Deutsche Itt Industries Gmbh

Dietmar Ehrhardt

Otmar Kappeler

Herbert Elmis

Hermannus Schat

Bernd Novotny

Sonke Mehrgardt

Gerhard G Gassmann

Gerhard Gunter

A color television channel that includes a video channel and at least one sound channel is converted by means of a low-IF converter from the RF band directly to the baseband by analog quadrature conversion. The quadrature output signals are digitized. A correcting stage eliminates the quadrature errors and forms a corrected quadrature pair which drives a video stage and a sound conversion stage. The sound conversion stage includes at least one sound channel converter which converts the low-IF sound channel to its baseband by another (digital) quadrature conversion.

Frequency conversion circuit for a color television channel

A television receiving section includes only a single A/D converter, and, thus, only a single interface between the analog portion and the digital portion. Preferably, the A/D converter is positioned after the intermediate-frequency stage of the television receiving section. The A/D converter is clocked at about 20 MHz. The digital portion of the television receiving section includes a video channel and an audio channel. The video channel includes at its input end a band-pass filter whose passband extends from 1 MHz to 6 MHz and whose output signals are fed directly and through a 90.degree. phase shifter to a first absolute-value stage, which delivers the digital composite color signal. The audio channel includes at its input end a quadrature mixer (operating from a locally generated clock having a frequency of 7 MHz to 7.5 MHz) whose two output signals are fed through a first decimator and a second decimator, respectively, to a second absolute-value stage and an angle-computing stage. The output of the angle-computing stage delivers a frequency-demodulated audio signal through a differentiating stage. The output of the second absolute-value stage provides an amplitude-demodulated audio signal.

Television receiving section with digital stages

A frequency converter circuit for television signals is disclosed which contains a tuner and a low-IF converter which converts the television signal to a low IF signal to obtain adjacent-channel selectivity with low-pass filters. The low-IF converter further includes a phase-correcting stage and an amplitude-correcting stage for the two quadrature-signal paths. By digitizing the two signal paths after the first quadrature mixing process, their amplitude and phase stability is further improved.

Frequency converting apparatus for converting an RF television signal to

The frequency conversion of an RF signal is performed by the 'third method' using a suitable frequency reversal which makes the frequencies of the picture carrier, the chrominance subcarrier, and at least one sound carrier appear transformed into the baseband, such that the frequencies of the transformed picture carrier and the transformed chrominance subcarrier coincide. Unavoidable differences in the signal paths of the frequency reversal result in a spurious signal which produces a temporally/locally varying moire on the screen. By means of a frequency offset, this spurious signal is transformed into a frequency range which is not found annoying by the observer, so that the moire becomes invisible. This frequency range is preferably the exact center region between two spectral lines of the horizontal frequency of the composite color signal in the baseband.

Frequency conversion of an RF signal transmitted for color-television

A television sound receiving circuit for at least one sound channel contained in an RF signal converts the transmitted or already down-converted television signal as a composite signal to the baseband in a single-sideband demodulator circuit using the 'phasing method', separates the first sound channel, corresponding to a lower sideband, and the second sound channel, corresponding to an upper sideband, and produces first and second sound signals at the desired frequency by subsequent frequency demodulation. Also shown are the interfaces for possible digitization and an advantageous use of the interfaces in which picture and sound signals are digitized together. The data can be combined into a single data stream which can be transferred over a bus system and is separable into the individual components if required.

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Freiburg i.Br., Germany

Dietmar Ehrhardt