Showing papers on "Voltage-controlled filter published in 1993"

Log-domain filtering: an approach to current-mode filtering

Abstract: A novel approach to filter design, based on Adams' [1] ‘log-domain’ filters, is proposed that yields a truly current-mode circuit realisation. Adams' idea, which was introduced in a limited context, is generalised to permit a complete distortionless synthesis procedure, which results in circuit implementations readily realisable using complementary bipolar processes. It is shown that, by introducing an exponential map on the state-space description of the desired linear system, a log-domain filter can be fully realised with transistors configured in current mirror-type groupings, current sources and capacitors. Owing to the mapping, the state variables are intrinsically related to current, and not voltage, in the resulting circuits, a fact that emphasises the current-mode nature of the design. A general biquadratic filter section is designed, and, following discussion of cascading sections, a seventh-order Chebychev lowpass filter is designed. All designed circuits are shown to be tunable over a two-decade range in frequency while their characteristics are accurately preserved, even for biquad sections whose f0Q product is greater than fT/10. The Chebychev filter is shown in simulation to possess nearly 60 dB dynamic range relative to 0.9% THD, with a cutoff frequency of nearly 5 MHz, using transistor models from AT&T's CBIC-R 300 MHz complementary bipolar process.

Input filter design for power factor correction circuits

Abstract: The issues involved in the design of power factor correction circuit input filters are significantly different than those involved in the design of input filters for DC-DC power converters. So far, there exist no guidelines for high-frequency AC power converter input filter design. This paper addresses these issues and proposes the use of a high order, actively damped filter to achieve the required EMI attenuation and power factor requirements. The new filter topology typically provides 50% filter size reduction over the standard filter designs, and simultaneously minimizes the filter-converter interaction. >

Analysis and design of a new active power filter to cancel neutral current harmonics in three phase four wire electric distribution systems

Abstract: An active power filter for cancelling harmonic currents in the neutral of a three-phase four-wire system is proposed. This approach employs a star/delta transformer along with a two-switch PWM (pulse-width-modulated) controlled active filter. The closed-loop control of the active power filter guarantees cancellation of neutral current harmonics under varying load conditions. The proposed system greatly improves the overall system performance and virtually eliminates transformer overheating due to harmonics. Experimental results from a prototype active power filter confirm the suitability of the proposed approach. >

A BiCMOS low-distortion 8-MHz low-pass filter

Abstract: An 8-MHz seventh-degree elliptic-function low-pass filter is described, demonstrating an approach to low-distortion antialias filtering for high-definition video applications. The filter's performance goals are achieved through the use of circuit design principles that capitalize on the strengths of BiCMOS technology. The integrator circuits composing the filter consist of a new wideband low-distortion transconductor circuit and a unique BiCMOS Miller-stage circuit. Integrator time constants are determined by stable RC products, enabling a simplified filter calibration scheme that is insensitive to temperature-induced variations and requires no phaselock circuits. The prototype filter IC, consisting of seven integrators assembled in an active-ladder configuration, was fabricated in a 10-V, 2- mu m 2.5-GHz BiCMOS technology that also features thin-film resistors and polysilicon-plate capacitors. Measured results from the calibrated filter show passband flatness of 0.2 dB, with aberrations of less than +or-1 dB over a 100 degrees C temperature range. Stopband attenuation meets its designed goal of 60 dB. Driven by 7-V/sub pp/, differential input signals, the filter exhibits less than -72-dBc third-order intermodulation distortion products at 1 MHz. For 5-V/sub pp/ inputs at 4 MHz, third-order intermodulation spurs remain below -65 dBc. >

Control and reduction of terminal voltage total harmonic distortion (THD) in a hybrid series active and parallel passive filter system

Abstract: A simple and cost-effective solution to reduce the passive filter terminal voltage total harmonic distortion (THD) is outlined. A modified synchronous reference frame (SRF) based controller for the series active filter allows injection of a controlled percentage of the higher harmonic load currents into the supply, in compliance with the IEEE 519 harmonic current standards, thereby reducing the passive filter terminal voltage THD. This implementation retains all the desirable features of the original SRF controlled hybrid series active filter system. It reduces the rating and size of the passive filter system and allows the use of simpler passive filter system structures such as only a simple high pass passive filter or a simple power factor correction capacitor as the passive filter system. Simulation and experimental results are used to establish the functionality and performance of the SRF controller and the modified SRF controller for the hybrid series active filter system. >

Universal active filter

Abstract: A universal filter is provided with three inputs Vh, Vb and V1, with one output Vout, with two transconductance amplifiers Gm1, Gm2, with four capacitors mCO, (1-m)CO, CO and LCO and an amplifier K as well as a voltage follower VF. Depending on the connections of the three inputs, the universal filter takes the form of a high-pass or low-pass or band-pass filter or a trap filter or an all-pass or an otherwise active filter. Advantageously, by selection of parameters (e.g., trans-conductance, gain, scaling), the various filter characteristics like quality (Q), slope, median frequency, amplification, etc., may be adjusted. A further advantage is that the low component count of the filter provides improved reliability, reduced cost and facilitates efficient and economic fabrication in discrete or integrated circuit form.

Universal active current filter with single input and three outputs using CCIIs

Abstract: A universal active filter with current gain and with single input and three outputs using second-generation current conveyors (CCIIs) is presented. The proposed circuit offers the following advantageous features: independent control of (ω0, Q and current gain through separate grounded resistors, use of only two grounded capacitors making it ideal for integration, and no requirements of critical matching condition/cancellation constraints in realising the lowpass, bandpass, highpass and notch filter responses.

Narrow-band MMIC filters with automatic tuning and Q-factor control

Abstract: Fully integrated, narrowband, tunable active filter monolithic microwave integrated circuits (MMICs) have been demonstrated at X-band. The three-section bandpass chip had a minimum insertion loss of less than 1.5 dB and a -3 dB bandwidth of 3% at 8.4 GHz. The notch filter chip exhibited a minimum -30 dB notch bandwidth of 20 MHz and a 2.7-GHz tuning range. A master-slave filter control circuit with fully integrated RF components was shown to track a reference signal over a frequency range greater than 2.5 GHz while maintaining the slaved filter notch depth at greater than 25 dB over that band. The same control circuit virtually eliminated the temperature dependence of the notch depth and provided a five-fold reduction in the notch frequency drift. >

Current-mode lowpass, bandpass and highpass biquads using two CCIIs

Abstract: Two current-mode second-order filter configurations which employ two second-generation current conveyors (CCIIs) and can realise lowpass and bandpass filter responses for one and highpass and bandpass filter responses for the other are presented. The proposed networks offer the following advantageous features: orthogonal control of ωo, and Q, use of only two grounded capacitors which make the networks ideal for integration, no requirement for critical matching condition/cancellation constraints, and low passive senitivities.

Transversal filter for use in a digital subscriber line transmission interface

Abstract: A transversal filter has a transfer function for which a zero point occurs outside a unit circle on z plane and thus the output waveform has a ringing characteristic having a change from negative to positive around a precursor and before a main cursor and is associated and integrated with another transversal filter, thereby forming a waveform shaping decimation filter or a pulse shaping high-pass filter. The waveform decimation filter can eliminate a high frequency noise, changes a high frequency input data to a low frequency output data, and performs a waveform shaping operation. Therefore it cannot require a pulse shaping filter separated from the decimation filter. The pulse shaping high-pass filter includes a pulse shaping filter whose number of the taps is decreased and performs high-pass filter function. A pulse shaping filter whose number of the taps is decreased can be used separately from the high-pass filter.

Receiver having an adjustable matched filter

Abstract: A radio receiver's digital matched filter (52') is intended to match a pulse-shaping filter (23) in the transmitter whose signals it receives. However, the clock signal on which the matched filter's timing is based is generated by a receiver clock (58') that is independent of the transmitter clock (56) and that is subjected to no timing adjustment to bring the two clock signals into synchronism. So as to ensure that the matched and pulse-shaping filters work together as a Nyquist filter, therefore, a timing-recovery circuit (60') senses the timing offset in the matched filter's output, and a coefficient generator (80) adjusts the matched filter's coefficients in such a manner that the filter itself imposes the delay needed for the required timing relationship between the filters.

Active control apparatus using adaptive digital filter

Abstract: An active control apparatus using an adaptive IIR digital filter includes a coefficient control portion for updating the filter coefficient of adaptive IIR digital filter so as to minimize an output error signal level, and a coefficient control portion for updating the filter coefficient of a recursive portion so as to minimize the output level of recursive portion. The filter coefficient of recursive filter is updated by these two coefficient control portions and in parallel or in a time-dividing manner.

Saw notch filter for improving stop-band attenuation of a duplex filter

Abstract: When the bandwidth of a duplex filter having a certain band-width, intended for a radio telephone, is increased by affecting the coupling between the resonator circuits, the stop band of the filter is at the same time deteriorated. According to the invention, the stop-band attenuation can be improved by coupling a surface-wave filter, coupled as a notch circuit, in parallel with one of the resonator circuits of the duplex filter.

Control method for a combined active filter system employing a current source converter and a high pass filter

Abstract: This paper describes a control method with a combined filter system which senses load current, source current and line voltage to create reference signals for an active filter. The transfer function of the active filter is identified and is used for the control system design. It is shown that the source current feedback is most effective to suppress the harmonic-enlarging effects due to parallel resonance and the harmonic current generated by source harmonic voltages. A small setup controlled by a DSP was built, and the validity of the proposed method was demonstrated by experimental results. >

Device and method for tuning a band-pass filter utilizing mixing results with DC component removed

Abstract: A device and a method for adjusting a bandpass filter, especially a combiner filter. The method includes deriving an RF sample signal proportional to the power of a modulated RF signal which is one of: passing forward to the bandpass filter, reflected from the input of the bandpass filter and passed through the bandpass filter; down-converting the sample signal by another RF signal; detecting the signal strength of the mixing result; adjusting the center frequency of the passband of the bandpass filter on the basis of the detected signal strength. There is an essential frequency or modulation difference between the signals to be mixed, and so the mixing result is an AC signal of a lower frequency. No accurate adjustment of the phase relation of the signals to be mixed is required. Preferably, the frequency or phase difference between the signals to be mixed is accomplished by utilizing the phase modulation contained in the transmission when one of the signals is unmodulated. The DC component is filtered off the AC signal, which eliminates the measuring problems that otherwise would be caused by the DC offset properties of the mixer.

Variable rate digital filter

Abstract: A variable digital filter employs a variable rate sample clock with combinations of various digital filter elements such as an efficient implementation of decimation to achieve various filter realizations allowing a selectable output bandwidth. More specifically, a digital filter apparatus is coupled to receive input analog signals from a fixed anti-aliasing analog filter and optionally includes one or several stages of digital decimation filters, a low-pass filter, an optional equalizer, and an optional high-pass filter each of which may be programmed so as to configure the device with a variety of transfer characteristics. The filter device employs an input sample clock in the range of F-K*F, where, in a specific embodiment K is selected to be 2. The selectable combination of elements and stages used to form the filter needed is operative at a broad range of sample rates over a predetermined bandwidth range without loss of resolution. An extremely simple digital filter with a bandwidth of 1/4 the input sample rate is also shown.

Passive harmonic filter system for variable frequency drives

Abstract: A Variable Frequency Drive Power Center incorporating a new passive Harmonic Filter in an improved housing structure for Variable Frequency Drives (VFDs). The new harmonic filter improves the overall system performance by drastically reducing the line side current harmonics generated by all VFDs. The harmonic filter includes a series inductance, a parallel capacitance, and a buck transformer. The filter provides a low impedance path for the harmonic currents generated by VFD and therefore prevents them from flowing into the input ac power lines. The filter also improves the input power factor of the VFD system because of its increased inductive reactance under full-load conditions. Although the filter causes an overvoltage across the VFD terminals because of its increased capacitive reactance at the fundamental frequency this problem is overcome by using the buck transformer. The power center includes a separate section for the harmonic filter and a set of vertically-disposed compartments for mounting a plurality of VFDs on sliding assemblies. This provides a more efficient use of space and ease of maintenance, service and inspection of each individual unit.

Cochlear filter bank with switched-capacitor circuits

Abstract: A parallel dilating-filters switched-capacitor filter bank is described in simulation of the cochlea. Area-saving is achieved by filter-sharing, effective sum-gain amplifier designs, and using area efficient nth-order filter designs, and in particular using a biquadratic filter design using charge-differencing. The structure is easily expandable to include more channels by extending with additional filters and output amplifiers, or by using several chips with different sampling frequencies in parallel connection. An offset-compensated area-efficient switched-capacitor sum-gain amplifier circuit design is described and can be used in the filter bank.

A 2- mu m CMOS fifth-order low-pass continuous-time filter for video-frequency applications

Abstract: A fifth-order elliptic low-pass continuous-time filter based on triode transconductors for applications in the video frequency range is presented. Fabricated in a standard 2- mu m CMOS technology, the circuit occupies 6 mm/sup 2/ of silicon area including the automatic tuning circuitry. The filter achieves a 7-MHz cutoff frequency using a parasitic pole compensation scheme. The dynamic range is 40 dB and power consumption is 30 mW for a 5-V supply. A transconductor biasing strategy which allows a continuous tuning range for the cutoff frequency of one decade is presented. >

A review of median filter systems for analog signal processing

Abstract: This paper presents a review of existing analog implementations of the median and other ranked-order filter operations. The basic properties of median signal processing are first reviewed. Different analog median filter architectural approaches and implementations, introduced by several authors, are then discussed. These include filters based on analog delay lines and either nonlinear selection networks or ramp voltage generators. The Linear-Median Hybrid filter concept is presented and two examples of analog circuit implementations are given. Finally, a neural network approach is discussed.

The design of nonuniform-band maximally decimated filter banks

Abstract: A design method for nonuniform-band maximally decimated filter banks is presented. It is based on the quadrature mirror filter (QMF) design method and allows the direct frequency domain design of two-band filter banks having arbitrary rational decimation ratios. The numerical design of nonuniform-band filter banks is achieved using a simple structure in which elementary modulators are used in the highpass channel to obtain almost-perfect reconstruction. >

Apparatus and method for high performance wide-band power amplifier monolithic microwave integrated circuits

Abstract: A distributed amplifier produced from monolithic microwave integrated circuit (MMIC) processes employs a bandpass filter structure as opposed to a low-pass filter network to enhance gain, efficiency and output power over wideband operation of 6 GHz to 18 GHz. Derivation of the preferred embodiment is shown from a three port circuit employing bandpass filter image-parameter half-sections.

A low-noise active bandpass filter

Abstract: The design of narrowband active bandpass filters with high gain and low noise figure is described. The filter configuration is a combination of low-loss suspended stripline resonators and active microstrip circuits with FET devices. Measured results of this filter configuration with two resonators and one active circuit are presented. >

Multi-passband, dielectric filter construction

Abstract: A filter duplexer (280), such as a filter duplexer for a radio transceiver, of minimum dimensions is disclosed. A first filter portion (304, 308, 312, 316) of the duplexer filter includes resonators of at least a first geometric configuration, and a second filter circuit portion (320, 324, 328, 332, 336) of the duplexer filter comprises resonators of a second geometric configuration. The geometric configuration of the two filter circuit portions are dissimilar, and the relative characteristic admittances of the resonators of the respective filter circuit portions are dissimilar. Because the resonators of the two filter circuit portions are of dissimilar electrical characteristics, a desired frequency response of the duplexer filter may be obtained with similar loading capacitances.

Running-average/decimation filter for an oversampling A/D converter

Abstract: A filter processing unit 2 receives the output of an oversampling-type analog/digital (A/D) converter circuit 1. Predetermined information is acquired by a compensation circuit 3-1 with predetermined timing from the filter processing unit 2 in the course of processing for producing a filter output for a predetermined integration-phase state and the predetermined information is fed back to the filter processing unit 2 as compensation information representing a difference in magnitude between a filter output with an integration phase lagging behind or leading ahead of the predetermined integration-phase state and a filter output with an unchanged integration phase in order to produce a controllable-phase filter output DMout. The timing for the acquisition of the compensation information by the compensation circuit 3-1 is controlled by a control circuit 7-1.

Passive circuit for improving the power factor

Abstract: A circuit arrangement for radio-frequency operation of one or more loads (18) which are connected in parallel to each other, having a noise filter (suppression filter) (10), a rectifier (12) connected to the noise filter (10), connected thereto a diode-capacitor network (14), and an RF inverter (16) to whose output the load(s) (18) is/are connected, the diode-capacitor network being a diode-capacitor filter network (14) which is connected in such a manner that their filter capacitors (C1 to C4) can be charged in series and discharged in parallel or in series by means of a diode-resistor network (D1 to D4, Z1, Z2).

Dual bandpass microwave filter

Abstract: A two port dual bandpass microwave filter (30) consisting of "n" resonant cavities (38,42). Each cavity resonates in two independent modes at displaced frequencies so that the filter has two passbands in a desired frequency band. By orienting an incoming waveguide (48) at an angle with respect to the filter, both TE and TM modes can be excited to produce two separate passbands. The passbands may have either equal or unequal characteristics. Fine tuning of the TE and TM modes is accomplished using tuning plungers or tuning screws. The dual bandpass response of the new filter is achieved by utilizing the TE 1,1,1 and TM 0,1,0 modes in right circular cylindrical cavities, or equivalent modes in rectangular, or other cavities. These modes are orthogonal so they do not couple to each other. The cavity loaded Qs are independently adjustable, so the two passbands can have the same or different bandwidths, the same or different amplitude ripples and the same or different phase responses. The dual bandpass microwave filter provides filtering with but one set of cavity resonators rather than two. It does not require three port microwave junctions with critical path lengths. The filter is well-suited to filter the output of a single transmitter capable of operation at two differential frequencies.

Adaptive electronic filter

Abstract: A programmable and adaptive electronic filter for filtering digital signals. The filter uses a table which contains the outputs corresponding to all possible inputs, so that the filter may be constructed of memory, adders and multiplexers, and does not require multipliers. The input sample is used as an address to determine the location in the memory which contains the output corresponding to that input. The table of outputs is placed in a particular order such that the change between the inputs corresponding to each two adjacent locations is a single digit, thus allowing the table to be easily calculated, since the difference between the outputs in those two locations is two times the weighting coefficient for the digit in the input which is changed. Adaptive filtering is accomplished by using a second filter which has as its input the difference between the actual output of the filter and the desired output, and as its output changes to the weighting coefficients of the filter.

Fast stabilized adaptive algorithm for IIR bandpass/notch filters for a single sinusoid detection

Abstract: In this paper, a new algorithm for the detection of a single sinusoid corrupted by Gaussian noise using IIR adaptive bandpass/notch filter is presented. As the first step, the relation between the convergence speed and the filter Q-factor in IIR adaptive bandpass filter is analyzed. Based on the result of analysis, an algorithm is derived in which the filter Q-factor and the adaptive control signal generator Q-factor are made continuously variable so that they are inversely proportional to the distance between the filter center frequency f0 and the frequency f of the sinusoid to be detected. This makes both the convergence speed of f0 and f and the resolution high. Then it is found that limiting the maximum amplitude response of the adaptive control signal generator to a value proportional to sin 2πf can suppress the coefficient fluctuation after convergence effectively. By this approach, an IIR adaptive filter with a high Q can easily be realized. As the next step, an additional high-speed and highly stable adaptive algorithm is proposed in which the step size of the filter coefficient update is made to vary inversely with the filter Q-factor. A realization of the IIR adaptive notch filter is also presented. Finally, the usefulness of the proposed adaptive algorithm is verified by a computer simulation.

A multi-bandwidth saw filter

Abstract: A multi-bandwidth SAW filter (405) for an input signal (90) is provided which includes a SAW transducer (402) having a selectable length corresponding to the desired bandwidth of the filter. The SAW filter is responsive to a control signal (430) which corresponds to a selectable bandwidth of the filter to present the input signal to an appropriate length SAW transducer.