Showing papers on "Voltage-controlled filter published in 1988"

A 4-MHz CMOS continuous-time filter with on-chip automatic tuning

Abstract: A third-order elliptic low-pass continuous-time filter with a 4-MHz cutoff frequency, integrated in a 3- mu m p-well CMOS process, is presented. The design procedure is based on the direct simulation of a doubly terminated LC ladder filter by capacitors and fully balanced, current-controlled transconductance amplifiers with extended linear range. The on-chip automatic tuning circuit uses a phase-locked loop implemented with an 8.5-MHz controlled oscillator that matches a specific two-integrator loop of the filter. The complete circuit features 70-dB dynamic range (THD >

Analysis and design of an active power filter using quad-series voltage source PWM converters

Abstract: The modeling, analysis, and design of an active power filter using quad-series voltage source pulsewidth modulated (PWM) converters are presented. Some instantaneous space vectors of voltage and current are used for the analysis. A vector differential equation derived in this paper makes it easy to achieve the analysis and design of the active power filter. Experimental waveforms obtained from a prototype active power filter with a rating of 7 kVA, along with simulation waveforms, are included to verify the theory presented. >

Design of a 4-MHz analog integrated CMOS transconductance-C bandpass filter

Abstract: A continuous-time eighth-order fully integrated CMOS transconductance-C bandpass filter is presented for operation at 4 MHz with 800 kHz bandwidth and 0.5 dB pass-band ripple. A phase-locked loop for frequency tuning and four-point amplitude-locking loop for Q-factor tuning at the reflection zeros of the filter are implemented. The transfer characteristics were found to be essentially within specifications: less than 1-dB passband attenuation, 75-dB stopband attenuation and S/N ratio, and 0.5% harmonic distortion for 0.5-V/sub p-p/ signal were observed. Offset of the transconductances was internally controlled by an offset-control loop to less than 4 mV. A temperature-insensitive transconductance design and the noise characteristics of the filter building blocks are also discussed. >

Development of active filter with series resonant circuit

Abstract: An active AC harmonic filter, composed of high-frequency inverters and a series-resonant LC circuit turned to the fundamental frequency, is proposed to solve harmonic distortion problems on distribution systems at lower cost and with higher efficiency. The design includes a voltage-source inverter for further decrease of the loss, a static-induction thyristor for instantaneous current response, control logic that takes into account the coupling circuit characteristics, and high-speed harmonic voltage detection to suppress overloading of the customer's LC filter. Operational experience with a prototype filter on a 6.6 kV system is presented, verifying reduction of the operating and improvement of the transient response. In particular, there is a sharp reduction of inverter rating and operating loss about one-third to one-fourth, compared to results for an active filter without a coupling circuit. >

Analog implementation of median filter for real-time signal processing

Abstract: A novel median filter using analog tapped delay lines is designed for real-time signal processing. It requires only N+1 analog comparators for a window size of size N. As an extension, a general order-statistics filter can also be realized with moderate increase of circuit complexity. For current available fabrication technology for MOS switched-capacitor circuits, the filter can work at a clock rate up to 10 MHz. This development opens up possibilities for practical applications of nonlinear filtering in real-time signal processing, since the analog circuitry is far less complex than the corresponding digital circuitry. >

Secondary LC filter analysis and design techniques for current-mode-controlled converters

Abstract: Small-signal characteristics of current-mode-controlled PWM converters with a second-stage LC filter are analyzed It is shown that a secondary filter can be designed to provide good attenuation of the switching ripple while maintaining adequate stability margins with capacitive loading The resonant frequencies and damping coefficients of the second filter are derived, and design guidelines are given It is shown that the current-loop gain of the buck converter is not affected by the addition of the second-stage filters when a small filter inductance is used Three design examples are presented to demonstrate the use of analysis results Two filter examples are designed for a buck converter One of the second filters shows the problems that arise with a poor design A third example is the design of a second-stage filter for a buck-boost converter In each of the design examples, the small-signal analysis was performed using EASY5 software and the circuits were simulated using the state-space simulation program COSMIR >

Signal processor implementation of variable digital filters

Abstract: The implementation of two recently introduced variable digital filter schemes using a TMS320-series digital signal processor is presented. One is a method for updating the coefficients of an FIR (finite-impulse response) filter in a simple manner such that the cutoff frequencies can be controlled through a single parameter. The other is a method for tuning the cutoff frequency of an IIR (infinite-impulse response) filter with one parameter using a series expansion of the low-pass-low-pass frequency transformation. The measured frequency responses compare well with the theory. >

TVRO receiver system with tracking filter for rejection of image frequencies

Abstract: A TVRO receiver for the reception of frequency modulated satellite broadcast signals is provided with the capability of efficiently rejecting image frequencies generated as the received signals undergo intermediate frequency translation. A TVRO tuner, which includes a super-heterodyne circuit having a voltage-controlled oscillator (VCO), means for supplying a controlling tuning voltage to the VCO, and a mixer for combining incoming 1st IF signals with the output frequency of the VCO to reduce the frequency of the 1st IF signals to a selected 2nd IF frequency, is provided with a tracking filter which is adapted to pass only the incoming 1st IF signals and effectively reject any image frequencies generated at the received signal frequencies. The tracking filter comprises at least one low-pass filter section and has a cut-off frequency which is controlled by the same tuning voltage used to regulate the output frequency of the VCO in such a way that the filter rejects frequencies exceeding the VCO output frequency. The filter is designed so that image frequencies, which are generated during the intermediate frequency translation stage as the sum of a given VCO output frequency and the selected 2nd IF frequency, fall substantially beyond the filter cut-off frequency and are thereby attenuated. The tracking filter allows adequate rejection of image frequencies without need for accurate tuning of the low-pass filter sections or precisely matched variable capacitance devices.

Differential-time-constant bandpass filter using the analog properties of digital circuits

Abstract: An integrated circuit filter wherein two digital inverters are used, with cutoff frequencies which bracket the desired passband frequency. (The cutoff frequency of the two digital inverters is selected by changing their RC time constants.) The inverter with the lower cutoff frequency has its output connected to the reset input of a counter, and the inverter with the higher cutoff frequency has its output connected to the clock input of a counter.

Implementation of a tracking Kalman filter on a digital signal processor

Abstract: A Kalman filter for tracking moving objects has been implemented on a TMS32010 digital signal processor. Tracking accuracy and quantization effects of the implementation have been measured by comparing the filter to one implemented on a general-purpose computer with a 32 bit word length. The filter design has been optimized to minimize the program memory requirements and execution speed. Although the filter has been implemented on a specific signal processing chip, the design is general enough to be applicable to any other digital signal processor. The filter can be used for tracking objects for industrial or other applications where range and bearing measurements are available. For motion on a plane, the filter can be used to track objects where the maximum system bandwidth is 1680 Hz; for three-dimensional motion the system bandwidth is 1120 Hz. Using the approach presented, higher system bandwidth can be accommodated through higher-speed digital signal processors. >

Programmable universal active filter

Abstract: The invention relates to a microprocessor-programmable, universal active filter. The filter has an input section, an operational amplifier with two input nodes, a bandpass section, a lowpass section and control circuitry which, under clock control, periodically brings one of the inputs of the operational amplifier to within a low, d.c. offset voltage, approaching zero volts, of the other input. The output of the lowpass filter section is coupled to the input of the bandpass filter section and the lowpass section also has a feedback loop back to the bandpass section. The selectivity "Q", the gain, center frequency and the output characteristics, such as bandpass, lowpass, allpass, highpass or notch, of the filter may be selected using MOS switches under microprocessor control.

Bandpass filter for a CATV converter

Abstract: A bandpass filter for a CATV converter is of the structure with a low-pass filter section with low-pass filters connected longitudinally in a plurality of stages and a high-pass filter section, and comprises a variable trap circuit including a varactor and an inductor, and another varactor connected to one of the capacitors belonging to the low-pass filter section. Capacitances of these varactors are controlled by a tuning voltage so as to eliminate the various problems which would occur in a double-balance mixer to be connected at a later stage in the CATV converter.

Calculation of filter factors for digital filter

Abstract: An apparatus for calculating a filter factor for a digital filter which can be simply constructed and in which the time period for calculation can be shortened as compared with conventional techniques. The apparatus has an input circuit for inputting a desirable frequency property, a division circuit for dividing the inputted frequency property into a plurality of frequency bands, and a calculating circuit for obtaining filter factors for realizing a frequency property of each of the divided frequency bands. The input circuit inputs the frequency property with a frequency resolution corresponding to the number of the filter factors. The division circuit performs a correction for a division so that the frequency property becomes zero from a frequency over the high cut-off frequency of a band-pass filter toward the Nyquist frequency of the frequency band corresponding to the transversal filter, the Nyquist frequency being 1/2 of the sampling frequency. The calculating circuit has a transformation unit for performing a Hilbert transformation or a linear phase transformation with respect to the respective frequency properties divided by the division circuit.

A low-pass notch filter for bioelectric signals

Abstract: Many bioelectric signals have relatively low-frequency content, but measurement devices are susceptible to power-line interference. The Type II Chebyshev low-pass filter can simultaneously perform the required low-pass filtering and removal of the narrowband interference. This filter has transfer-function zeros which result in zero gain (- infinity dB) at specific 'null' frequencies. A procedure for the low-pass filter design makes the first null frequency a design parameter so that the notch can occur at the interference frequency. >

Active filter unit

Abstract: An active filter unit comprising a first active filter which operates under low-frequency PWM control for controlling the fundamental and low-order harmonic capacity and a second active filter which operates under high-frequency PWM control for controlling the high-order harmonic capacity. The first and second active filters are connected in series through associated transformers that are in serial connection across the power lines. The divided filter arrangement reduces the required power rating of high-frequency switching devices.

Adaptive AM audio processor

Abstract: An audio processor for adaptively rejecting undesired noise and interference in an audio input which includes a variable Q, 10 kHz switched capacitor notch filter. The Q of the notch filter is varied by a control loop responsive to the 10 kHz content of the audio signal. The notch filter includes a summer section that is clocked at a predetermined frequency, and an integrator section which is clocked at a multiple of the predetermined frequency in order to prevent center frequency variation with changes in Q of the notch filter.

Digital anti-aliasing filter

Abstract: An original analog signal is supplied to A/D converter 2 through analog LPF 1. LPF 1 has a cutoff frequency of fa/2 (fa is the frequency of a clock pulse supplied to A/D converter 2). LPF 1 limits a frequency band determined by filter characteristics. An output from A/D converter 2 is supplied to sample circuit 4 through maximum filter 3. An output from sample circuit 4 is supplied to a circuit of the next stage as final output Dout. Maximum filter 3 can arbitrarily set the number of sampling interval data (filter width). Maximum filter 3 is a nonlinear filter for outputting a maximum value of input data within a set filter width as a representative value of the width. The clock pulse of frequency fa is also supplied to maximum filter 3 so that input/output operation of data is synchronized with the clock pulse. The filter width of maximum filter 3 is determined in accordance with fa/fb (fb is the frequency of a clock pulse supplied to sample circuit 4 , and fa≧fb).

A new modular VLSI filter architecture using computationally efficient recursive digital filter topology

Abstract: The authors introduce a modular VLSI architecture for a novel linear-phase FIR (finite impulse response) filter structure. The proposed linear-phase FIR filters have a highly reduced number of general multiplications per sample compared to conventional FIR filters. The novel filter structure is based on an IIR subfilter whose infinite impulse response is truncated into a finite one. Although the subfilter has a nonlinear phase response, it can be made exactly linear by reversing the data stream in time and using the same filter again. Another possibility is to use a maximum-phase version of the FIR filter in cascade. The choice between different realizations depends on the filter specifications. In the general case the filter coefficients cannot be represented with the simple shift-and-add procedure and the time reversal technique should be used. The authors prefer the maximum-phase FIR alternative. >

A reconfigurable 64-tap transversal filter

Abstract: A high-speed transversal filter processor with 64 8-bit multiplier accumulators using several innovative custom design techniques has been realized in 14-mm*14-mm silicon at 20-MHz speeds. The processor (L64240) can be configured as a one-dimensional filter for radar or as a two-dimensional filter for real-time image applications. The authors describe the internal architecture of the filter, its key components, and the critical concerns addressing the speed and size of the design. >

Electronically tunable band-stop filter

Abstract: The design procedures for an electronically tuned band-stop filter are presented. A technique for realizing tunable band-stop filters with coupled lines is discussed. The physical design and electrical performance of a five-section band-stop filter tunable from 6.5 GHz to 10 GHz, with a constant bandwidth, is given. The circuit required to drive the band-stop filter and the calibration procedures are described. >

The Corrugated-Waveguide Sand-Pass Filter - A New Type of Waveguide Filter

Abstract: A new type of waveguide band-pass filter has been realized by combining a corrugated low-pass structure and a high-pass configuration based on the cut-off effect. Low-pass and high-pass functions depend on each other. Therefore after an initial standard synthesis of both functions the overall filter geometry is optimized using an accurate CAD model to obtain the required band-pass response. The filter is especially suited for wide-band applications due to its good far out of band selectivity.

Variable linear phase FIR filters

Abstract: A class of linear-phase digital filters is discussed for which the filter coefficients are simple functions of the parameters determining the desired frequency response. In the case of lowpass filters, the 6-dB cutoff frequency is the parameter considered. High-pass, bandpass, bandstop, and notch filters can be obtained with simple transformations from a low-pass prototype. The filters are variable over nearly the whole frequency range from zero to half the sampling frequency. Due to direct control of filter coefficients, the length of the filter does not change when it is made variable. >

Analog front-end circuit for full-duplex communication

Abstract: In the high-group passband filter of an analog front-end circuit for full-duplex communications, switches enable an all-pass filter, a high-pass filter, and a low-pass filter to be connected in the optimum series for different band assignments, thus improving S/N performance.

Sigma-delta modulation adaptive digital filter

Abstract: A novel approach to the realization of an adaptive transversal filter without multipliers is presented. In the realization, a modified least-mean-square (LMS) algorithm is used for updating the filter coefficients. The input signal is encoded by a sigma-delta modulator, thus it eliminates the need for complicated analog-to-digital converters and requires no multipliers for any filter length. Computer simulations are included to confirm the convergence of the mean-squared error. Performances of the filter as adaptive noise canceller and adaptive line enhancer were also demonstrated by computer simulations. >

The master-slave IIR filter adaptation algorithm

Abstract: An adaptive IIR (infinite-impulse response) filtering algorithm is proposed which combines advantages of two error criteria. The algorithm is termed master-slave, as an auxiliary adaptive filter (the slave) is used to assist the adaptation of the main adaptive IIR filter. By using an additional FIR (finite-impulse-response) filter to minimize the output error criterion, an IIR filter can be adapted using the preferred equation error criterion, while noise present in the desired filter response will not lead to biased parameter values. This enables IIR filters to converge much more rapidly than is possible with output error minimization alone. A steepest-descent form of the algorithm has been derived which uses a simple test to guarantee stability of the adaptive filter. >

Single switch dual output DC-DC converter

Abstract: A novel DC-DC converter is proposed that provides two independently regulated DC outputs from a single DC voltage source using one power semiconductor switch. The operation is based on the use of a low-pass filter and a higher-frequency bandpass filter. The output voltage supplied from the low-pass filter is regulated by controlling the duty cycle of the switch, while the other output voltage is controlled by changing the switching frequency. >

The realization of high-order OTA-C filter

Abstract: A new high-order OTA-C active filter using operational transconductance amplifiers (OTAs) and capacitors is presented. The filter has low sensitivity performance and high cut-off frequencies. Its cut-off frequencies can be controlled by a DC voltage or current. In addition, this filter is suitable for integration. Experimental results are given to show its feasibility.

Design of multirate bandpass digital filters with complex coefficients

Abstract: The multirate digital filter is useful in realizing narrowband characteristics because multiplication can be reduced by using different sampling frequencies, at the same time reducing the order of the filter to be realized. This paper introduces the complex coefficient into the traditional design of the low-pass multirate filter. The construction method is proposed for the multirate bandpass digital filter with complex coefficients. By applying the complex coefficient filters to the decimeter and interpolator composing the multirate filter, bandpass characteristics can easily be obtained. By employing the multistage cascade structure, the number of multiplications and the memory capacity for coefficients can be reduced greatly. Then a new design method for the complex-coefficient filter is proposed based on the properties of the analytic signal. The discussion in this paper applies to both FIR and IIR filters.