Television receiver for terrestrial broadcasting
AssigneeMatsushita Electric Industrial Co., Ltd.
InventorsSeiji Sakashita, Hiroaki Ozeki, Ippei Kanno, Daisuke Hayashi
Life of this patent
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Abstract
In a television receiver in which image frequency signals for desired signals are removed when television broadcasting signals are frequency-converted through a local oscillator and mixers, the local oscillator generates biaxial orthogonal signals to be frequency-converted by respective mixers, an output signal of one mixer being phase-shifted to be added to an output signal of the other mixer so as to thereby offset only the image frequency signals. The local oscillator and a phase shifter operate so as to follow the frequency change of the intermediate frequency signal so as to thereby stabilize the suppression of the image frequency signal.
Claims5
A television receiver comprising:
- a channel selector, said channel selector generating a channel selection signal for selecting a desired signal of high frequency signals inputted from an antenna;
- a frequency converter, said frequency converter frequency-converting the desired signal of high frequency signals into an intermediate frequency signal in response to the channel selection signal from the channel selector;
- a local oscillation signal generator, said generator being capable of changing oscillation frequencies of biaxial orthogonal local oscillation signals;
- a first mixer and a second mixer, said first and second mixers frequency-converting said intermediate frequency signal in response to the respective biaxial orthogonal local oscillation signals;
- a phase shifter, said phase shifter phase-shifting an output signal of the first mixer by 90 degrees;
- an adder, said adder adding an output signal of said phase shifter and an output signal of the second mixer;
- a detector, said detector detecting an output signal of the adder;
- a frequency variation controller, said controller feeding a variation of the intermediate frequency outputted from said detector back to said local oscillation signal generator;
- a phase difference detector, said phase difference detector detecting a phase difference between said biaxial orthogonal local oscillation signals;
- and
- a phase-shift amount setter, said setter adding said channel selection signal from the channel selector to an output signal of the phase difference detector to generate a signal to change a phase-shift amount, whereby image frequency signals are offset when frequency conversion is carried out.
Dependencies are inferred from the claim text.