Showing papers on "Voltage-controlled filter published in 1981"

Diplexer for television tuning systems

Abstract: A diplexer comprises a first frequency selective filter coupled between its first input terminal and a circuit point, a second frequency selective filter coupled between the circuit point and its output terminal, and third frequency selective filter coupled between its second input terminal and the circuit point. The first filter selects frequencies higher than a first frequency and the second filter selects frequencies lower than a second frequency which is higher than the first frequency. The third filter selects frequencies lower than a third frequency which is lower than the first frequency. In a television receiver, the first and second filters serve as a bandpass filter for the UHF band, and the third filter passes the VHF and CATV bands.

A note on the use of windows for two-dimensional FIR filter design

Abstract: Using a one-dimensional window as a prototype, a two-dimensional window may be formulated having either a square region of support or a circular one. In this paper we compare the effects of using each of these window formulations for 2-D FIR filter design and present formulas for estimating filter order in terms of design specifications, using a Kaiser window as a prototype.

High-sensitivity fm signal demodulation system.

Abstract: The present invention relates to the improved demodulation system which improves the noise characteristics for the demodulation of a wideband television FM signal. A variable bandpass filter (8), the center frequency and the bandwidth of which are controllable, for improving C/N, is inserted at the output of a reference bandpass filter (7) in an FM signal path. The bandwidth of the variable bandpass filter (8) is controlled so that said bandwidth is wide when the input carrier level is high, and said bandwidth is narrow when the input carrier level is low. The center frequency of the variable bandwidth filter (8) is controlled so that said center frequency follows to the instantaneous frequency of the color sub-carrier component (3.58 MHz). Said color sub-carrier component is derived by a narrow-band bandpass filter (10) coupled with the output of said discriminator (9) for controlling the center frequency of the variable bandpass filter (8).

Linear phase filter with self-equalized group delay

Abstract: In modern communication systems, it has become important to provide filters, and in particular bandpass filters, which can provide substantially uniform group delay across the bandwidth of the filter while still achieving good amplitude response. In this regard, it is particularly desirable to substantially reduce the large variations in the phase characteristics found in conventional bandpass filters at the nominal band edge of the filter. To accomplish this, a filter is provided having at least one pair of lattice arms coupled in parallel to one another between the input and output of the filter. Each of the lattice arms includes a plurality of resonant LC resonators, each of the resonators having a different resonant frequency than the center frequency of the filter. In particular, within the bandwidth of the filter, the exponential damping coefficients for the resonators in each arm are set to decay at the same rate. This desired decay can be accomplished by exponential sizing of the components.

Integrated multi-stage electrical filter

Abstract: A multi-legged transformer core is employed to integrate into a single structure the discrete magnetic components required to form a multiple stage inductor-capacitor filter. The device may be employed in low pass filters used with inverters to remove high order harmonic frequency signals. The filter of the present invention is particularly useful in discharge lamp ballast circuits.

Real-Time Programmable Low-Power SC Bandpass Filter

Abstract: A real-time programmable switched-capacitor (SC) 2nd order bandpass filter is presented. It is based on voltage inverter switch (VIS) principle using inverse recharging devices. These devices are realized with dynamic amplifiers in order to achieve low power dissipation. The filter contains only grounded or virtually grounded network capacitances and therefore it is insensitive to the parasitics between the bottom plates of the implemented MOS capacitors and the substrate. It offers digital programming capability (two Q-factors and three center frequencies) and low power dissipation (185 ?W at sampling frequency 8 kHz and power supply voltage 10 V). The filter has been integrated in standard CMOS metal-gate technology.

Model and filter circuit for modeling an acoustic sound channel, uses of the model, and speech synthesizer applying the model

Abstract: Speech and music phonation formed by spectral formants is synthesized by a composite filter containing parallel filters in cascade. The composite filter design is generated by partial-function expansion of the approximate sound channel transfer function ##EQU1## and the composite filter is implemented with mutually adjacent formants in cascade filter elements.

Adjustable and selective electrical filters and methods of tuning them

Abstract: A notch filter is provided with an ancillary circuit including a non-inverting amplifier and a coupling which enables the filter to form part of an oscillatory loop of which the frequency of oscillation corresponds to the frequency of maximum rejection by the notch filter. Measurement of that frequency facilitates the tuning of the notch filter, which includes capacitors constituted by varactor diodes. The gain of the ancillary circuit may be adjusted to change its mode of operation from oscillation to that of a tuned amplifier so that a sweep of the center frequency of the notch filter through a range of interest facilitates a search for an unknown interfering frequency and the simultaneous tuning of the notch filter to reject that interference.

Hearing aid with controllable wide range of frequency response

Abstract: A hearing aid circuitry comprising a high pass filter and a low pass filter, for filtering the sound wave signals to permit adjustment of the gain of the high end of the frequency spectrum relative to its low end. The low pass filter is formed of a differential amplifier which performs a subtraction of the sound wave signal and the output signal of the high pass filter. The outputs of both filters are individually added together in proportional quantities by a single control. The use of the differential amplifier, or alternatively, a simple R-C filter of 6 dB fall off, minimizes frequency effects in the output signal in the frequency range where the high pass filter and low pass filter overlap.

Capacitive commutating filter

Abstract: A capacitive commutating filter provides a D C output voltage of amplitude responsive to the amplitude of an input waveform having a frequency substantially equal to the operating frequency of the filter The filter operating frequency is established by a digital signal The filter input is selectively and cyclically connected through N input resistances, wherein N is an integer greater than zero, to adjacently progressive N ones of (2N+1) nodes, each having one of (2N+1) capacitive filter elements connected to ground potential The equilibrium voltages across the capacitive filter elements, established during the N/(2N+1) segments of the input waveform during which each capacitor is connected to the input, are coupled to one set each of maximum-positive-polarity and maximum-negative-polarity diodes, for placing the maximum and minimum filter capacitive element voltages at respective ones of the inverting and non-inverting inputs of a differential amplifier, having the output thereof forming the filter output

Current mode biquadratic active filter

Abstract: A configuration of two transistors (Q1, Q2) and two capacitors (C1, C2) provides a current mode second-order active filter for IC implementation with low-pass, bandpass and high-pass capabilities. The filter frequency is tunable over a wide range, independently of filter Q and gain, by varying a DC bias current (Ibias1). The filter can provide one-port impedance functions, and two-port voltage, current and impedance transfer functions. With the addition of a second biasing current source (Ibias2), the filter Q can be controlled by adjusting the ratio of the two biasing current sources. Enhanced dynamic range and large signal performance can be achieved by the addition of linear resistors (R1, R2), with trade-offs in tunable frequency range and frequency linearity.

Serial minimum shift keyed modulator including notch and bandpass filters

Abstract: An SMSK modulator wherein the output of a bi-phase modulator is passed through a notch filter and a band pass filter to produce an SMSK signal for transmission. The notch filter and band pass filter are constructed to simulate the output (center lobe) of an SMSK conversion filter, which is defined as a filter that converts a bi-phase shift keyed (BPSK) modulated signal into MSK.

Monolithic IC general purpose active filter

Abstract: A general purpose active filter which can be fabricated as a single, monolithic IC. The IC includes two independent filter building blocks. Each filter block includes a pair of serially connected summers and a pair of serially connected switched capacitor positive integrators connected to the serial output of the summers. The IC further includes clock interface circuitry for receiving and conditioning first and second external clock signals. The interface circuitry drives the switches of the positive integrators of each filter block with one of the first and second conditioned clock signals. A plurality of input and output leads are interconnected with the components of each filter block to permit the filter blocks to be separately configured to perform various second order filter functions. The filter blocks may be tuned according to external resistance ratios and/or according to the frequencies of the external clock signals.

Wave digital filter hardware structure

Abstract: A large amount of literature has been published during the last decade on the design of digital filter structures with desirable attributes, such as low round off noise, simple coefficients or ease of implementation. In this paper, the hardware implementation of a structure based on a classical doubly-terminated distributed filter prototype is discussed. This structure has a prarticularly simple form as it is a cascade of identical 1st-order networks. The paper describes a programmable logic design centred on a high-speed bipolar LSI multiplier chip. It is shown that a complete 6th degree wave digital filter with analogue I/O can be implemented on a single S-100 printed-circuit board, and further that the filter can operate at a maximum sampling rate of around 150 kHs. The filter coefficients can be change in the controll program which is also stored in PROM.

Integrated CMOS SC filter with 170 kHz cutoff frequency

Abstract: Based on the theory of switched capacitor (SC) filters using voltage invertor switches (VIS) a third order lowpass filter has been designed and integrated in a standard CMOS metal gate technology. The filter uses a bottom plate stray-insensitive VIS and requires only unity gain buffers. Performance parameters of an integrated version are: cutoff frequency 170 kHz, dynamic range 70 dB, and power dissipation 12 mW.

Microprocessor-based digital filters

Abstract: The concepts of microprocessor-based digital filter implementation are presented via a case study of a lowpass filter designed using the bilinear z-transform method.Implementation aspects associated with an 8-bit generalpurpose microprocessor-based realization and a singlechip signal processor are discussed and results included.

Reduction of tolerance effects in the 2nd-order sallen-key filter

Abstract: In 1967, Saraga provided useful clarification of the factors involved in minimising the effect, on the performance of a 2nd-order Sallen-Key filter (in particular its Q-factor), of variations in its active and passive components. There existed at that time no automatic means of minimising the variation in circuit performance ensuing from component tolerances. For each class of circuit, a theoretical study - such as that of Saraga's for the Sallen-Key filter - was needed to provide guidelines for the designer. It is now possible to carry out such a minimisation by means of an iterative algorithm. The aim of this paper is to bring such an algorithm to the notice of filter designers, to demonstrate its application to the 2nd-order Sallen-Key filter, and to show how other factors (e.g. less than 100% yield) which are not tractable analytically can easily be taken into account.

A frequency shift maximum frequency follower Doppler demodulator with amplitude correction.

Abstract: A commonly used maximum-frequency follower Doppler demodulator uses a variable-frequency voltage controlled filter that requires two good quality multipliers and can be difficult to set up and stabilise. An alternative presented here has the advantage of cheapness, easy setting-up and amplitude independence over about 25 dB giving the potential for quantitative as well as qualitative results. A switching modulator is first used to convert the Doppler spectrum into a pair of sidebands disposed about the modulating frequency. The modulation frequency is continually adjusted so that the lower sideband edge, representing the highest Doppler frequency, just passes the skirt of a low pass filter. The filter output, after rectification and smoothing, provides drive to the voltage controlled oscillator (VCO) generating the modulation frequency and also forms the flow signal output. The fixed low pass filter results in a stable feed-back loop in which high loop gain can be used so that linearity depends mostly on the VCO. The characteristic slope is independent of signal amplitude above a threshold, but increasing signal causes an increasing offset voltage. A simple signal rectifier enables this offset to be largely cancelled, giving amplitude independence.

Low-noise state-space realisation of bandpass active filter

Abstract: An active 2nd-order bandpass state-space filter realisation known as the symmetric-form filter has been studied theoretically and practically and has been found to have desirable qualities, particularly those of low noise and good linearity. The noise and linearity performance of this realisation has been compared with that of the companion-form filter (feedforward filter).5.7 The dynamic range of the symmetric form, expressed as a power ratio, is shown to be 1000 times greater than that of the companion form having the same transfer function and using the same type of operational amplifier.

Monolithic tunable notch filter

Abstract: A MONOLITHIC SECOND-ORDER state variable filter has been realized using a standard bipolar technology. It is a continuous time filter configured to provide notch, bandpass and lowpass functions, and is tuneable over three decades of frequency by the ratio of two external dc voltages. It has a 90dB dynamic range,>4OdB power supply rejection, a response with a notch depth >50dB, and temperature drift of E200ppm. It does not require the clock input of the switched-capacitor filters??, or accurate passive components of RC active filters. It can serve as standalone filter.

A low-pass active filter with phase-lead compensation

Abstract: A second-order filter is described. A simple procedure is outlined for optimally satisfying a specified response.

Search circuit for car radio receiver for commercial vehicles - has 57 KHZ filter and LF filter for traffic news or ordinary broadcasting stations

Abstract: This car-radio receiver circuit specifically searches either for commercial or ordinary broadcasting stations. Selection is accomplished by a switch which activates an additional control stage, comprising a filter for the 57 kHz auxiliary carrier, followed by a second filter for the amplitude modulation signal of this carrier. When a manual switch is closed, a control stage which controls the tuning voltage generator becomes active at the start of the slow search phase. This is linked to a 57 kHz filter and a second, l.f. filter, to pass the l.f. signal modulating the carrier resulting in a control signal. With the switch open search facility for ordinary broadcasting stations is available.

Multiple-parameter tunable digital filters using submultiple sampling techniques

Abstract: A multiple-parameter variable digital filter is proposed which is derived from periodically switched analogue networks. A bilinear expansion of the system matrix with pairwise commutative matrices leads to a structure in which the significant parameters can be tuned independently. This method is demonstrated by a 2nd-order digital filter section. As an example, the results of a 2-parameter tunable 3rd-order lowpass filter are presented.

Three-layer low frequency hybrid electrothermal filter

Abstract: The heat transfer function for a three-layer structure with a heat source between layers is given. Measurements on a practically realised lowpass filter built with the described structure are given.

A high-quality digital filter instrument

Abstract: A high-quality real-time low power dissipation 12-bit low-pass digital-filter instrument is described. It is a hardware version of a recently proposed multirate ladder structure which can be implemented entirely without digital multipliers. The frequency response of the filter is user programmable and is determined by an operating sequence stored in a read-only memory. A numerical technique is described for determining the operating sequence corresponding to a particular low-pass response. Measured frequency responses are shown for four different cutoff frequencies between 2 and 5.5 kHz) for the fifth-order filter instrument.