Showing papers on "Linear phase published in 1977"

A comparison of algorithms for minimax design of two-dimensional linear phase FIR digital filters

Abstract: Linear programming algorithms for the design of finite impulse response (FIR), linear-phase digital filters can be extremely time-consuming. Two iterative design techniques using multiple-exchange ascent algorithms have been developed. These are the methods of Kamp and Thiran and Hersey and Mersereau. They are known to be much faster than the linear programming techniques. The mathematical basis for these algorithms is reviewed and differences in the algorithms are noted. Results of empirical efficiency comparisons are presented. A new algorithm for reducing the number of iterations for multiple-exchange ascent algorithms is also presented.

Frequency and Phase Lock Loop

Abstract: A new electronic subsystem has been developed: The frequency and phase lock loop. It has an extended acquisition range compared to the standard phase lock loop. It will be advantageous to use this new loop in all applications where a simultaneous need for large acquisition range and a narrow tracking bandwidth can justify the added complexity of the new loop.

Chirp phase distortion detector in a wideband linearization feedback control loop

Abstract: A phase distortion detector is used in a wideband feedback control loop to detect phase distortion on a wideband pulsed linearly frequency modulated waveform (chirped) without the use of excessively long delay lines. The detector mixes two reference signals, each of a predetermined frequency, one frequency higher than the other. A phase lock loop ensures that the two signals are phase coherent. Each signal is then mixed with the chirped waveform, delayed for different time intervals, and mixed again to produce an error signal proportional to the phase distortion on the chirp pulse which distortion is also an indication of the frequency non-linearity of the chirp pulse. The error signal is then used to correct such non-linearity.

Determination of a transfer function from amplitude frequency response data

Abstract: An iterative procedure for determining the transfer function (minimum phase) of a linear system from its amplitude frequency response data is presented. The transfer function is the best in the least-squared-error sense. Frequency response data spanning several decades are weighted evenly, so the procedure gives a good fit at all data points. A magnitude-squared function is first found that best fits the frequency response data, and the minimum-phase transfer function is obtained from the magnitude-squared function by spectral factorization. Examples are used to illustrate the application of this procedure in system reduction and system identification.

Technique for combatting jitter in multiple phase transmission system

Abstract: To eliminate the effects of phase jitter, successively measured phase values received in an N-phase transmission system are stored and compared with a phase node reference plot to derive values representative of the respective phase nodes to which the measured phase values are closest and the degree of deviation from these "closest" phase node values. The degree of deviation for a prescribed number of successive phase measurements is averaged over this number to obtain a mean phase error. The successive phase deviations are then adjusted by this mean deviation and, based upon the adjusted deviation values, the originally chosen node values may be changed to one of their immediately adjacent nodes. This process is carried out for each phase measurement in the sequence, so as to obtain a phase adjustment factor, by which each of the respective nodes relative to what the measured phase values were originally measured is shifted. This shifting effectively rotates the phase node reference plot by an amount which minimizes the mean square error of the phase node measurements for the prescribed number of phase measurements. The difference between the adjusted node values of the two adjacent phases located midway in the sequence is then taken to determine the transmitted symbol for that point in the transmission. The above process is then continuously repeated for successive sequences of prescribed numbers of phase measurements by advancing through the successive measurements one at a time and making whatever adjustments are necessary on the phase node reference plot after each sequence analysis.

Arithmetic synthesizer frequency generation with reduced phase jitter

Abstract: Arithmetic synthesizer having an output circuit that provides a linear phase output signal. A ramp generator controlled by the stepped output signal from the arithmetic synthesizer interpolates the value of the signal slope between steps to supply a phase output having low noise, i.e., reduced time jitter.

Effects of random phase changes on the formation of synthetic aperture radar imagery

Abstract: The effects of Gaussian random and linear phase change on the response of the matched azimuth processor of a synthetic aperture imaging radar is analyzed numerically.

Designing near linear phase recursive filters using linear programming

Abstract: Previous linear programming design techniques have concentrated on magnitude only specifications, In the technique presented here we design the filter to prescribed real and imaginary components of the frequency domain specifications. Although general phase characteristics have proved difficult to achieve, good results are obtained for constant group delay designs. The technique employed is to alter the value of the group delay in the specifications until a minimum error is achieved. Stable designs can be established by employing usual stability criteria. Results of the design technique are presented and an extension to two dimensional filter designs is discussed.

Phase lock loop carrier generator for receiver of phase modulated carrier pulse signals

Abstract: Demodulator for phase modulated carrier pulse signals or phase codes in which the pulses are coded according to a plurality of N phases of the carrier. It comprises a digital phase lock loop system for locking to a frequency equal to N times the carrier frequency which includes at least a two input phase detector, a loop integrator and a voltage controlled oscillator having an output connected to the first input of the phase detector, means for dividing by N the frequency of this oscillator and for generating a reference carrier signal. The phase codes are decoded by comparing the phases of the carrier of the phase codes to the phase of the reference signal. In order to derive from all the phase codes a train of synchronous pulses a multiphase shifter receives the carrier of the phase codes and locally generates a plurality of carriers having phase shifts equal to 0, 2π/N, 2×2π/N, . . . ([N/2]- 1) ×2π/N with respect to the carrier of the received phase code and means are provided for generating passing through zero pulses coinciding with the passage through zero of said received and locally generated carriers. Those of said passing through zero pulses which occur during the central part of each phase modulated carrier pulse are gated through gating means. These gated passing through zero pulses are applied to the second input of the phase detector.

Initial acquisition signal detection system for TDMA satellite communication

Abstract: A low level initial acquisition signal consisting of a continuous wave signal portion followed by a phase-modulated signal portion is transmitted via a satellite to a receiving station. The received CW signal is converted by a voltage-controlled variable frequency local oscillator to an intermediate frequency signal which is fed to a narrow passband filter. The local oscillator frequency is linearly swept, and the maximum signal passing through the filter during one sweep is detected. The local oscillator is then locked at the local frequency which produced the maximum signal, thereby effecting frequency acquisition. Next, the phase-modulated signal portion is multiplied by a phase-modulated signal output from a variable phase local signal generator. The phase of the local generator is also swept, and the maximum phase correlation signal passing through the band pass filter is again detected, and the phase of the generator output is corrected by the phase shift which produced the maximum phase correlation signal. This phase shift is used as a basis for determining the proper timing for acquisition of the correct time slot in the TDMA frame at the satellite for a transmitted data burst. The acquisition is confirmed by comparing the maximum phase correlation signal obtained during phase sweeping with the signal level obtained after the phase of the generator has been locked.

Crosstalk corrector and decision device for FSK

Abstract: Demodulation of M-ary continuous-phase FSK signals is effected in accordance with phase measurements taken at symbol transition times. The phase error caused by intersymbol interference is estimated by knowledge of the type and degree of distortion which is principally dependent upon the frequency difference between successive data symbols and phase distortion characteristics of the channel filter. Pairs of phase nodes are selected at each symbol transition time and, from each pair, a tentative choice is made by using the expected phase distortion based on adjacent phase node pairs. Refined choices are then made using the estimated phase distortion based on adjacent tentative choices. Differences between successive tentative choices of phase node selections yield a sequence of frequencies making up the FSK signal. Circuitry implementation embraces the use of phase-locked loop detectors and digital decision logic including programmable read-only memories.

Non-linearity correction in wide range voltage controlled oscillators

Abstract: A low-Q mechanical resonator is operated in its series resonance mode in a circuit that includes an amplifier and voltage variable phase shifter. As the phase shift is varied, the resonator will shift its frequency to compensate the phase shift. The result is a voltage variable oscillator frequency. The low-Q resonator has a non-linear phase versus frequency characteristic so that frequency is not a linear function of control voltage. A plural emitter transistor is employed in one side of a differential control amplifier. The resulting non-linear transfer characteristic is used to compensate the non-linear oscillator characteristic so that the frequency versus control voltage is linear.

Optimum pulse shaping application of binary transversal filters used in satellite communications

Abstract: The implementation of binary transversal filters (b.t.f.) is gaining wide acceptance, due to their operational adaptability to variable bit rates, their achievable high out-of-band attenuation and linear phase performance and to the recent availability of medium-scale integrated components such as charged-coupled devices.The design and evaluation results of a b.t.f. meeting the single channel per carrier Intelsat satellite communications specifications are presented, which are based on Mueller's synthesis method. The performance evaluation problems of these type of filters are also described and, in particular, emphasis is given to the following: out-of-band to in-band power ratio inaccuracies when wideband measurement techniques are employed, and the evaluation of the r.m.s. jitter of b.t.f. based on the jitter probability density function.

Fast switching phase lock loop system

Abstract: A phase lock loop system that includes a voltage controlled oscillator. The output of an integrator provides the voltage to a tuning port for determining the precise frequency and phase of the oscillator. In response to a change in frequency, the input to the integrator is switched off at the precise time that its output voltage reaches the value for the proper phase relationship at the new frequency. The output of a low pass filter fed by the loop's phase detector determines such precise time. At said precise time, the stabilized condition of the loop is sensed and corrected for minor deviations.

Design of f.i.r. linear phase digital filters to minimise the statistical word length of the coefficients

Abstract: A modification of the McClellan, Parks and Rabiner approximation program is proposed to design F.I.R. linear phase digital filters with minimum value of the statistical word length of the coefficients. The optimum solution may have an equal ripple statistical word length or not, and can be obtained in both cases by the mentioned program with small modifications.

Dual Mode Canonical Waveguide Filters

Abstract: This paper presents a new dual mode circular waveguide cavity structure which realizes the general class of coupled cavity transfer functions. Included are the exact elliptic function response and the linear phase and arbitrary phase responses. Experimental data taken on 4- and 8-pole narrowband elliptic function filters centered at approximately 4 GHz are described and shown to correlate well with theory.

Minimum phase transfer functions providing a compromise between phase and amplitude approximation

Abstract: Transfer functions of low-pass filters with no finite transmission zeros are introduced satisfying a number of phase flatness conditions at the origin and providing more stopband rejection than the corresponding Butterworth filters. If only one of the available degrees of freedom is used to shape the passband magnitude response, while all remaining are assigned to phase linearity, the largest fractional banwidth of phase linearity is obtained but the maximum passband loss cannot be specified beforehand and increases with increasing the order of the network. It is shown, however, that assigning two parameters to magnitude requirements in the resulting transfer function almost any prescribed maximum passband loss can be met while still retaining excellent phase linearity over a large part of the passband. In addition, a class of transitional filter functions is obtained the frequency and time domain characteristics of which can be adjusted over a wide range of filter specifications by varying one parameter only. It is shown that the time domain characteristics of these filters compare favorably with those for the well-known transitional Butterworth-Thomson filters.

A simplified computational algorithm for implementing FIR digital filters

Abstract: An N-point finite impulse response (FIR) digital filter, when implemented in software, generally requires N multiplications, N additions, and (N - 1) shifts per output sample. An obvious simplification is to implement the shift register required to store x(n) to x(n - N + 1) using a moving pointer, thereby eliminating the (N - 1) shifts per sample required in the most straightforward implementation. However, this simplification requires a check on the index of every sample to see if the end of the linear storage array has been passed, thereby voiding most of the gain in speed which was obtained. A simple technique is discussed for trading N storage locations for the (N - 1) shifts (or the (N - 1) index checks), thereby leading to an implementation in which only N multiplications, N additions, and one indexing operation are required per output sample. For implementing symmetric (i.e., linear phase) FIR filters, the resulting savings is even somewhat greater because two index pointers are required, and each must normally be checked to see that it remains within the bounds of the array.

Phase Noise Measurements in the Frequency Domain

Abstract: This paper describes two measurement systems used to measure phase noise of sources in the frequency domain at Fourier frequencies from 10 hertz to 13 megahertz from the carrier. One system measures the combined phase noise characteristics of two sources. The two source signals are applied in quadrature to a phase sensitive detector (double balanced mixer), the voltage fluctuations analog to the phase fluctuations are measured at the detector output. One measurement system is designed to measure the phase noise characteristics of a single oscillator. The single-oscillator measurement system is designed using delay lines to form an FM discriminator. Voltage fluctuations analog to the frequency fluctuations are measured at the detector output.

The measurement of phase distortion due to filtering in digital pictures

Abstract: This paper introduces a measure of phase distortion due to filtering in digital pictures. Given the amplitude spectrum of an input picture and the desired and actual frequency responses of a digital filter, the measure may be calculated. When the measure is applied to output pictures of a filter, the acceptability of the phase response of the filter may be judged. When the amplitude response of the input picture is modeled by a simple function, an estimate of the measure may be calculated with greatly reduced storage requirements and computation time. Examples illustrating the results are included.

On the problem of filters with arbitrary amplitude and phase constraints

Abstract: A simplified method—based on the concept of reflection filters—is presented for designing linear phase filters with arbitrary amplitude to phase constraints This method starts with transfer functions with 2: 1 amplitude to phase constraints, and through varying the recurrence relation of the polynomials involved, transfer functions with more selective amplitude are obtained

Frequency-and Amplitude-Dependent Phase Effects In Television Broadcast Systems

Abstract: The television broadcast system in this paper is defined as those elements between and including the modulation process at the transmitter and the demodulation process at the receiver. The effects to be considered include: 1. Time-domain distortion due to departure from linear phase vs frequency (and from flat amplitude response vs frequency). 2. Non-linear distortion (with envelope demodulation) due to the quadrature-phase signal component resulting from vestigial sideband asymmetry. 3. Differential phase and other distortions due to incidental phase modulation of the visual carrier. 4. Intercarrier noise due to visual carrier incidental phase or frequency modulation.

System for providing angular deviation data for locating a transmitter

Abstract: Disclosed is a system for locating a transmitter arranged for transmitting frequency-modulated signals. The system supplies data about the angular deviation between the direction of the transmitter considered from a reference point and a reference axis passing through that point and comprises two antennas disposed on the reference axis symmetrically relative to the reference point, and a receiver having two mixers which receive, on the one hand, the respective signals from the two antennas through time delay elements and, on the other hand, the signal from one of the antennas through a circuit which provides, during a given period of time, a linear phase shift. The beat frequencies at the mixer outputs are measured by frequency meters during said time period and the desired information is given by the relative deviation between the output signals of the two frequency meters.

System and method of performing a decisive phase coherence test

Abstract: Apparatus for ascertaining the phase coherency of the pulse trains comprising signals in which the phase relationship of pulse trains of one signal sorted from a first dwell of pulses is compared with the phase relationship of the pulse trains of another signal sorted from a second dwell of pulses to determine the phase shift between the signals. At a substantially later time, the process is repeated to again establish the phase shift between the signals, and the two phase shifts are then compared. If the phase relationships are substantially identical, the signals are considered to be phase coherent.

Average phase position circuit

Abstract: Method and apparatus for phase averaging of two phase position signals to derive a single phase position signal. The apparatus comprises phase discriminators for comparing each of the two phase position signals to the phase of the single phase position signal and a combining circuit for summing the output signals from the phase discriminators to derive an error signal when the single phase position signal is not midway between the phases of the two phase position signals. Circuitry is provided to modify the phase of the single phase position signal in response to the amplitude of the error signal.

Filter based on surface wave principle - has weighted and non-weighted transducers giving mean frequency with linear phase characteristic

Abstract: The filter has a piezoelectric substrate with weighted and non-weighted interdigital sender and receiver transducers. Overlapping range of sender interdigital electrodes is variable in accordance with the function L(x) = sin x/x, while overlapping range of receiver interdigital electrodes is constant. The weighted transducer has a max. length between 2.7 and 8.1. It is such that the first peak of the weighted transducer filter characteristic appears at the required frequency (fzl). The number of prongs of both transducers is calculated from specified equations. The mean frequency (fo) of symmetrical amplitude side-bands has linear phase characteristics.

Electrical energy transmission network

Abstract: The delay elements of a signal energy transmission network are divided into separate portions through which the transmitted energy is phase shifted in sequence by substantially equal amounts. A phase correction circuit reverses the phase shift through one of the divided delay portions by doubling the frequency of the signal at a reference phase angle and subtracting therefrom the input frequency of the signal phase shifted through said one of the divided delay portions in order to maintain a constant frequency vs. phase relationship.

Constant phase delay network having a coherent reference

Abstract: The delay elements of a signal energy transmission network are divided into separate portions through which the transmitted energy is phase shifted by substantially equal amounts. A phase correction circuit reverses the phase shift through one of the divided delay portions by providing a locked oscillator operating at twice the frequency of the signal at a reference phase angle and subtracting therefrom the input frequency of the signal phase shifted through said one of the divided delay portions in order to maintain a constant frequency vs. phase relationship.

Low Loss Linear Phase Filters

Abstract: A new filter structure in which low loss linear phase filters can be realized is described. These filters are longitudinal, employ TE/sub 103/ dual mode resonators. Experimental results of such a filter are presented, compared with results of equivalent fundamental mode Chebyshev, linear phase filters. These results demonstrate that such filters are suitable for multiplexer in satellite transponders operating above 10 GHz.

Self excited reference or calibration oscillator - has two phase shifting stages whose gains are constant and independent of oscillator frequency

Abstract: The oscillator is in the form of a phase shifter delivering polyphase balanced voltages. It consists of a feed-back loop with one phase shifting stage with constant gain, a second phase shifting stage with constant gain and adjustable phase shift depending on the oscillator frequency, and a basisc amplifier whose phase shift is zero or a multiple of 360 deg. Its gain is constant, and the total transmission function is such that at the required oscillator frequency the total gain is one, and total phase shift is 0 or 180 deg. Gains of the two phase shifting stages (2, 3) are constant and independent from oscillator frequency. They are determined only by the circuit parameters and need not readjustment. Phase shift (psi) generated by the first phase shifting stage (2) is held constant by fine adjustment independent from frequency.