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US 4,458,207 AGranted
FM Demodulator with variable bandpass filter
AssigneeThomson-CSF
InventorsMichel Favreau, Andre Marguinaud
Life of this patent
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Abstract
The demodulator combines a conventional frequency discriminator with a bandpass filter for removing the noise which is present from the band occupied at a given instant by the modulated signal. The center frequency of the bandpass filter is controlled in dependence on the instantaneous frequency of the modulated signal and its bandwidth b.sub.u is controlled in dependence on the instantaneous width of the band occupied by the modulated signal.
Claims5
A demodulator for a frequency-modulated signal, comprising:
- a bandpass filter having a first control input for adjusting its center frequency, a second control input for adjusting the width of its passband, a third input for receiving the modulated signal, and one output;
- a frequency discriminator having one input connected to the output of the filter and one output constituting the demodulator output for delivering the modulation signal;
- a control system comprising computation means for computing a value F.sub.i of the instantaneous frequency of the modulated signal and for computing, as a function of the rate of variation of the modulation signal, a value b.sub.u of the instantaneous width of the frequency band occupied by the modulated signal, said control means being provided with a first output connected to the first control input of the filter for delivering a signal which is a function of F.sub.i to said filter in order to adjust the center frequency to the value F.sub.i, and a second output connected to the second control input of the filter for delivering a signal which is a function of b.sub.u to said filter in order to adjust the bandwidth to the value b.sub.u.
A demodulator according to calim 1 for demodulating a television signal, wherein the computation means comprise:
- a first computation unit having an input connected to the output of the discriminator and an output for supplying a value F'.sub.i of the instantaneous frequency of the modulated signal;
- a second computation unit having an input connected to the output of the first computation unit and an output for supplying a value b'.sub.u of the instantaneous width of the frequency band occupied by the modulated signal;
- a delay circuit having two inputs connected respectively to the outputs of the first computation unit and of the second computation unit and having two outputs for delaying values F'.sub.i and b'.sub.u for a time corresponding to one image line, and delivering delayed values constituting values F.sub.i and b.sub.u respectively.
Dependencies are inferred from the claim text.