signal is applied. Since the left-handed transmission line shows high-pass filter response, harmonics generated are not seriously attenuated. However, because this synthetic transmission line is a very dispersive medium, strong dispersions and instabilities may arise. The circuit size and determined by the diode size and lumped-element inductor, allowing it to be compact. [ABSTRACT FROM AUTHOR]

This paper presents a novel cost-effective microwave phase-shifter technology using thick-film ferroelectric varactors as the tuning component. The devices are fabricated by conventional screen-printing techniques with silver/platinum as the conducting layers and Ba0.7 Sr0.3 TiO3 as the tunable dielectric layer. The microwave performance of the ferroelectric varactors is optimized in terms of both material process parameters and the varactor gate area dimensions. S-parameter measurements on a tunable reflective circuit are used to evaluate the performance of the varactor at around 2 GHz. The varactor parameters such as RF capacitance, tunability, and the Q factor of the varactor are studied as a function of the gate dimension. At 100-V dc-biasing voltage, the BSTO varactor loaded tunable reflective circuit exhibits a differential phase shift of 70° with a return loss of -1.2 dB. This is equal to a figure-of-merit value of 58°/dB. Full analog reflection-type and all-pass network phase shifters are also implemented in order to explore the monolithic integration of phase control devices into the RF system based on low-cost ceramic thick-film technology. [ABSTRACT FROM AUTHOR]

A tunable matching network (TMN) based on ferroelectric capacitors for cellular power-amplifier applications was designed, fabricated, and tested. When the matching network is operated for GSM850/900 frequency bands, the input impedance varied from 3.44 – jl.87 to 3.55 – j0.02 Ω with a power gain variation of -1.35 to -1.62 dB. When the circuit is operated for digital communication system/personal communication system/wideband code division multiple access frequency bands, the input impedance varied from 4.28 - j0.06 to 4.31 + j0.97 Ω with a power gain variation of -2.05 to -1.79 dB. The nonlinearity of the TMN was also characterized on an on-wafer load-pull system using a 1.95-GHz test signal with CDMA2000 and high-speed downlink packet access modulation strings. [ABSTRACT FROM AUTHOR]

Logic CMOS-based RF technology is introduced for a 10-Gb transceiver in which active and passive RF devices have been realized in a single chip. RF nMOS of 115-GHz fT, 100-GHz fmax, and sub-1.0-dB NFmin at 10 GHz have been fabricated by aggressive device scaling and layout optimization. High-Q MiM capacitor and spiral Cu inductors have been successfully implemented in the same chip by 0.13-μm low-K/Cu back end of integration line technology. Core 1.0 V MOS and/or junction varactors for VCO at 10 GHz are offerings free of extra cost and realized by the elaborated layout. [ABSTRACT FROM AUTHOR]

Three different configurations of liquid-crystal tunable capacitors were investigated, including fractal structures, comb structures, and square structures. The tuning ranges of the fractal structures, the comb structures, and the square structures at 4 GHz from 0 to 5 V were found to be 8.81%, 7.17%, and 11.85%, respectively. The square structures have the largest tuning ranges mostly because of the uniform electric fields dominated. The Q-values of the fractal structures, the comb structures, and the square structures at 4 GHz with an operation voltage of 5 V were 68.2, 98.3, and 31.0, respectively. Compared to the other two structures, the square structures perform the highest inductive effects, leading to the lowest Q-values. In addition, the liquid crystals with different chiral doping concentrations were injected into the capacitor structures to investigate the impact of different liquid crystals on the tunable capacitors. The threshold voltages (Vth) increase as the chiral doping concentrations enlarge. The steepness of the C-V curves increases as the chiral doping concentrations reduce. Furthermore, a liquid-crystal capacitor model was developed to qualitatively illustrate the performance of the liquid-crystal tunable capacitors. The model prediction and the measurement results were highly correlated. [ABSTRACT FROM AUTHOR]

A complete digitally controlled oscillator (DCO) system for mobile phones is presented with a comprehensive study. The DCO is part of a single-chip fully compliant quad-band GSM transceiver realized in a 90-nm digital CMOS process. By operating the DCO at a 4 × GSM low-band frequency followed by frequency dividers, the requirement of on-chip inductor Q and the amount of gate oxide stress are relaxed. It was found that a dynamic divider is needed for stringent TX output phase noise while a source-coupled-logic divider can be used for RX to save power. Both dividers are capable of producing a tight relation between four quadrature output phases at low voltage and low power. Frequency tuning is achieved through digital control of the varactors which serve as an RF DAC. Combining a MIM capacitor array and two nMOS transistor arrays of the varactors for the RF DAC, a highly linear oscillator gain which is also insensitive to process shift is achieved. The finest varactor step size is 12 kHz at the 1.6–2.0 GHz output. With a sigma-delta dithering, high frequency resolution is obtained while having negligible phase noise degradation. The measured phase noise of -167 dBc/Hz at 20 MHz offset from 915 MHz carrier and frequency tuning range of 24.5% proves that this DCO system can be used in SAW-less quad-band transmitters for mobile phones. [ABSTRACT FROM AUTHOR]

Ferroelectric capacitors made from Ba 1-x Sr x TiO 3 (BST) are applied as varactors in tunable, high frequency circuit applications. In this context, a voltage-controlled oscillator (VCO) is studied. VCOs are integral parts of phase locked loops, clock recovery circuits and frequency synthesizers and thus are widely used in both discrete and on-chip applications. Ferroelectric varactors are capable of out-performing solid-state varactors at microwave frequencies, due to their lower parasitic series resistance that leads to a higher Q-factor. In VCO implementations, this higher Q leads in turn to lower phase noise, a critical quality for these circuits. A VCO design is presented and the performance of ferroelectric varactors is compared with solid-state varactors. [ABSTRACT FROM AUTHOR]

A multi-rate 9.953-12.5-GHz low phase noise LC oscillator was realized in a 90-GHz fT 0.2 µm SiGe BiCMOS process. It achieves a 36% tuning range by combining a 35% open-loop frequency calibration range having a sub-0.1% residual error with a 1% closed-loop varactor frequency tuning. The oscillator gain is below 130 MHz/V, while having less than 10% variation over the entire tuning range. The varactor is realized with multiple parallel-connected cells consisting of constant capacitors and voltage-controlled resistors that bring a lower process variation and a higher quality factor in comparison with standard diode and MOS varactors. A dual regulator architecture was used to provide both high PSRR and low output voltage noise. The supply pushing was reduced below 100 kHz/V by using a pushing cancellation circuit that balances the negative and positive voltage coefficients of the different nonlinear capacitors connected to the LC tank. A discrete-time automatic amplitude control loop using a variable tail resistor architecture was implemented to optimize the VCO's phase noise performance. The VCO specifications include 9.953-12.5-GHz frequency range, 0.1% frequency calibration error, -122 dBc/Hz phase noise at 1 MHz offset, < 3 kHz 1/f³ corner frequency, < -80 dBc spurious tones, 250 × 400 µm² die area and 5-mA bias current from a 3.3-V supply. [ABSTRACT FROM AUTHOR]

A new technique for designing dual-band reconfigurable slot antennas is presented. Dual-frequency operation is achieved by loading a slot antenna with two lumped variable capacitors (varactors) placed in proper locations along the slot. Loading the slot antenna with lumped capacitors shifts down the resonant frequencies of the first and second resonances of the antenna. However, these frequency shifts depend not only on the values of the capacitors, but also on their locations along the slot antenna. Here, it is shown that by choosing the locations of the varactors appropriately, it is possible to obtain a dual-band antenna whose first and second resonant frequencies can be controlled individually. In other words, the frequency of either the first or the second band can be fixed, while the other one is electronically tuned. Using such a design, an electronically tunable dual-band antenna is designed and fabricated using two identical varactors having a capacitance range of 0.5-2.25 pF. The antenna is shown to have a frequency ratio (fR=f2/f1) ranging from 1.3 to 2.67. An important feature of this antenna is its consistent radiation pattern, polarization, and polarization purity at both bands and across its entire tunable frequency range. [ABSTRACT FROM PUBLISHER]

A new technique for designing dual-band reconfigurable slot antennas is introduced. The technique is based on loading a slot antenna with a lumped capacitor (or varactor) at a certain location along the slot. Given a fixed capacitor location along the slot, decreasing the capacitance results in increasing the first and second resonant frequencies of the slot antenna. However, the changes in the resonant frequencies are significantly different for the first and second resonances and, hence, a dual-band antenna with considerable frequency ratio tuning range can be obtained. Based on this technique, an electronically tunable dual-band antenna with a frequency ratio in the range of 1.2-1.65 is designed and fabricated using a single varactor with a capacitance range of 0.5-2.2 pF. The antenna has similar radiation patterns with low cross-polarization levels at both bands and across the entire tunable frequency range. [ABSTRACT FROM PUBLISHER]

Silicon carbide (SiC) offers significant advantages for microwave high power devises due to its unique electrical and thermal properties. This review presents a summary of the current position in the development of silicon carbide diodes operating at microwave frequencies: varactors, Schottky barrier mixer diodes, p-i-n and IMPATT diodes. Simplified theory of device operation is given for each kind of microwave diodes to derive the figures of merit, to estimate the potential silicon carbide performance for fabrication of these diodes and to compare SiC with conventional semiconductors. These analyses are followed by description of diode design, fabrication and measured characteristics. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes an up-converter circuit for a TV tuner chain that can be implemented in both analog and digital TV systems. The circuit is integrated into a low cost standard two metal layer 0.8μm SiGe technology and is composed with class AB Gilbert cell based active mixer and differential voltage-controlled oscillator (VCO). The use of a high quality balanced inductor in the VCO allows achieving a measured oscillator phase noise of −104.2dBc/Hz at 100kHz from the carrier. The frequency conversion is from TV standard IF to RF. The results obtained in a frequency up-conversion from 36 to 1775MHz are: a conversion gain of −2.25dB, a noise figure of 14.4dB and an OIP3 value of 9.1dBm. The core power consumption is 33mA from 5V power supply. [Copyright &y& Elsevier]

This work describes three variations of pattern-reconfigurable microstrip parasitic arrays (RMPAs) and provides measured results for each. Variation 1 uses two switches to reconfigure the radiation pattern into three directions in the H-plane. Variation 2 uses two varactors to scan the radiation pattern between -27° and 27° in the H-plane by controlling the value of the varactors. Variation 3 uses two inductors and varactors in series so that the scannable range of the H-plane pattern is from ±32° to ±54°. Each variation has a common 2:1 VSWR bandwidth throughout the switching and/or scanning of the radiation pattern. Copper strips or capacitors are used instead of switches or varactors for proof of concept. These three variations have potential applications in both mobile-communication devices and multiple-input multiple-output (MIMO) systems. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 369–372, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20826 [ABSTRACT FROM AUTHOR]

In this paper, a 5-GHz fully integrated voltage-controlled oscillator (VCO) using an InP-based RTD/HBT technology is demonstrated for the first time. A figure of merit for the oscillator is obtained to be -180.8 dBc/Hz. In addition, the VCO has demonstrated a wide tuning range of 710 MHz at 5 GHz. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 408–411, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20838 [ABSTRACT FROM AUTHOR]

Abstract: A new class of semiconductor devices is proposed with electrically controlled electrode’s area. It is shown that by implementing this basic idea within the commonly available technology one is able to construct the varactors (varicaps) with almost any prescribed C–U characteristic in contrast to severely limited functionality of traditional devices. More importantly, very promising new devices (which we call semiconductor capacitive transformers—SCTs) can be produced using these varactors. In contrast to known semiconductor devices SCTs are able to overcome the fundamental electronic constraint on the maximum power handling capability, which is currently a real stumbling block for any semiconductor device due to final velocity of mobile charge carriers and junction breakdown. SCT-based ultra-high-power frequency transducers and capacitive transformers can be easily fabricated by means of standard planar technology and are expected to replace bulky inductive transformers in high-frequency and microwave integrated circuits. Also described are some ‘proof-of-the-concept’ experiments performed by the authors. Results obtained are very encouraging. [Copyright &y& Elsevier]

A variable-capacitance (varactor) diode is widely applied in microwave devices, which utilize the characteristic property that the junction capacitance is varied by an externally applied voltage. In applications of capacitance-controlled devices, such as voltage-controlled oscillators, the capacitance is varied by the control-bias voltage, whereas the variation in capacitance for microwave RF-signal voltages should be minimized in order to suppress higher-order distortions in the output signal. The capacitance-voltage characteristic of a varactor diode is characterized by a slope exponent γ. This article discusses the slope exponent that gives a minimum of variation in capacitance for the microwave excitation in the circuit in which diodes are connected in anti-series. The analysis is based upon a time-domain-oriented method, in which we first obtain the voltage and current waveforms by solving differential equations with respect to time and then calculate the frequency-domain quantities by Fourier analysis of voltage and current waveforms. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14: 274–282, 2004. [ABSTRACT FROM AUTHOR]

Coventorware 2001.1® is used to identify key vertical dimensions for the low voltage operation of a two-gap widely tunable capacitor. Using identical masking stages, two varieties of tunable capacitor are presented. Nickel structures are demonstrated which have a tuning ratio of 5.1:1 from an initial capacitance of 0.7 pF. Gold devices exhibit a tuning ratio of 7.3:1 from an initial capacitance of 1.5 pF. These are the most widely tunable devices reported to date. [Copyright &y& Elsevier]