Television – Receiver circuitry – Demodulator
Patent
1996-02-28
1998-06-30
Peng, John K.
Television
Receiver circuitry
Demodulator
348 73, 348 11, 455 32, 455133, 455141, 455209, 455314, H04N 5455, H04N 720
Patent
active
057741948
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
The invention is based on a television tuner. In such a tuner, for terrestrial reception, a conversion to a 1st IF is in general carried out in a first mixing stage and a further conversion to a 2nd IF is carried out in a subsequent second mixing stage, which 2nd IF is then supplied to the IF amplifier. Conversion to an IF is likewise carried out in a first mixing stage for satellite reception. This IF is then supplied to an FM-PLL demodulator which supplies at its output the baseband signal of the satellite antenna signal. Two separate tuners are in general provided for the two different functions, specifically terrestrial reception and satellite reception.
The invention is based on the object of providing a common tuner for terrestrial reception and satellite reception, which requires only a low circuit cost overall and in which as many components as possible are used for both operating modes.
The invention is based on the following considerations and knowledge. For terrestrial reception, the first mixing stage and the second mixing stage for the double frequency conversion work up to the intermediate frequencies of 38.9 MHz and 33.4 MHz. For satellite reception, only the first mixing stage works as a frequency converter, since the baseband signal of the satellite antenna signal is obtained from the IF carrier, whose frequency has been reduced only once, directly in a PLL demodulator. In the case of invention, the second mixing stage is now used as a component of the PLL demodulator for satellite reception, to be precise preferably as a phase comparison stage of the PLL circuit. In this case, the mixing oscillator for the second mixing stage is preferably tuned to the first intermediate frequency. This double use of the second mixing stage, specifically as the second mixing stage for terrestrial reception for the second frequency conversion and as a phase comparison stage of the PLL demodulator for satellite reception, results in a lower circuit cost. A tuner is thus produced which can receive the antenna signal of a conventional terrestrial antenna and the antenna signal of a satellite antenna equally well.
The output of the second mixing stage is preferably connected via a changeover switch to the input of a second IF stage for terrestrial reception and to the input of a low-pass filter for satellite reception, the output of which low-pass filter is connected to the control input of the mixing oscillator for the second mixing stage and to a terminal which supplies the baseband signal. The control input of the mixing oscillator is in this case connected via a changeover switch to the output of a PLL circuit, which is controlled by the mixing oscillator and by an I.sup.2 C bus, for terrestrial reception and is connected to the output of the low-pass filter of the PLL circuit for satellite reception. The tuner preferably has a first input for a satellite antenna signal whose frequency has been reduced and a second input for a terrestrial antenna signal. The two inputs can also be combined to form one input. An antenna signal would then be supplied thereto which has already been combined in advance, for example in the vicinity of the antennas, from the antenna signal of the terrestrial antenna and that of the satellite antenna. The tuner preferably has a first output for the second intermediate frequency of a terrestrial antenna signal, and has a second output for the baseband signal of a satellite antenna signal.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is explained in the following text with reference to the drawing of an exemplary embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the figure, the satellite receiving dish 1 supplies a signal at a frequency in the order of magnitude of 11 GHz, which is converted in the LNC (low noise converter) 2 to a frequency range of 950-2050 MHz. This signal passes via the antenna input 3 to the filter 4, which is tuned to this frequency range. This signal passes via the amplifier 5, which is controlled by the AGC2, to the first
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Deutsche Thomson-Brandt GmbH
Emanuel Peter M.
Murrell Jeffrey S.
Peng John K.
Tripoli Joseph S.
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