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

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

Alfredo Fausone

Adler Tofanelli

Bruno Fabbri

Renato Ambrosio

Vittorio Seano

Alberto Brosio

Renato Rivelli

Agostino Moncalvo

A broadband signal broadcasting system comprising a circuit to encode video and audio signals forming a TV channel to be sent to a switching matrix, which is remotely operated by the subscriber; a circuit to multiplex two or more TV channel to be simultaneously transmitted on the subscriber's line, which can be a coaxial cable, a radio link or an optical fiber; and a circuit to receive the signals transmitted on the line, to separate two or more TV channels and to carry out channel decoding by supplying the subscriber's terminals with the corresponding video and audio signals. The system requires a single encoding and a single decoding of the nB.fwdarw.(n+m)B type on broadband signals, respectively at the output from signal sources and at the input of subscriber's terminals.

Broadband-signal broadcasting system

A bidirectional digital transmission system with echo-cancellation allows the measurement of the received data signal and the automatic adaptation of the attenuator and of the line equalizer. They are implemented by using circuits already present in a conventional system, in addition to auxiliary circuits.

Bidirectional digital transmission system with echo-cancellation

In order to determine the overall phase and amplitude distortion undergone by signals sent over a transmission channel, a pulse sequence generated at one end of the transmission channel is received at its other end at a first and a second input of a measuring instrument including, downstream of a receiving stage connected to the second input, regenerating circuitry for producing replicas of the original pulses. The latter are fed, along with the received distorted pulses, to a phase and amplitude comparator working into a spectral analyzer which displays the spectral-density difference between a received pulse and a replica of the corresponding transmitted pulse. The second input of the instrument may be connected to the output side or to the input side of an equalizer which supplies the received pulses to the first input thereof and whose parameters are to be adjusted on the basis of the measurements made.

Electronic instrument for measuring the overall phase and amplitude

A nonlinear signal transducer U, such as a light-emitting diode or a semiconductive laser, is maintained at a suitable operating point by a constant biasing current and receives an electrical input signal by way of a series resistor R from a main amplifier AM of variable gain. The output voltage of the main amplifier is detected and integrated to provide a first reference voltage which is compared with the load voltage of the transducer U in a differential amplifier AE1, forming part of a first feedback loop, to adjust a voltage generator GT controlling the output voltage of the main amplifier AM so as to eliminate any voltage drop across the series resistor R as long as the input signal is absent or has an instantaneous magnitude equal to its mean value. A second feedback loop includes a peak-to-peak detector DP which emits a voltage proportional to the signal amplitude, that voltage being compared with a second reference voltage in a differential amplifier AE2 serving to adjust a current generator GC1 which controls the gain of the main amplifier AM. The second reference voltage may be varied manually or in response to changes in the output of the transducer U.

Circuit arrangement for driving nonlinear threshold devices

An adaptive equalizer for a telecommunication system, designed to process high-frequency signals in a band on the order of 50 MHz, comprises several weighting networks with input connections to respective taps of a delay line and with output connections to a summing amplifier, each weighting circuit having a control input to which a selected corrective voltage is applied. Each weighting network includes a bridge with two arms constituted by respective secondaries of an input transformer and two other arms in the form of indirectly variable resistance elements, specifically photoresistors photoelectrically coupled to a pair of light-emitting diodes, capacitively isolated for direct current from other parts of the bridge. Energization of the control input with corrective analog voltage of either polarity unbalances the bridge by differentially exciting the light-conductive diodes through respective operational amplifiers also receiving feedback signals derived from the voltage drops across the associated photoresistors which are traversed by constant currents.

Growing community of inventors

Ivrea, Italy

Alfredo Fausone