System for demodulating a signal

1. A system for demodulating a phase-modulated input signal, the phase-modulated input signal comprising a carrier signal to which a phase modulation has been applied, the system comprising:

a complex demodulator having a first input for receiving the phase-modulated input signal and being configured to perform complex multiplication of the phase-modulated input signal with an approximation of an inverse of the phase modulation and in response thereto to output a demodulated product signal; and

a spectrum analyzing device receiving the demodulated product signal produced by the complex demodulator and capable of analyzing a frequency spectrum of the demodulated product signal.

2. The system of claim 1 , wherein the spectrum analyzing device comprises a complex fast Fourier transform (CFFT) device.

3. The system of claim 1 , wherein the spectrum analyzing device comprises a phase locked loop (PLL) device or a frequency locked loop (FLL) device.

4. The system of claim 1 , wherein the spectrum analyzing device comprises a PLL device or a FLL device in parallel with a CFFT device.

5. The system of claim 1 , wherein the spectrum analyzing device is capable of determining an estimate of the difference between a phase amplitude of the phase-modulated input signal and a phase amplitude of the demodulated product signal, and to provide an error signal that represents the estimate;

wherein the system for demodulating further comprises a modulation controller configured for receiving the error signal and generating a phase modulation information signal for the complex demodulator based on said error signal; and wherein the complex demodulator uses the phase modulation information signal to determine or adapt the approximation of the inverse of the phase modulation.

6. The system according to claim 5 , wherein the demodulated product signal has a carrier frequency and wherein the error signal represents an estimate of sideband phase and amplitude of a spectrum around the carrier frequency.

7. The system according to claim 5 , wherein the demodulated product signal has a carrier frequency and wherein the error signal represents an estimate of sideband phase and amplitude of a spectrum around an unwanted negative image of the carrier frequency.

8. The system of claim 7 , wherein the spectrum analyzing device derives demodulation information from an amplitude of an unwanted inverted frequency peak relative to an amplitude of a peak of the carrier frequency peak.

9. The system according to claim 5 , wherein the demodulated product signal has a carrier frequency and wherein the modulation controller shifts a phase modulation frequency in dependence of the carrier frequency in order to increase a distance between the carrier frequency and an unwanted frequency peak.

10. The system according to claim 5 , wherein the demodulated product signal has a carrier frequency and wherein the spectrum analyzing device is configured to determine a phase modulation frequency based on the carrier frequency;

wherein the spectrum analyzing device is configured to provide an output signal representing the phase modulation frequency; and

wherein said output signal is also received by the modulation controller and used to generate the phase modulation information signal for the complex demodulator.

11. The system according to claim 5 , wherein the demodulated product signal has a carrier frequency and wherein the modulation controller chooses the phase amplitude of the demodulated product signal for suppression of a peak close to 0 Hz.

12. The system according to claim 5 , wherein the demodulated product signal has a carrier frequency and wherein the phase amplitude of the phase-modulated input signal and a phase-modulation function applied to the input signal are chosen to substantially suppress unwanted AM modulation in the input signal.