JPH09205347A - Radio receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent malfunction at an automatic tuning reception by attenuating the amplification factor of a high frequency amplifier circuit when a search detection means detects a search state so as to exclude various faults caused when a broadcast radio wave is received in a strong electric field area. SOLUTION: The output of a 2nd frequency conversion circuit 4 and the output of a high frequency amplifier circuit 2 are processed for detection, rectification and arithmetic operation or the like at a level detection circuit 9 and a signal denoting a reception signal level of a reception broadcast station is outputted to an attenuator 10. Then an amplification factor of the high frequency amplifier circuit 2 is controlled in response to a signal from the level detection circuit 9 so that an output signal level to the 1st frequency conversion circuit 4 is nearly constant. When automatic music selection is operated, a search detection circuit 11 detects a searching state and a switch 13 is closed. Thus, the amplification factor of the high frequency amplifier circuit 2 is reduced by an attenuator 12. Thus, malfunction in the searching due to mis- detection of a broadcast station is prevented in a strong electric field strength region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique effective in reducing interference in a radio receiver and preventing a false stop operation during automatic tuning.

[0002]

2. Description of the Related Art FIG. 10 is a block diagram showing the configuration of a conventional double superheterodyne radio receiver having an automatic tuning function. Reference numeral 1 denotes a receiving antenna that receives a broadcast wave from a radio broadcasting station. A high-frequency amplifier circuit 2 amplifies the high-frequency signal, and amplifies the high-frequency signal received by the receiving antenna 1 from the radio broadcasting station. Reference numeral 3 is a transformer for converting the output of the high frequency amplifier circuit 2 into balanced and unbalanced states.

Reference numeral 4 denotes a first frequency conversion circuit, which mixes a broadcast signal with a local oscillation signal from the first local oscillator 41, converts a reception signal into a signal of a predetermined frequency (10.7 MHz), and outputs the frequency ( (10.7 MHz) bandpass filter. Reference numeral 5 denotes a second frequency conversion circuit, which receives the reception signal converted by the first frequency conversion circuit 4 from the second local oscillator 4
The local oscillation signals from 2 are mixed, and the intermediate frequency (usually AM
Then, it is converted to 450 KHz) and filtered by a band pass filter of the frequency.

The oscillation frequencies of the first and second local oscillators 41 and 42 are controlled so that the broadcast wave to be received has the predetermined frequency and the intermediate frequency. Reference numeral 6 denotes a demodulation circuit that demodulates the output signal from the second frequency conversion circuit 5 that has been converted to an intermediate frequency and filtered to take out a voice signal or the like. Reference numeral 7 is a power amplifier circuit that power-amplifies the low-frequency signal output from the demodulation circuit 6, and 8 is a speaker that outputs the low-frequency signal output from the power amplifier circuit 7 as an acoustic signal.

Reference numeral 9 is a level detection circuit for detecting the received signal level in the received broadcast frequency band, which comprises a detection circuit for detecting and rectifying the output signal of the first frequency converter 4 and the output signal of the high frequency amplification circuit 2, and the like. A signal is output according to a signal level in a relatively wide band and a narrow band in frequency.
An attenuator 10 controls the gain of the high frequency amplifier circuit 2 according to the output of the level detection circuit 9. In other words, the automatic gain adjustment circuit (AG
C circuit) is configured.

[0006]

In such a conventional radio receiver, in order to prevent interference that occurs in a high electric field area, the high frequency amplifier circuit is tuned or the AGC circuit is used.
Using a circuit. However, if the Q (Quality factor) of the tuning circuit is increased to improve the effect, the tracking error increases. Further, if the attenuation degree in the AGC circuit is increased, there is a problem that the S / N ratio at the time of receiving a weak electric field station in a weak electric field is deteriorated.

Therefore, the Q of the tuning circuit is increased or A
There is also a limit to increasing the attenuation of the GC circuit, and spurious interference due to strong input, intermodulation distortion, intermodulation distortion, etc. occur in areas of strong electric fields, such as directly below the transmitting antenna, and there is interference during automatic tuning. Problems such as malfunction (stopping the frequency sweep at a frequency where there is no broadcasting station) have occurred.

[0008]

In order to solve the above problems, the present invention sweeps a reception frequency and stops the sweep when a broadcast wave is detected based on the electric field strength of the received broadcast wave,
In a radio receiver having an automatic reception function for making a reception state at the frequency, a searching detection means for detecting an automatic reception operation, and an amplification degree of a high frequency amplification circuit when the searching is detected by the search detection means. It is characterized in that a first damping means for damping is provided.

Further, the radio receiver has gain control means for controlling the amplification degree of the high frequency amplification circuit according to the level of the received signal, and the first attenuation means shares the circuit with the gain control means. It is characterized by doing. Further, in a radio receiver having a gain control means for controlling the amplification degree of the high frequency amplification circuit according to the level of the received signal, an input level detection means for detecting an input signal level to the demodulation means for demodulating a broadcast wave, It is characterized in that a second attenuating means for attenuating the amplification degree of the high frequency amplifying circuit according to the level of the input signal detected by the input level detecting means is provided.

The second attenuating means shares a circuit with the gain controlling means. The input level detecting means has a comparing means for comparing the input signal level to the demodulating means with a predetermined level, and the second attenuating means outputs the input signal level to a predetermined level by the output of the comparing means. It operates in the above-mentioned case, and attenuates the amplification degree of the high-frequency amplifier circuit.

Further, the invention is characterized by further comprising a microcomputer for inputting an input signal level to the demodulating means and controlling the second attenuating means by a control value stored in the memory in correspondence with the input signal level. To do. The radio receiver is a radio receiver having a gain control means for controlling the amplification degree of the high frequency amplifier circuit according to the level of the received signal, and detects the input signal level to the demodulation means for demodulating the broadcast wave. The input level detecting means and the third attenuating means for attenuating the amplification degree of the high frequency amplifier circuit according to the level of the input signal detected by the input level detecting means are provided.

The output of the searching means and the input signal level to the demodulating means are input to determine whether or not the automatic receiving operation is in the memory, and the control value stored corresponding to the input signal level. , A microcomputer for controlling the first attenuating means and the third attenuating means. Further, the first damping means and the third damping means are
The gain control means and the circuit are shared.

Further, the first attenuating means is composed of a filter having a frequency characteristic in which a signal of a reception frequency is not attenuated. Further, the second attenuating means is composed of a filter having a frequency characteristic in which a signal of a reception frequency is not attenuated.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the first exemplary embodiment of the present invention. Reference numeral 1 denotes a receiving antenna that receives a broadcast wave from a radio broadcasting station. A high-frequency amplifier circuit 2 amplifies the high-frequency signal, and amplifies the high-frequency signal received by the receiving antenna 1 from the radio broadcasting station. Reference numeral 3 is a transformer for performing balanced / unbalanced conversion on the output of the high frequency amplifier circuit 2.

A first frequency conversion circuit 4 mixes a broadcast signal with a local oscillation signal from a local oscillator, converts a reception signal into a signal of a predetermined frequency (10.7 MHz), and a bandpass filter of the frequency. Filter with. Reference numeral 5 denotes a second frequency conversion circuit, which mixes the reception signal converted by the first frequency conversion circuit 4 with the local oscillation signal from the local oscillator to convert the reception signal to an intermediate frequency (normally 450 KHz in AM), Filter with an intermediate frequency bandpass filter. The oscillation frequency of the local oscillator is controlled so that the broadcast wave to be received has the predetermined frequency and the intermediate frequency.

The present embodiment is a circuit of the double superheterodyne system, in which the received broadcast wave is converted into a predetermined frequency by the first frequency conversion circuit 4 so that the frequency of the signal is once converted into a frequency band in which automatic tuning is easy. Then, the automatic tuning operation is performed. Reference numeral 6 is a detection circuit for converting the intermediate frequency and demodulating the filtered broadcast wave to extract an audio signal or the like. Reference numeral 7 is a power amplifier circuit that power-amplifies the low-frequency signal output from the detection circuit 6, and 8 is a speaker that outputs the low-frequency signal amplified by the power amplifier circuit 7 as an acoustic signal. Reference numeral 9 is a level detection circuit for detecting the received signal level in the received broadcast frequency band, which is composed of a detection circuit for detecting and rectifying the output of the first frequency converter 4 and the output signal of the high frequency amplifier circuit 2, and the like. A signal is output according to the signal level in a relatively wide band and a narrow band.

Reference numeral 10 denotes an attenuator, which controls the gain of the high frequency amplifier circuit 2 according to the output of the level detection circuit 9. That is,
The level detection circuit 9 and the attenuator 10 constitute an automatic gain adjustment circuit (AGC circuit). An attenuator 12 attenuates the gain of the high frequency amplifier circuit 2 by a certain amount. Reference numeral 11 denotes a search detection circuit that detects whether or not the search (automatic tuning operation: sweeps the reception frequency and stops the sweep when a broadcast wave is detected by the electric field strength, etc.) is detected. Then, the switch 13 is connected to attenuate the gain of the high frequency amplifier circuit 2. The detection during the search can be performed by a method such as monitoring the level of the search control output terminal of the microcomputer that controls the operation of the radio receiver.

Next, the operation of the circuit will be described. The radio wave received by the receiving antenna 1 is amplified and band-limited by the high frequency amplifier circuit 2. Then, the output of the high frequency amplifier circuit 2 is mixed with the local oscillation signal from the local oscillation circuit in the first frequency conversion circuit 4 to be converted into a predetermined frequency and filtered.
The frequency of the local oscillation signal is changed according to the instructed reception frequency so that the reception frequency instructed to select the channel is converted into a predetermined frequency.

The output of the first frequency conversion circuit 4 is converted by the second frequency conversion circuit 5 into an intermediate frequency by the local oscillation signal from the second local oscillation circuit, and then filtered by an intermediate frequency bandpass filter. The frequency of the second station-originated signal is varied according to the reception frequency instructed to convert the reception frequency instructed to tune into the intermediate frequency.
The output of the second frequency conversion circuit 5 is detected by the demodulation circuit 6 and converted into an audio signal. Then, the output of the demodulation circuit 6 is amplified by the power amplification circuit 7 and output as sound from the speaker 8.

The output of the second frequency conversion circuit 4 and the output of the high frequency amplification circuit 2 are detected and rectified by the level detection circuit 9.
Processing such as calculation is performed, and a signal indicating the reception signal level of the broadcast wave of the reception broadcasting station, that is, a signal indicating a good amplification degree of the high frequency amplification circuit 2 is output to the attenuator 10. Then, the attenuator 10 controls the amplification degree of the high frequency amplification circuit 2 in accordance with the signal from the level detection circuit 9 so that the output signal level to the first frequency conversion circuit 4 becomes substantially constant.

When the automatic tuning operation is performed, the search detection circuit 11 detects that the search is in progress, and the switch 13 is closed. Therefore, the amplification degree of the high frequency amplifier circuit 2 is lowered by the attenuator 12. Therefore, during the search, the amplification factor of the high-frequency amplifier circuit 2 becomes lower than that during normal reception, so that the malfunction of the search operation due to the false detection of the broadcasting station in the strong electric field area can be prevented. Further, since the amplification factor of the high frequency amplifier circuit 2 is not unnecessarily lowered during reception, the S / N ratio is reduced.
Does not cause a decrease in

Next, a second embodiment of the present invention will be described. The same components as those in the first embodiment shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, the attenuator 10 in the first embodiment shown in FIG.
12 is common, and the outputs of the level detection circuit 9 and the search detection circuit 11 are input to the common attenuator 10. The attenuator 10 controls the amplification degree of the high frequency amplifier circuit 2 according to the signal from the level detection circuit 9 during normal reception, and further lowers the amplification degree of the high frequency amplifier 2 during the search.

Next, a circuit example of the common attenuator 10 is shown in FIG.
This will be described with reference to FIG. FIG. 7 is a circuit diagram showing a circuit configuration of the attenuator 10. A power supply is connected to the emitter of the transistor Tr, and the output of the level detection circuit 9 is connected to the base. Resistors RC and RD connected in series are connected to the collector of the transistor Tr, and pin diodes P1 and P2 that operate as switching elements are connected to the connection points.
Is connected to a series circuit of and a capacitor forming a low-pass filter. Then, the pin diodes P1 and P2
The connection point of is connected to the input end of the high-frequency amplifier circuit 2 via a DC blocking capacitor. Further, a series circuit of a variable resistor RX and a switch element SW13 is connected between the emitter and the base of the transistor Tr. And
The switch element SW13 is composed of a relay, a switching transistor, and the like, and is controlled by the search detection circuit 11 so as to be closed during the search.

Next, the operation will be described. A signal according to the received electric field strength is applied to the base of the transistor Tr by the level detection circuit 9, and the impedance of the transistor Tr becomes according to the received electric field strength. Therefore, the current iB passing through the transistor Tr and the resistors RC and RD depends on the received electric field strength, and the voltage at the connection point of the resistors RC and RD also depends on the received electric field strength. Therefore, the bias voltages of the pin diodes P1 and P2 also change according to the received electric field strength, and the change in impedance causes the received signal to be attenuated by the pin diode P2 according to the electric field strength. Also, during the search, the switch element SW
13 is closed. Therefore, the current (iC) passing through the variable resistor RX and the switch element SW13 also flows through the resistors RC and RD. Therefore, the voltage between the resistors RC and RD also increases correspondingly, and the voltage applied to the pin diodes P1 and P2 also increases. Therefore, the impedance of the pin diode P2 is lowered, and the received signal is attenuated more than during normal reception. The resistance value of the variable resistor RX is adjusted so that the search operation operates properly.

As described above, in the present embodiment, the attenuating circuit is shared, so that the circuit structure can be simplified. Next, a third embodiment of the present invention will be described with reference to FIG. The same components as those in the first embodiment shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.
Reference numeral 15 is a signal (S) for detecting the electric field strength of the received broadcast wave
The level detection circuit is composed of an envelope circuit, a rectification circuit, etc., and detects the demodulation output level of the demodulation circuit 6 to detect the electric field strength. Reference numeral 14 denotes a comparison circuit, which compares the output of the S level detection circuit 15 with a set voltage of a predetermined voltage, and controls the switch element 13 when the electric field strength is a predetermined strength or more. D1 and D2 are diodes for blocking backflow and prevent interference between the comparison circuit 14 and the search detection circuit 11.

Next, the operation will be described. The description of the same operation as that of the first embodiment shown in FIG. 1 will be omitted, and the operation upon reception of a strong electric field station will be described. During reception by the strong electric field station, the output level of the S level detection circuit 15 rises. If the electric field strength of the receiving station becomes stronger as the output level of the S level detection circuit 15 becomes higher than the set voltage, the comparison circuit 14
Output is inverted and the switch element 13 is closed. Therefore, when the electric field strength of the receiving station exceeds a predetermined electric field strength, the amplification degree of the high frequency amplifier circuit 2 decreases.

FIG. 9 is a graph showing the relationship between the input signal level and the signal and noise output levels in the demodulation circuit. When the input level exceeds the predetermined level a, the signal and noise levels hardly change and the S / N becomes substantially constant.
The present embodiment utilizes this characteristic, and attenuates the input signal (maintains it at about a level or more) when the electric field strength is high and the input signal level is sufficiently high. As a result, according to the present embodiment, the signal level of the input other station is also attenuated and cross modulation is suppressed. However, since the input level of the receiving station is maintained at a level or higher, the S / N does not decrease.

Next, a fourth embodiment of the present invention will be described with reference to FIG. The same components as those in the third embodiment shown in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, the attenuators 10 and 12 in the third embodiment shown in FIG. 3 are made common, and the common attenuator 10 outputs the level detection circuit 9, the search detection circuit 11, and the comparison circuit 14. Is to be entered. The attenuator 10 controls the amplification degree of the high frequency amplifier circuit 2 in accordance with the signal from the level detection circuit 9 during normal reception, and further increases the amplification degree of the high frequency amplifier 2 during search and during reception of a strong electric field station. It lowers. The circuit shown in FIG. 7 and the like can be applied to the common attenuator 10.

Next, a fifth embodiment of the present invention will be described with reference to FIG. The same components as those in the third embodiment shown in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. In the present embodiment, the attenuator 12 in the third embodiment shown in FIG. 3 is controlled by a microcomputer. Reference numeral 21 denotes a microcomputer, which inputs the signals of the S level detection circuit 15 and the search detection circuit 11, and controls the attenuator 12 according to the input.

In the microcomputer 21, whether or not the search is being performed, and both parameters of the output of the S level detection circuit 15 and the control amount of the attenuator 12 are stored in a memory in a map form in association with each other. Then, the microcomputer 21 selects the control amount from the memory according to whether or not the search is being performed and the output of the S level detection circuit 15, and controls the attenuator 12 according to the value.

Therefore, according to this embodiment, the amplification factor of the high frequency amplifying circuit 2 can be finely controlled according to whether or not the search is being performed and the output of the S level detecting circuit 15, and a more appropriate receiving state can be obtained. The search operation can be realized. Next, a sixth embodiment of the present invention will be described with reference to FIG. FIG.
The same components as those in the fifth embodiment shown in are attached with the same notations and an explanation thereof will be omitted.

In this embodiment, the attenuators 10 and 12 in the fifth embodiment shown in FIG. 5 are used in common, and the common attenuator 10 has a level detection circuit 9 and a microcomputer 21.
The output of is input. Then, the attenuator 10 controls the amplification degree of the high frequency amplifier circuit 2 according to the signal from the level detection circuit 9 during normal reception, and during the search and during reception of the strong electric field station, the attenuator 10 further increases according to these states. The amplification degree of the frequency amplifier 2 is lowered. The circuit shown in FIG. 7 and the like can be applied to the common attenuator 10.

The output of the level detection circuit 9 is also the microcomputer 2
1, the microcomputer 21 may control the attenuator 10 according to the output of the level detection circuit 9, whether or not the search is in progress, and the output of the S level detection circuit 15. In this case, The microcomputer 21 may store these three inputs and the control amounts of the attenuator 10 in association with each other.

Next, a seventh embodiment of the present invention will be described with reference to FIG. The same components as those in the fifth embodiment shown in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted. In the present embodiment, the attenuator 12 in the fifth embodiment shown in FIG. 5 is modified, and the attenuator 12 has frequency characteristics. 23 is a variable band cutoff filter (V
BCF), which is composed of a coil L, a capacitor C, and a variable capacitance diode (varicap) CX. Reference numeral 22 is a tuning voltage generation circuit for applying an oscillation frequency control voltage to the local oscillation circuit.
The stop band of the BCF 23 is changed according to the reception frequency.
The constants of the respective elements are set so that the cutoff band of the VBCF 23 is approximately the reception frequency. RX2 is a variable resistor, and the microcomputer 21 determines whether or not a search is in progress and S
A control amount is selected from the memory according to the output of the level detection circuit 15, and the variable resistor RX2 is controlled according to the value.
That is, the degree of influence of the VBCF 23 on the reception signal is controlled according to the reception state. With these configurations, a signal having a frequency other than the reception frequency is selectively attenuated according to whether or not the search is being performed and the output of the S level detection circuit 15.

Therefore, according to this embodiment, the amplification factor of the high frequency amplifying circuit 2 can be finely controlled according to whether or not the search is being performed and the output of the S level detecting circuit 15, and a more appropriate receiving condition can be obtained. The search operation can be realized. Furthermore, because it selectively attenuates signals of frequencies other than the received frequency,
A more suitable reception state and search operation can be realized.

[0036]

As described in detail above, according to the present invention, it is possible to eliminate various obstacles that occur during reception of broadcast radio waves in the strong electric field area and prevent malfunctions during automatic tuning reception.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a configuration of a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing a configuration of a third embodiment of the present invention.

FIG. 4 is a configuration diagram showing a configuration of a fourth embodiment of the present invention.

FIG. 5 is a configuration diagram showing a configuration of a fifth embodiment of the present invention.

FIG. 6 is a configuration diagram showing a configuration of a sixth embodiment of the present invention.

FIG. 7 is a circuit diagram showing a circuit configuration of an attenuator 10.

FIG. 8 is a configuration diagram showing a configuration of a seventh embodiment of the present invention.

FIG. 9 is a S / N characteristic diagram of a demodulation circuit.

FIG. 10 is a configuration diagram showing a configuration of a conventional radio receiver.

[Explanation of symbols]

 1 ... Receiving antenna 2 ... High frequency amplification circuit 3 ... Balanced / unbalanced transformer 4 ... First frequency conversion circuit 5 ...・ ・ ・ ・ ・ ・ Second frequency conversion circuit 6 ・ ・ ・ ・ Demodulation circuit 7 ・ ・ ・ Power amplifier circuit 8 ・ ・ ・ Speaker

Claims (11)

[Claims] 1. Sweeping the reception frequency, stopping the sweep when the broadcast wave is detected based on the electric field strength of the received broadcast wave,
In a radio receiver having an automatic reception function for making a reception state at the frequency, a search-in-progress detection means for detecting an automatic reception operation, and an amplification degree of a high-frequency amplifier circuit when the search is in progress by the search detection means. A radio receiver comprising a first attenuating means for attenuating. 2. The radio receiver has gain control means for controlling the amplification degree of the high frequency amplification circuit according to the level of a received signal, and the first attenuating means shares the circuit with the gain control means. The radio receiver according to claim 1, wherein the radio receiver is provided. 3. A radio receiver having a gain control means for controlling the amplification degree of a high frequency amplifier circuit according to the level of a received signal, wherein an input level detection for detecting an input signal level to a demodulation means for demodulating a broadcast wave. A radio receiver comprising means and second attenuating means for attenuating the amplification degree of the high frequency amplifier circuit according to the level of the input signal detected by the input level detecting means. 4. The radio receiver according to claim 3, wherein the second attenuating means shares a circuit with the gain controlling means. 5. The input level detecting means includes a comparing means for comparing an input signal level to the demodulating means with a predetermined level, and the second attenuating means outputs the input signal level according to an output of the comparing means. 5. The radio receiver according to claim 3, wherein the radio receiver operates at a predetermined level or higher to attenuate the amplification degree of the high frequency amplifier circuit. 6. A microcomputer for inputting an input signal level to the demodulating means and controlling the second attenuating means by a control value stored in a memory in correspondence with the input signal level. The radio receiver according to claim 3. 7. The radio receiver is a radio receiver having a gain control means for controlling the amplification degree of a high frequency amplifier circuit according to the level of a received signal, wherein the input signal to the demodulation means for demodulating a broadcast wave. An input level detecting means for detecting a level and a third attenuating means for attenuating the amplification degree of the high frequency amplifier circuit according to the level of the input signal detected by the input level detecting means are provided. The radio receiver described. 8. The output of the searching means and the input signal level to the demodulating means are input to determine whether or not the automatic receiving operation is in the memory, and the control value stored corresponding to the input signal level. The radio receiver according to claim 7, further comprising a microcomputer that controls the first attenuating means and the third attenuating means. 9. The radio receiver according to claim 7, wherein the first attenuating means and the third attenuating means share a circuit with the gain control means. 10. The radio receiver according to claim 1, wherein the first attenuating unit is composed of a filter having a frequency characteristic in which a signal of a reception frequency is not attenuated. 11. The radio receiver according to claim 3, wherein the second attenuating unit is composed of a filter having a frequency characteristic in which a signal of a reception frequency is not attenuated.