Delay Equalization Research Articles

Polarization optics of twisted single-mode fibers

In twisted single-mode optical fibers the polarization of light is affected by an elastooptically induced optical activity and by a modification of any linear birefringence present. These effects are discussed theoretically and demonstrated experimentally. The activity/twist ratio is alpha/tau approximately 0.13 ... 0.16 universally in weakly guiding silica fibers. Twisted fibers may be used as polarization rotators. A fiber with a +/-68 degrees double twist operates as a fast/slow mode interchanger, suitable for delay equalization.

Optimum weights in delay equalization

In network design practice it is quite typical to design a network having a suitable amplitude response and to follow this with a network having unit amplitude response whose purpose is to modify the phase response so that the total network meets requirements on the phase response. Such phase-correcting networks are called all-pass delay equalizers. Their design amounts to function approximation of a special form. It is common practice to design equalizers so that the residual error in the envelope delay (d\phi/d\omega) has an equal ripple characteristic (constant weight function). The resulting residual distortion has a form which can be interpreted in a television system as two ghosts displaced in time from the desired signal by an amount inversely proportional to the ripple frequency. We determine a weight function, dependent upon the spectrum of the signal being processed, which minmmizes the power in these ghost distortions. These results are illustrated by application to example networks and signals.

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.

3-Level partial-response signalling for voice-grade circuits

Contrary to present practice, data transmission through voice-grade circuits becomes more efficient when p.r.s. codes are used. It is shown that 3-level and higher-level p.r.s. codes can achieve data rates up to 7.2 kb.p.s. when suitable delay equalisation of the bandpass channel (300–3400 Hz) is provided. Satisfactory eye pattern and error rates have been obtained.

WT4 Millimeter Waveguide System: Line and Repeater Equalization

The WT4 millimeter waveguide system requires equalization of the loss and delay of the line, which is made up of both the waveguide itself and the diplexer (waveguide channelizing filter) arrays. In the lower portion of the band (40 to 60 GHz) there is considerable linear delay (as much as 30.5 nsec per 400 MHz at 40 GHz), which is equalized by using a folded tape meander line delay equalizer. The remaining delay and amplitude deviation from the desired transfer characteristic is further reduced by field-adjustable trim equalizers. In this paper, we describe the equalization and measurement philosophy for the WT4 system and also the technologies used in achieving the resulting degree of equalization. We put special emphasis on the description of trim equalization because line equalization has been described in detail in a previous publication. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup>

An Economical RC Active Equalizer with Applications in Communications

A simple active equalizer network employing two operational amplifiers (OA's), five resistors, and a pair of capacitors is presented. The same network can be used for both amplitude and delay equalizations. Experimental results show that the circuit can be conveniently used for amplitude equalization in voice communications, and for delay equalization in private line data circuits.

Delay equalisation of vestigialsideband waveform transmission systems

The well known conditions for distortionless transmission through a vestigial-sideband (v.s.b.) system, i.e. that the v.s.b. shaping network should have amplitude and phase characteristics that are skew symmetric about the carrier frequency, form only one set from an infinite number of possible sets of conditions. A practical example shows that use of an alternative set of conditions proposed by Saraga considerably reduces the complexity of delay equalisation necessary when television or similar waveforms are to be transmitted. However, consideration of the effect of phase errors in the demodulating carrier signal and of noise in a practical system shows that, in these respects at least, conventional v.s.b. transmission is superior.

A simple inductance simulation scheme and its application in data communications

The properties of a circuit proposed earlier for the realization of an inductance using two unity gain amplifiers are first studied and an important application of the present circuit for delay equalization in data communications is also presented.

An active delay equalizer network

An active delay equalizer network using twin T and one operational amplifier is given. The network has zero loss and gives rise to adjustable peaky group delay characteristics under suitable conditions.

Magnetic bubble logic

Although the literature on the bubble logic devices is limited, the concepts and device configurations are diverse. In conductor-access devices, logic can be performed by bubble transfer operations. In field-access devices, logic can be performed by providing alternative paths which are selected by interaction between bubbles. Examples include the conjugate logic gates, the resident-bubble cellular logic, and the chevron 3-3 circuits. Logic can also be performed by counting bubbles, such as in the symmetric switching function implementation. The various mechanisms for implementing bubble logic are all described by truth tables. To assess their efficiency, they are compared in terms of space and delay when they are used to implement the same logic element - a full adder. They are all comparable except for the resident-bubble cellular logic which requires excessive space and delay. However, it is important to point out that only the symmetric switching function devices offer rewrite-ability to eliminate the part number problem, and accommodation for a large number of inputs to ease interconnection and delay equalization problems.

Ripple-pass function

The well-known relation for an all-pass function is generalized by the introduction of two parameters <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k_{a}</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k_{b}</tex> making <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F(s)=\frac{EvP(s)-k_{a}OdP(s)}{EvP(s)+k_{b}OdP(s)}</tex> where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P(s)</tex> is a Hurwitz polynomial, while <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EvP(s)</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OdP(s)</tex> are its even and odd parts, respectively. It is shown that the amplitude, phase, and group delay of such a generalized all-pass function ripple, and that the ripples are dependent on the two introduced parameters and their ratio <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K = k_{a}/k_{b}</tex> . Thus the name "ripple-pass function." Some interesting and important features of the discussed function have been considered here. The ripple-pass function is suitable for practical applications such as amplitude, phase, and/or delay equalization, or for design of narrow-bandpass or bandstop (notch) filters. The ripple-pass function can be easily realized by using simple passive and active networks.

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.

Circular Waveguide System for Trunk Communications

9-km waveguides of 70-ram inner diameter (ID) have been inserted from manholes into ducts of polyvinal chloride (PVC). Expansion joints are provided for taking up length variations. Only a slight increase in attenuation was measured for the helix waveguide after the laying works. Phase-shift-keyed (PSK) signals with bit rates of up to 640 Mbit/s have been transmitted via this line. A new approximation method for calculating the attenuation of practical line routes has been developed. Improved design of lined waveguides should, from theory, reduce the H 01 route and curvature loss to below 1 dB/km. Experimental repeaters work with a double conversion scheme. They have mm-wave branching networks in oversize rectangular waveguide, IMPATT oscillators and p-i-n modulators for two-phase modulation. Printed or folded tape meanderlines serve for delay equalization.

Active Adjustable Loss and Delay Equalizers

The design of active amplitude and delay equalizers to be used in private line data systems is considered. These equalizers provide sufficient flexibility of adjustment so that one type of amplitude equalizer and one type of delay equalizer are sufficient for all applications. They replace families of passive equalizers which permitted relatively limited or no adjustment.

Active adjustable loss and delay equalizers

The design of active amplitude and delay equalizers to be used in private line data systems is considered. These equalizers provide sufficient flexibility of adjustment so that one type of amplitude equalizer and one type of delay equalizer are sufficient for all applications. They replace families of passive equalizers which permitted relatively limited or no adjustment.

IF Variable Equalizers for FM Microwave Radio Links

The circuit configuration, operational principles, and some test data on three new types of equalizers applicable for use in FM microwave radio links are described. The equalizers are namely of the reflection type, frequency converter type, and AM-PM conversion type. The reflection type delay equalizer permits variation of relative delay time while keeping the absolute delay time constant at the center frequency or permits variation of absolute delay time while keeping the relative delay time constant. The frequency converter type equalizer adopts a principle whereby variation in local frequency (supplied to the frequency converter) facilitates continuous variation of the relative delay time, absolute delay time, and amplitude frequency response. The AM-PM conversion type differential gain equalizer enables equalization of differential gain through the combined use of the AM-PM converter circuit and the delay circuit.

IF variable equalizers for FM microwave radio links

The circuit configuration, operational principles, and some test data on three new types of equalizers applicable for use in FM microwave radio links are described. The equalizers are namely of the reflection type, frequency converter type, and AM-PM conversion type. The reflection type delay equalizer permits variation of relative delay time while keeping the absolute delay time constant at the center frequency or permits variation of absolute delay time while keeping the relative delay time constant. The frequency converter type equalizer adopts a principle whereby variation in local frequency (supplied to the frequency converter) facilitates continuous variation of the relative delay time, absolute delay time, and amplitude frequency response. The AM-PM conversion type differential gain equalizer enables equalization of differential gain through the combined use of the AM-PM converter circuit and the delay circuit.

Comment on "Delay equalizer using twin T and one operational amplifier"

Comment on "Delay equalizer using twin T and one operational amplifier"

Computer-Aided Group Delay Equalization for Broad-Band Satellite Transponder Applications

Equalization of the group delay characteristic of a satellite repeater has been examined. The channel group delay includes the transmit and receive filter group delay, and the transponder filter group delay. The perturbation of the transponder group delay of a satellite channel caused by the dual-path transmission effect resulting from an adjacent channel has also been studied. Various combinations of filter and equalizing sections have been examined. In the realization of wide passband filters, equalization of group delay presents some difficulties, especially when it is achieved by networks with many sections. The minimum peak-to-peak group delay deviation in the specified passband has been achieved by using a recent nonlinear programming technique with a penalty function approach.