Deutsche Itt Industries Gmbh

Otmar Kappeler

Dietmar Ehrhardt

Herbert Elmis

Hermannus Schat

Bernd Novotny

Gerhard G Gassmann

Gerhard Gunter

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.

Television sound receiving circuit for at least one sound channel

A generator circuit according to the invention generates two 90.degree. phase-shifted frequency-variable sinusoidal signals by mixing the output signal of a fixed-frequency oscillator and of a continuously variable oscillator with the aid of two multipliers operating as mixers. The fixed-frequency signal is applied to the second multiplier via a 90.degree. phase shifter. The output signal of the multipliers which contains the sum and the difference frequency of its input signals, is respectively fed to a low-pass filter or to a band-pass filter, which suppresses the sum frequency or the difference frequency respectively. By the 90.degree. phase shifter, the sinusoidal signal is phase-shifted with respect to the sinusoidal signal by exactly 90.degree.. During the continuous variation process, the signal as applied to the 90.degree. phase shifter remains stable in its frequency, whereas the output signal of the continuously variable oscillator as fed directly to the two multipliers, is changed in its frequency.

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Neuenburg, Germany

Otmar Kappeler