FM-AM demodulator and control method therefor

1. An FM-AM demodulator comprising:

an FM signal amplifier configured to amplify an input FM signal;

a local oscillator configured to generate a local oscillation signal for converting the FM signal to an intermediate frequency signal;

an image oscillator configured to generate an image signal in FM frequency band;

a first selector configured to select one of a signal from the FM signal amplifier and a signal from the image oscillator to output;

a first orthogonal mixer configured to generate and output an I signal and a Q signal by performing frequency conversion using the local oscillation signal generated by the local oscillator and the signal selected by the first selector;

an AM signal amplifier configured to amplify an input AM signal;

a first frequency divider configured to generate a local oscillation signal for converting the AM signal to an intermediate frequency signal by performing frequency division on the output signal from the image oscillator;

a second frequency divider configured to perform frequency division on the output signal from the local oscillator;

a second selector configured to select one of a signal from the AM signal amplifier and a signal a signal from the second frequency divider to output;

a second orthogonal mixer configured to generate and output I signal and Q signal by performing frequency conversion using the signal selected by the second selector and a signal from the first orthogonal mixer;

a third selector configured to select one of the I signal from the first orthogonal mixer and the I signal from the second orthogonal mixer to output;

a first filter configured to remove a high frequency signal component from the I signal selected by the third selector and output it;

a first amplifier configured to amplify the I signal output from the first filter;

a fourth selector configured to select one of the Q signal from the first orthogonal mixer and the Q signal from the second orthogonal mixer to output;

a second filter configured to remove a high frequency signal component from the Q signal selected by the fourth selector to output it;

a second amplifier configured to amplify the Q signal output from the second filter;

a first gain controller configured to receive the I signal the first amplifier outputs and the Q signal the second amplifier outputs, and control the first and the second amplifiers so that the input I signal and the input Q signal have predetermined amplitudes;

an I/Q compensation unit configured to perform a compensation operation on the gain and the phase of the I signal from the first amplifier or the Q signal from the second amplifier or both of the I and Q signals and output;

an IF oscillator configured to generate and output a signal having a predetermined frequency when the intermediate frequency signal for the FM received signal or AM received signal is demodulated;

a third orthogonal mixer configured to generate and output an I signal and a Q signal by performing frequency conversion using the I and Q signals output from the I/Q compensation unit with a signal output from the IF oscillator;

an adder configured to add the converted I and Q signals output from the third orthogonal mixer to output;

a channel filter configured to extract a signal with a predetermined frequency band from the signal output from the adder;

a third amplifier configured to amplify the signal output from the channel filter to output;

a second gain controller configured to control the third amplifier to output a signal having a predetermined amplitude;

a demodulator configured to generate and output an output signal by demodulating the output signal from the third amplifier; and

an I/Q compensation controller configured to generate an I/Q compensation signal to be used for adjusting phase and gain of the I signal in the I/Q compensation unit by detecting the amplitude of the output signal from the demodulator, and output the generated signal to the I/Q compensation unit.

2. The FM-AM demodulator of claim 1 , further comprising:

a first A/D converter configured to receive the I signal output from the first amplifier and convert the input signal to a digital signal; and

a second A/D converter configured to receive the Q signal output from the second amplifier and convert the input signal to a digital signal,

wherein an I/Q compensation unit, an IF oscillator, a third orthogonal mixers, an adder, a channel filter, the third amplifier, a demodulator, and a I/Q compensation controller are digital circuits.

3. The FM-AM demodulator of claim 1 , wherein the image oscillator has low phase noise characteristics compared to the local oscillator.

4. An FM-AM demodulator of claim 1 , wherein the image oscillator, which has low noise performance, generates the local oscillation signal when an AM broadcast is received.

5. An FM-AM receiver employing the FM-AM demodulator of claim 1 , comprising an FM antenna and an AM antenna,

wherein the FM-AM receiver demodulates the FM signal input from the FM antenna and the AM signal input from the AM antenna using the FM-AM demodulator.

6. An electronic equipment which employs the FM-AM demodulator of claim 1 .

7. A control method of performing image compensation adjustment of an FM signal for an FM-AM demodulator, comprising the steps of:

setting a first selector to select a output signal from an image oscillator;

inputting the selected signal to a first orthogonal mixer;

outputting an I signal to a third selector and a Q signal to a fourth selector, the I signal and Q signal generated by multiplying an image signal frequency from the image oscillator and a local oscillation signal frequency from a local oscillator at a first orthogonal mixer;

setting a third selector to select the I signal output from the first orthogonal mixer;

inputting the I signal output from the first orthogonal mixer to an I/Q compensation unit through a first filter and a first amplifier;

setting a fourth selector to select the Q signal output from the first orthogonal mixer;

inputting the Q signal output from the first orthogonal mixer to the I/Q compensation unit through a second filter and a second amplifier;

setting a gain controller to give a third amplifier a fixed gain;

adding the I signal to the Q signal, the I signal and the Q signal generated by multiplying the I and the Q signals output from the I/Q compensation unit by the local oscillation signal frequency output from the IF oscillator at the third orthogonal mixer;

inputting added signal to a channel filter;

amplifying an output signal through the channel filter;

inputting the output signal from the amplifier to a demodulator;

generating a compensation signal so as to make the output signal from the demodulator a minimum value;

inputting the compensation signal to the I/Q compensation unit; and

adjusting phase and gain on one of the I and Q signals or both of the I and Q signals in the I/Q compensation unit in accordance with the compensation signal.

8. The control method of claim 7 , wherein, when the FM signal is demodulated, further comprising the steps of:

setting the first selector to select the signal output from the FM amplifier;

inputting the signal from the FM amplifier to the first orthogonal mixer;

canceling the fixed gain of the amplifier caused by the gain controller; and

inputting the compensation signal generated in the image compensation adjustment operation for the FM signal to the I/Q compensation unit.

9. The control method of performing image-compensation-adjustment for an FM-AM demodulator according to claim 7 ,

wherein when the AM signal is received, the local oscillator is put into sleep mode.

10. A control method of performing image compensation adjustment of an AM signal for an FM-AM demodulator, comprising the steps of:

setting a second selector to select the output signal from a second frequency divider;

inputting the selected signal to a second orthogonal mixer;

outputting an I signal to a third selector and a Q signal to the fourth selector, the I signal and Q signal are generated by multiplying a image signal frequency from the second frequency divider by the local oscillation signal frequency from a first frequency divider at the second orthogonal mixer;

setting a third selector to select the I signal output from the second orthogonal mixer;

inputting the I signal output from the second orthogonal mixer to a I/Q compensation unit through a first filter and a first amplifier;

setting a fourth selector to select the Q signal output from the first orthogonal mixer;

inputting the Q signal output from the second orthogonal mixer to the I/Q compensation unit through a second filter and a second amplifier; and

adjusting phase and gain on one of the I and Q signals or both of the I and Q signals in the I/Q compensation unit in accordance with the compensation signal.

11. The control method of claim 10 , wherein, when the AM signal is demodulated, further comprising the steps of:

setting a second selector to select the signal output from the AM amplifier;

inputting the signal from the AM amplifier to the second orthogonal mixer;

canceling the fixed gain of the amplifier caused by the gain controller; and

inputting the compensation signal generated at the image-compensation-adjustment operation for the AM signal to the I/Q compensation unit.

12. The control method of performing image-compensation-adjustment for an FM-AM demodulator according to claim 10 ,

wherein when the AM signal is received, the local oscillator is put into sleep mode.