Frequency demodulator having circuit cancelling undesired signal components

A frequency demodulation apparatus for demodulating a frequency-modulated signal obtained by modulating a carrier frequency f.sub.c with a signal frequency f.sub.s, comprising:

• a demodulating means for demodulating the frequency-modulated signal to obtain a demodulated signal which contains an m-times-multiplied carrier frequency mf.sub.c, which m is a natural number, the signal frequency f.sub.s and second order through nth-order lower sideband components mf.sub.c -2f.sub.s through mf.sub.c -nf.sub.s as undesired moire components, where n is a natural number larger than 2;
• a moire component generating means which comprises:
• a first filter means for extracting the carrier frequency mf.sub.c from the demodulated signal;
• a second filter means for extracting the signal frequency f.sub.s from the demodulated signal;
• a first multiplying means for multiplying the extracted signal frequency f.sub.s by two through n, respectively, to obtain 2f.sub.s through nf.sub.s frequency components;
• an adding means for adding the 2f.sub.s through nf.sub.s components from said first multiplying means;
• and a second multiplying means for multiplying the carrier frequency mf.sub.c and the added result from the adding means so as to thereby obtain second through nth-order moire components mf.sub.c -2f.sub.s through mf.sub.c -nf.sub.s corresponding to said undesired moire components;
• and
• a subtracting means for subtracting the moire components generated by said moire component generating means from the demodulated signal so as to thereby obtain a demodulated signal from which said undesired moire components are eliminated.

A frequency demodulation apparatus for demodulating a frequency-modulated signal which is obtained by modulating a carrier frequency f.sub.c with a signal frequency f.sub.s, comprising:

• a demodulating means for demodulating the frequency-modulated signal to obtain a demodulated signal which contains an m-times-multiplied carrier frequency mf.sub.c, where m is a natural number, the signal frequency f.sub.s and an nth-order lower sideband component nf.sub.1 -(n-m)f.sub.c as an undesired moire component, where n is a natural number and f.sub.1 is a first-order lower sideband component, expressed as f.sub.1 =f.sub.c -f.sub.s, of the frequency-modulated signal;
• a moire component generating means for extracting the carrier frequency f.sub.c and the first-order lower sideband component f.sub.1 from the frequency-modulated signal and for generating a moire component nf.sub.1 -(n-m)f.sub.c corresponding to said undesired moire component;
• and
• a subtracting means for subtracting the moire component generated by the moire component generating means from the demodulated signal so as to thereby obtain a demodulated signal from which said undesired moire component is eliminated.

A frequency demodulation apparatus for demodulating a frequency-modulated signal which has a carrier frequency f.sub.c and contains a low-frequency signal f.sub.L and a cross-modulation signal component expressed as f.sub.c -2f.sub.L, comprising:

• a demodulating means for demodulating the frequency-modulated signal to obtain a demodulated signal which contains a frequency component 2f.sub.L as an undesired cross-modulation moire component;
• a moire component generating means for extracting the low-frequency signal f.sub.L from the frequency-modulated signal and for generating a 2f.sub.L component as a moire component corresponding to said undesired cross-modulation moire component;
• and
• a subtracting means for subtracting the moire component generated by said moire component generating means from the demodulated signal so as to thereby obtain a demodulated signal from which said undesired cross-modulation moire component has been eliminated.

A signal recording and reproducing apparatus comprising:

• a means for extracting a first signal from an input signal and frequency-modulating a carrier frequency f.sub.c with the first signal to obtain a frequency-modulated signal;
• a means for extracting a second signal from the input signal and for generating from the second signal a low-frequency signal f.sub.L ;
• a means for adding the frequency-modulated signal and the low-frequency signal to obtain a recording signal;
• a means for recording the recording signal on a recording medium and reproducing the recorded signal from the recording medium, the reproduced signal containing a reproduced low-frequency signal and a reproduced frequency-modulated signal which contains a component f.sub.c -2f.sub.L as a cross-modulation component;
• a means for extracting the reproduced frequency-modulated signal from the reproduced signal and demodulating the extracted signal to obtain a reproduced first signal which contains a component 2f.sub.L as an undesired cross-modulation moire component;
• a means for generating a reproduced second signal from the reproduced low-frequency signal;
• a means for adding the reproduced first and second signals to obtain a reproduced signal;
• a moire component generating means for extracting the low-frequency signal f.sub.L from the reproduced signal reproduced from the recording medium and for generating a moire component 2f.sub.L corresponding to said undesired cross-modulation moire component;
• and
• a subtracting means for subtracting the moire component generated by said moire component generating means from the reproduced signal so as to thereby obtain a reproduced signal from which said undesired cross-modulation moire component is eliminated.

A signal recording and reproducing apparatus comprising:

• a means for extracting a first signal from an input signal and frequency-modulating a carrier frequency f.sub.c with the first signal to obtain a frequency-modulated signal;
• a means for extracting a second signal from the input signal and for generating from the second signal a low-frequency signal f.sub.L ;
• a means for adding the frequency-modulated signal and the low-frequency signal to obtain a recording signal;
• a means for recording the recording signal on a recording medium and reproducing the recorded signal from the recording medium, the reproduced signal containing a reproduced low-frequency signal and a reproduced frequency-modulated signal which contains a component f.sub.c -2f.sub.L as a cross-modulation component;
• a means for extracting the reproduced frequency-modulated signal from the reproduced signal and demodulating the extracted signal to obtain a reproduced first signal which contains a component 2f.sub.L as an undesired cross-modulation moire component;
• a means for generating a reproduced second signal from the reproduced low-frequency signal;
• a means for adding the reproduced first and second signals to obtain a reproduced signal;
• a moire component generating means for extracting the low-frequency signal f.sub.L from the reproduced signal reproduced from the recording medium and for generating a moire component 2f.sub.L corresponding to said undesired cross-modulation moire component;
• and
• a subtracting means for subtracting the moire component generated by said moire component generating means from the reproduced second signal so as to thereby obtain a reproduced signal from which said undesired cross-modulation moire component is eliminated.