Showing papers on "Electronic filter published in 1973"

Quasi-Optimum Digital Phase-Locked Loops

Abstract: Quasi-optimum digital phase-locked loops (DPLL) are derived utilizing nonlinear estimation theory. Nonlinear approximations are employed to yield realizable loop structures. Baseband equivalent loop gains are derived, which, under high signal-to-noise ratio conditions may be calculated off line. Additional simplifications are made that permit the application of the Kalman filter algorithms to determine the minimum mean-square error (MSE) loop filter. Consideration is given to sampling rate and implementation requirements. Performance is evaluated by a theoretical analysis and by simulation. Theoretical and simulated results are discussed and a comparison to analog results is made.

A bandpass filter using the operational amplifier pole

Abstract: The pole of an operational amplifier and a grounded capacitor are used for obtaining a high Q bandpass function. The utilization of the pole of the operational amplifier enables the extension of its useful frequency range. The gain and the bandwidth of the operational amplifier are the primary factors determining the filter performance. The experimental results of a low-sensitivity filter circuit are presented. The circuit is suitable for integration.

Design formulas for biquad active filters using three operational amplifiers

Abstract: A circuit configuration and its design formulas are presented for the realization of all the useful forms of a biquadratic voltage transfer function. The circuit employs three single-ended operational amplifiers, two capacitors, and at most eight resistors. With an additional resistor, it can realize any biquadratic voltage transfer function.

Hybrid power filters employing both active and passive elements

Abstract: A hybrid power filter employing both active and passive filtering elements retaining the advantages of these elements while overcoming the main disadvantages of each when used separately. In one embodiment of the invention, the passive element comprises a capacitor and inductor in series across the power conductors connecting a source section to a load section and tuned to the frequency of the major ripple component. In shunt with the inductor, or possibly the capacitor, is an active element which generates a synthetic ripple which opposes and eliminates any residual ripple component which may pass from the source to the load section, or vice versa, due to the inherent resistance of the passive filter or to detuning of the filter formed by the passive elements. Multiple hybrid filters of this type may be connected across the power conductors, each filter being tuned to a selected frequency in a range of expected harmonic frequencies. In another embodiment of the invention, the passive element comprises a capacitor and an inductor in parallel, the parallel combination being connected in series between the source and load, together with an active element connected across the inductor of the filter.

Adaptable notch filter

Abstract: The present invention modifies a 2-stage Biquad notch filter by adding an inverter at the input to each stage and by replacing certain of the Biquad resistors with a set of resistors in the filter circuit. The notch width, notch depth, and notch center frequency of this modified Biquad filter may now be varied independently among a set of discrete values.

A universal low-Q active-filter building block suitable for hybrid-integrated circuit implementation

Abstract: A highly versatile second-order active-filter building block for low- Q applications (Q is described. The versatility is obtained by combining features inherent in the Sallen-Key circuit topology and those pertaining to hybrid-integrated circuits (HIC's). A high degree of circuit stability is obtained by designing individual network functions to depend primarily on the characteristics of stable thin-film resistors and capacitors. Frequency- and Q -sensitivity are examined in detail. Methods of minimizing Q -variation with respect to the active and passive elements are discussed. Lower bounds on the Q-variation obtainable with the hybrid-integrated filter building blocks are given. All possible second-order network functions, including the allpass function, can be obtained with the building block. The resulting universality and standardization permit the complete design of active filters consisting of cascaded building blocks by computer.

Circuit for generating a single high voltage subnanosecond pulse from a step recovery diode

Abstract: A series connected electronic circuit including in combination a trigger generator, an impulse generator, a filter circuit having an inductance L, a step recovery diode having a forward resistance RF and a reverse capacitance CR and an optimal bias circuit coupled to the step recovery diode. The trigger generator produces a train of pulses having a relatively long time interval, T, between each pulse; these pulses are then coupled to the impulse generator which produces an impulse having a Fourier component predominant at a frequency omega in response to each trigger pulse. The filter circuit converts each impulse into a damped sine wave having an angular frequency omega and a damping constant delta RF/2L. The sine wave is coupled to the step recovery diode which generates a single high voltage subnanosecond pulse having a half period, tp/ pi square root LCR in response to each damped sine wave.

Frequency filter apparatus and method

Abstract: An electrical filter is provided by a transmission line from which a coupling probe extends into a quarter wave (or odd multiple of a quarter wave) cavity tuned to resonate at the frequency that it is desired to pass along the line, the probe being tuned to produce frequency rejection notches in the line. A diplexer may consist of two such filters, each separated by an odd number of quarter wave lengths of transmission line from a common terminal, each filter causing its associated line to pass the frequency to which its cavity is tuned and to reject the frequency passed by the other line.

Airborne target recognition system

Abstract: In a radar target acquisition system means are provided for analyzing the video return including an automatic gate circuit causing the range gate to sweep out, and to sequentially sample the video return; a filter acquisition video processing circuit including means for discriminating between random and sinusoidal amplitude modulation appearing on the video return and having known frequency characteristics equal to the scan and pulse repetition frequencies of the radar within the pass band of the filter circuit, and means for comparing the discriminated amplitude modulated video return signal to at least one established threshold; and a track circuit which remains de-activated during the sweeping mode and is activated upon command from the filter acquisition circuit. Means are provided for manually initiating the gate circuit and for inhibiting the track circuit to await response from the filter acquisition circuit.

Active filter circuit

Abstract: An active element sharp cut-off bandpass filter circuit having independently tunable center frequency and Q characteristics. The filter circuit incorporates a high performance operational amplifier having one input connected to ground and a pair of feedback paths interconnecting the amplifier output and the other input. One feedback path includes two capacitors connected in series and the other path includes two resistors connected in series. The input to the filter circuit is connected, via an input resistor, to the common juncture of the capacitors; and the amplifier output is connected to the filter output terminal, as well as to one end of a grounded voltage divider having a movable tap. The common juncture of the feedback resistors is connected, via a capacitor, to the movable tap of the voltage divider. In one embodiment the capacitors have equal values and the feedback resistors have values which are four times the value of the input resistor.

Digital filter circuits

Abstract: An intrusion alarm system for providing an alarm indication in response to the detection of an intruder within a protected area includes Doppler radar apparatus having a transmitter for radiating energy into the protected area, a receiver for receiving Doppler signals provided whenever radiated energy is reflected off a moving body within the protected area and a signal detecting and filter circuit having a level detector circuit and a low pass digital filter circuit responsive to Doppler signals in excess of a predetermined amplitude and frequency to provide a logic level output indicative of the detection of an intruder within the protected area. In addition to the low pass digital filter circuit, there are described a high pass digital filter circuit and a digital band pass filter circuit.

Modulator arrangement for catv systems

Abstract: A modulator capable of distinguishing up-signals from one another and used in a bi-directional CATV system intended for various kinds of information services includes an arrangement wherein output terminal of a modulating portion is connected to a down-signal input terminal via a filter circuit for letting an up-signal frequency band or predetermined frequencies transmitted from the modulating portion and within the up-signal frequency band pass therethrough. The input terminal of the modulating portion is connected to a down-signal output terminal via a filter circuit for letting signals having frequencies transmitted from suscriber''s alarm transmitters a filter circuit is connected between down-signal input and output terminals for letting downsignals pass therethrough.

Ceramic filter circuit

Abstract: Reactance networks are connected just before and just after the ceramic filter element to adjust the linearity of the phase characteristic thereof, thereby reducing distortion.

Design of active filters with zero passive Q-sensitivity

Abstract: A new biquadratic active filter configuration is described which requires only two resistors, two capacitors, and two finite gain summing amplifiers. The circuit is shown to have zero Q -sensitivity to the resistors and capacitors and extremely low Q - sensitivity to the amplifiers.Other sensitivities of interest are also shown to be low. Practical realizations using one operational amplifier and additional resistors for each summing amplifier are given for bandpass, low-pass, high-pass, and notch filtering.

Circuit for improving rf pulse reception frequency resolution without rise-time degradation

Abstract: A filter circuit for detecting short pulses of radio frequency (RF) energy centered at a given center frequency and within a given narrow bandpass region. Received pulses of RF energy are upconverted in a frequency multiplier circuit to achieve resultant pulses at the same repetition rate and pulse width as the received pulses but having frequency spectrum components centered at a new center frequency of n times the given center frequency of the received pulses. These frequency spectrum components have the same absolute frequency and amplitude relationship to their new center frequency as the frequency spectrum components of the received pulses had to their given center frequency. The resultant pulses are then passed through a bandpass filter circuit having its bandpass region centered at the new center frequency and having a bandpass region wider than the width of the given narrow bandpass region. A detector circuit detects the passage of resultant pulses through the bandpass filter circuit. The multiplication of the received pulses by a factor of n allows the use of a bandpass filter circuit having a wider width than the given narrow bandpass region. This wider width bandpass filter allows the detection of relatively short pulses of RF energy. In one embodiment, it is desired to detect pulses of RF energy having a width of 0.1 microsecond or more, and having the RF spectrum of the received pulses centered at 90 megahertz. Further, it is desired to detect the pulses within a bandpass region of ±2.5 megahertz of the center frequency of 90 megahertz. The received pulses of RF energy are multiplied in a X3 frequency multiplier which allows the use of a bandpass filter having a width of 15 megahertz and centered at 270 megahertz.

A technique for accurate identification of alpha frequency in the EEG

Abstract: An economical and highly accurate electronic filter for the detection of narrow frequency bands in the electroencephalogram (EEG) is described. The apparatus employs solid state integrated circuits and digital logic to detect and provide feedback output. In the example given, this device acts as an alpha rhythm discriminator and provides the accuracy of a more expensive computer simulated filter.

Gated filter circuit

Abstract: The system is of the type that comprises a Gunn oscillator, transmitting and receiving antennas, and a mixer circuit. If there is intruder motion the doppler signal from the mixer circuit passes by way of a filter circuit and integrator to an output alarm circuit. In one embodiment the filter circuit is a notch filter that exhibits infinite attenuation above a predetermined frequency, such as 120 hertz, while passing lower intruder frequency signals. The system is also provided with novel supervisory alarm circuitry.

A low-sensitivity active RC low-pass filter

Abstract: A new active canonic RC low-pass filter is given. The sensitivities, with respect to all passive and active circuit components, are low. The frequency limitations of the filter are derived based on the one-pole rolloff model of the operational amplifier (OA) and the results arrived at are compared with other well-known low-pass filters. Experimental results agree with the theoretical ones.

An approach to active filter design problems using gyrators: A fresh look

Abstract: The conventional approach to active filter design problems using gyrators has been to replace each individual inductor (grounded or ungrounded) of the passive filter by an active network using one or more grounded gyrators. The method fails to realize three terminal versions when the passive filter is itself a balanced one (four-terminal two-port(. Another approach is to replace the passive filter as a whole by an equivalent active network using gyrators. The transfer function as a whole is synthesized as an active network. This method makes possible the realization of three terminal versions of certain active filters which are not possible by the conventional method. The method has been illustrated for the cases of a driving-point impedance function and a constant resistance lattice filter. An all-pass transfer function has been synthesized as an example.

Influence of capacitor losses on Q of active filters

Abstract: The Q and center frequency of a second-order RC filter are evaluated assuming a three-element dissipative capacitor model A comparison with the lossless case indicates that though the center frequency changes little, substantial variation in circuit Q Can occur.