Varactor Tuning Research Articles

A phase shifter with one tunable component for a reflectarray antenna

The combination of a dipole and a tunable varactor forms a phase shifter with one tunable component that provides a phase shift over a wide range, from 0deg to nearly 360deg. The dipole, loaded with a tunable varactor, is used as a patch component of a low-profile reflectarray antenna. An economic assessment shows that the production price of the suggested phase shifter with one tunable component is more than 10 times smaller than the price of the traditional phase shifter, based on p-i-n diode components. The design of such a phase shifter is the goal of this paper. Simulations of the phase shift and loss of the reflected wave as a function of control voltage applied to the varactor were used, based on an analytical model verified by fullwave analysis. The results of simulations are in agreement with measurements. The fast and correct simulation of the reflection coefficient from the dipole loaded with the tunable varactor can be used for the design and optimization of a low profile steerable reflectarray antenna.

A Millimeter-Wave 90-nm CMOS Self-Mixing Frequency Divider

This letter presents a millimeter-wave 90 nm CMOS divide-by-four frequency divider using self-mixing technique. The output of the push-push oscillator mixes with the input signal, and the resulting intermediate frequency signal locks the fundamental oscillation frequency of the oscillator at exactly one-fourth of the input signal frequency. The frequency divider is implemented in TSMC 90 nm 1P9M digital CMOS technology and the overall die size is 0.91 mm times 0.53 mm. For low-power mode, the divider consumes only 0.8 mW with a 0.8 V supply voltage, and the measured locking range is 300 MHz. For normal mode, the divider consumes 2 mW with a 1 V supply, and the locking range is extended to 1100 MHz. The operating range of the divider covers from 46.1 to 52.8 GHz with varactor tuning and band switching.

A Differentially-Tuned Voltage ControlledOscillator Using Symmetric Transformer

This letter proposes a new voltage controlled oscillator (VCO) topology that cancels common-mode noise by adoption of differential tuning varactor. To suppress common mode noise effectively, a symmetric three-coil transformer is proposed as a differential tuning resonator. The measured phase noise shows -128.7 dBc/Hz at 1 MHz offset frequency from the 1.2 GHz oscillation frequency. Over the whole frequency range, common-mode noise rejection is larger than 36 dB. Measured tuning range of the proposed VCO is about 204 MHz from the 1.18 GHz to 1.38 GHz while dissipating 1.2 mA at 1.8 V power supply.

A digitally controlled band‐switching VCO using switching inductors and capacitors in 0.18 μm CMOS

AbstractIn this article, a digitally controlled band‐switching voltage controlled oscillator (VCO) is designed and fabricated using TSMC 0.18 μm CMOS technology. Design considerations regarding the power requirement and the phase noise of the VCO are discussed. Eight bands are set by three bits, with one bit controlling switching inductors, and two bits controlling switching capacitors. The VCO covers 2.9–3.45 GHz and 3.6–4.3 GHz using varactors for continuous frequency tuning. Phase noise of the VCO stays constant around −110 dBc/Hz at 1 MHz offset for all bands. The fabricated VCO consumes 11 mA of current with 1.8 V supply voltage and has a small size of 730 μm × 660 μm. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1970–1973, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23496

A 0.8-mW 55-GHz Dual-Injection-Locked CMOS Frequency Divider

This paper presents the dual-injection-locking technique to enhance the locking range of resonator-based frequency dividers. By fully utilizing the voltage and current injection of the input signal, the divider locking range is extended significantly. The 0.8-mW dual-injection-locked frequency divider was developed in 90-nm digital CMOS technology. The total chip size is 0.77 mm times 0.5 mm. Without any varactor or inductor tuning, the input signal frequency coverage of the divider is from 35.7 to 54.9 GHz. Combined with the excellent locking range and sub-milliwatt power consumption, the figure-of-merit of this work surpasses those of the previous resonator-based dividers by more than one order.

Reconfigurable RF active bandpass filter with Ba x Sr 1-x TiO 3 varactor

An RF tunable active bandpass filter employing a BaxSr1-xTiO3 (BST) based capacitor is proposed. This filter consists of an active capacitance circuit together with a BST tunable varactor. The active capacitor is made of a field effect transistor that exhibits negative resistance as well as capacitance. BST thin film was deposited by Sol-Gel solution and using the metal-insulator-metal capacitor process. The fabricated capacitor showed capacitance of 2.7–1.5 pF at 1.8 GHz for a maximum applied electric field of 34 V/µm. The measured second-order active bandpass filter showed bandwidth of 100 MHz, insertion loss of+0.48 dB at 1.8 GHz centre frequency and tuning frequency of 220 MHz with the application of 34 V/µm.

Analysis and Design of a Double-Quadrature CMOS VCO for Subharmonic Mixing at $Ka$-Band

In this paper, we analyze the potentials of a four-phase 14-GHz CMOS voltage-controlled oscillator, tailored to a sub-harmonic receiver, for signal processing at Ka-band. When mild phase accuracies between in-phase and quadrature down-converted signals are required, the four-phase oscillator displays roughly the same phase noise figure-of-merit as quadrature oscillator counterparts. However, the operation at half-frequency leads to an improved performance due to a higher quality factor of the tuning varactors, and because the local oscillator circuitry and signal path run at different frequencies, relaxing coupling issues. A detailed time-variant analysis of phase noise in multiphase oscillators is introduced and validated by both simulations and experiments. Prototypes realized in a 65-nm technology occupy an active area of 0.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and show the following performances: a 26% frequency tuning range (from 12.2 to 15.9 GHz), maximum phase error from pi/4 of 2deg, and a phase noise of -110 dBc/Hz at 1 MHz from 14 GHz, while consuming 18 mA from 0.8-V supply.

Analysis and experiment on harmonic radiation and frequency tuning of varactor-loaded microstrip antennas

Analysis and experiments on microstrip antennas with varactor tuning are presented. Results are given for the frequency tuning of rectangular half and quarter wavelength microstrip antennas. Double tuning range was observed for quarter wavelength antennas. Emphasis is also given to the study of harmonic radiation generated because of the varactor nonlinearities. A description of the varactor model as a nonlinear capacitor in the finite difference time domain method and its validation is reported. Harmonic radiation levels and patterns were measured and investigated by full wave analysis.

Properties Optimization for Perovskite Oxide Thin Films by Formation of Desired Microstructure

Perovskite oxide materials are very important for the electronics industry, because they exhibit promising properties. With an interest in the obvious applications, significant effort has been invested in the growth of highly crystalline epitaxial perovskite oxide thin films in our laboratory. And the desired structure of films was formed to achieve excellent properties. Y₁Ba₂Cu₃O 7-x (YBCO) superconducting thin films were simultaneously deposited on both sides of 3 inch wafer by inverted cylindrical sputtering. Values of microwave surface resistance R s (75 K, 145 ㎓, 0 T) smaller than 100 mΩ were reached over the whole area of YBCO thin films by pre-seeded a self-template layer. For implementation of voltage tunable high-quality varactor, A tri-layer structured SrTiO₃ (STO) thin films with different tetragonal distortion degree was prepared in order to simultaneously achieve a large relative capacitance change and a small dielectric loss. Highly a-axis textured Ba 0.65 Sr 0.35 TiO₃ (BST65/35) thin films was grown on Pt/Ti/SiO₂/Si substrate for monolithic bolometers by introducing Ba 0.65 Sr 0.35 RuO₃ (BSR65/35) thin films as buffer layer. With the buffer layer, the leakage current density of BST65/35 thin films were greatly reduced, and the pyroelectric coefficient of 7.6×10?? C ㎝?² K?¹ was achieved at 6 V/㎛ bias and room temperature.

Exploring the possibility of enhancing the bandwidth of μ‐negative metamaterials by employing tunable varactors

AbstractWe analyze here the performance of μ‐negative metamaterials in different configurations at microwave and optical frequencies that employ variable values of capacitances or tunable varactors, with the purpose of increasing their bandwidth of operation. The proposed method shows moderately good results both in resonant‐like and in transmission‐line configurations. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 55–59, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22036

Ultra-Low Voltage Analog Integrated Circuits

The operation of analog circuits from ultra low supply voltages becomes necessary due to semiconductor technology scaling. Yet traditional design techniques cannot be used. In this paper, we review techniques that allow analog circuits to operate with supply voltages as low as 0.5 V. Biasing considerations are given, and robust bias circuits are discussed. For frequency-tunable circuits, a low-voltage MOS varactor tuning technique is presented. The techniques discussed are applied to two different OTA topologies, as well as to an automatically tuned, fifth-order active RC filter. This material is largely based on the work of the authors as described in [1]-[5].

A CMOS Finite Impulse Response Filter With a Crossover Traveling Wave Topology for Equalization up to 30 Gb/s

This paper describes a fully differential 3-tap finite impulse response filter in 90-nm CMOS. A traditional traveling wave filter topology is modified to alleviate its inherent delay-bandwidth-gain tradeoffs. Each tap gain is comprised of two transconductors whose outputs superimpose with the same group delay, similar to a distributed amplifier. This doubles the bandwidth of the filter for a given tap spacing and gain. Digital control is provided for the tap gains, an integrated pre-amplifier, and tuning varactors. Coupled differential spirals are used in the delay lines to help the design fit into an area 600 /spl mu/m/spl times/500 /spl mu/m. A 1-V supply voltage and 25-mW power consumption are enabled by the use of parallel differential pairs for sign control of the transconductances instead of Gilbert cell amplifiers. The input return loss is better than 16 dB and the output return loss is better than 9 dB up to 30 GHz. Equalization of NRZ data over a coaxial cable channel was demonstrated up to 30 Gb/s, making it faster than any previously reported CMOS equalizer.

Stepped impedance hairpin design of a tunable bandpass filter with harmonic suppression

AbstractStepped impedance hairpin resonators (SIHRs) with harmonic suppression and capability of frequency tuning are incorporated into a bandpass filter design. A tapped‐in U‐shaped feed structure is introduced to suppress harmonics and to reduce the passband insertion losses. The passband flexibility is accomplished by using a pair of tuning varactors. A simple method to implant a zero in the frequency response is also studied herein to further deepen the passband skirt. A 176% (4.32 GHz) stopband bandwidth is observed under more than 20‐dB band rejection. A measured minimum insertion loss of 1.19 dB is observed for the circuit with absence of the tuning varactors. Using the varactors, this filter has achieved a 22% frequency tuning range with all the insertion losses less than 5 dB. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 697–701, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21447

A novel varactor diodeless push-push VCO with wide tuning range

A Ku-band push-push VCO for low-cost applications is proposed. The proposed push-push oscillator achieves a wide tuning range in the Ku-band by the collector bias tuning instead of varactor tuning. The designed Ku-band VCO shows a wide tuning range of 900 MHz, excellent fundamental suppression of −30 dBc, and good phase noise of −115 dBc at 1-MHz offset. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1569–1572, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21726

C-shaped slot loaded reconfigurable microstrip antenna

A new electronically reconfigurable dual frequency microstrip patch antenna with highly simplified varactor tuning circuitry is presented. The proposed design allows relatively independent selection of the two operating frequencies. Tuning ranges of 7.1 and 4.1% are realised for the two resonant frequencies without the use of any matching circuits.

Design of a Steerable Reflect-array Antenna with Semiconductor Tunable Varactor Diodes

The demonstrator of a steerable reflect-array antenna was designed as a system of dipoles loaded by varactor diodes. The microwave response of a dipole loaded by varactor has been simulated in closed form based on equivalent circuit approach. The circuit analytical model has been verified by the full-wave analysis. Change of the varactor capacitance in the range of 0.3–1.3 pF was provided by biasing voltage 0–20V. The array consists of 20 dipoles structured as two parallel lines. The operational frequency is 11GHz, the length of the dipole is 9.2mm, spacing between dipoles is 18mm. The double-side metallized PTFE with e = 2.8 and thickness of 1mm was used as a substrate. Dipole structure was manufactured by a photolithographic process and formed with surface mounted varactor diodes. The radiation pattern of the array is characterized by the width of the main beam ≈ 8◦, the side lobe level -(12÷20) dB, the steering range ±15◦. Control voltage was set manually with variable resistors separately for each varactor. The fine alignment of the control voltage for each varactors turned out to be very important. Inherited data are used for correction of the operational principle of a varactor steerable antenna controller.

Low Phase Noise, InGaP/GaAs HBT VCO MMIC for Millimeter-Wave Applications

A fully integrated voltage controlled oscillator (VCO) MMIC for millimeter-wave applications has been designed and implemented in InGaP/GaAs heterojunction bipolar transistor (HBT) technology. To achieve a fully integrated VCO, a base-emitter diode is employed as the tuning varactor, and microstrip lines are employed for the transmission lines. The fabricated VCO MMIC chip size is 0.86 mm x 1.34 mm and delivers an output power of 5.1 dBm at 28.7 GHz and a free-running phase noise of -118 dBc/Hz at 1 MHz offset. The dc current consumption is only 20 mA.

A Distributed Capacitance Analysis of Co-Planar Inductors for a CMOS QVCO with Varactor Tuned Buffer Stage

A Distributed Capacitance Analysis of Co-Planar Inductors for a CMOS QVCO with Varactor Tuned Buffer Stage

Angular Vertical Comb-Driven Tunable Capacitor With High-Tuning Capabilities

This paper reports on a novel tunable capacitor with electrostatic angular vertical comb-drive (AVC) actuators. The AVC tunable capacitor creates a large offset in comb fingers through a small rotation angle-an advantage not found in conventional lateral comb-drive devices. High capacitance and large continuous tuning ratio is achieved in a compact device area. The largest tuning varactor demonstrates capacitance values between 0.27-8.6 pF-a tuning ratio of more than 31:1, the highest ever reported. The maximum quality factor Q is 273 at 1 GHz near the minimum capacitance value.

A Distributed Capacitance Analysis of Co-Planar Inductors for a CMOS QVCO with Varactor Tuned Buffer Stage

A quadrature voltage controlled oscillator (QVCO) topology exhibiting low power consumption and high phase noise performance at low supply voltages is presented. The QVCO buffer includes varactors to maximize the output voltage and minimize the current consumption. Microstrip theory and the principle of conservation of energy have been used to evaluate the distributed capacitances of symmetrical inductors to better predict the resonance frequency. The QVCO is implemented in a 0.25 ?m CMOS process from Agere Systems. The total current consumption including the buffer is 5.4 mA at 1.3 V supply, where of the QVCO uses 2.0 mA. The phase noise measures below ?138 dBc/Hz at 3 MHz offset frequency over the 8.9% tuning range 1.715 GHz-- 1.875 GHz.