Showing papers on "Voltage-controlled filter published in 1982"

Combination speech synthesis and recognition apparatus

Abstract: A reconfigurable lattice filter is employed to permit the same circuitry to function as a speech synthesizer and as a speech analyzer or recognizer. The lattice filter can be configured both as an all-pole filter (for synthesis) and as an all-zero filter (for analysis), with the choice being determined by the state of an analysis/synthesis signal (i.e., mode control signal) provided thereto. The connections between various elements in the circuitry are controlled by the analysis/synthesis signal, also. In synthesis mode, partial correlation coefficients are supplied to the filter from a microprocessor. The filter is excited by a one of a number of stored patterns simulating a glottal pulse for voiced sounds and by a pseudo-random noise generator for unvoiced sounds. In analysis mode, appropriate feedback control paths are enabled so as to provide to the filter coefficients which change in response to changes in the input speech waveform. Coefficient values thus determined are averaged over fixed intervals and successions of such averaged coefficient sets produce representations of words or phrases which can then be used for speech recognition.

Filter and demodulation circuit

Abstract: A filter and demodulation circuit is proposed which, when used in a radio-frequency receiver, produces an increase in the sensitivity of the receiver. In the filter and demodulation circuit, the intermediate frequency is divided into at least two parallel channels (11, 12) at the input (10). Each channel contains a series circuit comprising a mixing and oscillator circuit (13, 15; 14, 16), a controllable IF filter (17, 18), a demodulator (19, 20) and a high-pass filter (21) or low-pass filter (22). One transmission channel essentially transmits the modulation frequencies of a first frequency range only and the other transmission channel transmits the modulation frequencies of a second frequency range. The AF voltage at the output of each transmission channel re-adjusts the IF filter of this channel and the oscillator circuit of the mixing and oscillator circuit of the other channel.

Miniaturized antenna duplexer using saw filter

Abstract: An antenna duplexer is made compact by a use of a SAW filter, and yet it eliminates the possibility that the SAW filter might be burned, and it avoids additional circuits, e.g., an impedance compensation circuit. The antenna duplexer comprises a local oscillation filter. A reception filter is coupled to the local oscillation filter. The coupled side is partly constituted by a SAW filter. A transmission filter is coupled to the reception filter and an antenna is coupled between the reception filter and the transmission filter.

Communications receiver having a switchable filter input stage

Abstract: A multichannel communications receiver, e.g. a CATV converter, includes a switched filter for reducing third order intermodulation distortion by limiting the number of channels processed by the receiver. In a preferred embodiment, the filter is switchable between a highpass and a lowpass configuration by a control signal supplied to two switching diodes. The input and output of the filter are coupled by a mutual inductance which partially compensates for the effect of parasitic inductance at higher frequencies.

Frequency synthesizers adaptive loop filter with compensation for transients

Abstract: An improved adaptive loop filter for modulatable frequency synthesizers containing digital phase comparators is described. The unique adaptive loop filter provides a wide bandwidth during a signal acquisition mode and a narrow bandwidth during a signal tracking mode. The adaptive loop filter includes a current limiter coupled to the error signal from the digital phase comparator for generating a current-limited output signal; a filter coupled by a resistor to the current limiter output signal and including a series-coupled resistor and capacitor for filtering the current limiter output signal to provide a steering line voltage; an amplifier coupled to the junction between the filter resistor and capacitor for generating a feedback signal; a resistor for coupling the feedback signal to the current limiter output signal for substantially reducing the duration of voltage transients; and a reference filter for coupling the steering line voltage to the steering input of a voltage-controlled oscillator. The wide acquisition loop bandwidth and the narrow tracking loop bandwidth are provided by switchably coupling different resistors to the filter capacitor. The phase shift produced by the reference filter is also changed depending on whether the acquisition or steering mode is active.

Broadband filter and tuning system

Abstract: A method and apparatus is disclosed for automatically and exactly tuning a boradband filter. Upon the detection of a tuning change, the filter is automatically switched end to end so that the output terminal of the filter is connected to the radio frequency power source. Radio frequency in this application refers to any signals whose frequency facilitates propagation of data via electromagnetic waves. The input terminal is terminated into a known load such as 50 ohms and C1, an input variable reactance is adjusted until a 90° phase relationship exists between the input resonator and the output resonator's node voltages. These actions set the exact tune condition for the broadband filter. The filter is then automatically reconnected in its normal operating position with its input terminal being connected to the RF power source and its output terminal being connected to its load, such as an antenna, and additional adjustments performed by varying the capacitance of the output capacitance C2 and the coupling capacitance C3.

Sampled data CT system including analog filter and compensating digital filter

Abstract: A CT scanner in which the amount of x-ray information acquired per unit time is substantially increased by using a continuous-on x-ray source and a sampled data system with the detector. An analog filter is used in the sampling system for band limiting the detector signal below the highest frequency of interest, but is a practically realizable filter and is therefore non-ideal. A digital filter is applied to the detector data after digitization to compensate for the characteristics of the analog filter, and to provide an overall filter characteristic more nearly like the ideal.

A monolithic audio spectrum analyzer for speech recognition systems

Abstract: A speech recognition monolithic audio spectrum analyzer, using NMOS switched capacitor filter technology, will be covered. Chip consists of 16 channels, each containing a bandpass filter, half-wave rectifier and low-pass filter to detect the frequency components of the voice signal.

Self-corrected electric filters

Abstract: A self-corrected electric filter with localized constant elements having two inputs, two outputs, input and output matching means, a group of an even number of filter elements in cascade for filtering the wide band signal, group delay time correction means comprising adjacent secondary couplings connected between at least two successive filter elements and secondary non-adjacent couplings connected between at least two non-adjacent filter elements

Adaptive control signal filter for audio signal expander

Abstract: A resistance-capacitance filter smoothes the control voltage of an audio signal expander. An analog gate couples the greater, in a given sense, of the smoothed control voltage and a further voltage to the control terminal of a variable gain device in the audio signal path, the further voltage being equal to the filter input voltage less a constant equal to Vbe. A time constant modifier circuit reduces the filter time constant when the filter input voltage differs in either sense from the smoothed control voltage by a fraction, less than unity, of Vbe. The resultant, relatively "narrow" dead zones of the adaptive filter enable operation of the expander with relatively low signal voltage levels thereby enabling a corresponding reduction in supply voltage requirements and providing further advantages such as reduced power dissipation, reduced heat build-up and improved reliability.

Variable bandwidth filter

Abstract: The filter has a fixed Q and is coupled to a source of AC signals. A source of pulses is applied to a variable-voltage circuit, the circuit being responsive to each pulse to produce a threshold voltage which varies from a first value toward a second value. A comparator circuit has one input coupled to the filter and a second input coupled to the variable voltage circuit. The comparator produces a signal for a duration related to the time the amplitude of an AC signal from the filter is at least equal to the threshold voltage.

Signal processing means acting as a frequency range translator and as a filter

Abstract: A signal processor for use in association with a frequency analyzer, can operate in the frequency translation mode or the filter mode. The signal processor comprises a first low pass filter, the signal from which is fed to two first parallel programmable gain amplifiers controlled by a first digital function controller. The signals then pass via two, second low pass filters to two second programmable gain amplifiers controlled by a second digital function controller. The signals from the second amplifiers are then added by an adder and filtered by a third low pass filter. The first controller is controlled by a frequency signal equal to the frequency in the middle of the bandwidth being translated and the first filter is controlled by a frequency which is a multiple of the control frequency to the first controller. In the range translation mode, the second filters and second controller have a control signal equal to the bandwidth frequency and the third filter is controlled by a signal which is a multiple of the control signal to the second filter and the second controller. In the filter mode, the cntrol signals to the first and second controllers are equal to each other and the control signals to the first and third are equal to each other.

Multifrequency eddy current testing device

Abstract: The prior art of multifrequency eddy current instruments has required a band pass filter to separate each individual frequency. The drawback of the above mentioned method is the requirement to change the bandpass filter if the inspection frequency is changed. This invention relates to a design that eliminates the requirement for a bandpass filter. The aggregate of inspection frequencies are applied to linear multipliers which shift the information from one of the inspection frequencies to a base band signal. The information is then separated from the signals of other frequencies with a low pass filter. The advantage is that an inspection frequency may be changed by changing the oscillator frequency only.

Diplexer useful especially for television tuning systems

Abstract: A diplexer for electrical signals comprises a first frequen­ cy selective filter (22) coupled between a first input terminal (20A), and a circuit point (24), a second frequency selective filter (26) coupled between the circuit point (24) and an output terminal (20C), and third frequency selective filter (28) coupled between a second input terminal (20B) and the circuit point (24). The first filter (22) selects frequencies higher than a first frequency and the second filter (26) selects frequencies lower than a second frequency which is higher than the first frequency, The third filter (28) selects frequen­ cies lower than a third frequency which is lower than the first frequency. In a television receiver, the first and second filters (22,26) serve as a bandpass filter for the UHF band, and the third filter (28) passes the VHF and CATV (cable television) bands.

Digital wave filter.

Abstract: 1. A digital wave filter formed with adders, delay elements and multipliers, characterised in that the sampling rate is increased by the factor N by directly connecting the reflected signal (b1 ) available at the input gate (R1 ), to a terminal provided for the input signal (a1 ) at those N-1 clock pulse times at which the source does not supply a signal (q), in such a manner that no delay-free loop is formed (Fig. 1, Fig. 2).

Eliminating device of interference wave

Abstract: PURPOSE:To automate the adjustment of the center frequency of a narrow band stop filter, by controlling this center frequency so that the phase of a signal in the input side and the output side of the narrow band stop filter which eliminates an interference wave coincide with each other. CONSTITUTION:A control voltage generator 27 is adjusted manually while watching the output of a variable band pass filter 26 on an indicator 28 to approximate the center frequency of the variable band pass filter 26 to the frequency of an interference wave. The control voltage from the control voltage generator 27 is supplied to a narrow band stop filter 13 and band pass filters 21 and 22 by a switch 29. When the switch 29 is connected to a phase comparator 25 in this state, the center frequency of the narrow band stop filter 13 is controlled automatically to coincide with the frequency of the interference wave accurately.

Active-phase-compensated biquadratic highpass filter

Abstract: A new three-amplifier active-phase-compensated biquadratic highpass filter is presented. It is shown that for the matched amplifiers the circuit exhibits a stable Q-factor and, unlike the Akerberg and Mossberg highpass circuit, feedforward paths are not required.

Low Loss RF Filter Using SAW Resonator

Abstract: A new SAW resonator filter on LiTaO3 (X-112°Y) substrate has been developed. The filter is a transducer coupling 3-poles filter with Butterworth response. It is constructed monolithically and requires no external elements. 3.5 dB minimum insertion loss, 5 10 kHz 3 dB-bandwidth, and 46 dB image signal rejection level are obtained at 280 MHz. This new filter, designed for a front-end filter, enables single super-heterodyne radio paging receivers to be offered.

Design of high-order filters with restricted component values

Abstract: The feasibility of realising a high-order LC filter with a small set of different capacitor values, without sacrificing the frequency response specifications, is indicated. This idea could be conveniently adopted in other filter structures also—for example the FDNR transformed filter realisations.

A CMOS time-multiplexed digital filter for vocoder applications

Abstract: In vocoder systems speech is spectrally analysed with filter banks containing 16 to 19 narrowband filters. Digital techniques can be used to realize these filter banks in an economical manner by using single time multiplexed second order filters. A hardware implementation of a fourth and an eighth order filter, realized with one time-shared second order section is described. A software package is developed to simulate the filter performance, and validate the experimentally measured response. The CMOS design of a programmable filter is presented. A second order section is time multiplexed to realize up to 32 poles of filtering. The configuration is mask programmable and the filter coefficients are programmable with a UV-PROM. The bank of contiguous bandpass filters for vocoder use can be implemented with three multi-function filter chips.

New filter for radar use and its microprocessor realization

Abstract: A new digital filter is presented for use in radar systems to extract smoothed range and range rate data from noisy range data. The performance of a real-time micro-processor realization of the filter is discussed, and comparisons are provided with fillers that have been previously reported.

Acoustic antialiasing filter having one resistive element for digitized microphone

Abstract: The synthetic method of electrical passive networks is successfully applied to the development of an acoustic antialiasing filter for an electret condenser microphone. The Butterworth type lowpass filter of order nine is realized as a tandem connection of an acoustic filter of order five and an electronic filter of order four which is imbeded in the microphone amplifier. The merit of this synthetic design is that the filter can be so realized with only one acoustic resistance that makes the adjustment at the production easy.

Tunable state-variable bandpass filter

Abstract: A simple method for tuning a state-variable bandpass filter over more than one octave without serious loss in the Q-value is presented. This is accomplished by modifying the input stage by adding one extra variable resistor. Analytical calculations show that there will be a 6% loss in quality factor over the tuning range.