Signal processing circuit and signal processing method

1. A signal processing circuit comprising:

a demodulator to demodulate a received signal and output a demodulated signal;

a filter to output a signal corresponding to a prescribed frequency component of the demodulated signal;

a blending unit to blend the demodulated signal with an output signal of the filter at a prescribed blending ratio;

an electric field strength change amount detection unit to detect a change in electric field strength and output an electric field strength change amount; and

a blending ratio determination unit to determine the prescribed blending ratio according to the electric field strength change amount.

2. The signal processing circuit according to claim 1 , wherein the electric field strength change amount detection unit includes:

an envelope detector to output an envelope signal corresponding to an envelope of the electric field strength; and

a subtractor to subtract a signal indicating the electric field strength from the envelope signal.

3. The signal processing circuit according to claim 1 , wherein the blending unit includes:

a first attenuator to attenuate the demodulated signal based on the prescribed blending ratio;

a second attenuator to attenuate the output signal of the filter based on the prescribed blending ratio; and

an adder to add an output of the first attenuator and an output of the second attenuator together.

4. The signal processing circuit according to claim 3 , wherein

the first attenuator attenuates the demodulated signal by (1−α) times where α is a value less than 1, and the second attenuator attenuates the output signal of the filter by α times.

5. The signal processing circuit according to claim 1 , wherein the blending ratio determination unit includes:

a register to store a relationship of a blending amount with respect to the electric field strength change amount; and

a blending amount calculator to calculate a blending amount based on the electric field strength change amount and the relationship stored in the register.

6. The signal processing circuit according to claim 1 , wherein the blending ratio determination unit determines the prescribed blending ratio when the electric field strength change amount exceeds a prescribed change amount.

7. The signal processing circuit according to claim 1 , further comprising:

a specified component detection unit to detect a specified component of the demodulated signal; and

a blending control unit to control the blending based on electric field strength of the received signal and a detection result of the specified component detection unit.

8. The signal processing circuit according to claim 7 , wherein the specified component of the demodulated signal is 19 kHz component of the demodulated signal.

9. The signal processing circuit according to claim 7 , wherein the blending control unit controls the blending unit to start blending when the specified component of the demodulated signal exceeds a prescribed amount, and the prescribed amount is determined based on electric field strength of the received signal.

10. The signal processing circuit according to claim 1 , further comprising:

a modulation factor detection unit to detect a modulation factor of the demodulated signal; and

a blending control unit to control the blending based on a detection result of the modulation factor detection unit.

11. The signal processing circuit according to claim 1 , further comprising:

a modulation factor detection unit to detect a modulation factor of the demodulated signal;

an attenuator to attenuate a signal corresponding to a specified frequency component of the demodulated signal; and

a gain adjuster to determine a gain of the attenuator based on a detection result of the modulation factor detection unit.

12. The signal processing circuit according to claim 1 , further comprising:

a channel equalizer; and

a blending control unit to control the blending based on operation of the channel equalizer.

13. The signal processing circuit according to claim 12 , wherein the blending control unit controls blending by the blending unit and equalization by the channel equalizer to be complementary to each other.

14. A signal processing circuit that blends a demodulated signal demodulated from a received signal and a signal corresponding to a specified frequency component of the demodulated signal at a prescribed blending ratio, wherein the blending ratio is determined based on a change amount of electric field strength of the received signal.

15. The signal processing circuit according to claim 14 , wherein the change amount of electric field strength of the received signal is calculated by subtracting the electric field strength of the received signal from a waveform corresponding to an envelope of the electric field strength of the received signal.

16. A signal processing method that blends a demodulated signal demodulated from a received signal and a signal corresponding to a specified frequency component of the demodulated signal, comprising:

detecting a change amount of electric field strength of the received signal;

calculating a blending ratio of the demodulated signal and the signal corresponding to a specified frequency component of the demodulated signal based on the change amount of electric field strength; and

outputting a signal generated by blending the demodulated signal and the signal corresponding to a specified frequency component of the demodulated signal at the blending ratio.

17. The signal processing method according to claim 16 , wherein the detection of a change amount of electric field strength includes:

detecting a waveform corresponding to an envelope of a signal indicating electric field strength, and

subtracting the signal indicating electric field strength from the waveform.

18. The signal processing method according to claim 16 , wherein the calculation of a blending ratio includes:

calculating a blending amount with respect to the change amount of electric field strength detected by the detection, and

determining a blending ratio according to the blending amount.

19. The signal processing method according to claim 16 , wherein the blending is performed based on a specified component of the demodulated signal and the electric field strength of the received signal.

20. The signal processing method according to claim 19 , wherein the blending is performed when the specified component of the demodulated signal exceeds a prescribed level, and the prescribed level at which the blending is started decreases as the electric field strength of the received signal increases.