Low-pass Filter Structure Research Articles

Minimizing cross-talk in high-precision motion systems using data-based dynamic decoupling

To minimize cross-talk in high-precision motion systems, the possibilities of data-based dynamic decoupling are studied. Atop a model-based and static decoupling, a multi-input multi-output (MIMO) and finite impulse response (FIR) dynamic decoupling structure is considered for machine-specific and performance-driven fine tunings. The coefficients of the FIR filters are obtained via data-based optimization, whilst the machine operates under nominal and closed-loop conditions. The FIR filters provide the ability to generate zeros outside the origin. These zeros are needed in the description of the low-frequency inverted plant dynamics. In addition, a low-pass filter structure supports the ability to generate poles outside the origin as to account for plant zeros. Both filter structures are effectively used in the high-precision motion control of a state-of-the-art scanning stage system and an industrial vibration isolation system.

A 4th-order reconfigurable analog baseband filter for software-defined radio applications

This paper presents a 4th-order reconfigurable analog baseband filter for software-defined radios. The design exploits an active-RC low pass filter (LPF) structure with digital assistant, which is flexible for tunability of filter characteristics, such as cut-off frequency, selectivity, type, noise, gain and power. A novel reconfigurable operational amplifier is proposed to realize the optimization of noise and scalability of power dissipation. The chip was fabricated in an SMIC 0.13 μm CMOS process. The main filter and frequency calibration circuit occupy 1.8 × 0.8 mm2 and 0.48 × 0.25 mm2 areas, respectively. The measurement results indicate that the filter provides Butterworth and Chebyshev responses with a wide frequency tuning range from 280 kHz to 15 MHz and a gain range from 0 to 18 dB. An IIP3 of 29 dBm is achieved under a 1.2 V power supply. The input inferred noise density varies from 41 to 133 according to a given standard, and the power consumptions are 5.46 mW for low band (from 280 kHz to 3 MHz) and 8.74 mW for high band (from 3 to 15 MHz) mode.

Optimized dynamic decoupling in active vibration isolation

To improve performances of a multi-input multi-output (MIMO) active vibration isolation system, the possibilities of dynamic decoupling are studied. This to avoid spill-over of disturbances from one controlled direction toward another via cross-coupling. The decoupling structure consists of two parts. For course decoupling a set of low-pass filters is selected and tuned about the coupled suspension-mode resonances. For fine decoupling a finite impulse response (FIR) decoupling structure is added for machine-specific tunings. The FIR coefficients are obtained by data-based optimization in which perturbed-parameter experiments are conducted to obtain the required gradients. The optimization maps the single-input single-output (SISO) low-pass filter structure onto a MIMO dynamic decoupling. Its effect is demonstrated on a 6-DOF professional isolation system both in time- and frequency-domain.

Active Vibration Control and Isolation for Micromachined Devices

Some harsh environments contain high frequency, high amplitude mechanical vibrations. Unfortunately some very useful components, such as micro-electro-mechanical systems (MEMS) gyroscopes, can be very sensitive to these high frequency mechanical vibrations. Passive micromachined silicon low-pass filter structures (spring-mass-damper) have been demonstrated in recent years. However, the performance of these filter structures is typically limited by low damping. This is especially true if operated in low pressure environments, which is often the optimal operating environment for the attached device that requires vibration isolation. An active micromachined vibration isolator can be realized by combining a state sensor, and electrostatic actuator and feedback electronics with the passive isolator. Using this approach, a prototype active micromachined vibration isolator is realized and used to decrease the filter Q from approximately 135 to approximately 60, when evaluated in a low pressure environment. The physical size of these active isolators is suitable for use in or as packaging for sensitive electronic and MEMS devices, such as MEMS vibratory gyros.

Method for widening the reject-band in low-pass/band-pass filters by employing coupled C-shaped defected ground structure

Two new compact defected ground structure low-pass filters with broad stop-band and low insertion loss in the pass band are presented. The structures of these new microstrip low-pass filters are simple as they are composed of a pair of DGS-slots and an openstub. One filter is realised through the multi-layer method, and the second filter by cascading. With these configurations, two LPF with compact size, wide reject band and sharp transition from pass to stop-band are realised. The design formulas are derived by using an equivalent circuit model of coupled DGS resonators. Demonstration filters are designed, fabricated and tested. The experimental results show good agreement with theoretical results and demonstrate that the required characteristics of LPF could be simply obtained through the proposed methods. Finally a simple gap-method will be used in order to transform the LPF to BPF.

Ultra‐wideband bandpass filter using hybrid microstrip‐defected‐ground structure

AbstractA novel ultra‐wideband (UWB) bandpass filter (BPF) with a fractional bandwidth (FBW) of about 110% is presented using the hybrid microstrip‐defected‐ground structure (DGS). The proposed filter was designed using a combination of hybrid microstrip‐defected‐ground structure lowpass filter (LPF) with typical quarter‐wavelength short‐circuited stubs highpass filter (HPF), followed by an optimization for tuning in‐band performance. The high selectivity LPF using hybrid microstrip and four backside slots on ground plane is equivalent to a typical 9‐ploe stepped‐impedance LPF. The proposed LPF is employed to attenuate the upper stopband and etching on the ground plane with four rectangular slots provides attenuation pole to suppress the second spurious harmonic. Four shunt quarter‐wavelength short‐circuited stubs are used to realize the lower stopband for an optimum distributed HPF. The design was successfully realized in theory and verified by full‐wave EM simulation of the full layout and the experiment. The proposed filter had a good performance, including an ultra‐wideband bandpass (3.1–10.6 GHz), low insertion loss, sharp rejection, and a group delay of about 0.12 ns over the most center band. The filter also demonstrated an UWB reject band from 11.4 GHz to more than 19 GHz at −30 dB. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3085–3089, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23875

A coupled‐defected ground structure lowpass filter using inductive coupling for improved attenuation

AbstractA coupled‐defected ground structure (C‐DGS) with closely located DGS cells is proposed for the application of high‐performance lowpass filters (LPFs). The closely located DGS cells create the coupling of ground currents between adjacent DGS cells, and the coupling effect greatly improves the stopband characteristics because of an additional attenuation pole without structural modification. A LPF that uses the C‐DGS has an attenuation slope of 110.8 dB/GHz and a −20‐dB rejection band that ranges from 3.8 to 15.6 GHz. The C‐DGS improves the DGS circuit performance and extends the scope of DGS applications. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1541–1543, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23419

Compact quasi-elliptic lowpass filter using symmetric rectangular coupled capacitors

A compact microstrip lowpass filter using symmetric rectangular coupled capacitors is proposed. The introduction of an interdigital structure between the symmetric rectangular capacitors can reduce the filter size, owing to the increase in the loading capacitance, and also can provide the finite attenuation poles, thus quasi-elliptic function and stopband extension are fulfilled. Finally, a demonstration filter is designed, fabricated and tested to show the validity of the proposed lowpass filter structure.

On the temperature stability of integrated MIS low-pass filter structures

Integrated analogue MIS low-pass filters are considered. They consist mainly of a thin metal film representing a distributed resistance R on a dielectric representing a distributed capacitance C. A major criterion with respect to their technical application is the temperature stability. Assuming that the capacitance does not change with varying temperature the crucial point to meet the requirements of reliability is the resistivity of the metal film. In order to improve the temperature stability we applied an annealing process for filter structures with Pd as the metal film. The results show that the temperature stability can be improved by a temperature conditioning process.

Micromachined Vibration Isolation Filters to Enhance Packaging for Mechanically Harsh Environments

Some harsh environments, such as those encountered by missiles, rockets and various types of industrial machinery, contain high frequency mechanical vibrations. Unfortunately, some very useful components are sensitive to these high frequency vibrations. Examples include MEMS gyroscopes, oscillators and some micro-optics. Exposure to high frequency mechanical vibrations present in the operating environment can result in problems ranging from an increased noise floor to component failure. Passive micromachined silicon lowpass filter structures (spring-mass-damper) have been demonstrated in recent years. Since they usually possess a low vertical profile, they can be utilized as the packaging substrate for the sensitive component requiring vibration isolation. The performance of these filter structures is typically limited by low damping and a lack of tunability after fabrication. However, filter performance can be enhanced by integrating fluidic damping techniques with the passive filter or by integrating a micromachined actuator with state feedback to realize an active filter. The active filter has the additional advantage of post fabrication tunability.

Structure generation and performance comparison of elliptic Gm‐C filters

AbstractStarting from a set of matrices describing a general Gm‐C filter topology, a procedure is developed for generating structures of lowpass filters. As the matrices and the filter topologies have a one‐to‐one correspondence, an algebraic method is used to identify filter topologies with desired properties, here, transfer functions with finite jω‐axis transmission zeros, specifically elliptic filters. Sensitivity expressions for these structures are derived and a performance comparison based on a set of chosen criteria is made. For a specified elliptic transfer function, filters with only grounded capacitors and those containing also floating capacitors emerge as alternative realizations, as are filters with a single input and those with distributed inputs. For third‐order functions, a detailed comparison is performed of leapfrog (LF) and inverse follow‐the‐leader‐feedback (IFLF), the most popular special cases, and of topologies that have also floating capacitors (LFf, IFLFf), as well as of a novel configuration that uses also distributed inputs (DIf) and leads to a reduced element count. Design guidelines and restrictions are given, which follow from the derived results with focus on the circuits' sensitivity performance and other properties important for IC implementation. Copyright © 2004 John Wiley & Sons, Ltd.

Compact folded line bandstop and lowpass filters

AbstractCompact multiple‐coupled folded line bandstop and lowpass filter structures are presented in this paper. A common design procedure is used to design both types of filters. The procedure for obtaining the reduced two‐port network parameters is described. The effect of mutual coupling among the lines, curved‐line sections, and interconnecting lengths of sections are taken into account in order to obtain the network parameters. The filter designs have been validated by using full‐wave EM simulation, as well as by comparison with the measurements. The distinct advantages of the folded‐line filter designs are a compact footprint and realizable physical dimensions. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 44–46, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20202

Design of high-temperature superconducting low-pass filter for broad-band harmonic rejection

A new type of low-pass filter based on a coupled line and transmission line theory is proposed for suppressing harmonics and spurious frequency. The seventh-order coupled-line low-pass filter with strip line configuration was fabricated using a high-temperature superconducting (HTS) thin film on MgO(100) substrate. The seventh-order low-pass filter has five attenuation poles in the stop band. Its cutoff frequency is 1 GHz with a 0.01-dB ripple level. The fabricated filter exhibits a characteristic stop band in the range from 1 to 7 GHz. A measured insertion loss at the pass-band of the HTS low-pass filter is 0.2 dB at 77 K, while the maximum return loss is 17.1 dB. These results match well with those obtained by the EM simulation. The new low-pass filter structure is shown to have attractive properties such as compact size, wide stop band range, and low insertion loss.

A 1.5 GHz highly linear CMOS downconversion mixer

A CMOS mixer topology for use in highly integrated downconversion receivers is presented. The mixing is based on the modulation of nMOS transistors in the triode region which renders an excellent linearity independent of mismatch. With two extra capacitors added to the classical cross-coupled MOSFET-C lowpass filter structure, GHz signals can be processed while only a low-frequency opamp is required as output amplifier. The downconversion mixer has an input bandwidth of 1.5 GHz. The measured third-order intercept point (IP3) of 45.2 dBm demonstrates the high linearity. The mixer has been implemented in a 1.2 /spl mu/m CMOS process. It takes up 1 mm/sup 2/ of total chip area and its power consumption is 1.3 mW from a single 5 V power supply. >

A production ready, 6-18-GHz, 5-b phase shifter with integrated CMOS compatible digital interface circuitry

A producible, high-yield, monolithic 6-18-GHz, 5-b phase shifter with integrated standard CMOS compatible digital interface circuitry has been developed for use over the -55 to +90 degrees C temperature range. Differential phase shift is achieved using high-pass and low-pass filter structures. The integrated digital interface circuitry produces complementary outputs that are used to bias the phase-shifter bits. The integration of the digital interface circuitry, made with microwave FETs, reduced the phase-shifter bit control bias lines by a factor of 2. The phase shifter was fabricated at both Raytheon's and Texas Instruments' GaAs foundries in production quantities using a standard microwave process. Complete on-wafer RF tests were performed to screen the phase-shifter circuits and determine electrical yield. The phase shifter has an r.m.s. phase error >

Novel variation of distributed amplifier for millimetre-wave operation

The letter describes a novel variation of the distributed amplifier circuit which enables the upper operating frequency to be increased well beyond the limit set previously by the gate capacitance in a conventional circuit design. The modified design uses bandpass instead of lowpass filter structures. A 17–30 GHz experimental amplifier has been designed and constructed as a hybrid demonstrator.

Design Consideration for High-Isolation Coaxial Broad-Band p-i-n Diode Switches and Limiters

Broad-band coaxial p-i-n diode switches and limiters are realized using a low-pass filter structure in which shunt capacitances are realized by the capacitances of reverse- or zero-biased p-i-n diodes. Usually, the design considerations are given only for insertion-loss state. No design guideline exists in the literature to optimize isolation for these type of switches and limiters. This paper shows that using low-pass filter structure with series inductance as the first element, higher isolation without increasing insertion loss can be achieved.

Cutoff frequency of microwave coaxial multimode limiter

Broad-band microwave diode limiters are realized in a coaxial low-pass filter structure. It is shown here that there is a cutoff frequency of the coaxial limiter above which the limiter will not function as a limiter. The cutoff frequency depends on diode package inductance, package capacitance, and the capacitances of the coaxial structure used to realize the limiter.

Nonlinear Distortion Analysis in the Frequency Demodulator Using Feedback

A general method for the accurate analysis of the response of a frequency demodulator using feedback (FMFB) to an arbitrary frequency modulated (FM) signal is developed. This approach is employed to determine the FMFB outputs for two specific modulating signals, Gaussian noise, and a single sine wave. The proposed method is then applied to three different FMFB configurations differing in their low-pass filter structure. As a result, generalized curves enabling easy evaluation of the intermodulation (IM) distortion and the harmonic distortion are obtained. When designing the FMFB on the basis of these results, the influence of the relevant system parameters, such as IF filter bandwidth, feedback factor, position of the channel in the baseband, structure of the low-pass filter, etc., on the nonlinear properties of the FMFB can be controlled, simply and in a straightforward manner. The accuracy of the method has been verified in those rare cases for which solutions are already known.

Low-pass, quasi-optical filters using dielectric with metal-strip inclusions

A low-pass filter structure for use in millimeter-wave oversized waveguide or focused-beam systems is described. Tests on a trial structure demonstrated the feasibility of obtaining a low-loss passband and a broad stopband. The structure described uses a number of dielectric plates with copper strips on them.