Arrangement for demodulating a vestigial sideband signal

Abstract

An arrangement is described for demodulating a vestigial sideband signal component contained in an amplitude-modulated frequency signal, and preferably in a vision intermediate-frequency signal derived from a television signal. What distinguishes the invention is that there are provided two parallel, preferably identical, mixing stages (8a, 8b) that operate at a phase shift of substantially, and preferably exactly, 90 DEG , of which mixing stages a first one (8a) produces from the frequency signal a first output signal and a second one (8b) produces from the frequency signal a second output signal that is phase shifted by substantially, and preferably exactly, 90 DEG relative to the first output signal, a downstream phase-shifter (12) that causes a phase shift between the first and second output signals from the mixing stages (8a, 8b) of substantially, and preferably exactly, a further 90 DEG , an adder (14) that adds together the output signals from the phase shifter (12), which output signals have been phase shifted relative to one another by substantially, and preferably exactly, 180 DEG , a local oscillator (10) that drives the mixing stages with a phase shift of substantially, and preferably exactly, 90 DEG , and a setting device for setting the frequency and phase of the local oscillator (10), the setting device setting the frequency and phase of the local oscillator (10) substantially, and preferably exactly, to the frequency and phase of the frequency signal.

Description

technical field [0001] The invention relates to a device for demodulating vestigial sideband signal components contained in an AM frequency signal, preferably a vestigial sideband signal component contained in a visual intermediate frequency signal derived from a television signal. Background technique [0002] This type of demodulation equipment is used in particular in analog and digital television systems, where it is mainly used to demodulate the high frequency ( HF) and VSB modulated television signals in the intermediate frequency (IF) stages. [0003] Broadcasting of analog TV signals with vestigial sideband modulation can only be processed and demodulated by very specialized signal stages and filters, whereas DVB (Digital Video Broadcasting) broadcasting with OFDM modulation requires completely different signal processing because in this case Downstream requires frequency mixing, filtering, and analog-to-digital conversion. [0004] Especially for the mentioned app...

AI Technical Summary

Problems solved by technology

[0004] Especially for the mentioned applications, the demodulation circuits used until now have an overly complex construction, especially because of the use of Nyquist filter stages to generate the Nyquist edges in the vestigial sideband TV signal (in analog systems) and the use of window filter stages (in digital systems), which in either type of system are usually formed by surface acoustic wave (SAW) filters

For all current standards, in analog and digital video broadcasting systems, they will be brought to a greater degree of difficulty in the construction of the previous demodulation circuit

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