Center Frequency Tuning Range Research Articles

Precise frequency and bandwidth control of microstrip switchable bandstop filters

AbstractIn this article two switchable bandstop filters able to switch precisely between two different center frequency and bandwidth states are presented. The filter topologies allow precise control over the design parameters frequency and bandwidth, achieved by choosing adequate resonator sections switched by PIN diodes. Center frequency control was obtained by modifying resonator length. Bandwidth control was achieved by choosing a resonator width and controlling the normalized reactance slope parameter of the decoupling resonators by means of switchable resonator extensions. Both filters were designed to have a 32.5% center frequency tuning range at L band between a low and high filter center frequency. One topology focuses on producing an 8% fractional stopband bandwidth for both filter states. The second filter topology focuses on producing 7 and 9% fractional stopband bandwidths for the low and high filter center frequency states, respectively. Measured results show a very good agreement with the simulations, for the first topology a 32.2% measured center frequency tuning range was obtained with 8.1 and 8.75% fractional stopband bandwidths for the low and high filter center frequency states, respectively. The second filter topology showed a 31.2% measured center frequency tuning range with 6.94 and 9.66% fractional stopband bandwidths for the low and high filter center frequency states, respectively. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2573–2578, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24679

High- κ dielectrically transduced MEMS thickness shear mode resonators and tunable channel-select RF filters

Electrically coupled, high quality factor ( Q), tunable channel-select ladder filters comprised of dielectrically transduced thickness shear mode resonators are presented using integrated circuit compatible bulk micromachining technology. The filters are fabricated on the 3.2 μm thick device layer of heavily doped SOI wafers with a 20 nm thick hafnium dioxide film sandwiched between the polysilicon electrodes and the silicon device layer. The ladder filter consists of shunt and series resonators operating in the half-wave thickness shear vibration mode. Dielectric transduction provides a k 2 reduction in motional impedance relative to air-gap electrostatic transduction. Each constituent resonator of the filter can be excited at above 810 MHz resonant frequency with Q of 7800 in air and a motional impedance ( R X ) of 59 Ω. The ladder filter demonstrates a center frequency tuning range 8–817 MHz and an adjustable bandwidth from 600 kHz to 2.8 MHz, while maintaining an insertion loss <4 dB, stop-band rejection >30 dB and pass-band ripple <2 dB. By having a tunability feature, RF MEMS filters can accommodate various signal waveforms with bandwidth range 0.1–5 MHz. In addition, errors due to fabrication can be compensated and capacitive loading in receiver architecture can be minimized.

Silicon-Integrated Differential Bandpass Filters Based on Recursive and Channelized Principles and Methodology to Compute Their Exact Noise Figure

In this paper, two silicon-integrated differential active bandpass filters are presented. The first one is a recursive filter based on a cellular approach. This circuit is independently tunable in terms of power transmission gain, center frequency, and bandwidth. The chip surface is less than 1.4 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . For this prototype, measurements demonstrate a 1.9-2.4-GHz center-frequency tuning range with a typical gain of 15 dB and a 3-dB bandwidth of 60 MHz. Gains of up to 40 dB and bandwidths as low as 20 MHz are also achievable in the 2.05-2.38-GHz range. Subsequently, the design of an integrated three-branch channelized bandpass filter is addressed. The proposed filter uses an active power splitter at its input. Moreover, the channels are based on elementary first-order tunable recursive stages derived from the previously described topology, thus making the overall filter fully reconfigurable. This second circuit, whose layout size is smaller than 3 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , can exhibit 3-dB bandwidths of ap90 MHz and gains of up to 20 dB within a 1.95-2.23-GHz tuning range. Controllable high selectivity for each rejected band can be obtained through the generation of adjustable out-of-band transmission zeros. Furthermore, a dual-band behavior is also feasible through this filter. To conclude, an original method to extract the exact noise figure of differential circuits is reported, and applied to the filter prototypes developed in this study. The Philips QUBIC4 0.25-mum silicon BiCMOS process has been used for the design of the two circuits presented

New high-Q discrete-time LC bandpass filter design with center frequency broadband tuning

Discrete-time switched-capacitor filters have been in wide-spread used for a few years, for the realization of stable, accurate and high quality filters. This paper describes the design of a new 8-path pseudo switched-capacitor LC bandpass filter and its command circuit made up by a ring voltage controlled oscillator (VCO) with `XOR' gates. The proposed architecture presents the possibility of tuning over a frequency broadband allowing to sweep different channels with a high quality factor. This circuit is intended to replace the surface acoustic wave (SAW) filters in broadband wireless applications. Experimental results carried out on a prototype show quality factors up to 200, and a tunable center frequency range of 300 MHz [250---550 MHz].

An Active Recursive RF Filter in 0.35 μm BiCMOS

An active recursive filter approach is proposed for the implementaion of an inductorless, tuneable RF filter in BiCMOS. A test circuit was designed and manufactured in a 0.35 ?m SiGe BiCMOS technology. In simulations, the feasibility of this type of filter was demonstrated and reasonably good performance was obtained. The simulations show a center frequency tuning range from 6 to 9.4 GHz and a noise figure of 8.8 to 10.4 dB depending on center frequency. Gain and Q-value are tunable in a wide range. Simulated IIP-3 and 1-dB compression point is ?26 and ?34 dBm respectively, simulated at the center frequency 8.5 GHz and with 15 dB gain. Measurements on the fabricated device shows a center frequency tuning range from 6.6 to 10 GHz, i.e. slightly higher center frequencies were measured than the simulated.

1.33 mW, 2 V CMOS continuous-time bandpass filter with two decades of centre frequency tuning range and high Q

A gm-C bandpass biquad filter featuring two decades of centre frequency tuning capability and a wide range of quality factor tunability is presented. It uses a new linear operational transconductance amplifier (OTA) based on two crosscoupled class-AB pseudo-differential pairs, which exhibits a wide transconductance adjustability range with low power consumption. The filter has been fabricated in a standard 0.8 μm CMOS process. Experimental results show a frequency tuning range from 300 kHz to 32 MHz and a maximum quality factor of 501. The filter is operated at 2 V supply voltage with a power consumption ranging from 1.18 to 1.8 mW.

CMOS RF switched capacitor bandpass filter tuned by ring VCO

A new RF switched capacitor bandpass filter and its command circuit made up of a ring voltage controlled oscillator with ‘XOR’ gates are proposed. Implemented in a standard 0.35 μ m CMOS technology, this circuit is intended to be used in a subset of professional mobile phone applications [380–520 MHz]. Experiments carried out on a prototype show a tunable center frequency range of 260 MHz [240–500 MHz], with a quality factor that can be as high as 300.

CMOS active-LC bandpass filters with coupled-inductor Q-enhancement and center frequency tuning

A novel CMOS circuit for obtaining a bandpass response from a triple-coupled-inductor arrangement is presented, featuring Q-enhancement and center frequency tuning by means of vector-modulating a current flowing through one of the coupled inductors. A 0.35-/spl mu/m CMOS LC filter prototype employing the technique has been fabricated and exhibits a center frequency tuning range of 11% around 1 GHz and Q values up to 180. The input 1-dB compression point is -13 dBm with Q set to 20 and a power consumption of 12.2 mW. Additionally, an input impedance matching scheme around a spiral transformer is presented, which tracks the center frequency of the filter. The active-LC approach can be applied to higher order filter responses and find applications in tunable building blocks for agile RF front ends and multistandard radios.

New command circuit design for tuning high-Q pseudo 8-path switched-capacitor filter

This paper describes a new association of a high-Q pseudo 8-path switched-capacitor (S-C) bandpass filter and its command circuit made up by a ring VCO with `XOR' gates. The proposed circuit presents the possibility of tuning over a radio-frequency (RF) broadband allowing to sweep different channels with a high quality factor. Designed with CMOS process (0.35µm, for instance), this circuit is intended to replace the surface acoustic wave (SAW) filters in modern wireless receivers. Measurements carried out on a circuit demonstrator show a tunable center frequency range of 200MHz [300-500MHz], with a quality factor higher than 300.

Tunable lumped-distributed capacitively-coupled transmission-line filter

A wide tuning range filter is proposed based on lumped-distributed capacitively-coupled transmission lines. The proposed structure maintains a constant inter-resonator coupling factor over a wide centre-frequency tuning range leading to a constant fractional bandwidth design. A bandpass filter with a two-octave tuning range has been designed, fabricated and measured.

X-band magneto-optic Bragg cells using bismuth-doped yttrium iron garnet waveguides

Guided-wave magneto-optic Bragg cells at X-band microwave frequencies using magnetostatic forward volume waves (MSFVWs) in bismuth-doped yttrium iron garnet-gadolinium gallium garnet (Bi-doped YIG-GGG) waveguides are reported for the first time. Performance figures that have been obtained at an optical wavelength of 1.303 μm include a center frequency tuning range of 3.7–12.0 GHz, a diffraction efficiency of 12% at the magnetostatic wave power of 56 mW, a linear dynamic range &amp;gt;40 dB, and a −3 dB magneto-optic bandwidth of 150 MHz. These results represent a significant improvement over those obtained previously with the Bragg cells using pure YIG-GGG waveguides. Maximum scan angle of 6° and 5.3° were also measured, respectively, by tuning the rf frequency ∼10.0 GHz at a fixed dc magnetic field of 3660 Oe and by varying the dc magnetic field ∼3660 Oe at a fixed rf frequency of 10.0 GHz. A frequency resolution of 30 MHz was measured with rf spectral analysis experiments carried out at 12 GHz. Finally, a Faraday rotation coefficient as large as −2313°/cm was measured for the Bi-doped YIG-GGG waveguides.