Intermediate-frequency type radio signal receiver
View Patent ↗A radio signal receiver includes an input for receiving an input signal having an input carrier frequency modulated by a payload signal to be detected. A frequency converter changes the carrier frequency of the input signal and produces an intermediate signal that is an image of the input signal, and has a carrier frequency equal to an intermediate frequency. A filter circuit filters the intermediate signal. A demodulator eliminates a component, with a frequency equal to the intermediate frequency, from the filtered intermediate frequency, and produces the payload signal. The receiver also includes a detection circuit to produce a level signal representative of a level of the payload signal. A control circuit applies a control signal representative of the level signal to a control input of the frequency converter, the filter circuit and the demodulator.
1. A radio signal receiver comprising:
an input for receiving an input signal having a carrier frequency modulated by a payload signal;
a frequency changer for changing the carrier frequency of the input signal, and generating an intermediate signal having a carrier frequency equal to an intermediate frequency;
a filter circuit for filtering the intermediate signal;
a demodulator for removing a component, with a frequency equal to the intermediate frequency, from the filtered intermediate signal for generating the payload signal;
a detection circuit for generating a level signal representative of a level of the payload signal; and
a control circuit for applying the level signal as a control signal to said filter circuit, to said demodulator, and to a control input of said frequency changer.
2. The receiver according to claim 1 , wherein said frequency changer comprises:
a reference generator for generating a reference signal having a reference frequency that is a function of the control signal; and
a mixer for mixing the input signal and the reference signal, and generating the intermediate signal whose carrier frequency is a function of the reference frequency.
3. The receiver according to claim 2 , wherein said reference generator increases the reference frequency when a level of the level signal decreases, and decreases the reference frequency when the level of the level signal increases.
4. The receiver according to claim 3 , wherein said reference generator modulates the reference frequency according to the equation f00*(1+A/|COM|), where f00 and A are constants and |COM| is an absolute value of the level signal.
5. The receiver according to claim 3 , wherein said filter circuit comprises:
a bandpass analog filter whose center frequency is a function of the control signal for filtering low-frequency noise from the intermediate signal for generating a filtered analog signal;
a converter for converting the filtered analog signal to a corresponding digital signal; and
a bandpass digital filter whose center frequency is a function of the control signal for removing adjacent components from the digital signal for generating a demodulated digital signal.
6. The receiver according to claim 1 , wherein said filter circuit converts the intermediate signal to a digital intermediate signal and generates a filtered, demodulated digital signal.
7. The receiver according to claim 1 , wherein said demodulator comprises:
a second reference generator for generating, as a function of the control signal, a digital reference signal having a reference frequency that is a function of the control signal; and
a second mixer for mixing the filtered intermediate signal with the digital reference signal for generating the payload signal.
8. The receiver according to claim 7 , wherein said detection circuit comprises a detector for detecting a modulation amplitude of the demodulated digital signal output from said bandpass digital filter.
9. A receiver comprising:
an input for receiving an input signal having a carrier frequency modulated by a payload signal;
a frequency changer for changing the carrier frequency of the input signal, and generating an intermediate signal having a carrier frequency equal to an intermediate frequency;
a filter circuit for filtering the intermediate signal for generating a demodulated digital signal;
a demodulator for removing a component, with a frequency equal to the intermediate frequency, from the demodulated digital signal for generating the payload signal;
a detector for detecting a modulation amplitude of the demodulated digital signal from an output of said filter circuit, and for generating a level signal representative of a level of the payload signal; and
a control circuit for applying the level signal as a control signal to said filter circuit, to said demodulator, and to a control input of said frequency changer.
10. The receiver according to claim 9 , wherein said frequency changer comprises:
a reference generator for generating a reference signal having a reference frequency that is a function of the control signal; and
a mixer for mixing the input signal and the reference signal, and generating the intermediate signal whose carrier frequency is a function of the reference frequency.
11. The receiver according to claim 10 , wherein said reference generator increases the reference frequency when a level of the level signal decreases, and decreases the reference frequency when the level of the level signal increases.
12. The receiver according to claim 11 , wherein said reference generator modulates the reference frequency according to the equation f00*(1+A/|COM|), where f00 and A are constants and |COM| is an absolute value of the level signal.
13. The receiver according to claim 11 , wherein said filter circuit comprises:
a bandpass analog filter whose center frequency is a function of the control signal for filtering low-frequency noise from the intermediate signal for generating a filtered analog signal;
a converter for converting the filtered analog signal to a corresponding digital signal; and
a bandpass digital filter whose center frequency is a function of the control signal for removing adjacent components from the digital signal for generating a demodulated digital signal.
14. The receiver according to claim 9 , wherein said filter circuit converts the intermediate signal to a digital intermediate signal and generates the demodulated digital signal.
15. The receiver according to claim 9 , wherein said demodulator comprises:
a second reference generator for generating, as a function of the control signal, a digital reference signal having a reference frequency that is a function of the control signal; and
a second mixer for mixing the modulated digital signal with the digital reference signal for generating the payload signal.
16. A method for operating a radio signal receiver comprising:
receiving an input signal having a carrier frequency modulated by a payload signal;
changing the carrier frequency of the input signal using a frequency changer, and generating an intermediate signal having a carrier frequency equal to an intermediate frequency;
filtering the intermediate signal using a filter circuit;
removing a component, with a frequency equal to the intermediate frequency, from the filtered intermediate frequency using a demodulator, for generating the payload signal;
generating a level signal representative of a level of the payload signal; and
applying the level signal as a control signal to the filter circuit, to the demodulator, and to a control input of the frequency changer.
17. The method according to claim 16 , wherein the frequency changer comprises:
a reference generator for generating a reference signal having a reference frequency that is a function of the control signal; and
a mixer for mixing the input signal and the reference signal, and generating the intermediate signal whose carrier frequency is a function of the reference frequency.
18. The method according to claim 17 , wherein the reference generator increases the reference frequency when a level of the level signal decreases, and decreases the reference frequency when the level of the level signal increases.
19. The method according to claim 18 , wherein the reference generator modulates the reference frequency according to the equation f00*(1+A/|COM|), where f00 and A are constants and |COM| is an absolute value of the level signal.
20. The method according to claim 16 , wherein the filter circuit converts the intermediate signal to a digital intermediate signal and generates a filtered, demodulated digital signal.
21. The method according to claim 20 , wherein the filter circuit comprises:
a bandpass analog filter whose center frequency is a function of the control signal for filtering low-frequency noise from the intermediate signal for generating a filtered analog signal;
a converter for converting the filtered analog signal to a corresponding digital signal; and
a bandpass digital filter whose center frequency is a function of the control signal for removing adjacent components from the digital signal for generating a demodulated digital signal.
22. The method according to claim 16 , wherein the demodulator comprises:
a second reference generator for generating, as a function of the control signal, a digital reference signal having a reference frequency that is a function of the control signal; and
a second mixer for mixing the filtered intermediate signal with the digital reference signal for generating the payload signal.
23. The method according to claim 22 , wherein the detection circuit comprises a detector for detecting a modulation amplitude of the demodulated digital signal output from the bandpass digital filter.