Frequency demodulator having circuit cancelling undesired signal components

Claim 2

A frequency demodulation apparatus for demodulating a frequency-modulated signal obtained by modulating a carrier frequency f c with a signal frequency f 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 c , where m is a natural number, the signal frequency f s and an nth-order lower sideband component mf c -nf s as an undesired moire component, where n is a natural number; a moire component generating means for extracting the carrier frequency mf c and the signal frequency f s from the demodulated signal and for generating a moire component mf c -nf s corresponding to said undesired moire component; and a subtracting means for subtracting the moire component generated by said moire component generating means from said demodulated signal so as to thereby obtain a demodulated signal from which said undesired moire component is eliminated.

Claim 3

A frequency demodulation apparatus as in claim 1, wherein said moire component generating means comprises: a first filter means coupled to said demodulating means for passing the carrier frequency mf c ; a second filter means coupled to said demodulating means for passing the signal frequency f s ; an n-times-multiplying means for multiplying the signal frequency f s from said second filter means by n to obtain the frequency component nf s ; and a multiplying means for multiplying the carrier frequency mf c from said first filter means and the frequency nf s from said n-times-multiplying means so as to thereby obtain the moire component mf c -nf s .

Claim 4

A frequency demodulation apparatus as in claim 1, wherein said moire component generating means includes means for adjusting the gain and amplitude of the generated moire component.

Claim 5

A frequency demodulation apparatus as in claim 1, further comprising a delay means provided between said demodulating means and said subtracting means for compensating for a time delay caused in said moire component generating means.

Claim 6

A frequency demodulation apparatus for demodulating a frequency-modulated signal obtained by modulating a carrier frequency f c with a signal frequency f 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 c , which m is a natural number, the signal frequency f s and second order through nth-order lower sideband components mf c -2f s through mf c -nf 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 c from the demodulated signal; a second filter means for extracting the signal frequency f s from the demodulated signal; a first multiplying means for multiplying the extracted signal frequency f s by two through n, respectively, to obtain 2f s through nf s frequency components; an adding means for adding the 2f s through nf s components from said first multiplying means; and a second multiplying means for multiplying the carrier frequency mf c and the added result from the adding means so as to thereby obtain second through nth-order moire components mf c -2f s through mf c -nf 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.

Claim 7

A frequency demodulation apparatus for demodulating a frequency-modulated signal obtained by modulating a carrier frequency f c with a signal frequency f 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 c , which m is a natural number, the signal frequency f s and second order through nth-order lower sideband components mf c -2f s through mf c -nf 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 c from the demodulated signal; a second filter means for extracting the signal frequency f s from the demodulated signal; a first multiplying means for multiplying the extracted signal frequency f s by two through n, respectively, to obtain 2f s through nf s frequency components; an adding means for adding the 2f s through nf s components from said first multiplying means; and a second multiplying means for multiplying the carrier frequency mf c and the added result from the adding means so as to thereby obtain second through nth-order moire components mf c -2f s through mf c -nf 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.

Claim 8

A frequency demodulation apparatus for demodulating a frequency-modulated signal which is obtained by modulating a carrier frequency f c with a signal frequency f 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 c , where m is a natural number, the signal frequency f s and an nth-order lower sideband component nf 1 -(n-m)f c as an undesired moire component, where n is a natural number and f 1 is a first-order lower sideband component, expressed as f 1 =f c -f s , of the frequency-modulated signal; a moire component generating means for extracting the carrier frequency f c and the first-order lower sideband component f 1 from the frequency-modulated signal and for generating a moire component nf 1 -(n-m)f 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.

Claim 9

A frequency demodulation apparatus for demodulating a frequency-modulated signal which is obtained by modulating a carrier frequency f c with a signal frequency f 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 c , where m is a natural number, the signal frequency f s and an nth-order lower sideband component nf 1 -(n-m)f c as an undesired moire component, where n is a natural number and f 1 is a first-order lower sideband component, expressed as f 1 =f c -f s , of the frequency-modulated signal; a moire component generating means for extracting the carrier frequency f c and the first-order lower sideband component f 1 from the frequency-modulated signal and for generating a moire component nf 1 -(n-m)f 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.

Claim 10

A frequency demodulation apparatus as in claim 6, wherein m=2 and n=2, and wherein said moire component generating means comprises: a filter means for extracting the first-order lower sideband component f 1 from the frequency-modulated signal; and a multiplying means for multiplying the extracted component f 1 by 2 so as to thereby obtain a component 2f 1 as the moire component.

Claim 11

A frequency demodulation apparatus as in claim 6, wherein m=2 and n=3, and wherein said moire component generating means comprises: a first filter means for extracting the carrier frequency f c from the frequency-modulated signal; a second filter means for extracting the first-order lower sideband component f 1 from the frequency-modulated signal; a first multiplying means for multiplying the extracted component f 1 by 3 to obtain a 3f 1 component; and a second multiplying means for multiplying the extracted carrier frequency f c and the 3f 1 component so as to thereby obtain a component f c -3f 1 as the moire component.

Claim 12

A frequency demodulation apparatus as in claim 6, wherein said moire component generating means includes means for adjusting the phase and amplitude of the generated moire component.

Claim 13

A frequency demodulation apparatus as in claim 6, further comprising a delay means provided between said demodulating means and said subtracting means for compensating for a time delay caused in said moire component generating means.

Claim 14

A frequency demodulation apparatus for demodulating a frequency-modulated signal which has a carrier frequency f c and contains a low-frequency signal f L and a cross-modulation signal component expressed as f c -2f L , comprising: a demodulating means for demodulating the frequency-modulated signal to obtain a demodulated signal which contains a frequency component 2f L as an undesired cross-modulation moire component; a moire component generating means for extracting the low-frequency signal f L from the frequency-modulated signal and for generating a 2f 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.

Claim 15

A frequency demodulation apparatus for demodulating a frequency-modulated signal which has a carrier frequency f c and contains a low-frequency signal f L and a cross-modulation signal component expressed as f c -2f L , comprising: a demodulating means for demodulating the frequency-modulated signal to obtain a demodulated signal which contains a frequency component 2f L as an undesired cross-modulation moire component; a moire component generating means for extracting the low-frequency signal f L from the frequency-modulated signal and for generating a 2f 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.

Claim 16

A frequency demodulation apparatus as in claim 11, wherein said moire component generating means comprises: a filter means for extracting the low-frequency signal f L from the frequency-modulated signal and a multiplying means for multiplying the extracted signal f L by 2 so as to thereby obtain the 2f L component.

Claim 17

A frequency demodulation apparatus as in claim 11, wherein said moire component generating means includes means for adjusting the gain and amplitude of the generated moire component.

Claim 18

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 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 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 c -2f 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 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 L from the reproduced signal reproduced from the recording medium and for generating a moire component 2f 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.

Claim 19

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 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 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 c -2f 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 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 L from the reproduced signal reproduced from the recording medium and for generating a moire component 2f 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.

Claim 20

An apparatus as in claim 14, wherein said input signal is a video signal, and said first and second signals are a luminance signal and a chrominance signal, respectively.

Claim 21

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 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 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 c -2f 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 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 L from the reproduced signal reproduced from the recording medium and for generating a moire component 2f 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.

Claim 22

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 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 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 c -2f 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 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 L from the reproduced signal reproduced from the recording medium and for generating a moire component 2f 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.

Claim 23

An apparatus as in claim 16, wherein said input signal is a video signal, and said first and second signals are a luminance signal and a chrominance signal, respectively.