Showing papers on "Voltage-controlled filter published in 2003"

Output filter design for a grid-interconnected three-phase inverter

Abstract: Traditionally, LC filter is used for an inverter power supply. A grid-interconnected inverter, however, has some unique requirements that an LC filter may not be sufficient. This paper comprehensively discusses the design considerations of the output filter for the grid-interconnected inverter. Different passive damping filter solutions are compared and the optimized design guidelines are also proposed. Simulation results are provided to validate the design.

A compact second-order LTCC bandpass filter with two finite transmission zeros

Abstract: A novel implementation and associated design formula for a compact low-temperature cofired ceramics (LTCC) lumped-element second-order bandpass filter are proposed in this paper. The filter schematic that provides two finite transmission zeros is well known. It is shown in the paper that the filter schematic is built on a pair of conventional inductive coupled resonator tanks with a feedback capacitor between input and output. While revealing its working mechanism both graphically and mathematically, a simple design procedure for such a compact filter is also given. The proposed filter has been implemented in a six-layer ceramic substrate using LTCC technology, showing promising application potentials in miniaturized mobile terminals and Bluetooth RF front-ends. The measured results agree very well with the full-wave electromagnetic designed responses.

RF bandpass filter design based on CMOS active inductors

Abstract: In this paper, a second-order RF bandpass filter based on active inductor has been implemented in a 0.35 /spl mu/m CMOS process. Issues related to the intrinsic quality factor and dynamic range of the CMOS active inductor are addressed. Tuned at 900 MHz with Q=40, the filter has 28-dB spurious-free-dynamic-range (SFDR) and total current consumption (including buffer stage) is 17 mA with 2.7-V power supply. Experimental results also show the possibility of using them to build higher order RF filter and voltage-controlled oscillator (VCO).

Tunable microstrip bandpass filters with two transmission zeros

Abstract: This paper presents an analytical technique for positioning the locations of two transmission zeros for a microstrip bandpass filter. In addition, this paper discusses how the tapping positions of asymmetric feed lines affect the coupling between resonators. The bandpass filter uses two resonators with two transmission zeros to obtain lower insertion loss than a conventional cross-coupled microstrip filter. Also, by using four resonators, the bandpass filter has better out-of-band rejection than the conventional cross-coupled microstrip filter. The filter designs using four cascaded resonators provide a sharp passband that can be tuned using a piezoelectric transducer to change the effective dielectric constant. The filters demonstrate high selectivity, compact size, and can be used in many wireless communication systems.

An adaptive filter for synchronous extraction of harmonics and distortions

Abstract: This paper provides an adaptive filter for synchronous detection and extraction of harmonics. The filter can be used as integral part of the control system of a power electronic apparatus (e.g., STATCOM, APF, and UPFC) to generate the desired control signals. Stability and convergence analyses of the adaptive filter are presented based on the dynamical systems theory. Performance of the filter is verified as a means for reference signal generation in a shunt active power filter.

Comparisons in circuit configuration and filtering performance between hybrid and pure shunt active filters

Abstract: This paper deals with a hybrid shunt active filter for harmonic compensation of a three-phase diode rectifier in a 480-V adjustable-speed drive system. The hybrid filter is formed by a three-phase single-tuned current LC filter for the 7-th harmonic frequency and a small-rated three-phase voltage-source PWM inverter. Computer simulation is carried out to compare the hybrid filter with a pure shunt active filter in terms of circuit configuration and filtering performance. The simulation results indicate effectiveness and viability of the hybrid filter. In addition, theoretical analysis confirms the validity of the simulation results.

RF filter for an electrosurgical generator

Abstract: Disclosed is an electrosurgical generator that comprises a circuit and method to produce a filtering technique that utilizes the output transformer as the inductive element of the filter and places two capacitors on the output of the transformer to produce the desired filtering. The output filter configuration eliminates the use of power inductors and still creates the filtering required in electrosurgical applications. The filter utilizes the inductive properties of the output transformer along with several capacitors to form the bandpass filter.

Bandwidth and central frequency control on tunable bandpass filter by using MEMS cantilevers

Abstract: This paper deals with a tunable bandpass filter topology which controls independently and simultaneously both the central frequency and bandwidth. This tunable filter results from the association of MEMS cantilevers, used as variable capacitors, with an original passive topology. The latter is based on dual behavior resonators (DBRs), each of them is constituted of low- and high-frequency open-ended stubs. The associated filter electrical response is characterized by tunable frequency transmission zeros. A millimeter bandpass filter with central frequency and relative bandwidth tunability of about 10 and 75%, respectively, is presented.

A novel open-loop control method for a current-source active power filter

Abstract: This paper presents a new control system for a current-source active power filter. The harmonic current compensation is realized using only a feedforward control of the load currents. The LC filter resonance of the converter is damped in an open-loop manner using the dynamic equations of the supply filter. The benefits of the proposed control system are that it is simple and straightforward, the number of measurements and sensors can be minimized, and also that the LC filter size can be optimized according to proper harmonic distortion level of the supply currents without care about the stability issues of the closed-loop system. This usually leads to reduction of the filter size. Also, the changes in fundamental current components of the active filter can be effectively realized when the active power filter can also be used as a fast reactive power compensator. The control system also includes the calculation delay compensation of the digital control system. The control system is realized using a single-chip Motorola MPC555 microcontroller. The tests with the prototype show effective current harmonic compensating performance of the nonlinear loads.

Wideband monolithic tunable high-Q notch filter for image rejection in RF application

Abstract: A notch filter with a high Q factor, which is integrated with a first and a second cascoded LNA, is totally contained on an integrated chip. The notch filter, comprising two Q-enhancement circuits, is coupled to the second differential LNA. The two Q-enhancement circuits are combined to generate sufficient negative impedance to compensate for the loss in the on-chip low Q inductors. To improve the image rejection of the notch filter in a wide frequency band, the notch filter uses an automatic current tuning circuit which consists of an analog multiplier and fixed and voltage controlled current sources. Furthermore, by modifying the connection and location of the tunable varactor, another wideband tunable notch filter is implemented. The notch filter can be applied in all current wireless receiver systems.

An ultra-narrowband HTS bandpass filter

Abstract: This paper presents the measured results of an HTS ultra-narrowband bandpass filter with a 100 kHz bandwidth. This filter, with a fractional bandwidth of 0.014% and a center frequency of 700 MHz, represents a previously unrealized portion of filter parameter space. This filter was realized using a five-pole Chebyshev filter design and was fabricated using an HTS microstrip configuration. This filter required very high Q, very weak coupling, and a strong reduction in parasitics. Unloaded Qs of 135,000 were achieved with a resulting insertion loss of 1.37 dB. Even resonator Qs of 20,000 would lead to a filter loss of 9 dB. A noise figure of 1 dB was achieved for a complete system with this filter and a cryogenic low-noise amplifier.

Continuous-time, low-frequency-gain/high-frequency-boosting joint adaptation equalizer and method

Abstract: In a class of embodiments, an adaptive equalization circuit that implements a joint adaptation algorithm. Other embodiments are receivers that include such an adaptive equalization circuit, and joint adaptation equalization methods. The equalization circuit includes a filter having a low-frequency-gain path (sometimes referred to as a low-frequency filter) and a high-frequency-boosting path (sometimes referred to as a high-frequency filter). The high-frequency filter typically includes a high-pass filter in series with an amplifier having adjustable gain. A high-frequency-boosting tuning loop controls the adjustable gain applied by the high-frequency filter. A low-frequency-gain tuning loop controls the adjustable gain applied by the low-frequency filter.

Tunable allpass filter for low voltage operation

Abstract: A novel high-performance first-order allpass filter with electronically adjustable filter parameters is presented. The core of the circuit is an inverting unity gain amplifier with electronically adjustable output resistance, which leads to an allpass filter realisation with tunable time constant. The circuit is composed of a simple CMOS cascode circuit and a level shifter and is also very suitable for low voltage operation, since it employs two active devices between its rails. SPICE simulation and experimental results verifying theoretical analyses are also given.

A 600 kHz electrically-coupled MEMS bandpass filter

Abstract: This paper presents a 600 kHz MEMS bandpass filter implemented using electrical coupling of single crystal silicon HARPSS micromechanical resonators. Passive and active filter synthesis approaches based on electrical coupling of capacitive MEMS resonators are introduced and discussed. A third order passive bandpass filter at the center frequency of 600 kHz with a bandwidth of 125 Hz, a stopband rejection of 48 dB, and a 20 dB-shape-factor of 2.1 is demonstrated. A quality factor (Q) enhancement technique based on active electrical cascading of the resonators is also presented. A 3-stage active cascade at 600 kHz demonstrated a 2/spl times/ increase in the effective Q.

Method and apparatus for optimizing dynamic range of a wideband analog-to-digital converter

Abstract: A direct down conversion receiver (100) includes a signal filter (105) having a selectable frequency response for receiving an input signal (102). The filtered signal is amplified by a variable gain amplifier (112), and the amplified signal is received as input by an analog-to-digital converter (114). The analog-to-digital converter generates a series of digital samples representative of the filtered signal. A controller (116) measures a corresponding peaking ratio of the filtered signal from the series of digital samples for each of a plurality of frequency bands and selects the frequency response of the signal filter as a function of the measured peaking ratios. The signal filter may include an adjustable highpass filter (108) and an adjustable lowpass filter (106). The cutoff frequency of the lowpass filter and the cutoff frequency of the highpass filter are selected to attenuate the level of the input signal in one or more of the plurality of frequency bands so that the signal presented to the analog-to-digital converter has a peaking ratio approximately equal to a selected peaking ratio threshold across the frequency range of the input signal.

Integrated circuit tuner with broad tuning range

Abstract: An integrated front end filter for a tuner provides an array of from several to a multitude of passbands, each for passing at least one but less than all channels designated in a band of frequencies. Each passband is exclusively selectable. The integrated front end filter can include at least one active filter unit with an active reactance element in either of fixed and variable filter configurations and a decoder coupled to said at least one active filter unit and being responsive to a control signal for selecting a one of the passbands. In one example, a multitude of active filter units of fixed filter configuration provide the multitude of passbands. In another example, a plurality of data corresponds to a like plurality of selectable passbands in combination with a filter element of the variable filter configuration. Each data is stored at a predetermined location and reproduced in response to a corresponding control data signal from a tuner controller. Each data characterizes one of the plurality of passbands. The filter element is switchable from one passband to another in response to the control data signal. Lower power dissipation and lesser requirements of an on-following integrated circuitry tuner permit a reduction of “off chip” connections and cost.

Digital control of an integrated series active filter and diode rectifier with voltage regulation

Abstract: The integration of a series active filter with a 12-pulse diode rectifier can provide a cost-effective and efficient means of supply current harmonic-free AC/DC conversion. Controlling the series active filter as a frequency-selective impedance requires low delays and is not well suited for digital control. This paper suggests a current-mode control strategy to allow full digital control of the active filter. The suggested current-mode control method for supply current balancing and voltage regulation is verified experimentally.

FPGA realization of multipurpose FIR filter

Abstract: A multipurpose FIR filter has been designed and realized by field programmable gate arrays (FPGA) for real-time filtering applications. The design can accomplish an arbitrary filter frequency response and variable filter order up to 127. The coefficients are computed through the Hamming windowing technique. The model is capable of performing filtering operations, like lowpass, highpass, bandpass and bandstop based on selection that is embedded into the design. The filter is set to 8-bit signed data processing. Linear constant coefficient difference equation (LCCDE) has been used to filter the input data in time domain. The design is coded with VHDL to cope with the parallelism of digital hardware. Simulation, compilation and synthesis have been done to verify the validity of the design outputs. To test the correctness of the design the observed output is compared with the calculated output results from MATLAB implementation that confirms the effectiveness of the design.

Optical receiver and optical transmission system

Abstract: The present invention includes an optical band-limiting filter which imposes a band-limitation on an input optical signal, an opto-electric converter which converts the optical signal output from the optical band-limiting filter into an electric signal, a lowpass filter which imposes the band-limitation on the electric signal output from the opto-electric converter, an amplifier which amplifies the output signal of the lowpass filter, and an electric equalizer which performs an equalization processing on a waveform of the electric signal output from the opto-electric converter are provided, and a full width at half maximum of the optical band-limiting filter is set to be equivalent to or smaller than a bit rate frequency of the optical signal.

Optimized Prototype Filter Based on the FRM Approach for Cosine-Modulated Filter Banks

Abstract: A design procedure for frequency-response masking (FRM) prototype filters of cosine-modulated filter banks (CMFBs) is proposed. In the given method, we perform minimization of the maximum attenuation level in the filter's stopband, subject to inter- symbol interference (ISI) and intercarrier interference (ICI) constraints. For optimization, a quasi-Newton algorithm with line search is used, and we provide simplified analytical expressions to impose the interference constraints, which greatly reduce the computational complexity of the optimization procedure. The result is lower levels of ISI and ICI for a predetermined filter order, or a reduced filter complexity for given levels of interferences. It is then illustrated how the FRM-CMFB structure is suitable for implementing filter banks with a large number of bands, yielding sharp transition bands and small roll-off factors, which is an attractive feature for a wide range of practical applications. Ke yw ords: filter banks, cosine-modulated filter banks, frequency-response masking, high resolution spectrum analysis.

Active EMI filter

Abstract: An active EMI filter (100) senses current in a ground line or a power transmission line as a voltage cross a capacitor (C1) coupled to the line. The EMI filter (100) senses common mode voltage and determines a difference between the common mode voltage and noise to provide an output to drive the difference to zero. The resulting active closed loop EMI filter (100) produces good EMI dampening with greatly increased performance over a current transformer type EMI filter. A voltage regulator for the error amplifier (102) improves noise reduction while increasing filter efficiency. The active EMI filter (100) operates in a wide linear range that is greater than that of an equivalent current transformer circuit, while providing low cost and reliability.

A dual-mode bandpass filter with enhanced capacitive perturbation

Abstract: A dual-mode ring bandpass filter with two pairs of capacitors has been designed. The capacitors are used to control the location of the even- and odd-mode frequencies independently, allowing weak coupling for narrow-band filter design with realizable capacitance values. Theoretical expressions have been derived for these frequencies. A 4% bandwidth bandpass filter centered at 1.9 GHz was designed and tested with good agreement between theoretical and measured results.

Digital pre-distortion for the linearization of power amplifiers with asymmetrical characteristics

Abstract: An input signal is pre-distorted to reduce spurious emissions resulting from subsequent signal amplification. Frequency-dependent pre-distortion is preferably implemented in combination with frequency-independent pre-distortion, where the frequency-dependent pre-distortion corresponds to amplifier distortion that has a magnitude that is proportional to the frequency offset from the carrier frequency and a ±90° phase shift on either side of the carrier frequency. The frequency-dependent pre-distortion is generated by differentiating waveforms corresponding to two different sets of pre-distortion parameters with respect to time. In one embodiment, one of the differentiated waveforms is applied to a positive-frequency filter and the other to a negative-frequency filter to generate positive- and negative-frequency pre-distortion signals, respectively, to account for asymmetries in the amplifier characteristics. In another embodiment, only one of the differentiated waveforms is applied to an asymmetric filter (i.e., either a positive-frequency filter or a negative-frequency filter).

Closed loop active EMI filter for reducing common or differential noise based on an error value

Abstract: An active EMI filter senses current in a ground line or a power transmission line as a voltage cross a capacitor coupled to the line. The EMI filter senses common mode voltage and determines a difference between the common mode voltage and noise to provide an output to drive the difference to zero. The resulting active closed loop EMI filter produces good EMI dampening with greatly increased performance over a current transformer type EMI filter. A voltage regulator for the error amplifier improves noise reduction while increasing filter efficiency. The active EMI filter operates in a wide linear range that is greater than that of an equivalent current transformer circuit, while providing low cost and reliability.

RC and SC filter compensation in a radio transceiver

Abstract: Disclosed is apparatus for operating with an RC filter ( 26, 26 A), and a corresponding method. The apparatus includes circuitry ( 32 ) for use in measuring an actual value of at least one filter component and a controller ( 34 ), coupled to the measurement circuitry, for determining at least one adaptive filter ( 36, 46 ) coefficient using the measured actual value to so as to compensate for a deviation of at least one filter component value from an ideal value. Where the filter is embodied as an RC network, the circuitry measures an actual value of both a resistor and a capacitor, and the controller uses the measured actual value of the capacitor when determining the value of a resistor.

Tunable optical filtering device and method

Abstract: An optical device and method are presented for processing a multi-frequency light signal to separate therefrom a desired frequency range. The device comprises a filter structure that has an input for receiving the multi-frequency input light signal, a first output for outputting a first light component of the input light signal including light of said predetermined frequency range, a second output for outputting a second light component including a remaining portion of the input light signal, and an intermediate input. The first output and the intermediate input of the filter structure may be connected to, respectively, input and output of a tunable frequency-selective optical unit, which may be a second filter structure, amplifier, attenuator. By using the second filter structure with a different tuning range as compared to that of the first filter structure such that these tuning ranges define overlapping spectra of the filter structures, a two-stage filter device is provided.

A windowing approach for designing critically sampled nearly perfect-reconstruction cosine-modulated transmultiplexers and filter banks

Abstract: A very fast technique for designing nearly perfect-reconstruction (NPR) critically sampled cosine-modulated M-channel transmultiplexer (TMUX) and filter bank (FB) systems is proposed. This technique is based on using the windowing technique for designing the prototype filter so that its 3-dB cutoff frequency is located at /spl omega/=/spl pi//(2M). The motivation for this is the observation that if the prototype filter cascaded with itself is a 2Mth filter, then the resulting TMUX (in the case of an ideal channel being a pure delay) or FB system has approximately a perfect-reconstruction (PR) property. This implies that for this cascade the 6-dB cutoff point should be approximately located at /spl omega/=/spl pi//(2M), and, correspondingly, the 3-dB cutoff frequency of the prototype filter is located at this angular frequency. The main advantage of the proposed design scheme is that it significantly lowers the computational complexity when compared with other existing techniques proposed for designing critically sampled cosine-modulated TMUX or FB systems. The PR property is not achieved, but for the resulting TMUX (FB) systems, the intersymbol interference and crosstalk errors (the amplitude and alias errors) are small. Both of these errors are small enough in practical systems. Several examples are included illustrating these desired properties.

Method and apparatus for controlling the bandwidth frequency of an analog filter

Abstract: An analog filter ( 10 ) having a bandwidth tracking circuit includes an analog filter element ( 14 ) and a digital tracking loop ( 22 ). The digital tracking loop ( 22 ) compares a magnitude difference to a predetermined threshold to generate an error signal. The magnitude difference is determined during a closed loop bandwidth calibration by subtracting a first magnitude of an analog input signal over a predetermined frequency range to a second magnitude of the analog input signal over the predetermined frequency range located near the bandwidth frequency. Use of the digital tracking loop ( 22 ) provides a digital approach for achieving bandwidth tracking of an analog filter without the need for achieving any manufacturing process matching between the analog filter and the tracking circuit itself. The analog filter element ( 14 ) may be either a lowpass, highpass, bandpass, active or passive filter element.

Continuous-time integrating filter with minimum phase variation, and bandpass sigma delta modulator using such a filter

Abstract: The disclosure pertains to continuous-time filtering. More particularly, it relates to filtering in a feedback control loop, for example in a sigma-delta (ΣΔ) modulator. The making of a filter for this type of application comes up against a major problem linked to the relativity between the amplitude and phase responses. This limits the possibilities of choice in order to take steps against the instability of the loop. A continuous-time filter with minimum phase variation carries out the bandpass integration of the signal presented at its input. The making of the continuous-time filter as a bandpass integrator raises the problem of achieving a compromise between gain variations and phase variations close to the −1 critical point, This compromise must lead to the stability of the loop. This problem is resolved by using a continuous-time bandpass integrating filter comprising at least one resonance device with minimum phase variation.