Showing papers on "Voltage-controlled filter published in 1979"

Ultrasonic wave generating apparatus with voltage-controlled filter

Abstract: The present invention deals with an ultrasonic wave generating apparatus with voltage controlled filter, comprising a phase comparator which detects a shifted value from a predetermined phase difference between a driving voltage or a driving current of an ultrasonic transducer and a vibratory velocity signal, and a voltage-controlled band-pass filter which is controlled by the output of the phase comparator and which is provided in a feedback loop from the vibratory velocity signal to an input of a driving amplifier of the ultrasonic transducer, wherein the oscillating frequency is changed while following the resonant frequency of the ultrasonic transducer, so that stable operation is materialized without developing abnormal oscillation in subresonant frequencies and permitting very small following error.

Optimum Filter Design for a Single-Phase Solid-State UPS System

Abstract: A systematic design procedure for the output filter of a singlephase uninterruptible power supply (UPS) system is developed. The basic specifications for the UPS system are first established. Four different output filter configurations are then analyzed and compared for sinusoidal pulsewidth and single-pulse modulated inverter output (i.e., filter input) voltage. On the basis of the above comparison, ``optimum'' filters are selected for both modulation techniques. Using a minimization function for filter cost and size, a set of filter design parameters corresponding to each type of modulation are obtained on the per unit basis. The theoretical results are verified on an experimental breadboard utilizing a current commutated thyristor inverter. Finally, the overall filter design procedure is outlined and a design example is presented.

Loss sensitivities in singly and doubly terminated filters

Abstract: The loss of a conventional doubly terminated filter is far less sensitive than the loss of a singly terminated filter to errors in the component values. This property, first pointed out in 1966, has motivated many new high quality RC-active and digital filter design techniques. It is not so widely appreciated, however, that this superiority of the doubly terminated filter also holds for errors in the terminating resistances as well as for errors in the components inside the filter. The nature of these sensitivities in both types of filter is discussed in some detail, and Illustrated by means of a numerical example.

Band-pass filter circuit

Abstract: A band-pass filter circuit comprising a band-pass filter for removing noise modulation components from an input signal comprising a carrier sine wave, a phase detector for detecting a phase difference between input and output signals of the band-pass filter, a loop filter supplied with the output from the phase detector, and automatic control means for effecting control by the output from the loop filter so that a difference between the frequency of the input sine wave and the center frequency of the band-pass filter is reduced to zero. For carrier recovery in a burst mode, the loop filter is selected for each particular case so that high-speed pulling-in is possible even if a narrow-band filter is employed as the band-pass filter for the removal of noise components. Also, high-speed and high-precision pulling-in is achieved when many bursts of different frequencies are applied in one frame period. Further, when common and individual frequency variations occur at the same time, high-speed pulling-in is also achieved for each burst.

Tracking filter for FM threshold extension

Abstract: A tracking filter suitable for use in the IF stage of FM receiver circuitry incorporates a bandpass filter the components of which yield a characteristic that permits the filter to provide substantially the entirety of a required 90° phase shift for phase detection control circuitry that rapidly actively tunes capacitive components of the filter without imparting unacceptable group delay behavior to the configuration. The filter is a two-pole pair, single zero at the orgin, bandpass filter inserted in the signal path between a pair of signal power splitters. Part of the input signal is applied from the first splitter to one input of a phase comparator the other input of which is derived from the output signal via the second power splitter. The output of the phase comparator is applied through a broadband control amplifier to actively adjust the center frequency of the bandpass filter. Advantageously, this configuration enables the filter to have its center frequency effectively coincide with the instantaneous frequency of the deviating input signal, whereby an increase in performance over conventional filter approaches is obtained.

Q Enhanced resonator

Abstract: An active microwave filter for use in both bandpass and notch filter applications is herein described, the filter incorporating a distributed resonator to which is coupled an amplifier which provides a positive feedback and cancels the net dissipation in the resonator.

An electrically programmable analog NMOS second-order filter

Abstract: A fully-integrated NMOS electrically-programmable switched capacitor filter will be described. Digital words independently set the filter gain and Q between 1 and 65 in steps of 1, and the center frequency can be set to 1 of 8 values which span one frequency octave.

Active ladder filter for voicing electronic musical instruments

Abstract: A multiple-stage active RC distributed filter having multiple inputs and a single output for producing filtering of large groups of notes for tone coloration in electronic musical instruments. Output signals from the keying circuits may be applied to selected input stages of the filter through a resistor matrix to produce the desired tone coloration. Voicing may be further modified by one or more compensation networks at the filter output.

CMOS switched-capacitor filter for a two-chip PCM voice coder

Abstract: This paper will cover a CMOS switched-capacitor filter for a PCM CODEC Circuit consists of an elliptic low-pass ladder, a biquadratic high-pass filter and a state-space elliptic low-pass filter with a built-in sin X/X corrector

A comparison of different window formulations for two-dimensional FIR filter design

Abstract: Two-dimensional windows are generally derived by beginning with a one-dimensional window as a prototype and either rotating that window in the 2-D plane to produce a window with a round region of support or forming the outer product of that window with itself to produce a window with a square region of support. In this paper we present a comparison of results obtained using these two window formulations for 2-D FIR filter design. Design formulas are produced for estimating filter order for a given set of frequency domain specifications when a one-dimensional Kaiser window is used as the prototype window. The results suggest some interesting differences from the one-dimensional case.

Integrable analog active filter and method of same

Abstract: Integrable analog active filter suitable for MOS monolithic implementation. The filter utilizes only integrating amplifiers and ratioed capacitors thus being implementable in MOS technology and compatible for use in MOS digital systems. Filters of unlimited complexity and having arbitrary transfer functions can be implemented by the integrable analog active filter.

Automatic tuning circuits for voltage controlled filters, by digital phase control

Abstract: Automatic tuning circuit for voltage controlled filters, by digital phase control, including an oscillator and a path to be filtered associated with the voltage controlled filter, wherein the voltage controlled filter must be adjusted on a frequency equal or shifted by a preset amount with respect to the oscillator frequency, including means to scan the filter response while it is fed by the signal of the oscillator, means to detect the shift (positive or negative) of the filter response with respect to the oscillator frequency, means to measure in a digital way such a shift and arranged to provide a signal to correct the filter response, and means for digital storage of that correction signal.

Interrogating radar for use with tagged targets

Abstract: An interrogating station includes apparatus for transmitting a frequency modulated signal having a relatively low modulation rate to a plurality of uniquely tagged targets and for receiving therefrom a further modulated reply signal at a relatively high modulation rate, a mixer for mixing the transmitted and reply signals, to produce range modified tag modulation frequencies for all tagged targets, a voltage controlled filter for selectively passing the mixer output signal corresponding to any one of the tagged targets and a sweep and hold circuit for providing the frequency selecting voltage to the filter. The frequency selecting voltage is caused to change when no signal is passed by the filter and is fixed at the voltage corresponding to the signal frequency when a signal is passed by the filter. The magnitude of the frequency selecting voltage when fixed is used to determine the identity of the tag and the signal passed by the filter is further processed to determine range and/or range rate of the associated target.

Bandpass filter circuit

Abstract: An improved bandpass filter circuit for selecting a relatively narrow band portion of an input sinusoidal signal. The improved bandpass filter circuit produces an output signal whose phase deviation from the input signal is substantially constant for small variations in the frequency of the input signal. The improved bandpass filter circuit in accordance with the present invention does not use feedback control in its operation and therefore is free from the inherent delay time of a tracking type bandpass filter utilizing feedback control in handling transitory input signals.

Electronically tunable filter blocks

Abstract: Circuit blocks,suitable for integrated circuits, for realizing electronically tunable high-pass and low-pass filters, where the relationship between the controlling signal and the cut-off frequency can be both linear and inverse, are presented.

Active high-power bandpass filter

Abstract: An active power-line filter which provides bandpass filtering and transientuppression. The high-power signal to be filtered is modulated to form a chopped waveform within an envelope defined by the input waveform and the modulation is removed by passing the chopped signal through a low-pass filter. The output of the low-pass filter is then compared in a differential amplifier with a low-power reference signal which is phase-locked to the primary component of the high-power signal. The output of the differential amplifier is phase-compensated for the effects of the low-pass filter and is compared to the reference in a phase-detection multiplier to produce an error signal to adjust the duty cycle of the chopped waveform so that the waveform at the output of the low-pass filter is identical to the reference waveform. For periods when the high-power signal is out of phase with its primary component, the polarity of the high-powered signal is reversed at the input of the active filter to allow the filter to compensate for this situation.

High pass filter and method of making same

Abstract: There is provided a high pass switched capacitor filter having low bandpass ripple. The present filter does not have peaking near its center frequency when sampled at switching frequencies used in communication systems. The high pass filter has three switched capacitor integrators providing a 3-pole Chebyshev high pass switched capacitor filter. A fourth switched capacitor integrator is used to provide an output for the filter. A method of implementing the high pass filter from a set of parameter requirements is also provided. The capacitors used in this filter are ratios of each other and the filter readily lends itself to being implemented as a monolithic integrated circuit, particularly as a CMOS circuit.

Active filter for providing improved notch and band pass filters

Abstract: An active filter is disclosed for providing improved notch and band pass filters. The output to input frequency response of an active filter is mathematically expressed as a ratio of two polynominals in the Laplace operator S. In any notch filter, the coefficient of the S term in the numerator must be reduced to zero, while in any band pass arrangement the coefficient of the S term in the denominator is reduced to zero. The improved notch filter provides an input circuit for the operational amplifier portion of the filter which eliminates the S term in the numerator so that adjustments to reduce this term are unnecessary. Similarly, in the improved band pass filter, the S term in the denominator is eliminated in the feedback circuit provided for the operational amplifier, so that adjustment is unnecessary to eliminate the coefficient of S.

A simple filter design procedure using compensated operational amplifiers

Abstract: The effect of using a compensated operational amplifier in the design of second-order, minimum capacitor, active RC filters is [studied. A state-space description for the filter leads to a set of necessary conditions, in algebraic and topological forms, such that important properties of the ideal filter structure are achieved. These conditions are easily derived from the ideal structure. A simple design procedure enables the designer to get the moat out of the gain-bandwidth of the amplifier, obtaining an exact location for the pair of complex poles, while increasing considerably the frequency range where the structure is usable.

Commutating narrowband filter

Abstract: A signal to be filtered is applied to a commutating filter which is contred by a tunable oscillator tuned to a desired filter frequency. The commutating filter includes a plurality of RC networks to which the input signal is sequentially connected. The output of the commutating filter is a series of discrete voltages from the capacitor sections and of the RC networks which are fed to an analog to digital converter. The resulting digital words produced by the converter are stored in a microprocessor and used to compute the spectral content of the input signal by means of the Discrete Fourier Transform. The computed output from the microprocessor represents the effect of the cascaded filter sections of the system.

Minimal distortion video bandpass filter

Abstract: The present video bandpass filter passes a sinusoidal video output in response to a square pulse input. The video band-pass filter rejects d.c. and low frequency signal components as well as noise and spurious signals generated at the transmitting source. The video bandpass filter is comprised of an M-derived filter, a series-tuned notch filter, and a final d.c. blocking series-tuned filter which, together, pass the desired video with minimal distortion.

Self-adjusting bell filter circuit for use in SECAM coders

Abstract: A method and circuit for adjusting the frequency response of a bell filter in a SECAM camera samples the output signal from the filter. A frequency control voltage is applied to the filter in accordance with the sampled voltage.

Switched capaciter filter and method of making same

Abstract: There ist provided a high pass switched capacitor filter having low bandpass ripple The present filter does not have peaking near its center frequency when sampled at switching frequencies used in communication systems The high pass filter has three switched capacitor integrators (10, 25, 40) providing a 3-pole Chebyshev high pass switched capacitor filter A fourth switched capacitor integrator (50) is used to provide an output for the filter A method of implementing the high pass filter from a set of parameter requirements is also provided The capacitors used in this filter are rations of each other and the filter readily lends itself to being implemented as a monolithic integrated circuit, paricularly as a CMOS circuit

Fail-safe active bandpass filter using a modified twin-T filter

Abstract: A fail-safe active bandpass filter circuit is disclosed; that is, one having voltage gain and which is arranged to be fail-safe in the sense that opens, shorts and component value changes will not cause the circuit to self-oscillate and thereby produce a spurious signal that would cause unsafe effects.

Noise cancellation and inverse filtering using a compact high-performance c.c.d. adaptive filter

Abstract: This letter describes results obtained from a compact adaptive filter based on a charge-coupled device, programmable, analogue transversal filter. The adaptive algorithm used was the Widrow l.m.s. algorithm and results are presented for the 64-filter-point system used as a self-tuning filter, a noise canceller and as an inverse filter. The results illustrate the high quality of performance possible using this structure.

Alternative approach to the design of switched-capacitor filters

Abstract: An alternative switched-capacitor filter design is shown to be possible using an economic form of c.c.d. A simple example of a biquadratic digital-filter section is included to illustrate the point. This leads to comment on the relationship between switched-capacitor filters, the N-path filter and the digital filter.

Hybrid realisation of an adaptive filter for real-time noise-cancelling applications

Abstract: An efficient hybrid realisation of an adaptive filter for real-time noise-cancelling applications is described. The filter is based on an analogue tapped delay line but its coefficients are digital and are updated according to a simplified l.m.s. algorithm. A single multiplying d.a. device is used for performing the multiplications. The structure of the filter, its performance and processed examples are presented.

Explicit design formulae for wideband bandpass filters

Abstract: A new design technique is developed for the realization of wideband bandpass filters synthesized in the form of a lowpass filter cascaded with a highpass filter For the maximally flat and chebyshev response cases, approximate explicit design formulae are provided to allow a direct design technique to be used Results obtained by using this design technique agree with those obtained by direct synthesis and offer a significant improvement over the direct lowpass—highpass cascade obtained by frequency scaling