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US 5,838,395 AGranted
IF demodulator circuit with variable IF gain control
AssigneeU.S. Philips Corporation
InventorJoachim Brilka
Life of this patent
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AssigneeU.S. Philips Corporation
InventorJoachim Brilka
Estimating the term…
An IF demodulator circuit with IF gain control at a variable time constant, which receives an IF carrier including synchronizing pulses, a black porch and picture information with a positively modulated picture signal, in which the IF picture signal is amplified to a nominal amplitude value by the gain control, and which includes an IF demodulator (3) which demodulates the IF picture signal and supplies a picture signal from the output, while, for a gain control which is independent of DC offsets that may occur in the picture signal, the demodulator circuit is constructed in such a way that a black level detector (8) for generating a black level signal used as a threshold value signal in conformity with the amplitude value of the black porch of the picture signal supplied by the amplitude demodulator (3) is provided, that a DC offset circuit (4) is provided, which raises the DC component of the picture signal and/or lowers the DC component of the threshold value signal in such a way that both signals are offset by a predetermined value relative to each other, that a comparator circuit (7) is provided which receives the two signals which are offset relative to each other, in which signals the comparator circuit compares the voltage value of the synchronizing pulses occurring in the picture signal with the voltage value of the threshold value signal, and that the comparator circuit (7) supplies a comparison signal in dependence upon this comparison, in dependence upon which comparison signal the time constant of the gain control is changed.
An IF demodulator circuit with IF gain control at a variable time constant, said IF demodulator circuit receiving an IF carrier, comprising synchronizing pulses, a black porch and picture information with a positively modulated picture signal, and amplifying the IF picture signal to a nominal amplitude value by means of the IF gain control, said IF demodulator circuit comprising an IF demodulator for demodulating the IF picture signal and for supplying a picture signal from an output, characterized in that said IF demodulator circuit further comprises a black level detector for generating a black level signal used as a threshold value signal in conformity with an amplitude value of the black porch of the picture signal supplied by the IF demodulators;
A television tuner including an IF demodulator circuit with gain control at a variable time constant, said IF demodulator circuit receiving an IF carrier, comprising synchronizing pulses, a black porch and picture information with a positively modulated picture signal, and amplifying the IF picture signal to a nominal amplitude value by means of the IF gain control, said IF demodulator circuit comprising an IF demodulator for demodulating the IF picture signal and for supplying a picture signal from an output, characterized in that said IF demodulator circuit further comprises a black level detector for generating a black level signal used as a threshold value signal in conformity with an amplitude value of the black porch of the picture signal supplied by the IF demodulator;
A picture display device including a television tuner which is provided with an IF demodulator circuit with gain control at a variable time constant, said IF demodulator circuit receiving an IF carrier, comprising synchronizing pulses, a black porch and picture information with a positively modulated picture signal, and amplifying the IF picture signal to a nominal amplitude value by means of the IF gain control, said IF demodulator circuit comprising an IF demodulator for demodulating the IF picture signal and for supplying a picture signal from an output, characterized in that said IF demodulator circuit further comprises a black level detector for generating a black level signal used as a threshold value signal in conformity with an amplitude value of the black porch of the picture signal supplied by the IF demodulator;
Dependencies are inferred from the claim text.