Showing papers on "Voltage-controlled filter published in 1977"

Adaptive noise canceling applied to sinusoidal interferences

Abstract: This paper investigates a new method for eliminating sinusoidal or other periodic interference corrupting a signal. This task is typically accomplished by explicitly measuring the frequency of the interference and implementing a notch filter at that frequency. The method proposed herein uses an adaptive filter to eliminate the interference. The procedure is called adaptive noise canceling and is applicable when an auxiliary reference input is available containing the interference alone. The reference input is filtered in such a way that it closely matches the interfering sinusoid, and is then subtracted from the primary input leaving the signal alone. The results of this research show that when a sum of sinusoids is applied to an adaptive filter, the filter converges to a dynamic solution in which the weights of the filter are time varying. This time-varying solution implements a tunable notch filter, with a notch located at each of the reference frequencies. When used in noise-canceling applications, this adaptive notch filter provides a simple alternative to other methods of tracking and eliminating sinusoidal interferences.

Electrically reprogrammable transversal filter using charge coupled devices

Abstract: A charge coupled device analog multiplier is used to weigh the sampled and delayed signals for a transversal filter The digital filter coefficients for the analog multiplier can be electrically programmed and therefore dynamic time-varying systems, such as matched filters, can be designed with reduced circuit complexity The digital filter includes means for sampling without destroying an analog signal at various points and providing voltages proportional to each sampled signal The voltages are separately applied to a charge coupled device analog multiplier which accepts the voltages and provides means for multiplying the digital filter coefficient by the analog voltage The multiplied sample signal is then dumped into a means for summing all of the weighted sample signals to produce an analog signal modified by the digital filter coefficients

FM Feedback demodulator having threshold extension circuit with two-pole crystal filters

Abstract: Demodulation of FM signals employing an FM feedback loop of the present invention includes a first mixer circuit for mixing an IF input signal with a voltage controlled oscillator signal to down-convert the IF input signal to a predescribed center frequency IF signal. This signal is coupled through a tuned amplifier having an automatic gain control loop and is then filtered in a predetection filter and amplified. The predetection filter is composed of a two-pole crystal bandpass filter having a very narrow bandwidth. The filtered signal is then coupled to a frequency discriminator circuit comprised of a frequency detection second mixer and filter circuit, the frequency detection filter circuit being composed of a second two-pole crystal bandpass filter, the bandwidth of which is an order of magnitude larger than that of the predetection filter. The output of the frequency discriminator is coupled through a loop compensation filter to the voltage controlled oscillator so that changes in the output frequency of the voltage controlled oscillator reduce the deviation of the FM signal in the intermediate frequency and frequency discriminator stages. The use of two-pole crystal bandpass filters improves the frequency stability of the system and significantly reduces post detection noise levels, as compared with conventional limiter/discriminator techniques. The two-pole crystal bandpass filters have a Butterworth configuration. In addition to the FM feedback loop, a squelch circuit is also coupled to the output of the frequency discriminator.

A general second-order digital filter with controlled rounding to exclude limit cycles for constant input signals

Abstract: In this paper a new general second-order digital filter section is proposed. One of the two quantizers used in the filter applies controlled rounding which has the effect that limit cycles are completely eliminated under constant-input conditions. Furthermore, the configuration of the filter is such that multipliers can be saved in case the filter is used as an all-pass filter or as a filter with zeros of transmission on the unit circle in the z domain.

Selective interference filter

Abstract: Filtering means for biophysical recording apparatus for removing interference from a signal source which includes a band rejection or notch filter and means for inserting the filter into the signal circuit when the signals have a certain characteristic and for removing the filter when the signals have another characteristic.

Digital filter circuit

Abstract: Apparatus in a digital filter circuit for substantially eliminating limit cycle noise comprises means for randomly inhibiting the rounding signal in at least one of the multipliers comprising the digital filter circuit.

Electrically tunable bandpass filter

Abstract: A bandpass filter is described for filtering a television signal. The filter has a passband which may be selectively centered for filtering signals in one of two channels of the television receiver. The television channel at which the filter passband is centered is selectable by applying a voltage to a control terminal. The filter frequency response for each channel selected may be independently controlled and a linear phase response is realized for the selected channel minimizing distortion.

Filtering technique based on high-frequency plant modeling for high-gain control

Abstract: This invention is an improvement in aircraft control systems that utilize feedback motion sensors to generate a control signal to control the aircraft. The improvement consists essentially of a complementary filter comprising a simplified model of the aircraft, a high-pass filter, a low-pass filter and a summing amplifier. The control signal is applied to the simplified model of the aircraft which ateempts to compute the vehicle response to the signal. This computed response is then fed into the high-pass filter to eliminate long-term errors in the calculated response, with the result that a good estimate of the high frequency content of the aircraft motion is obtained. In order to obtain a good estimate of the low frequency content of the motion a rate gyro signal is fed through the low-pass filter that eliminates all of the offending noise. The outputs from the high-pass and low-pass filters are summed by the summing amplifier to produce an estimated rate which is then used as a motion feedback signal. The use of the complementary filter permits a substantial increase in frequency band-width due to the simultaneous reduction in noise amplificaton and control limit-cycle tendencies.

Double-split-electrode transversal filter

Abstract: A novel structure for onchip tap-weight implementation in integrated c.c.d.-transversal-filter applications is presented. The new ‘double-split-electrodersquo; structure provides improved filter performance over the common-split-electrode technique by reducing the common-mode signal, sensing electrode capacitance and noise pickup.

Grounded-capacitor bandpass filter using the operational-amplifier pole

Abstract: A configuration for realising a 2nd-order bandpass filter based on the single-pole roll-off characteristics of the operational amplifier with a single grounded external capacitor is presented. The filter has low sensitivity to all the circuit parameters. Experimental results verify its suitability in high-frequency applications with moderately high selectivity. Independent control of centre frequency, frequency selectivity and midband gain is possible.

Plug-in filter network for separating a communication frequency into discrete frequency channels

Abstract: A filter network for separating a transmitted communication frequency into discrete channels. A separator, exemplified by a triplexer, includes a pluggable mid-range high Q bandpass filter and a diplexer of low Q bandpass filters. Circulators receive signals reflected from the high Q filter and pass them to the low Q filters. A combiner circuit takes the attenuated signal from the low Q filters and sends it through a circulator to a high Q plug in filter where the signal passes through a circulator where it is combined with the signal from the high Q filter of the separator as output.

Simple electronically tunable 2nd-order active filter

Abstract: A new current-tunable 2nd-order active filter is described which is based on the variation of the transconductance of a bipolar transistor with bias current. The circuit can give a lowpass or bandpass 2nd-order response or can be cascaded to give a high-order all-pole tunable filter. Measurements have indicated that a tuning range of at least four decades is possible with a dynamic range of 75 dB.

Electronically controllable filter

Abstract: An active filter, capable of being electronically controlled over a 50:1 or greater frequency range, while maintaining a fixed filter characteristic and a constant, nearzero DC offset voltage. The filter utilizes passive element-multipliers, either capacitor-multiplier or resistor-multiplier circuits, as the frequency determining networks, depending upon whether the filter is a low-pass or a high-pass filter. Tuning is accomplished by varying the gain of a variable gain amplifier connected in series with the capacitive or resistive element of the multiplier networks. Also disclosed is an implementation of the variable gain amplifier which permits the filter's cut-off frequency to be controlled digitally. The filter may be designed to have any desired type of filter characteristic. Several filter sections may be connected in cascade to provide any desired number of filter poles.

Apparatus for extracting the fundamental frequency from a complex audio wave form

Abstract: Apparatus for extracting the fundamental frequency from a complex audio wave form and for producing a pulse representation of said fundamental frequency includes a low pass filter having a frequency response characteristic which tends to exclude harmonics together with a control circuit including amplifier means, peak detector means and voltage to current converter means for supplying a control signal to the low pass filter thereby to vary the cutoff frequency of the filter and to maintain substantially constant amplitude of the fundmental wave form together with voltage comparator means for comparing the peaks of an alternating current quantity dependent upon the output of said filter with a direct current quantity proportional to the output of the filter, said comparator means thereby producing a pulse per cycle of said fundamental frequency.

Highly selective programmable filter module

Abstract: A programmable filter module includes a charge transfer device bandpass filter and a phase locked loop. The bandpass filter has a plurality of passbands dependent upon the frequency of a clocking signal. The phase locked loop receives a reference signal of one frequency and in response thereto, generates the clocking signals in the form N1 divided by N2 times the frequency of the reference signal, where N1 and N2 are programmable integers.

Programmable frequency converting filter

Abstract: Disclosed is a programmable frequency converting filter having a plurality of selectable operating modes, and having frequency passbands of a unique width for each of the operating modes. The programmable frequency converting filter is comprised of a charge transfer device transversal filter, a non-sampling filter, and a frequency band selector. The transversal filter has an output lead coupled to an input of the non-sampling filter, and has clock leads coupled to the output of the frequency band selector. The frequency band selector has control leads for receiving logic signals which together select operating modes from the plurality of modes. The frequency band selector generates, on the clock leads, clocking signals having a unique frequency for each mode of the plurality.

A fast microprogrammed digital filter design

Abstract: In this paper the design of a fast bipolar microprocessor based digital filter bank is considered. The filter is completely microprogrammed and can be used to realize modular digital filter structures. Several steps have been taken in the design to minimize the processing time, e.g. a separate RAM address processor and a separate hardware array multiplier are included.

High-performance low-pass filter utilising a mechanical energy store

Abstract: A novel low-pass power filter is proposed, in which a d.c. machine is used as a reactive element, replacing the conventional electrostatic capacitor. The equivalent capacitance of a suitably operated d.c. machine is, typically, several times larger than commercially obtainable electrostatic capacitors, and, therefore, a filter using a machine as one of its elements should have exceptional characteristics. The primitive machine filter, i.e. one in which the machine directly replaces the capacitance, is shown to be unsatisfactory because of the rotor's leakage inductance and resistance. The critical parameters in the compensation circuit necessary to overcome the effects of these factors are derived together with the required VA ratings of the machine and inductance in a typical L-type filter. Based on the derived principles, a machine filter, using a standard solid-iron-frame d.c. machine, has been assembled and tested, and the results show an output-voltage waveform which contains less than 0.333% total distortion. A theoretical study of the filter is presented using the proposed equivalent circuit. Finally, the machine filter is compared with classical passive-element systems under steady-state and transient conditions, and possible improvements are suggested. It is concluded that the machine filter is somewhat better than the classical filter in terms of cost and size, and that the noise and vibration problem may be offset in a number of applications by the machine filter's superior transient performance and extended temperature range.

A Universal Active-R Filter

Abstract: Different novel biquadratic active-Η filters are proposed; all of them use the first pole model of op. amp. instead of external capacitors. At first, the general block diagram of the universal filter is shown and analyzed; the corresponding circuit is given. As special cases L. P., B. P., H. P., notch, and allpass filters are derived from the proposed configuration; the simplest one of them is a H. P. — B. P. one which consists of two op. amps, and two resistors only. A design procedure and some curves are given for practical purposes. This universal filter has the advantage that it is of low sensitivities usable for high frequencies, and tunable by varying the resistors ratios. Verschiedene neue biquadratische aktivc-R Filter werden vorgeschlagen, die anstelle externer Kapazit ten den durch die inneren Kapazit ten der Operationsverst rker verursachten Frequenzgang der Verst rkung ausnutzen. Zuerst wird das Blockdiagramm des Universalfilters analysiert sowie eine Realisierung angegeben. Als Sonderf lle der universellen Schaltung werden Filter mit Tief-, Bandund Hochpa sowie Bandsperrencharakter angegeben. Die einfachste Anordnung besteht aus nur zwei Widerst nden und zwei Operationsverst rkern und verwirklicht eine Hochund Bandpa bertragungsfunktion gleichzeitig. Ein Entwurfsverfahren mit zugeh rigen Kurven wird vorgeschlagen. Das neue Universalfilter zeigt niedrige Empfindlichkeiten und ist auch f r hohe Frequenzen verwendbar. Das Netzwerk kann durch Variation von Widerstandsverh ltnissen abgestimmt werden. F r die Dokumentation: Aktive-R Filter / Operationsverst rker / Filtertheorie

A new high-Q active band-pass filter with low-gain stages

Abstract: The paper describes a simple high-Q insensitive active band-pass filter having relatively few passive components and active elements with low closed-loop gains, using positive feedback Q enhancement scheme. The proposed filter has minimum dependence on the bandwidth of the operational amplifiers and is capable of operating over a wide frequency range with relatively stable Q and resonant frequency.

Stereo tuner low frequency noise suppression - has voltage controlled stage switching to high pass filter mode in presence of noise

Abstract: Low frequency noise signals in stereo tuners are suppressed by a voltage controlled filter switched into a high pass mode in the presence of low frequency noise. The high frequency stage (1) is coupled to a timing potentiometer (2) and coupled over a demodulator (3) to the switching control stage (5). The switching control stage operates as a voltage controlled high pass filter supplying signals for the output stage (4) couple to the stereo loudspeakers (6). With constant tuning voltage applied (5a) the high pass effect is switched out, thus transmitting normal low frequency signals. When the tuning voltage increases the stage (5) switches to the high pass mode, thus blocking any low-frequency noise.

Interference-rejection filter using charge-coupled devices

Abstract: An application of c.c.d. is described to realise a multiple-notch filter which can be made to track and remove a periodic interfering signal and its harmonics. It is shown that, to first order, the filter notches are not dependent on incomplete charge transfer.

Performance of a Digital Filter With Rom-Rounding

Abstract: In order to keep the word size of a digital filter fixed, a round-off procedure is usually adopted. This can result in errors in the filter output. In this paper several round-off techniques, including a novel method called ROM-rounding are applied in the implementation of a second-order low pass filter. Results indicate that ROM rounding is a viable and cost effective technique for use in filter implementations.

Study of the use of a nonlinear, rate limited, filter on pilot control signals

Abstract: The use of a filter on the pilot's control output could improve the performance of the pilot-aircraft system. What is needed is a filter with a sharp high frequency cut-off, no resonance peak, and a minimum of lag at low frequencies. The present investigation studies the usefulness of a nonlinear, rate limited, filter in performing the needed function. The nonlinear filter is compared with a linear, first order filter, and no filter. An analytical study using pilot models and a simulation study using experienced test pilots was performed. The results showed that the nonlinear filter does promote quick, steady maneuvering. It is shown that the nonlinear filter attenuates the high frequency remnant and adds less phase lag to the low frequency signal than does the linear filter. It is also shown that the rate limit in the nonlinear filter can be set to be too restrictive, causing an unstable pilot-aircraft system response.