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US 4,658,423 AGranted
FM-stereo receiver
AssigneeU.S. Philips Corporation
InventorWolfgang Nolde
Life of this patent
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Abstract
In an FM-stereo receiver the demodulated stereo-difference signal is mixed with a non-sinusoidal signal of the sub-carrier frequency and the mixing product is used to modulate the frequency of an oscillator by means of which the aerial signal is converted to the intermediate frequency range. Interference in the reception is avoided because of the fact that the signal used for modulating the oscillator is free from third and fifth harmonics of the sub-carrier frequency.
Claims5
An FM-stereo receiver comprising:
- a frequency controlled oscillator having a control input for receiving a frequency control voltage;
- means for mixing a received radio frequency input signal with a signal from said oscillator, whereby an intermediate frequency signal is produced;
- an FM demodulator for demodulating said intermediate frequency signal;
- means for deriving a control voltage for said oscillator from a demodulated signal produced by said FM demodulator comprising a first low pass filter, and bandpass filter connected in parallel with said low pass filter to receive said demodulated signal, said bandpass filter including a stereo signal demodulator for producing a stereo difference signal when a stereo signal is included in said radio frequency input signal, a second low pass filter for supplying said stereo difference signal to a first mixer stage, said first mixer stage receiving a second, non-sinusoidal signal having a frequency of a subcarrier frequency of said stereo difference signal;
- and
- means responsive to said first low pass filter and an output of said first mixer for removing mixing products produced by third and fifth harmonics of said non-sinusoidal signal fundamental frequency from said first mixer stage output signals, to thereby generate said control voltage.
3 more elements
An FM-stereo receiver comprising:
- a frequency controlled oscillator having a control input for receiving a frequency control voltage;
- means for mixing a received radio frequency input signal with a signal from said oscillator, whereby an intermediate frequency signal is produced;
- an FM demodulator for demodulating said intermediate frequency signal;
- means for deriving a control voltage for said oscillator from a demodulated signal produced by said FM demodulator comprising:
- a first low pass filter connected to receive said demodulated signal;
- a stereo difference signal demodulator connected to receive said demodulated signal and provide a stereo difference signal;
- a second low pass filter connected to receive said stereo difference signal;
- first, second and third mixer stages for receiving a signal from said second low pass filter, and for receiving respectively, first second and third square wave signals having frequencies which are, respectively, the fundamental, third and fifth harmonics of a subcarrier frequency associated with said stereo difference signal;
- means for combining output signals from said first, second and third mixer stages in an amplitude and phase relationship for suppressing undesired mixing products from said first mixer stage which are harmonically related to said subcarrier;
- and,
- an adder for producing said control voltage from a signal from said means for combining and a signal from said first low pass filter.
8 more elements
Dependencies are inferred from the claim text.