JPH08274663A - Radio receiver - Google Patents

Abstract

PURPOSE: To surely eliminate the noise of long pulse width and the noise of short generation period also. CONSTITUTION: It is noticed that an FM reception part is idle at the time or reception or AM broadcast, the AM intermediate frequency signal passing an AM band pass filter 5 is inputted to a limiter amplifier 14 and has the amplitude limited. The noise component is demodulated by a quadrature detection circuit 15, and only the noise component is extracted by a band pass filter 19, and the noise component is converted to a DC voltage by a noise amplification circuit 20 and a noise detection circuit 21. An AM intermediate frequency amplification circuit 6 is subjected to AGC control by this DC voltage. Thus, an influence of noise is reduced not to output the noise offending ears even if a noise pulse is continuously generated with a short period or the pulse width of each noise pulse is long. The FM reception part is applied to obtain a maximum noise reduction effect without costing neither making a receiver main body large-sized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio receiver for removing noise contained in received AM broadcast radio waves.

[0002]

2. Description of the Related Art A reception system for converting broadcast radio waves received by an antenna into a low frequency signal and then demodulating it is generally called a superheterodyne system. FIG. 7 is a block diagram showing a schematic configuration of a conventional AM radio receiver using the superheterodyne system (EMC 1993.11.5 <N
o.67>). In FIG. 7, 1 is a high-frequency amplifier circuit that selects and amplifies radio waves of a predetermined frequency among broadcast radio waves input from the antenna 2, and 3 is a signal that is selected and amplified by the high-frequency amplifier circuit 1 and converted into a low frequency signal. Is a mixer circuit. Reference numeral 5 is a bandpass filter for extracting only a signal in a predetermined frequency band from the output of the mixer circuit 3, and AM
When receiving a broadcast, an intermediate frequency signal in a frequency band of ± 6 to 10 kHz with a center frequency of about 450 kHz is extracted. Reference numeral 6 is an intermediate frequency amplifier circuit for amplifying the intermediate frequency signal, and 7 is a detection circuit for demodulating the amplified intermediate frequency signal into an audio signal before modulation.

Reference numeral 50 denotes a noise canceller for removing a noise component contained in the output of the detection circuit 7, which is divided into a noise detecting section 51 and a gate section 52 as shown in detail in FIG. The intermediate frequency signal that has passed through the bandpass filter 5 is input to the noise detection unit 51, and the intermediate frequency signal is amplified by the amplification circuit 51A and then demodulated by the detection circuit 51B. The output of the detection circuit 51B is input to the amplification circuit 51C and the AGC circuit 51D, and
Feedback control by the C circuit 51D suppresses fluctuations in the output level of the detection circuit 51B. On the other hand, the output of the amplifier circuit 51C is input to the bandpass filter 51D and only the noise component is extracted. Hereinafter, the extracted noise component will be referred to as a noise pulse.

For example, when noise as shown in FIG. 9A is superimposed on the intermediate frequency signal input to the noise detecting section 51, the detection circuit 51B and the bandpass filter 5 are included.
The outputs of 1D are as shown in FIGS. 9B and 9C, respectively.

The noise pulse extracted by the bandpass filter 51D is input to the pulse generation circuit 51E and the noise AGC circuit 51F, and the noise AGC circuit 51F performs feedback control to suppress fluctuations in the output of the bandpass filter 51D. Further, the pulse generation circuit 51E outputs a switching pulse for removing noise, and the switching pulse is the switching circuit 5 in the gate unit 52.
Input to 2A and 52B.

On the other hand, the detection signal demodulated by the detection circuit 7 is input to the phase circuit 52C of the gate section 52, and after the processing of delaying the phase of this detection signal is performed, it is input to the switch circuit 52A. The detection signal from the detection circuit 7 is also input to the switch circuit 52B, and each of the switch circuits 52A and 52B removes noise included in the detection signal based on the switching pulse from the pulse generation circuit 51E. Specifically, noise is removed by blanking the detection signal while the switching pulse is being output. As a result, for example, the phase circuit 52C shown in FIG.
When the signal shown in (d) is input, the outputs of the switch circuits 52A and 52B are as shown in FIG. 9 (e).

The outputs of the switch circuits 52A and 52B are both input to the waveform compensation circuit 52D, and the waveform compensation circuit 52
The waveform is corrected inside D to create an audio signal with less distortion. This audio signal is amplified by the volume adjusting circuit 53 and the low frequency amplifying circuit 54 of FIG. 7, and output as sound from a speaker (not shown).

[0008]

In the conventional radio receiver shown in FIG. 7, a switching pulse corresponding to the magnitude of noise is created inside the noise canceller 50, and the detection signal is blanked based on this switching pulse to cause noise. Is effective for a single noise pulse or an intermittent noise pulse having a long generation interval. However, when noise pulses are generated continuously or when the pulse width of the noise pulse is long, the blanking period of the signal becomes long, so the noise reduction effect is reduced and unpleasant noise remains due to annoyance. I will end up.

In particular, when a radio receiver is installed near an electric device such as an electric vehicle which controls a load by an inverter, the switching element in the inverter circuit is turned on / off at a frequency of several tens to several hundreds of kHz. Since the operation is repeated, the harmonic component of the switching frequency may reach the AM broadcast band and strong noise may be generated.

An object of the present invention is to provide a radio receiver which can reliably remove noise pulses even if noise pulses are continuously generated in a short cycle or the pulse width of each noise pulse is long. Especially.

[0011]

[Means for Solving the Problems] FIGS.
The present invention will be described with reference to No. 7. In the present invention, an AM high frequency amplifier circuit 1 that selects and amplifies a predetermined frequency signal of an AM broadcast radio wave received by an antenna 2 is selected and amplified. AM mixer circuit 3 for converting a frequency signal into an AM intermediate frequency signal having a frequency different from that frequency
An AM intermediate frequency amplifier circuit 6 that amplifies the AM intermediate frequency signal; an AM detection circuit 7 that demodulates the amplified AM intermediate frequency signal into an audio signal; and an AGC voltage that suppresses fluctuations in the output level of the audio signal. The present invention is applied to a radio receiver including an AGC circuit 8 for outputting, and before the AM intermediate frequency signal is amplified by the AM intermediate frequency amplifier circuit 6, the amplitude variation component of the AM intermediate frequency signal is removed to make the amplitude constant. Among the signals converted by the amplitude limiting means 14, the amplitude converting means 15 for converting the frequency fluctuation component included in the output of the amplitude limiting means 14 into the amplitude change, only the signals in the predetermined frequency band are extracted. The extraction means 19 is provided so that the output level of the AM detection circuit 7 decreases as the noise mixed in the received AM broadcast radio wave increases. By providing the AGC circuit 8 for adjusting the voltage value of the AGC voltage based on the extracted signals, the above-described object can be attained.

According to a second aspect of the present invention, an AM high frequency amplifier circuit 1 for selecting and amplifying a predetermined frequency signal of the AM broadcast radio wave received by the antenna 2, and the selected and amplified frequency signal. , A of a frequency different from that frequency
AM mixer circuit 3 for converting to M intermediate frequency signal, and AM
An AM intermediate frequency amplifier circuit 6 for amplifying the intermediate frequency signal, an AM detection circuit 7 for demodulating the amplified AM intermediate frequency signal into an audio signal, and an AGC for outputting an AGC voltage for suppressing fluctuation of the output level of the audio signal. And an amplitude limiting means for applying a constant amplitude to the AM intermediate frequency signal by removing the amplitude fluctuation component of the AM intermediate frequency signal before amplifying the AM intermediate frequency signal by the AM intermediate frequency amplifier circuit 6. 14
An amplitude converting means 15 for converting a frequency fluctuation component included in the output of the amplitude limiting means 14 into an amplitude change; and an extracting means 19 for extracting only a signal in a predetermined frequency band from the signals converted by the amplitude converting means 15. And an attenuator 22 that attenuates the output level of the AM detection circuit 7 based on the signal extracted by the extraction means 19,
The above objective is accomplished. According to a third aspect of the present invention, in the radio receiver according to the first or second aspect, an FM high-frequency amplifier circuit 9 that selects and amplifies a predetermined frequency signal of the FM broadcast radio waves received by the antenna 2. And an FM mixer circuit 10 for converting the selected and amplified frequency signal into an FM intermediate frequency signal having a frequency lower than that frequency.
An amplitude limiter 14 that removes the amplitude fluctuation component of the FM intermediate frequency signal; an FM detection circuit 15 that converts the frequency fluctuation component included in the output of the amplitude limiter 14 into an amplitude change and demodulates into an audio signal; Selection switch 1 for selecting whether to receive broadcast radio waves or FM broadcast radio waves
3 and 18, and A is selected by the selection switches 13 and 18.
When the reception of M broadcast radio waves is selected, the AM mixer circuit 3
The AM intermediate frequency signal output from is input to the amplitude limiter, the amplitude limiter 14 is used as the amplitude limiter 14, the FM detector circuit 15 is used as the amplitude converter 15, and the output of the FM detector 15 is extracted. It is input to the means. According to a fourth aspect of the present invention, in the radio receiver according to any one of the first to third aspects, a noise canceller for suppressing a decrease in reception sensitivity due to a single noise pulse or a noise pulse having a long generation period. The circuit 50 is provided and the output of the AM detection circuit 7 is input to the noise canceller circuit 50.

[0013]

According to the first aspect of the invention, the amplitude variation component contained in the AM intermediate frequency signal output from the AM intermediate frequency amplifier circuit 6 is removed to make the amplitude constant, and the amplitude converting means 15 is provided.
The frequency fluctuation component is converted into an amplitude change by. Thereby, for example, when noise is mixed in the AM intermediate frequency signal, the noise is detected as an amplitude difference. And
Only the noise component is extracted by the extraction means 19, and the voltage of the AGC voltage is adjusted based on the extracted noise component.
By controlling the output level of the AGC detection circuit by the adjusted AGC voltage, the output level of the AM detection circuit 7 can be set to the optimum level according to the magnitude of noise. According to the second aspect of the invention, the amplitude variation component contained in the AM intermediate frequency signal output from the AM intermediate frequency amplification circuit 6 is removed to make the amplitude constant, and the amplitude variation means 15 transforms the frequency variation component into an amplitude variation. Convert. Then, only the noise component is extracted by the extraction means 19, and the output level of the AM detection circuit 7 is attenuated based on the extracted signal. Specifically, the greater the noise, the greater the degree of attenuation so that no offensive noise is output as voice. In the invention according to claim 3, when reception of the AM broadcast radio wave is selected by the selection switches 13 and 18, the AM intermediate frequency signal output from the AM mixer circuit 3 is input to the AM intermediate frequency amplification circuit 6 and The amplitude fluctuation component is removed by inputting to the amplitude limiter in the FM receiver. Next, it is input to the FM detection circuit 15 to extract the frequency fluctuation component as an amplitude change. Next, the output of the FM detection circuit 15 is input to the extraction means to extract only the noise component. That is, the noise component is detected using the FM receiving unit, paying attention to the fact that the FM receiving unit is vacant when receiving the AM broadcast radio wave. In the invention according to claim 4, the noise canceller circuit 50 is connected to the output of the AM detection circuit 7 to detect a single noise pulse or a noise pulse having a long generation period.

Incidentally, in the section of means and action for solving the above-mentioned problems for explaining the constitution of the present invention, the drawings of the embodiments are used for the sake of easy understanding of the present invention. It is not limited to.

[0015]

【Example】

-First Embodiment- Hereinafter, a first embodiment of the radio receiver according to the present invention will be described with reference to FIGS. The radio receiver according to the present embodiment is capable of receiving broadcast waves of both AM and FM, and an example in which the radio receiver is installed in an electric vehicle will be described.

FIG. 1 is a block diagram of a first receiver of a radio receiver. In addition, in FIG. 1, the same components as those of the conventional radio receiver shown in FIG. 7 are denoted by the same reference numerals. Reference numeral 1 denotes an AM high frequency amplifier circuit that tunes and amplifies radio waves of a predetermined frequency among AM broadcast radio waves input from an antenna 2, and 3 converts the signal tuned and amplified by the AM high frequency amplifier circuit 1 to a low frequency. It is an AM mixer circuit. This A
The M mixer circuit 3 converts the frequency fC selected by the AM high frequency amplifier circuit 1 and the local oscillation signal fL output from the AM local oscillation circuit 4 into a signal having a difference frequency fC-fL. Hereinafter, this difference frequency is referred to as an AM intermediate frequency signal.
In this way, by converting to a low frequency AM intermediate frequency signal, it becomes easy to selectively separate only desired frequency components.

Reference numeral 5 is an AM bandpass filter for removing the noise component contained in the output of the AM mixer circuit 3 and extracting only the AM intermediate frequency signal. 6 is an AM for amplifying the AM intermediate frequency signal extracted by the AM bandpass filter 5.
It is an intermediate frequency amplifier circuit. 7 is an AM intermediate frequency amplifier circuit 6
It is an AM detection circuit 7 for converting the output signal of the above into an audio signal before modulation. The above 1 to 7 are common to the conventional AM radio receiver shown in FIG.

Reference numeral 8 is an AGC circuit for outputting an AGC voltage for suppressing fluctuations in the output level of the AM detection circuit 7,
The output AGC voltage is input to the AM intermediate frequency amplifier circuit 6. The AGC voltage value is adjusted based on the output of the AM detection circuit 7 and the output of the noise detection circuit 21 described later.
An AM receiving unit is configured by the above 1 to 8.

Reference numeral 9 is an FM high frequency amplifier circuit for selecting and amplifying FM broadcast radio waves inputted from the antenna 2, and 10 is an output signal of the FM high frequency amplifier circuit 9 using the FM local oscillation circuit 11 at a low frequency (about 10. It is the FM mixer circuit 10 for converting to 7 MHz). 12 removes a noise component included in the output of the FM mixer circuit 10 and outputs about 10.7 MHz.
A signal in a predetermined frequency band having a center frequency of
This is an FM bandpass filter that extracts only the intermediate frequency signal). 13 will receive FM broadcast, FM
It is a selection switch for selecting whether to receive a broadcast. 1
4 is a limiter amplifier for removing the amplitude fluctuation component of the FM intermediate frequency signal to make the amplitude value constant, and 15 is a limiter amplifier 1.
4 is a quadrature detection circuit for converting the frequency fluctuation component of the output of No. 4 into an amplitude change and demodulating it into an audio signal. The output of the quadrature detection circuit 15 is amplified by a low frequency amplifier circuit (not shown) and then output as voice. The quadrature detection circuit 15 includes a tuning circuit 16 used for receiving FM broadcasting and a tuning circuit 17 used for receiving AM broadcasting.
Are connected via the selection switch 18, and one of them is selected by switching the selection switch 18. The FM receiving unit is configured by the above 9 to 18.

Reference numeral 19 denotes a bandpass filter for extracting only a signal in a predetermined frequency band included in the output of the quadrature detection circuit 15, for example, a frequency band of ± 10 kHz with a center frequency of about 30 kHz. Reference numeral 20 is a noise amplifier circuit for amplifying the signal that has passed through the bandpass filter 2,
Reference numeral 1 is a noise detection circuit that detects the signal amplified by the noise amplification circuit 20 and converts it into a low-frequency signal.
The output is input to the AGC circuit 8.

Next, the operation of the radio receiver of the first embodiment constructed as shown in FIG. 1 will be described. In the following, a case where AM broadcast reception is selected by the selection switches 13 and 18 will be described. A received by antenna 2
The M broadcast radio wave is tuned and amplified by the AM high frequency amplifier circuit 1, converted into an AM intermediate frequency signal by the AM mixer circuit 3 and input to the AM band pass filter 5. The AM band pass filter 5 extracts only the AM intermediate frequency signal in the frequency band necessary for receiving the AM broadcast, and the extracted AM intermediate frequency signal is input to the AM intermediate frequency amplifier circuit 6 and the selection switch. It is also input to the limiter amplifier 14 via 13 and 18. AM intermediate frequency amplifier circuit 6
Is an AG from the AGC circuit 8 so that its output is not distorted.
Feedback control is performed by the C voltage, and the output of the AM intermediate frequency amplifier circuit 6 is input to the AM detection circuit 7 and demodulated into an audio signal.

On the other hand, the limiter amplifier 14 limits the amplitude of the AM intermediate frequency signal that has passed through the AM bandpass filter 5 to make the amplitude value constant. The AM intermediate frequency signal whose amplitude is limited by the limiter amplifier 14 is input to the quadrature detection circuit 15, and the frequency modulation component contained in the AM intermediate frequency signal is converted into an amplitude change and output. In this way, the AM intermediate frequency signal is extracted by passing through the limiter amplifier 14 and the quadrature detection circuit 15 so that all the AM broadcast signal components are removed and only the carrier components are converted into DC voltage. Further, when the AM intermediate frequency signal includes a noise component, this noise component is also extracted together with the carrier component.

FIG. 2 is a diagram showing an output spectrum of the quadrature detection circuit 15 at the time of receiving an AM broadcast, and a curve a shows a case where the inverter circuit inside the electric vehicle is not operated.
Curve b shows the case where the inverter circuit is operated to intermittently generate noise. As shown by the curve a, it is understood that the signal strength in the frequency band of 10 kHz or more is very weak when the inverter circuit is not operated. This is because the AM intermediate frequency signal is band-limited by the AM bandpass filter 5. On the other hand, as shown by the curve b, when the inverter circuit is operated to generate noise, switching noise also appears in the frequency band of 10 kHz or higher. Therefore, the magnitude of the generated noise can be accurately detected by detecting the signal strength in the frequency band of 10 kHz or more.

Therefore, in this embodiment, the output of the quadrature detection circuit 15 is input to the bandpass filter 19 to extract the signal in the frequency band of ± 10 kHz with the center frequency of 30 kHz. Since the signal in this frequency band is considered to be due to noise, the signal that has passed through the bandpass filter 19 is a signal that reflects the magnitude of noise.

The signal that has passed through the bandpass filter 19 is amplified by the noise amplification circuit 20, and then the noise detection circuit 2
1 is rectified and converted into a DC voltage according to the magnitude of noise. The AGC circuit 8 is responsive to the DC voltage from the noise detection circuit 21 and the output of the AM detection circuit 7 for AGC.
Adjust the voltage. Specifically, the AGC voltage is set so that the amplification degree of the AM intermediate frequency amplification circuit 6 is lowered as the voltage level of the DC voltage output from the noise detection circuit 21 is higher, that is, as the noise is larger.

On the other hand, FIG. 3 is a diagram showing an output spectrum when inter-station noise other than radio waves of the broadcasting station of AM broadcasting is received. A curve c indicates that the inverter circuit is not operated, and a curve d indicates that the inverter circuit is operated. It shows the case. Curve d
The periodically appearing peak points (hereinafter referred to as carrier peaks) in the inside indicate the respective frequencies of the fundamental wave of the switching frequency of the inverter circuit and its harmonics. In this way, since the switching noise due to the inverter circuit has a periodic carrier peak, by detecting the presence or absence of this carrier peak, whether the generated noise is due to the switching noise of the inverter circuit or other inter-station It is also possible to distinguish between noise and external noise.

To summarize the operation of the first embodiment described above, when receiving an AM broadcast, the AM intermediate frequency signal that has passed through the AM bandpass filter 5 is input to the limiter amplifier 14 in the FM receiving section and the amplitude is input. Limiting is performed, the noise component is demodulated by the quadrature detection circuit 15, only the noise component is extracted by the bandpass filter 19, and the noise component is converted to a DC voltage by the noise amplification circuit 20 and the noise detection circuit 21. Since the AM intermediate frequency amplifier circuit 6 is AGC controlled by the above, it is possible to effectively reduce annoying noise. That is, according to this embodiment, it is possible to reliably remove a noise pulse that is continuously generated in a short cycle or a noise pulse that has a long pulse width.

Further, in the present embodiment, paying attention to the fact that the FM receiving section is vacant at the time of receiving the AM broadcast, noise is detected by using the FM receiving section, so that the receiver main body does not cost much. Noise can be reduced without increasing the size.

FIG. 4 is a diagram showing the S / N sensitivity characteristic of the AM receiving section. A curve A (solid line) in the drawing shows a sensitivity distribution in which a signal (S) component and a noise (N) component are added in a state where no noise is mixed, and a curve B (dashed line) is a state where no noise is mixed. Conventional noise (N) component sensitivity distribution,
A curve C (solid line) shows the sensitivity distribution of the conventional noise (N) component in a state where noise such as inverter noise is mixed.
On the other hand, the curve D shows the sensitivity distribution of the noise (N) component of the present embodiment when no noise is mixed therein, and the curve E shows the sensitivity distribution of the noise (N) component of this embodiment when noise is mixed therein. Are shown respectively. As shown in the figure, when the electric field strength of the received AM broadcast radio wave is weakened, the noise (N) component is conventionally increased to the same level as or more than the signal (S) component, and the noise rises, which is very annoying. However, according to the present embodiment, AGC is performed according to the noise level.
By controlling the circuit 8, the noise component can be reduced and S /
The N ratio is improved. Therefore, even if the vehicle runs in a tunnel, a weak electric field area such as a shadow of a building, or even if inverter noise occurs, the audio output level is adjusted to such an extent that the noise does not make the ear jarring. Further, the same effect can be obtained for inter-station noise and continuous external noise.

-Second Embodiment- In the second embodiment, an attenuator 22 is newly provided and the attenuator 22 is controlled according to the magnitude of noise. Figure 5
Shows a block diagram of a radio receiver of the second embodiment, and the same components as those in FIG. 1 are designated by the same reference numerals. In the following, differences from the first embodiment will be mainly described.

In FIG. 5, the attenuator 22 receives the detection signal demodulated by the AM detection circuit 7 and the DC voltage from the noise detection circuit 21, and the attenuation degree of the detection signal is adjusted according to the DC voltage. Done. Specifically, the greater the noise, the greater the attenuation. The output of the attenuator 22 is amplified by a low frequency amplifier circuit (not shown) and then output as voice.

Thus, according to the second embodiment, the AM
Since the noise included in the intermediate frequency signal is detected and the AM detection signal is attenuated by the attenuator 22 according to the magnitude of the noise, the same effect as that of the first embodiment can be obtained.

-Third Embodiment- The first and second embodiments are used when a noise pulse is periodically generated like inverter noise or when continuous noise, that is, a pulse width of noise is long. Is effective, but is not so effective when a single noise or a noise pulse has a long generation period. Therefore, the third embodiment is
This is a combination of the conventional noise canceller 50 shown in FIG. 7 and the configuration of the first embodiment. FIG. 6 shows a block diagram of a radio receiver of the third embodiment, in which the same components as those in FIG. 1 are designated by the same reference numerals, and the differences from the first embodiment are mainly described below. Explained.

In FIG. 6, reference numeral 23 is a noise canceller having the same structure as the conventional noise canceller 50 shown in FIG. The output of the AM detection circuit 7 and the output of the AM bandpass filter 5 are input to the noise canceller 23. It is common with the first embodiment except that the noise canceller 23 is provided.

According to the third embodiment, the periodic noise and the continuous noise mixed in the AM broadcast radio wave can be reduced by the AGC control using the FM receiver, as in the first embodiment. On the other hand, the noise canceller 23 can remove single-shot noise and noise having a long cycle interval. This allows any kind of noise to be removed or reduced.

In the first embodiment, the AM intermediate frequency amplifier circuit 6 is generated by the AGC voltage output from the AGC circuit 8.
Although the example in which the gain is controlled has been described, the low frequency amplifier circuit (not shown) may be controlled by the AGC voltage. Further, the third embodiment is different from the first embodiment in that the noise canceller 2 is used.
Although 3 is added, a noise canceller may be added to the second embodiment. Furthermore, in the above-described embodiment, the FM broadcast radio wave is demodulated using the quadrature detection circuit 15, but the detection method is not limited to the embodiment.

In the embodiment configured as described above, the limiter amplifier 14 functions as the amplitude limiting means and the amplitude limiting device.
The quadrature detection circuit 15 corresponds to the amplitude converting means, and the bandpass filter 19 corresponds to the extracting means.

[0038]

As described above in detail, according to the present invention, the noise included in the AM intermediate frequency signal is detected, and the AGC voltage is adjusted according to the magnitude of the detected noise. Even if the pulse generation period is short or the pulse width of each noise pulse is long, no annoying noise is output as audio from the radio receiver.
According to the second aspect of the present invention, the output of the AM detection circuit 7 is attenuated according to the magnitude of the detected noise. No sound is output. Claim 3
According to the invention described in, when receiving an AM broadcast, the FM broadcast is received.
Focusing on the fact that the receiving section is vacant, the FM receiving section is used to detect the noise mixed in the AM broadcast radio wave, so that the noise can be detected by adding a small number of parts, which may increase the cost. In addition, the radio receiver itself does not increase in size. According to the invention of claim 4,
AM noise canceller that is effective in suppressing the sensitivity deterioration due to single-shot noise pulses and noise pulses with long generation cycles
Since it is connected to the output of the detection circuit 7, any kind of noise can be effectively reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment of a radio receiver according to the present invention.

FIG. 2 is a diagram showing an output spectrum of a quadrature detection circuit when receiving an AM broadcast.

FIG. 3 is a diagram showing an output spectrum of a quadrature detection circuit when receiving inter-station noise.

FIG. 4 is a diagram showing S / N sensitivity characteristics of an AM receiving unit.

FIG. 5 is a block diagram of a second embodiment of a radio receiver according to the present invention.

FIG. 6 is a block diagram of a third embodiment of a radio receiver according to the present invention.

FIG. 7 is a block diagram of a conventional radio receiver.

FIG. 8 is a block diagram showing an internal configuration of a noise canceller.

FIG. 9 is a diagram showing signal waveforms of respective parts inside the noise canceller.

[Explanation of symbols]

 1 AM high frequency amplification circuit 3 AM mixer circuit 4 AM local oscillation circuit 5 AM band pass filter 6 AM intermediate amplification circuit 7 AM detection circuit 8 AGC circuit 9 FM high frequency amplification circuit 10 FM mixer circuit 11 FM local oscillation circuit 12 FM band pass filter 13, 18 Selection switch 14 Limiter amplifier 15 Quadrature detection circuit 19 Bandpass filter 20 Noise amplification circuit 21 Noise detection circuit

Claims (4)

[Claims] 1. An AM high-frequency amplifier circuit that tunes and amplifies a predetermined frequency signal of AM broadcast radio waves received by an antenna; and a frequency signal different from the frequency of the tuned and amplified frequency signal. An AM mixer circuit for converting into an AM intermediate frequency signal, an AM intermediate frequency amplifier circuit for amplifying the AM intermediate frequency signal, an AM detection circuit for demodulating the amplified AM intermediate frequency signal into an audio signal, and the audio signal AGC for suppressing fluctuation of output level
In a radio receiver including an AGC circuit that outputs a voltage, an amplitude fluctuation component of the AM intermediate frequency signal is removed to make the amplitude constant before the AM intermediate frequency signal is amplified by the AM intermediate frequency amplifier circuit. Amplitude limiting means, an amplitude converting means for converting a frequency fluctuation component included in the output of the amplitude limiting means into an amplitude change, and an extraction for extracting only a signal in a predetermined frequency band from the signals converted by the amplitude converting means. The AGC circuit is configured to reduce the output level of the AM detection circuit as the noise mixed in the received AM broadcast radio wave is larger, based on the signal extracted by the extraction unit. A radio receiver characterized by adjusting a voltage value of the AGC voltage. 2. An AM high-frequency amplifier circuit that tunes and amplifies a predetermined frequency signal of AM broadcast radio waves received by an antenna; and a frequency signal different from the frequency of the tuned and amplified frequency signal. An AM mixer circuit for converting into an AM intermediate frequency signal, an AM intermediate frequency amplifier circuit for amplifying the AM intermediate frequency signal, an AM detection circuit for demodulating the amplified AM intermediate frequency signal into an audio signal, and the audio signal AGC for suppressing fluctuation of output level
In a radio receiver including an AGC circuit that outputs a voltage, an amplitude fluctuation component of the AM intermediate frequency signal is removed to make the amplitude constant before the AM intermediate frequency signal is amplified by the AM intermediate frequency amplifier circuit. Amplitude limiting means, an amplitude converting means for converting a frequency fluctuation component included in the output of the amplitude limiting means into an amplitude change, and an extraction for extracting only a signal in a predetermined frequency band from the signals converted by the amplitude converting means. Means and the A based on the signal extracted by the extracting means.
An attenuator for attenuating the output level of the M detection circuit. 3. The radio receiver according to claim 1, wherein an FM high frequency amplifier circuit that selects and amplifies a predetermined frequency signal of the FM broadcast radio wave received by the antenna; An FM mixer circuit for converting the amplified frequency signal into an FM intermediate frequency signal having a frequency lower than that frequency; an amplitude limiter for removing an amplitude fluctuation component of the FM intermediate frequency signal to keep the amplitude constant; An FM detection circuit that converts a frequency fluctuation component included in the output of the amplitude limiter into an amplitude change and demodulates into an audio signal, and a selection switch that selects whether to receive AM broadcast radio waves or FM broadcast radio waves. When the selection switch selects reception of an AM broadcast radio wave, the AM output from the AM mixer circuit is output.
The intermediate frequency signal is input to the amplitude limiter, and the amplitude limiter is used as the amplitude limiter.
A radio receiver characterized in that a detection circuit is used as the amplitude conversion means, and an output of the FM detection circuit is inputted to the extraction means. 4. The radio receiver according to claim 1, further comprising a noise canceller circuit for suppressing a decrease in reception sensitivity due to a single noise pulse or a noise pulse having a long generation period, A radio receiver, wherein the output of the AM detection circuit is input to the noise canceller circuit.