Cselt-centro Studi E Laboratori Telecomunicazioni S.p.a.

Sip - Societa Italiana Per L-esercizio Delle Telecomunicazioni P.a.

S.i.p. Societa' Italiana Per L'esercizio Telefonico P.a.

Carlo M Bruno

Adler Tofanelli

Renato Ambrosio

Gianfranco Panarotto

Fabrizio Gagliardi

Flavio Cucchietti

Giorgio Paschetta

The instrument measures directly the phase jitter of analog signals emitted n the line by the device under test, even when clock information is not available and when particular specifications and limitations do not allow the use of analog instruments. It uses a circuit which generates a square-wave clock signal with the same phase and frequency characteristics as the signal to be measured, so as a phase comparison with a reference signal can be made. Error signal obtained is filtered, measured and displayed.

Instrument for measuring the phase jitter of analog signals

The digital phase-locked loop circuit extracts the clock signal from a serial flow of coded data by operating so as to determine the phase of the received signal and comparing this phase with that of a locally-generated signal. The error signal obtained from the comparison is digitally filtered and used to correct the phase of local signal. The error with respect to the signal extracted from a prior data stream is stored and used to effect corrections even in the absence of the data flow at the input or in presence of long zero sequences.

Digital phase-locked loop circuits with storage of clock error signal

The echo canceller for bidirectional digital transmission systems cancels the echo queues of a desired number N of digital symbols, transmitted on the line in the last N signalling periods. It consists of a part which effects very simply the summation of the last N transmitted symbols, so as to ease the system implementation by an integrated circuit, and of a part which computes the estimated sample of the echo-channel pulse response. The results of the two parts are multiplied by one another and the estimated echo signal is obtained.

Echo canceller for bidirectional digital transmission

A bidirectional transmission system with echo cancellation allows simultaneous interchange of digital information between an exchange and subscribers on a single transmission line. Data flows are transmitted by packets separated by short silence intervals within which clock signals are extracted and echo-cancellation adjustment is accomplished. Use of an adaptive equalizer and a single sampling operation per sampling period are possible.

System for bidirectional digital transmission with echo cancellation

The digital circuit extracts synchronism signals from a serial flow of coded data according to a process which uses a phaselocked loop where the different level transitions of the signal received are separately considered and a phase is determined for each type, the latter being compared with a specific reference phase, established in the initialization step. The error signal obtained from the comparison is used for correcting synchronism signal frequency.

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Turin, Italy

Carlo M Bruno