Showing papers on "Low-pass filter published in 1987"

A 4-MHz CMOS Continuous-Time Filter with On-Chip Automatic Tuning

Abstract: This paper presents a 3rd order low-pass continuous-time filter with 4 MHz cut-off frequency, integrated in a 3 ?m CMOS process. The design approach is based on the direct simulation of a doubly-terminated LC ladder using capacitors and fully-balanced, current-controlled transconductance amplifiers with extended linear range. PLL techniques, involving a 8.5 MHz controlled oscillator that matches a specific part of the filter, are used to realize on-chip automatic tuning. The complete circuit features 71 dB dynamic range and consumes only 16 mW from a single 5 V supply.

A New Class of Detail-Preserving Filters for Image Processing

Abstract: A new class of median type filters for image processing is proposed. In the filters, linear FIR substructures are used in conjunction with the median operation. The root signals and noise attenuation properties of the FIR-median hybrid filters are analyzed and compared to representative edge preserving filtering operations. The concept of multilevel median operation is introduced to improve the detail preserving property of conventional median and the FIR-median hybrid filters. In the multilevel filters there exists a tradeoff between noise attenuation and detail preservation. The analysis and examples indicate that FIR-median hybrid filters preserve details better and are computationally much more efficient than the conventional median and the K-nearest neighbor averaging filters.

Design of doubly-complementary IIR digital filters using a single complex allpass filter, with multirate applications

Abstract: It is shown that a large class of real-coefficient doubly-complementary IIR transfer function pairs can be implemented by means of a single complex allpass filter. For a real input sequence, the real part of the output sequence corresponds to the output of one of the transfer functions G(z) (for example, lowpass), whereas the imaginary part of the output sequence corresponds to its "complementary" filter H(z) (for example, highpass). The resulting implementation is structurally lossless, and hence the implementations of G(z) and H(z) have very low passband sensitivity. Numerical design examples are included, and a typical numerical example shows that the new implementation with 4 bits per multiplier is considerably better than a direct form implementation with 9 bits per multiplier. Multirate filter bank applications (quadrature mirror filtering) are outlined.

Fast Convolution with Laplacian-of-Gaussian Masks

Abstract: We present a technique for computing the convolution of an image with LoG (Laplacian-of-Gaussian) masks. It is well known that a LoG of variance a can be decomposed as a Gaussian mask and a LoG of variance ?1 < ?. We take advantage of the specific spectral characteristics of these filters in our computation: the LoG is a bandpass filter; we can therefore fold the spectrum of the image (after low pass filtering) without loss of information, which is equivalent to reducing the resolution. We present a complete evaluation of the parameters involved, together with a complexity analysis that leads to the paradoxical result that the computation time decreases when ? increases. We illustrate the method on two images.

Design of two-dimensional FIR digital filters by using the singular-value decomposition

Abstract: Singular-value decomposition (SVD) is applied to the design of two-dimensional (2-D) FIR (finite-impulse-response) digital filters. It is shown that three realizations are possible, namely, a direct realization, a modified version of direct realization, and a realization based on the combined application of SV and LU decomposition. Each of the realizations consists of a parallel arrangement of cascaded pairs of 1-D filters; hence extensive parallel processing and pipelining can be applied. The 1-D FIR filters can be designed using standard methods, and linear-phase causal 2-D filters that are suitable for real-time or quasi-real-time applications can also be designed. The three realizations are compared, and it is shown that the realization based on combined SV and LU decomposition leads to the lowest approximation error and involves the smallest number of multiplications. SVD, the McClellan transformation, and 2-D window design methods are used to design a bandpass and a fan filter, and the results are compared. >

Frequency Domain Analysis and Synthesis of Image Pyramid Generating Kernels

Abstract: Construction of image pyramids is described as a two-di-mensional decimation process Frequently employed generating kernels are compared to the optimal kernel that assures minimal information loss after the resolution reduction, ie, the one corresponding to an ideal low pass filter Physically realizable, optimal generating kernels are presented The amount of computation required for generation of the image pyramid can be reduced significantly by employing half-band filters as components of the optimal kernel Image pyramids generated by the optimal kernel show a better command of details than the ones generated by a simple 4 × 4 averaging, or a computationally equivalent kernel

Optimum time domain signal transmission and source location in a waveguide

Abstract: The research on transmission and filter operations has two purposes. The first purpose is to reduce channel distortion and the second is to locate a source. It uses impulse responses of transmissions between a source and a receiver in a waveguide. A time reversal of the impulse response gives the matched filter for the transmission. The matched filter is an optimum filter for the reduction of transmission distortion. A numerical example demonstrates distortion reduction. Since the impulse response between a source and receiver is a function of waveguide structure, source position, and receiver position, one can use the impulse response to determine source position by passing the received signal through a set of reference or theoretical impulse response functions for trial source positions. The ambiguity of source locations depends on waveguide structure and the complexity of the impulse response. Basically ambiguity decreases as complexity increases. A plane‐layered waveguide requires at least three receivers that are not in a line. The signal processing consists of match filtering each receiver for a trial source location and then cross correlating the trial filter outputs. The pairwise cross correlations have a maximum when the trial location is the same as the source position. The cross correlation at match also gives an estimate of the autocorrelation of the source. The source can radiate impulsive transients or continuous random signals.

Video processing in which high frequency luminance components are folded into a mid-band spectrum

Abstract: Apparatus is disclosed for processing incoming scanning lines of video information having a nominal bandwidth for use with a bandwidth degrading path, such as magnetic tape. A preprocessor includes a preprocessor comb filter (16) for comb filter processing of the incoming scanning lines to assure the presence of spectral gaps between energy groups in the spectrum of the video information. A fold over circuit (42) folds over high frequency luminance components of the video information about a predetermined folding frequency to provide folded video. A low pass filter (46) filters the resultant folded video to limit the spectrum thereof to be not generally in excess of one half of the folding frequency. A postprocessor includes an unfolding circuit (66) for unfolding the signal from the path about the predetermined folding frequency. A postprocessor comb filter (68) processes the unfolded signal to eliminate unwanted alias components therein resulting during the unfolding process and provides a resultant video signal closely approximating the bandwidth and content of the original video information.

Sample data band-pass filter device

Abstract: The sampled-data band-pass filter device is based on the phenomemon of aliasing, and allows the substantially unattenuated passage of the components of an input signal at a frequency included within an interval comprised between a first frequency (fsL) and a second frequency (fsH), arranged around a third frequency (fsO), while it substantially attenuates the components of the input signal at frequencies outside said interval, and furthermore automatically performs the shift to low-frequency, around a fourth frequency (fO), of the components of the input signal which have passed without attenuation. According to the invention, the device comprises, as filter element, a sampled-data band-pass filter which employs, as sampling frequency, a fifth frequency (fs) equal to a whole submultiple of a sixth frequency (nfs) equal to the sum of the third frequency (fsO) and the fourth frequency (fO), having, as lower and upper cutoff frequencies, respectively the difference between the sixth frequency and the second frequency (nfs -fsH) and the difference between the sixth frequency and the first frequency (nfs -fsL).

GaAs switched-capacitor circuits for high-speed signal processing

Abstract: Switched-capacitor building blocks are presented which are suitable for implementation in GaAs MESFET technology. They include gain stages, operational amplifiers, and transmission gates. Switched-capacitor design techniques are discussed that minimize filter sensitivity to GaAs op-amp limitations. Experimental results are presented on a variety of GaAs switched-capacitor circuits, including a gain stage, a second-order bandpass filter, and a third-order low-pass filter. The circuits demonstrate sampling rates exceeding 100 MHz without significant loss of accuracy.

Time constant automatic adjustment circuit for a filter circuit

Abstract: An automatic adjustment circuit for adjusting the time constant of a filter circuit. The adjustment circuit includes a source of reference frequency signal, an oscillator for generating an oscillation signal, and a detector for detecting the difference in one of phase and frequency between the reference frequency signal and the oscillation signal and generating a control signal for automatically adjusting the time constant of the filter circuit.

Hearing aid circuit

Abstract: A hearing aid that is compact and efficient and that provides a high degree of control over its frequency response and also over its output level versus input level characteristic. The frequency response control includes an adjustable four pole high pass filter and an adjustable four pole low pass filter, to define the pass band, and an adjustable slope filter, to define the slope within the pass band. The control over the output level versus input level characteristic includes an input AGC system with well defined, independent control of compression threshold and compression ratio, an adjustable peak clipper, and a selectable output AGC system that tracks the peak clipper setting. The hearing aid incorporates a number of novel circuits including a state variable filter with adjustable corner frequency, a filter that can be continuously adjusted from a single pole low pass characteristic to a single pole high pass characteristic, a circuit to provide a range of reference voltages to accurately set the range of control currents used to control the corner frequencies of the state variable filters, a compansion system surrounding the filter network to effectively increase its limited dynamic range, a differential voltage threshold detector, a differential voltage controlled current source with an exponential relationship of output current to differential input voltage, an adjustable clipping circuit, a voltage clamp to prevent voltage excursions from going substantially below a substrate voltage, and bias compensation circuit to supply the input bias current of a transistor.

Color display apparatus for displaying a multi-color visual pattern derived from two audio signals

Abstract: An apparatus is disclosed for displaying two-channel audio input signals in a three-color visual pattern. In general, the visual pattern may be formed on a viewing screen by an apparently moving spot having three color components. Phase shifting means is employed to phase shift one of the two audio input signals, and both audio input signals are subsequently processed by low pass filters to produce positioning signals in X-Y coordinates for the spot which forms the visual pattern. In addition, the two audio input signals are also mixed and separately processed by a high pass filter, a band pass filter and a low pass filter to produce frequency separated signals for controlling the intensity of each of three color components of the spot forming the visual pattern. Automatic color balance means utilizing negative feedback is employed to control the amplitude of the separate frequency-discriminated audio signals. In a preferred embodiment, the display unit employs a color cathode ray tube and may comprise equipment of the type normally found in video games or in a color television receiver altered to accept X-Y position and color information.

A Low-Cost Multichannel Preamplifier for Physiological Signals

Abstract: A preamplifier for physiological signals (ECG, EMG, etc.) is described for general use in mnltichannel applications. The limited number of components made it possible to implement eight channels on one Eurocard printed circuit board (160 x 100 mm) and 64 channels in a 9.5 in cabinet in a cost-effective manner (about $ 50 per channel). The use of a monolithic instrumentation amplifier based on the current feedback principle resulted in high dc suppression combined with excellent noise performance and high common mode rejection. A second-order Butterworth low-pass filter was implemented using switched capacitor circuits, so that in a multichannel setup the rolloff frequency of all channels can be (digitally) controlled by one clock frequency.

Multiplierless decimating low-pass filter for a noise-shaping A/D converter

Abstract: A method and means for filtering the quantization noise from the output of a 1-bit analog-to-digital converter (noise-shaping coder) is disclosed. The A/D utilizes oversampling of the analog input signal, and decimation of the digital output signal. The multiplierless low-pass filter is comprised of a coefficient ROM for storing the filter coefficients, a counter for addressing the memory, and a true/complement gate for selectively complementing the output of the memory in response to the 1-bit data stream from the noise-shaping coder. An accumulator sums the selectively complemented output words for all samples, and the accumulated output is then applied to the decimator. A second embodiment is also disclosed which utilizes an overlapping digital filter approach, wherein a plurality of digital multiplierless filters are overlapped to provide an arbitrary length filter capable of producing an arbitrary filter response.

Microwave band-pass filter

Abstract: A microwave band pass filter comprises a band pass filter of the coaxial type which is formed by connecting plural coaxial type resonators in series through capacitors, and another band pass filter of the comb line type connected in series to the coaxial type band pass filter, wherein lower cutoff frequencies for the coaxial type band pass filter are included in a pass band for the comb line type band pass filter while higher cutoff frequencies for the comb line type band pass filter are included in a pass band for the coaxial type band pass filter, so that the skirting characteristic can be made sharp at high and low bands even with fewer resonator stages

A 3.6-MHz cutoff frequency CMOS elliptic low-pass switched-capacitor ladder filter for video communication

Abstract: The high frequency (HF) behavior of the switched-capacitor (SC) LDI ladder filter is studied. This study shows that using low sampling frequency with respect to the cutoff frequency reduces the HF error due to the reduction in amplifier gain. Design techniques are also given for the HF SC filters, such as double-sampling scheme, a low sampling frequency with an exact synthesis algorithm, as well as a fast-settling folded-cascode amplifier. These techniques are applied to an experimental fifth-order elliptic SC filter fabricated in a 2-/spl mu/m CMOS technology. The experimental results show that a 3.6-MHz cutoff frequency is attained. All the capacitors are scaled down in order to reduce the setting time of the amplifiers. The active area of the filter is 0.9 mm/SUP 2/. The F/SUB sampling//F/SUB cutoff/ is only 5. The circuit operates from /spl plusmn/5 V and typically dissipates 80 mW when sampled at 18 MHz.

Digital demodulator for frequency-division-multiplexed signals

Abstract: An improved digital demodulator capable of demodulating a frequency multiplexed input signal is disclosed. The frequency division multiplexed input signal is sampled in an analog-to-digital converter. The samples are translated by mixing with base band frequency signals to yield real and imaginary values corresponding to phase information in the original modulation signals. After translation, the translated samples are filtered in real and imaginary digital filters. After filtering, the original modulation information is recovered by analysis of the position of vectors in the complex plane represented by the real and imaginary values. In the preferred embodiment, a successive approximation technique is used to determine the angle of the vectors to the real axis. Low pass output filtering may be employed after recovery of the modulation signal for improvements in signal to noise ratio. In the preferred embodiment, the translation is performed by multiplying the input samples by digital values corresponding to sine and cosine values of local oscillator signals at base band frequencies. Preselect filtering may be employed prior to translation to decimate the input samples where possible to reduce subsequent processing requirements. In the preferred embodiment, the unit is operated in a first initialization mode in which a microprocessor supplies appropriate filter coefficients corresponding to the frequencies of the channels to be demodulated. Thereafter, the microprocessor does not directly control supply of samples or coefficients to the filters for evaluation. Very high data rates are thus made possible.

Minimal transistor-only micropower integrated VHF active filter

Abstract: A minimal integrated filter containing four MOS transistors as the only circuit elements is presented. Voltage tuning is used to set the cutoff frequency and band-edge peaking. A filter test chip occupies an active area of 0006mm2, has acutoff frequency of 40 MHz and dissipates 580W.

Iterative technique for the synthesis of distortion-invariant optical correlation filters.

Abstract: A procedure is presented for designing distortion-invariant correlation filters. Optical correlation filters designed using this technique retain full position invariance. The filter design begins by finding the distortion-invariant modes (eigenfunctions) for a particular image. The input image, filter, and correlation response are all spectrally expanded in terms of these orthogonal eigenfunctions. An iterative technique between the spatial domain and the spectral domain is used to rephase the invariant modes so that a filter composed of a linear combination of modes has the proper overall invariance. The iterative technique also controls the information content of the filter by maintaining specified amplitudes for each invariant mode in the filter. Targets are detected by spanning the filter to determine points of constant amplitude.

Some Aspects of Nonstationary Myoelectric Signal Processing

Abstract: Nonstationary myoelectric signal processing is considered. A midpoint moving average estimator for the signal variance is developed. The performance of the estimator is analyzed and optimum window size criteria are derived. Comparison of the theoretical performance to experimental performance shows good agreement. The resultant estimation error is only moderately (2-3 percent) degraded from the equivalent stationary case. Finally, the developed estimator is compared to a typical squarer followed by a low-pass filter myoelectric processor. Provided that the low-pass filter has a linear phase characteristic in the passband, the two systems have essentially the same error performance.

Tone signal processing device using a digital filter

Abstract: At least two sets of filter coefficients corresponding to different filter characteristics are interpolated by using a control signal for controlling tone color as a parameter of interpolation. Filter coefficients obtained by the interpolation are supplied to a digital filter to determine its filter characteristics and an input tone signal is modified in accordance with the filter characteristics thus determined. Filter characteristics of diverse variation as compared with the number of prepared filter coefficients can thereby be realized. Further, timewise change of filter characteristics can be realized by changing a parameter of interpolation with lapse of time or changing two sets of filter coefficients to be interpolated with lapse of time. Designation of filter coefficients can be made by designating coordinate data of coordinates having at least two axes. In this case, filter coefficients can be changed by changing coordinate data of at least one axis in accordance with tone color control information whereby filter characteristics can be variably controlled.

A High-Speed Wave Digital Filter using Carry-Save Arithmetic

Abstract: To test the performance of recursive digital filters for high sampling rate applications, such as pulse former filters or filters for intermediate frequencies of TV sets and radios, a bit-parallel third order lowpass filter has been designed and fabricated in a 2 ?m CMOS technology. This filter has a bireciprocal transfer function and is fully functional at a sampling frequency of 35 MHz. In order to obtain such high frequencies with a recursive filter, a carry-save arithmetic has been used rather than a conventional carry-propagate arithmetic. This gives rise to several realization problems which will be described in this contribution. The prototype chip contains about 9000 transistors and occupies an area of 14.7 mm2.

CAD of Waveguide Low-Pass Filters for Satellite Applications

Abstract: Corrugated-waveguide low-pass filters are analysed by successive reflection coefficient transformations. The discontinuities are modelled by waveguide equivalent circuits, including interaction of higher order modes. The filter response is determined by TEm0-transfer functions (m=1,2...) each of which can be calculated independently. Implementing this method in an optimization routine allows complete computer-aided design according to given specifications.

Navigation mode selection apparatus

Abstract: An aircraft navigation system supporting a plurality of navigation modes An error estimator for each navigation mode provides an estimated navmode error signal representative of an estimate of the error in the position signal generated by the associated navmode A navigation mode selector enables the navmode having the smallest estimated navmode error signal that is consistent with procedure specified navaid criteria The navmode computed position signal is processed through a low pass position filter The estimated navmode error signal associated with the selected navmode is processed through a low pass position error filter having the same time constant as the low pass position filter to provide an estimated position error The estimated position error is utilized in providing the INS and DEAD RECKONING navigation as well as to set a threshold for estimated navmode error signals sensor data validation

Measuring adjacent channel power

Abstract: A signal source from a transmitter is down-converted by being mixed with a locally generated signal so that a desired adjacent channel band is converted to base band and the adjacent channel power measured after filtering by a low pass filter. To eliminate the notch in the filter characteristics that occurs when the power is measured by a.c coupled means, the locally generated signal is modulated or swept around the center of the adjacent channel band.

Filter adjustment apparatus and method

Abstract: Filter adjustment apparatus for adjusting cut-off frequencies or dip frequencies, for example, may be adjusted to desired optimum properties, during application of an input signal of a constant frequency. The optimum filter adjustment data are found, based on data manifested when the level detected output of the filter output crosses a prescribed reference level whereby the filter adjustment operation is simplified and accuracy is improved with a simplified structure, and it is possible to achieve automatic adjustment of the filter characteristics.

Color image pickup device in which the level of a sequential color-difference signal is controlled on the basis of the level of the luminance signal

Abstract: A color image pickup device suppresses false color signals in order to provide true color reproduction. That is, the device incrementally or continuously reduces false color signals. More particularly, this device includes a color separation filter through which an optical image passes to an image pickup device such as a CCD sensor or the like. A suppression circuit that includes a low pass filter and a high brightness detector detects when the brightness of the optical image exceeds a predetermined level. A color signal forming circuit forms a plurality of color signals from the output of the image pickup device and this plurality of color signals are output by a sequencing circuit in a predetermined cycle. The output level of the sequencing circuit is adjusted in response to the output of the detector by a control circuit, and this output is modulated by a modulator. Thus, in accordance with the present invention, the output level of the sequencing circuit is controlled in accordance with the brightness level of the optical image before modulation of the output color signal from the sequencing circuit.

Spread spectrum communications with resistance to multipath at differential delays both larger and smaller than a chip width

Abstract: A spread spectrum communications system resistant to multipath due to differential delays equal to or less than a chip width. At the transmitter, a pseudonoise sequence is combined with data for transmission purposes and the result of that combining operation is then encoded. Manchester encoding or differential encoding are described. At the receiver, a differential demodulator is used with a delay of either a one-half chip width or a full chip width. In the receiver embodiment employing a one-half chip width delay, a notch filter is used at the output of the demodulator with a notch located at a frequency corresponding to the chip rate. The output of the notch filter is then input to a low pass filter. The output of the low pass filter is a base band signal which can be applied to a correlator to extract the original digital data. For the receiver embodiment which employs a full chip width delay, the output of the demodulator is applied to a low pass filter. The output of the low pass filter is then a base band signal which can be provided to a correlator for extracting the original digital data.