Group Delay Equalization Research Articles

Simulation of Dispersion Tolerant Long-Haul Optical Fiber Communication Systems with Distributed In-Line Group-Delay Equalizers

Article Simulation of Dispersion Tolerant Long-Haul Optical Fiber Communication Systems with Distributed In-Line Group-Delay Equalizers was published on December 1, 1994 in the journal Journal of Optical Communications (volume 15, issue 6).

OTA-C biquad-based filter silicon compiler

An integrated software system that facilitates the design, and integrated-circuit layout of continuous-time OTA-C filter biaquad-based structures with typical cutoff frequenceis for a 3µmtechnology in the 500 kHz-8 MHz range is described. The proposed integrated software system consists of three separate software modules written in the C language for the Apollo workstation (DN3000). The first module is a general filter approximation package. This program can approximate conventional magnitude, arbitrary magnitude, arbitrary group delay equalizer, arbitrary magnitude with group delay specifications. The second module aides in the synthesis of the biquad-based OTA-C filter structures. This module is unique in that the C code has the rule-based language CLIPS embedded within the code, and takes into account OTA-C filter nonidealities. An expert system using CLIPS was developed to select an appropriate OTA-C filter structure based on the nonidealities of the structures. After the filter structure has been chosen, the program will guide the user in the calculation of the capacitor values. These calculations are based on the nonidealities of the OTAs included in the standard cell library for layout, in addition the design of special purpose OTA as another alternative is also considered. Furthermore, the program will develop the necessary input files for the layout generator. The final module is a modified version of AIDE2, a standard cell layout generator for switched-capacitor circuits. The input files to the modified AIDE2 is a C language program that describes the circuit (i.e., standard cells and their netlist). The output file is a CALTECH Intermediate Format (CIF) file that is required for fabrication.

On two-dimensional group delay equalization

The authors focus on some peculiarities of 2-D group delay equalization by means of cascades of 2*2 sections, a 2-D equalization technique that has lately received considerable attention. It appears that the group delay performance obtained by just one or two 2*2 section equalizers cannot be significantly improved by using equalizers with a greater number of sections. As a consequence, this type of 2-D group delay equalizer can seldom reach the group delay error performance of its 1-D counterpart. The work shows how the characteristics and the possibilities of 2-D group delay equalization markedly differ from those of the 1-D case.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design of IIR group delay equalisers

This paper describes a method for equalising group delay distortion through a cascade of second-order IIR allpass filters. The filter design is performed using the gradient algorithm, to get the set of poles that minimise the integral of the squared difference between the desired group delay and the group delay of the filter.

The digital all-pass filter: a versatile signal processing building block

The properties of digital all-pass filters are reviewed and a broad overview of the diversity of applications in digital filtering is provided. Starting with the definition and basic properties of a scalar all-pass function, a variety of structures satisfying the all-pass property are assembled, with emphasis placed on the concept of structural losslessness. Applications are then outlined in notch filtering, complementary filtering and filter banks, multirate filtering, spectrum and group-delay equalization, and Hilbert transformations. In all cases, the structural losslessness property induces very robust performance in the face of multiplier coefficient quantization. Finally, the state-space manifestations of the all-pass property are explored, and it is shown that many all-pass filter structures are devoid of limit cycle behavior and feature very low roundoff noise gain. >

An approximation procedure for selective linear phase filters

A method is proposed for the simultaneous approximation of attenuation and group delay characteristics of analog and digital filters. The attenuation is approximated to be equal ripple in the passband and the stopband, while the group delay is equalized in the passband using a least-mean-square norm. The number of attenuation ripples in the passband, and the degrees of freedom for the group delay equalization can be traded off for the best possible approximation.

Comsat's tdma traffic terminal

AbstractCOMSAT has installed two traffic terminals in the Etam earth‐station and is currently installing a third in the new Roaring Creek earth‐station to access the INTELSAT TDMA network. This paper describes the COMSAT TDMA traffic terminal equipment from the supergroup interface to the antenna. COMSAT's 1: N redundancy approach for terrestrial interface equipment and DSI unit back‐up is described as well as electrical path length, amplitude and group delay equalization techniques, special on‐line RF monitoring and failure reporting facilities and the operation and maintenance centre which can operate and perform diagnostic testing on up to four traffic terminals from a central location.

The Design of a Multiple Cavity Equalizer

A simplified design method for a group delay equalizer with multiple poles has been developed, which replaces the conventional approach of cascading several C- and D-type equalizers by one equalizer with multiple poles. A prototype 4-pole equalizer has been designed and tested with satisfactory performance.

Synthesis and Realization of Narrow-Band Canonical Microwave Bandpass Filters Exhibiting Linear Phase and Transmission Zeros

The present study is concerned with the synthesis and realization of narrow-band canonical microwave bandpass filters exhibiting additional couplings between nonsuccessive resonant circuits. These bypass couplings effect, on the one hand, attenuation poles at finite frequencies and, on the other hand, make the bandpass filter nonminimum-phase, and therefore offer degrees of freedom for group delay equalization in the passband. The realization of canonical network structures with bypass couplings is possible by extracting from the chain matrix an ideal transformer, the input of which is connected, for example, in shunt with and its output in series with the remainder two-port. The extraction is associated with the reduction by 2 of the degree of the denominator polynomial of the chain matrix elements. To realize a clear correlation between the bypass elements and the electrical performance, canonical structures with sections that are bypassed only once or twice are proposed. Theoretical and measured curves of the examples of realization for 1235 MHz, consisting of coaxial cavities, and for 4000 MHz, consisting of dual-mode cavities, are seen to be in close agreement.

Arbitrary phase polynomials

A constructional method is presented for phase-matching a polynomial at a number of preselected points on the frequency axis. For a polynomial with n complex coefficients, the phase can be matched at 2n+1 points. Such polynomials are useful in the design of filters and group-delay equalisers.

Effect of Phase Ripple on Class 4 Partial Response Data Signals

An expression is derived for the mean square error of a SSBAM or a baseband multilevel class 4 partial response data signal when distorted by a channel which has a sinusoidal phase ripple. Such characteristics are approximated when the channel has been equalized by so called bump group delay equalizers. Included are the expressions for the optimum carrier phase and sampling time. For a low frequency group delay ripple, it is shown that the error can vary by a factor of seven for differing frequency and phasing of the ripple with the same peak group delay variation.

RC active variable group-delay equalizers with independent Q and ω controls

The high-speed transmission of data over voice frequency telephone links creates the need for variable group-delay equalization networks. This paper describes two alternative group-delay sections, the characteristics of which may be continuously adjusted over the approximate bandwidth (300 to 3000 Hz). Both of the proposed networks provide for the desired degree of group-delay adjustment using only two resistive controls neither of which demand high precision components.

Microstrip system for voltage-controlled phase equalisation for microwaves

A group-delay reflective-mode microwave equaliser is proposed. The required delay is obtained combining several voltagecontrolled circulator-coupled elementary cells. For an assigned phase response, the circuit is designed by an interactive program. Experimental results are reported relative to L band systems with constant and linear delay.

Magnetostatic delay lines for group delay equalization in millimetric waveguide communication systems

This paper considers the application and performance of magnetostatic surface wave delay lines as adjustable group delay equalisers in the high data rate, long haul millimetric waveguide system under study by the British Post Office. The initial 14.58 km link requires differential delays between 42 nsec and 12 nsec over a 500 MHz bandwidth for 32 channels in the 32- 48 GHz band. Test group delay equalisers have been fabricated from narrow linewidth yttrium iron garnet films, grown by liquid phase epitaxy in the 5 μm to 50 μm thickness range. These have been operated at the system IF, 1.0-1.5 GHz, in the magnetostatic surface wave mode utilising microstrip input and output couplers. Theory as well as experimental results for this frequency range are presented. Investigations have been carried out on magnetostatic wave terminations, and the effect that residual mismatches from these terminations, as well as input-output electromagnetic mismatches from the transducer 3-port networks, have on the phase and amplitude ripple of the equaliser. The effects of anisotropy field on the minimum operating frequency have been studied and optimum crystallographic orientations chosen.

Surface Wave Device Applications in Microwave Communication Systems

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.

Development of group-delay equalisers for 4 Gc/s

Group-delay equalisers operating at microwave frequencies may find application in multicharinel-telephony radio-relay systems, e.g. in systems without translation to an intermediate frequency in repeaters. Studies to ascertain the feasibility of such equalisers operating in the 4 Gc/s band are described. Several equalisers have been designed and constructed in standard waveguide WG11, using a pair of identical bandpass ladder networks terminating a waveguide hybrid or a 3dB directional coupler. In all cases except one, the equalising networks had delay characteristics that were arbitrarily assumed; the exception was a network designed to equalise the group-delay performance, over a bandwidth of 20 Mc/s, of a pair of bandpass filters in tandem. Basic equaliser insertion losses of 0.5–2dB have been observed, the figure depending on the complexity of the network. The effect of temperature changes on the equaliser and filters in tandem resulted in the midband frequency of the equaliser shifting in step with the frequency of the filters, so that the group-delay performance remained equalised over a temperature range of 20degC. It is concluded that, although the performance of the equalisers is satisfactory, they are less flexible in operation and are mechanically bulky compared with intermediate-frequency equalisers.

Intermodulation noise in linear f.m. systems

By applying a series of detailed approximations to the Rice and Bosse theory of f.m. intermodulation noise, the recent formulae of Medhurst and Roberts for intermodulation noise/signal ratios in f.m. systems with white-noise modulation and networks of polynomial frequency characteristics are extended in three respects: (a) to the calculation of the noise ratio at any modulation frequency, (b) to network real and imaginary characteristics of eighth and seventh degree, respectively, and (c) to the case of pre-emphasis. The theory is illustrated by application to the cases of a signal with C.C.I.R. pre-emphasis passing a stagger-tuned triple without and with groupdelay equalization.