JP2003273754A - Am receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove noise mixed into the received frequency band of a main signal in an AM receiver for receiving an AM signal wave to detect the main signal having a specific frequency band for outputting it to a rear stage circuit. <P>SOLUTION: The AM receiver is provided with a first reception/detection circuit 2 to which the reception/detection frequency band of the main signal can be set, a second reception/detection circuit 3 to which a reception/detection frequency band deviated from that of the first reception/detection circuit 2 can be set, and a phase conversion circuit 4 for performing phase inversion to the output of the second reception/detection circuit 3, and adds the output of the phase conversion circuit 4 to the first reception/detection circuit 2 to obtain a detection output. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AM receiver which receives an AM signal wave, detects a main signal having a specific frequency band, and outputs the signal to a subsequent circuit.

[0002]

2. Description of the Related Art An AM receiver, as shown in FIG. 3, includes a reception / detection circuit (5) for receiving an AM signal wave from an antenna (1) and detecting a main signal from a desired broadcasting station. AM
The receiver is easily affected by the noise N inside the device and the external noise due to its reception band, and still, due to the characteristics of amplitude modulation / demodulation,
It has a drawback that noise in the band is detected as it is. For example, as shown in FIG. 5, when the main signal S from the selected broadcasting station has a center frequency Fa, the reception / detection circuit (5) provides a constant reception / detection frequency band Bs centered on the center frequency Fa. Is set, but the noise N is
Since it has a relatively wide band centering on a certain frequency Fc, the reception / detection frequency band Bs of this signal also contains the frequency component Na, and the amplitude fluctuation of this frequency component Na causes the main signal S to vary. AM detection will be performed together with the amplitude fluctuation.

As a result, the detection output obtained from the reception / detection circuit (5) of FIG. 3 is the detection output Sa of the main signal S superimposed with the detection output Na 'of the noise Na as shown in FIG. When the voice is reproduced based on such a detection output (Sa + Na '), the voice of this signal may not be heard due to a large noise. Therefore, conventionally, measures such as increasing the number of elements of an IF (intermediate frequency) filter and cutting low and high frequencies of the detection output have been taken.

[0004]

However, although the above measures can remove noise having a frequency close to the reception frequency band of the selected broadcasting station and noise outside the audible band, the selected broadcasting station can be removed. Noise in the audible band mixed into the reception frequency band of the station, for example, display tube,
Noise generated from the D / D converter, the switching power supply, and other digital circuits cannot be easily removed. Therefore, an object of the present invention is to provide an AM receiver capable of removing noise mixed in the reception frequency band of the present signal.

[0005]

SUMMARY OF THE INVENTION An AM receiver according to the present invention receives an AM signal wave, detects a main signal having a specific frequency band, and outputs the signal to a post-stage circuit. It is possible to set a first reception / detection means capable of setting a reception / detection frequency band of this signal and a reception / detection frequency band deviated from the reception / detection frequency band of the first reception / detection means. Second reception / detection means, phase inversion means for performing phase inversion on the output of the second reception / detection means, and addition of the output of the phase inversion means to the output of the first reception / detection means to obtain a detection output And means.

In the AM receiver of the present invention, the first
The signal contained in the reception / detection frequency band of this signal is detected by the reception / detection means, and this signal is mixed with the reception / detection frequency band of this signal in addition to the detection component of this signal. The noise component is included. On the other hand, noise having a frequency component in the reception / detection frequency band of the main signal is received / detected by the second reception / detection means, and the detection output is phase-inverted to thereby invert the phase of the noise component. A signal of opposite phase (noise cancellation signal) is created. A noise component included in the reception / detection signal from the first reception / detection means is added to the reception / detection signal obtained from the first reception / detection means by adding the anti-phase noise cancel signal, The noise canceling signals of the opposite phase cancel each other, and the noise is canceled.

In a concrete configuration, the phase inverting means comprises a gain adjusting means. As a result, the noise cancellation signal has a signal level substantially equal to that of the noise component, and the noise is substantially completely canceled.

More specifically, the reception / detection frequency band of the second reception / detection means is as close as possible to the reception / detection frequency band of the first reception / detection means, and other main signals are Deviation from the reception / detection frequency band. Therefore, by adding the noise cancellation signal to the reception / detection signal obtained from the first reception / detection means, it is possible to remove noise having a large signal component in the reception / detection frequency band of this signal.

[0009]

According to the AM receiver of the present invention, noise mixed in the reception frequency band of the present signal can be removed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to the drawings. AM according to the present invention
As shown in FIG. 1, the receiver includes a first receiving / detecting circuit (2) for receiving an AM signal wave by an antenna (1) and detecting a main signal from a desired broadcasting station, and 1 receiving / detecting circuit (2) in parallel with the 1st receiving / detecting circuit
The second that can set the reception / detection frequency band that is deviated from the reception / detection frequency band of (2) by about 1 to 2 steps
It has a receiving / detecting circuit (3). For example, the first reception /
When the reception / detection frequency of the detection circuit (2) is 990 kHz, the reception / detection frequency of the second reception / detection circuit (3) is 2
100 shifted by a step (9 kHz x 2 = 18 kHz)
It is set to 8 kHz.

At the output end of the second receiving / detecting circuit (3), a phase inverting circuit (4) composed of an operational amplifier with a power supply or the like is provided.
Are connected. The gain of the phase inversion circuit (4) can be adjusted by the variable resistor R2. And
The output end of the first reception / detection circuit (2) and the output end of the phase inversion circuit (4) are connected to each other through a DC component cutting and mixing capacitor and a resistor, respectively, and a detection output obtained at the connection point Is supplied to the subsequent circuit.

As shown in FIG. 5, when the main signal S from the selected broadcasting station has the center frequency Fa, the first receiving / detecting circuit (2) has a constant centering on the center frequency Fa (990 kHz). Is set to the reception / detection frequency band Bs.
Further, the second receiving / detecting circuit (3) has a center frequency Fc (10
It is set to a constant reception / detection frequency band Bn centered at (08 kHz). Here, the noise N having a frequency band overlapping with the reception / detection frequency band Bn of the second reception / detection circuit (3) has a frequency component Na in the reception / detection frequency band Bs of this signal as shown by a broken line. Is included. Even if there is another broadcasting station having a reception frequency Fb adjacent to the reception frequency Fa of the selected broadcasting station, since the reception frequencies of both broadcasting stations are actually sufficiently separated from each other,
The second signal receiving / detecting circuit (3) does not receive the main signal S'of the other broadcasting station.

Therefore, from the first receiving / detecting circuit (2),
As shown in FIG. 2A, the detection component Sa of the main signal S and the noise N
a detection signal (Sa + N
a ') will be output. Further, the second reception / detection circuit (3) outputs the detection output Nc 'of the noise Nc included in the constant reception / detection frequency band Bn shown in FIG. Here, the detection output N of the noise Na
a ′ and the detection output Nc ′ of the noise Nc are the same noise N
The amplitude fluctuations are basically the same and the waveforms of the AM detection outputs Na 'and Nc' are substantially the same.

Therefore, by inverting the phase of the output of the second receiving / detecting circuit (3) by the phase inverting circuit (4), as shown in FIG. 2 (b), it is opposite to the detection component Nc 'of the noise Nc. A phase noise cancel signal Nc ″ is created.
The noise cancel signal Nc ″ is the phase inversion circuit described above.
By adjusting the resistance R2 of (4), the noise detection output Na '
The gain is adjusted to almost the same signal level as. And the first
The detection signal of FIG. 2 (a) obtained from the reception / detection circuit (2)
By adding the noise cancellation signal Nc ″ shown in FIG. 7B to (Sa + Na ′), the noise detection output N
The a'and the noise cancel signal Nc "are canceled by each other to obtain a detection component Sa of the main signal containing no noise as shown in FIG. 7C, and the detection component Sa is detected as a detection output to the subsequent circuit. It will be supplied.

As described above, according to the AM receiver of the present invention, noise in the audible band mixed in the reception frequency band of the selected broadcasting station, such as the display tube, the D / D converter, and the switching. Noise generated from the power supply and other digital circuits can be removed with a simple circuit configuration.

The configuration of each part of the present invention is not limited to the above-described embodiment, and various modifications can be made within the technical scope described in the claims. For example, it is possible to equip a phase adjusting means for finely adjusting the phase of the noise canceling signal output from the phase inverting circuit (4).

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration of an AM receiver according to the present invention.

FIG. 2 is a waveform diagram illustrating signal processing in the AM receiver.

FIG. 3 is a block diagram showing a configuration of a conventional AM receiver.

FIG. 4 is a waveform diagram showing a detection output of a conventional AM receiver.

FIG. 5 is a diagram illustrating frequency distributions of a main signal and noise.

[Explanation of symbols]

(1) Antenna (2) First reception / detection circuit (3) Second receiving / detecting circuit (4) Phase inversion circuit

Claims (3)

[Claims] 1. An AM receiver that receives an AM signal wave, detects the main signal having a specific frequency band, and outputs the main signal to a subsequent circuit, wherein a reception / detection frequency band of the main signal can be set. 1 reception / detection means, 2nd reception / detection means capable of setting a reception / detection frequency band deviated from the reception / detection frequency band of the 1st reception / detection means, and output of the 2nd reception / detection means An AM receiver comprising: a phase inverting means for performing a phase inversion on the output signal; and an adding means for adding an output of the phase inverting means to an output of the first receiving / detecting means to obtain a detection output. 2. The AM receiver according to claim 1, wherein the phase inverting means comprises gain adjusting means. 3. The reception / detection frequency band of the second reception / detection means is as close as possible to the reception / detection frequency band of the first reception / detection means, and the reception / detection frequency of another main signal. The AM according to claim 1 or 2, which is out of band
Receiving machine.