Showing papers on "Voltage-controlled filter published in 1978"

High pass switched capacitor filter section

Abstract: A high-pass switched capacitor biquadratic filter based on the bilinear z-transform The filter comprises first and second integrating operational amplifiers connected in series and in combination with a third operational amplifier that serves as a sample and hold and also generates one simple pole and zero pair in the circuit transfer function thereby enabling the circuit to provide for a high degree of filter efficiency in a preselected frequency range The operational amplifiers are connected to and operate in cooperation with capacitors of a predetermined size which are switched on and off continuously by two phase clock signals supplied to the circuit The loss characteristic of the filter can be programmed by varying the clocking frequency Higher order filters can be obtained by the tandem connection of second order circuit sections followed by one or more first order pole-zero section

Filter which tracks changing frequency of input signal

Abstract: A tracking band-pass filter useful for locking onto, and passing, an input signal which changes rapidly in frequency. The filter has a frequency pass band controlled by a rectangular voltage waveform which is derived from the output signal passed by the filter. The filter output signal is translated from a sine wave to a pulse wave. The period between each two successive pulses is measured by counting the cycles of an oscillator during each respective period. The time-representing count is inverted to a frequency-representing count which controls the duty cycle of a rectangular wave used to make the filter track the changing frequency of the input signal.

Moving-average notch filter

Abstract: A moving-average notch filter with a well-defined phase characteristic for use in eliminating oscillation frequencies in a sound amplification system, wherein this moving-average filter is designed to have an output Y K in accordance with the system equation ##EQU1## where b 1 are the weighting coefficients, X K-i are input samples, and K is a constant. This filter may be designed to have a linear phase characteristic. In one embodiment, the location of the notch in the frequency response of the filter may be made to automatically track the drift of an acoustic oscillation frequency.

Adaptive filter network

Abstract: An adaptive filter network comprising a controllable filter having an adjustable cut-off frequency and adapted for varying the pass-band of the network. The adaptive filter network further includes a serial arrangement of an algebraic adder for generating control signals, connected to the controllable filter; a weighting filter for converting the control signal spectrum in response to the load sensitivity variation with frequency; a threshold limiter for setting the noise reduction threshold level of the adaptive filter network; a control signal frequency corrector; and an amplitude detector for shaping control signals applied to the control input of the controllable filter. The network analysis of the input audio signal spectrum and the width of its pass-band is varied depending on the present frequency limit of the input audio signal wanted components.

Variable response notch filter for machine resonance elimination in a servo control system

Abstract: This invention relates to a flexible notch filter for use in a servo system to eliminate natural mechanical resonance. The filter is an improved "twin-T" type where the "in-phase" output of the filter is fed back into the filter. Varying the feedback varies the bandwidth of the filter. The improved filter further provides for attenuation control in addition to control of the center frequency of the filter. The advantage of this filter over prior art designs is that one filter may be manufactured and adapted to be used in many servo systems since the filter can be easily adjusted to effectively eliminate the natural resonating frequency of the machine in addition to reducing phase lag at frequencies below the center frequency of the notch filter.

Citizens band transmitter with overall envelope feedback from antenna coupling filter

Abstract: A citizens band transmitter employing negative overall envelope feedback in the final RF stage obtains the feedback signal from a filter in the antenna coupling network which has a phase shift of 90 degrees or an odd multiple thereof at the radio frequency. A pair of detector diodes have their cathodes connected to opposite ends of filter and their anodes connected to a low pass filter to provide an envelope of the higher of the two voltages at either end of the filter in the coupling circuit in negative feedback to the modulating signal.

Amplifier nonlinearities in the multiple‐negative‐feedback bandpass filter

Abstract: A unified treatment is presented of the effect of both linear and nonlinear imperfections in an operational amplifier on the frequency response of a bandpass multiple-negative-feedback active filter. Linear computer models and describing-function techniques are used to evaluate performance for comparison with measurements. The critical peak-input voltage to avoid jump resonance is derived and performance limits illustrated on a Q–frequency plane.

A c.t.d. adaptive inverse filter

Abstract: An inverse filter, incorporating a charge-transfer-device (c.t.d.), tapped analog delay line and digitally programmed tap weights, is reported. This computer controlled analog processor performs a zero-forcing algorithm under software control. The inverse filter (or transversal equaliser) is demonstrated with an LC resonator as the distorting medium. The results show that this processor permits partially overlapping distorted impulses to be clearly discriminated.

An estimate of the order of an optimal FIR band-pass digital filter

Abstract: The computer program of McClellan, Parks and Rabiner [1] for designing optimal (minimax) FIR filters requires the order of the filter as an input parameter. Although a reliable estimate for the lowpass case is known [2], no such estimate exists for the bandpass case. In this paper we investigate the problem of estimating the order of an optimal bandpass filter. The effects of the design specifications on filter order are studied, and a simple estimate of the filter order is presented.

Programmable dynamic filter

Abstract: A programmable dynamic filter for use with a time-shared electronic organ or the like includes a filter circuit responsive to a logical state of a control signal for tracking notes generated by the instrument. Means are provided for programming the filter independently of generated notes by selectively adjusting the pulse width of the control signal to achieve desired musical effects.

A new active R bandpass filter

Abstract: A new active R filter which realizes a second order bandpass transfer function is given. The network employs only resistors and two operational amplifiers. Sensitivities to all passive and active circuit components are very low. Design equations are given and experimental results are also included.

Implementation of a 64-point adaptive filter using an analogue c.c.d. programmable filter

Abstract: This letter describes the construction and operation of an adaptive filter based on the Widrow least-mean-square adaption algorithm using a 64-point analogue programmable c.c.d. transversal filter as the main processing element. Initial test results are presented to confirm the principle of the system and these results may be readily compared with previously published simulation results.

Stripline Bandpass Filter with Variable Physical Dimensions

Abstract: A theory for the design of coupled-line bandpass filters has been derived. The filter comprises cascaded sections of two-port stepped coupled-line sections of length ?/4 and with individual wave impedance parameters within each ?/8 section. The design includes the possibility of altering the band-pass center frequency for a given length of the resonators. Narrow-band maximally flat or equal-ripple filter can be designed. The flexibility in filter length can be exploited for reducing space at low frequencies or for increasing the transmission line length-width ratio at high frequencies where the effect of end capacitance can be troublesome.

Multirate multiplierless discrete ladder filters

Abstract: Multirate discrete ladder filter structures are proposed that, when implemented as a digital filter, achieve better passband accuracy than the corresponding uniform-rate filter and, of more importance, may be implemented without the use of digital multipliers and consequently with simpler hardware and reduced filter processing times.

Interferences reduction for use in an FM radio receiver

Abstract: Information signals, 19 KHz stereo pilot signals and interference signals are received at an antenna and then applied to a low-pass filter and a high-pass filter. The interference signals derived from the high-pass filter control a gate which is disposed in a circuit path including the low-pass filter, a subcarrier generator and an FM multiplexer for the interference reduction purposes. A trap filter is provided between the antenna and the FM multiplexer for arresting the 19 KHz stereo pilot signals, while the signals derived from the low-pass filter are introduced into the above mentioned circuit path.

Monolithic, 64-Point, Programmable, Analogue CCD/MOST Transversal Filter

Abstract: A 64-point, monolithic, fully progromable, CCD/MOST transversal filter is reported. Its circuit principles and limitations are reviewed, and results for the device when used as a matched filter and a frequency filter are illustrated.

Implementation of a channel vocoder synthesizer using a fast, time-multiplexed digital filter

Abstract: This report describes the implementation of a 19-channel vocoder synthesizer, with a computer driven digital filter. The digital filter is a special purpose digital processor, which produces the transfer function of a second order section, with two poles and two zeros. Since up to 128 indipendent filter calculations can be completed during one sampling interval of the resulting speech wave, it can be time multiplexed into 128 indipendent filter sections; these can be interconnected in several ways, under computer control. The sections are used to implement the filter bank of a channel vocoder; coefficients determining both the structure of the system, and frequency response are also supplied by a computer, in this case a PDP 11/20. The basic scheme of the realized vocoder and its driving program will be discussed in detail. Possible applications include automated voice response systems in which the synthesizer is either controlled by data derived from naturally spoken sentences, or by parameters computed according to dyadic synthesis techniques.

An optimal filter design for variable sampling rates

Abstract: Digital filters in future speech communications terminals should be alterable to allow for various services, bandwidths, customer loads, and digital line rates. A filter structure which maintains a constant frequency response as the sampling rate is varied is considered for such an application. The filter structure requires several times the number of design parameters than in the cascade canonic form of the digital filter in order to maintain the constant frequency response. The filter design problem is formulated as a minimax optimization problem and solved using direct search techniques. An example is then solved using a modified version of Rosenbrocks Rotating Coordinate System Method. The example illustrates the considerable compromises needed over standard computer aided design techniques when solving this class of problems.

Electronically Tunable Active-RC All-pass Filter

Abstract: A second-order active all-pass filter is realized with three op. amp. biquad circuit. The tunability of the filter is achieved by the use of periodically-switched conductances within the circuit in which the regulation of the switching parameter allows the independent adjustment of the delay characteristics. It is shown that the maximum delay time and its corresponding frequency are adjustable independently by changing the ratio of the on-duration in a period to the period of switching. The electronically tunable active all-pass filter can be used for data transmission systems because of its sufficient flexibility of adjustment.