Showing papers on "Electronic filter published in 1974"

Low-sensitivity active filters using the operational amplifier pole

Abstract: The utilization of the operational amplifier pole in the design leads to filters with satisfactory high-frequency performance. The approach reduces the number of capacitors required leading to circuits suitable for integration. Circuit arrangements for a bandpass filter and a second-order Butterworth low-pass filter have been suggested using only resistors and two operational amplifiers. The circuits have low parameter sensitivities.

Bucket-brigade transversal filters

Abstract: The bucket-brigade delay line (BBDL) is a sampled data circuit in which signal samples are stored and manipulated as packets of charge under the control of a digitally generated clock. The clock-controllable time delay function that is realized by the BBDL may be used to implement a number of signal processing functions. The tapped delay line or transversal filter structure is of particular interest, however, since it has wide application in the field of signal processing. The implementation of transversal filters via BBDL's is examined. The impact of nonideal delay line parameters on filter performance is considered and the results of computer simulations are presented. The practicability of monolithic transversal filters is demonstrated and the performance of experimental filters is described.

Capacitance multiplier and filter synthesizing network

Abstract: A circuit using a differential amplifier multiplies the capacitance of a discrete integrating capacitor by (R1 + R2)/R2 where R1 and R2 are values of discrete resistor coupling an input signal e1 to the amplifier inputs. The output eo of the amplifier is fed back and added to the signal coupled by the resistor R2 to the amplifier through a resistor of value R1. A discrete resistor Rx may be connected in series for a lag filter and a discrete resistor may be connected in series with the capacitor for a lead-lag filter. Voltage dividing resistors Ra and Rb may be included in the feedback circuit of the amplifier output eo to independently adjust the overall circuit gain ei /e o. ORIGIN OF INVENTION The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42 USC 2457). BACKGROUND OF THE INVENTION This invention relates to filter networks, and more particularly to networks for synthesizing an effective capacitance much larger than that provided by an included capacitor. There is a need in many applications for a circuit to synthesize a capacitor or other impedance, such as in an integrating circuit, with an effective capacitance much larger than that provided by a discrete capacitor. For example, in a communications system for spacecraft intended to be used in the exploration of planets, microminiaturization of the circuits aboard the spacecraft is essential. If a very large capacitor or other impedance is required in the system, such as a long term integrator of about 5,000 seconds in a phase-lock-loop filter, it becomes necessary to synthesize the capacitor with microminiaturized components. In synthesizing an effective filter with a time constant much larger than that provided by discrete elements, it is frequently important that the filter transfer function have a particular lead-lag characteristic, or that it have either only a lead or a lag characteristic. In addition, it may be desirable, or even necessary, for the filter to have a finite voltage gain. Consequently, it is desirable or necessary to be able to adjust the gain of the filter independently of the transfer function, where the transfer function is of the form: eo /e1 = A ([1 + τ2 S]/[1 + τ1 S]) (1) where S is equal to jω, j is equal to √-1 and ω is the angular frequency 2πf. A straight-forward circuit for synthesizing this transfer function may consist of a high gain inverting amplifier with an input resistor R1, a feedback resistor Rf and an RC circuit in parallel with the feedback resistor consisting of a resistor R2 in series with a capacitor C. In that circuit the time constant τ1 is equal to Rf C, the time constant τ2 is equal to R2 C, and A is equal to Rf /R1. It is evident that in this straightforward circuit, any change of Rf necessary to change the lag characteristic of the filter will cause a change in the gain A. Consequently, the larger the effective capacitor between the input terminal and circuit ground, the greater the gain. Therefore, an attenuator would be required at the output to compensate for increased gain whenever gain must not be affected. An attenuator at the input to the filter circuit may not be acceptable to compensate for increased gain because of the voltage offset which would be introduced. What is needed is a circuit having the general transfer function of Equation 1 with an adjustable gain independent of the lag or lead-lag characteristics of the circuit, i.e., independent of the integrating RC time constant of the circuit. OBJECTS AND SUMMARY OF THE INVENTION An object of the invention is to provide a circuit for synthesizing an effective capacitive element value much greater than that of included elements without causing large voltage swings and subsequent power supply limitations. Another object is to provide a circuit for synthesizing an effective filter with an integrating RC time constant much greater than that of included discrete elements with a desired lag or lead-lag characteristic. Still another object is to provide a circuit for synthesizing a lag or lead-lag filter with an independently adjustable voltage gain. These and other objects of the invention are achieved by a differential amplifier having one input terminal connected to an input junction by a first resistive means, an output terminal connected to a second input terminal by a second resistive means and to the input junction by a third resistive means, and an impedance means connected between the one input terminal of the amplifier and circuit ground. The effective impedance of the impedance means is inversely proportional to the ratio of the sum of the first and third resistive means to the third resistive means. A fourth resistive means couples an input signal to the input junction to implement a filter having a transfer function of the following general form: eo /e1 = (1 + τ2 S)/(1 + τ1 S) (2) to provide a DC gain factor A for the entire circuit, the second resistive means is comprised of two resistors in series with a resistor between circuit ground and the connection between the two series resistors. The transfer function is then of the form given by Equation 1. The gain A can be adjusted independently of time constants τ1 and τ2 by adjusting the ratio of the resistor connected to circuit ground to the sum of that resistor and the resistor connected in series with the resistive means, but when that is done the ratio of the fourth resistive means to the third resistive means must be readjusted to reset τ1 to the desired value, i.e., a desired gain A can be achieved independently of τ1 and τ2 by suitable selection of resistor values. Other objects and advantages of the invention will become apparent from the following description with reference to the drawings.

Velocity correction circuit for video discs

Abstract: Velocity and phase errors in signals derived from a rotating video disc are minimized with the use of a voltage controlled oscillator and an electromechanical transducer. A control circuit employing an active and a passive filter maintains an appropriate frequency response to the voltage controlled oscillator and electromechanical transducer in order to appropriately share a single controlling error signal.

A high-Q temperature insensitive bandpass filter using the operational amplifier pole

Abstract: A bandpass filter using only two resistors and two operational amplifiers is suggested. The circuit has a Q equal to the ratio of the ressistors. While Q and gain are insensitive to temperature variations, the variations in center frequency is minimized uing a compensation scheme.

Bucket-Brigade Transversal Filters

Abstract: The bucket-brigade delay line (BBDL) is a sampled data circuit in which signal samples are stored and manipulated as packets of charge under the control of a digitally generated clock. The clock-controllable time delay function that is realized by the BBDL may be used to implement a number of signal processing functions. The tapped delay line or transversal filter structure is of particular interest, however, since it has wide application in the field of signal processing. The implementation of transversal filters via BBDL's is examined. The impact of nonideal delay line parameters on filter performance is considered and the results of computer simulations are presented. The practicability of monolithic transversal filters is demonstrated and the performance of experimental filters is described.

An electrically-reprogrammable analog transversal filter

Abstract: A basic building block constructed with CCD and MNOS technologies will be described. The tap weights are analog and electrically reprogrammable to realize Fourier transformers, matched filters and correlators, and adaptive filters.

Circuit arrangement for digitally processing a given number of channel signals

Abstract: An arrangement for digitally processing a given number of analog channel signals, more particularly a digital multiplexer and demultiplexer provided with a number of signal paths each comprising a recursive digital filter and delay circuits arranged in cascade therewith, said filter circuits having an amplitude-frequency characteristic of a lowpass filter having a cut-off frequency which is equal to half the bandwidth of a channel signal and a phase-frequency characteristic which is such that the difference between such a phase-frequency characteristic and the phase-frequency characteristic of a reference digital filter has a sawtooth-shaped variation, the slope of the sawtooth being opposite to the slope of the cooperating delay circuit. The arrangement furthermore comprises in cascade a discrete Fourier transformer connected to the signal paths.

Non-recursive matched filters using charge-coupled devices

Abstract: CCD bandpass transversal filters using overlapping aluminum/polysilicon gate technology have been fabricated and tested. The measured out-of-band rejection was more than 50 db and the dynamic range was greater than 80 db with good linearity using single-phase clocking. This CCD filter performance has been extended to include the matched filter concept. Fifty tap CCD filters matched to complex signal and noise spectra have been fabricated and tested. These filters are intended to replace conventional analog filter amplifiers in scanning sensors. Test results confirm the substantial increase in signal-to-noise ratio (SNR) predicted. It was also confirmed that the filters remained matched for a range of scan rates (time-domain scaling) by suitably changing the CCD clock frequency and input pulse width. As noted for the bandpass filter, other parameters compare well with those typical of analog filter performance.

Noise reduction apparatus

Abstract: A noise reduction apparatus is provided which comprises a variable filter circuit which has a frequency characteristic which changes in response to an input signal of from a program source applied thereto so that the noise component of high frequency can be reduced and high fidelity reproduction of the input signal from the program source can be performed.

Parallel resonator with a resistance and a frequency dependent negative resistance realized with a single operational amplifier

Abstract: Bandpass RC active filters can be realized, according to Bruton's transformation method, with resistively coupled parallel resonators which are formed by parallel connecting of a resistance and a frequency-dependent netative resistance. This paper describes a single operational amplifier resonator which has an inherent finite quality factor. Bandpass RC active filters can be thus implemented when the passband is relatively narrow, with performance characteristics comparable to that of currently used LC filters, up to frequencies of a few kilohertz.

Transportation system with brake control and combined brake and field power supply

Abstract: A solid-state static power converter receives a three-phase A.C. input and directly supplies direct current to a D.C. motor armature circuit to operate a traction sheave to control the movement of an elevator car in response to an error signal derived by the selective summation of a speed signal from a tachometer and a vehicle speed command signal. A combined solidstate static power converter receives the three-phase A.C. input and directly supplies direct current to a field circuit of the D.C. motor in response to the operation of a field gating control circuit and also directly supplies direct current to a brake operating solenoid circuit controlling a friction braking element selectively coupled to an output shaft of the D.C. motor. The combined field and brake static power converter includes three controlled rectifying devices and three diodes connected to selectively supply half-wave rectified uni-directional power to the field circuit while a fourth controlled rectifier is connected to one of the phases and cooperates with one or more of the diodes utilized in the field current conversion together with one field output lead to supply uni-directional energy to the brake solenoid. The brake gating control includes a summing circuit receiving an alternating phase reference signal from the source through a lag filter circuit, a disable signal from the source through lead and lag filtering circuits, a constant reference signal, and a brake energy command signal supplied from a second summing circuit. The second summing circuit receives a brake lifting command signal in response to the supervisory control and a brake energy sensed feedback signal.

Rejection filter to remove TV channel 6 and FM radio interference

Abstract: A two terminal electronic filter network is provided for connection across TV antenna input terminals to reduce interference from noncommercial FM radio stations operating within a frequency band near the TV channel 6 frequency band. The two terminal electronic filter circuit which exhibits a rapid change of reactance for changes in frequency, and having a resonant frequency provides sufficient FM signal rejection without significant attenuation of any VHF channel by the provision of a highly reactive network tuned below the resonant frequency of the filter network as a whole.

Surface Wave Device Applications in Microwave Communication Systems

Abstract: The application of certain prototype devices, already realized in the complementary surface acoustic wave (SAW) and magnetostatic wave (MSW) technologies, is examined in the context of analogue and digital microwave communications equipments. The specifications of Gaussian response IF bandpass filters and satellite channel multiplexing filters are detailed in the context of SAW designs. Extensions of SAW filter technology to the construction of IF remodulating modems incorporating frequency modulated oscillators and discriminators are examined. Stable SAW oscillators are also reviewed in the context of lightweight, rugged, spacequalified local oscillator drives. The application of MSW technology to the design of a group delay equalizer for millimetric waveguide long-haul digital communications equipments is surveyed. Finally, the paper addresses the design of fixed and variable delay lines realized in both technologies, and SAW code generators, for application to path-length equalization and test{ng of high data rate microwave radio relay systems, respectively.

Sub networks for filter ladder networks

Abstract: The invention concerns a subnetwork of a filter circuit which is useful for detecting the dialing tone used in a telephone system. The arrangement employs active devices such as operational amplifiers in circuit with passive resistive and capactive elements to simulate an inductance S. Although it is known to modify a gyrator circuit to produce a 1/s2 function it has hitherto been considered that the use of such simulated functions in a ladder filter network would produce an unstable arrangement. It has been found that the combination of a 1/s2 element in series with a simulated 1/s element is stable and suitable for use in ladder filter networks.

Power measurement circuit

Abstract: A method and apparatus for detecting and measuring nonsynchronous frequency oscillatory power in a power transmission system. Current measuring devices and voltage measuring devices are connected to supply signals corresponding to instantaneous currents and voltages in the system. The current and voltage signals are combined in a multiplier to produce a signal proportional to instantaneous power in the system. The power signal is processed through a filter circuit to remove the average value component and the component at synchronous power generating frequency to produce an output signal representative only of non-synchronous frequency oscillatory power.

Active RC low-pass filter suitable for integration

Abstract: A canonic active RC low-pass filter having both capacitors earthed is given. The ω0 and the Q sensitivities with respect to all circuit components are derived. A unique feature of the circuit is that uo, is absolutely insensitive to the gain-bandwidth of the operational amplifiers.

Modifications of Tarmy-Ghausi active filter

Abstract: In the Tarmy-Ghausi active filter, a realisation of a summing amplifier plays an important role with respect to the Q-sensitivity of the transfer function. Here, some small sensitivity summing-amplifier configurations for this filter are presented. Examples of modified Tarmy-Ghausi circuits are given, and their sensitivity properties are compared.

Synthesis of narrowband cascaded crystal-capacitor lattice filters

Abstract: A design procedure is given for crystal lattice filters with a maximum bandwidth for quartz of approximately 0.15% of the centre frequency; the method results in simple formulae in terms of the elements of a low-pass ladder of any order.

Active filter with distributed RC line having zero Q-sensitivity

Abstract: The concept and properties of an active filter with a fourlayer distributed RC line in a feedback loop are presented. Due to specific properties of the four-layer RC line, it is possible to obtain zero Q -sensitivity of the filter to active-element gain variations. A design procedure for the bandpass filter with prescribed Q and center frequency \omega_{o} -values is given.

Electrically controlled acoustic-surface-wave filters

Abstract: The field-effect transistor is used for a linear control of the acoustic radiation of single-electrode section of the surface-wave transducer. The electrically controlled surface-wave filters and delay lines, the characteristics of which may be specified by a set of constant control voltages, are described on this basis.

Multichannel microwave filter

Abstract: Filter miniaturization is achieved by utilizing a dielectric resonator as the resonant circuit in each individual filter of a multichannel microwave filter bank. The filter circuits are mutually isolated and compactly stored in a multiple compartment filter housing structure. The housing structure consists of a center conductor, multiple conductive sheet members spaced transversely along the center conductor and multiple conductive sheet members parallel to and radiating from the center conductor. All conductive sheet members are interlocked to form a multiplicity of individual compartments that envelope the center conductor. The center conductor and the proximal edges of the parallel conductive sheet members define a coaxial microwave transmission line from which input microwave signal energy is coupled by means of coupling loops or probes to each individual filter circuit.

Welding arc stabilization - using trigger pulse generator

Abstract: The stabilizer unit is fed by one phase, of the three phase supply to the welding transformer, using an interwinding screened isolating transformer whose secondary charges two trigger pulse capacitors via antiparallel diodes and limiting resistors. the discharge of the capacitors into the primary of a pulse transformer whose secondary is connected to the welding electrode and workpiece, in parallel with the main weld current feed is controlled by a pair of antiparallel thyristors triggered from the choke and filter circuit by that main feed.

Two channel balance control device

Abstract: A signal level control device for varying the level of an input signal through the variation of a variable resistor. A switching circuit is turned ON for a period of time determined by the resistance of the variable resistor. The input signal is gated through the switching circuit during the ON time of the switching circuit. The output of the switching circuit is applied to a low pass filter which filters out the high frequency components due to the switching such that the output of the filter circuit is a signal having the same wave shape as the input signal and an amplitude proportional to the ON time of the switching circuit. By adjusting the variable resistor the ON time of the switching circuit is varied and thus the amplitude of the output signal is varied.

Flexible active filter design using three-operational amplifiers

Abstract: Active circuits containing three-operational amplifiers are presented from which various filter transfer functions can be easily obtained via open-circuiting appropriate passive elements. Any element value of the circuit depends only on a single coefficient of the biquadratic voltage transfer function realized.

Synthesis of sub-optimal RC filters

Abstract: In the design of filters, the main emphasis has been on the realization of ideal ‘brick wall’ characteristics of normalized low pass filter. Many attempts in this direction were aimed to achieve LC filters being lossless. But now inductorless filters are becoming attractive because resistors and capacitors are comparatively cheaper, simpler and more close to ideal than inductors, particularly, where low frequencies are encountered. A major breakthrough in this direction has been after the advent of integrated circuits.In this paper, well known Butterworth response is approximated by means of a physically RC realizable transfer function. Only passive components are used as these yield cheaper, more exact and least sensitive networks. The designed filters are only sub-optimal as RC transfer functions can not have their derivatives zero at ω=0. The performance of these RC filters is comparable with the Butterworth LC filter, both in frequency and time domains. An experimental verification for the same has be...