JP2008109348A - Fm radio receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an FM radio receiver capable of preventing sounds from deteriorating in quality by disturbance signals because the reading of a signal meter is small and AGC is put in an inactive zone when AGC is changed in sensitivity according to the reading of a signal meter of the intensity of an electric field received by an antenna through an AGC function possessed by the FM radio receiver itself. <P>SOLUTION: Radio waves are received by an antenna 1, a gain is controlled by an RF circuit 2, and the reading of a signal meter from an electric field intensity detecting circuit 9, where the radio waves are converted to a first intermediate frequency by a first mixer 3, is compared with a reference voltage through a comparison circuit 10. The attenuation volume of an attenuator 11 is adjusted according to a comparison result, so that the attenuation volume is set large when the reading of a signal meter is smaller than the reference voltage, and on the contrary, the attenuation volume is set small when the reading of signal meter is larger than the reference voltage. The output of the attenuator 11 is amplified by an AGC detection signal amplifier 12 to control the gain of the RF circuit 2. The comparison circuit 10 is composed of a first to an n-th comparators which are different in attenuation volume to the signal meter, and the selection of two or more comparators and the amplification factor of an amplification factor controller 13 are switched by a changeover switch 15 to adjust an AGC volume to set an optimal AGC sensitivity, so that AGC sensitivity is kept staying out of an insensitive zone. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an FM receiver, and more particularly to an FM radio receiver having an AGC function.

  A superheterodyne system is generally used for a receiver that receives an FM signal. The superheterodyne system is a system that mixes the signal from the broadcast station and the signal from the local oscillator circuit, converts it to a single-frequency intermediate frequency signal, and demodulates it. There are advantages such as easy wave attenuation (strong against interference) and good reception sensitivity by repeated amplification.

  Further, the FM receiver has an AGC function, and is controlled to an optimum input signal level that can be processed by a circuit by the AGC function in order to obtain a high-quality audio signal. Since the operating frequency range of this AGC function is defined by the bandwidth of the signal for detecting AGC, when detecting AGC with a relatively wide RF circuit or mixer output, not only the desired signal but also the interference signal Can also operate AGC. However, if the AGC operates on the interference signal with the desired signal being small, the desired signal level is attenuated and the sound quality is deteriorated. Therefore, a function for suppressing the amount of AGC when the desired signal level is low is provided (see Patent Document 1).

  The operation of the conventional FM receiver shown in FIG. 7 will be described. As shown in FIG. 7, the FM receiver includes an antenna 1, an RF circuit 2, a first mixer 3, a local oscillator 4, an IFT 5, a narrow band filter 6, an IF unit 7, a detection circuit 8, a field strength detection circuit 9, It comprises a comparison circuit 10, an AGC detection signal attenuator 11, an AGC detection signal amplifier 12, an amplification factor controller 13, an AGC control circuit 14, and a changeover switch 15.

  The FM modulated signal received by the antenna 1 is gain-controlled by the RF circuit 2 and converted to the first intermediate frequency (IF signal) by the first mixer 3. The output signal of the first mixer 3 is input as two systems of an AGC detection signal and an IF processing signal. The AGC detection signal is input to the attenuator 11. On the other hand, the IF processing signal converts the current output of the first mixer 3 into a voltage by the IFT 5.

  This IFT 5 has a sufficiently wide pass band as compared with the band of the FM receiving station, and the output signal passes through a narrow band filter 6 close to the bandwidth of the FM receiving station, and passes to the IF unit 7 that performs signal processing for amplification and filtering. The signal is input and converted into an FM audio signal by the detection circuit 8 via the IF unit 7. The electric field strength detection circuit 9 converts the electric field strength of the signal that has passed through the narrow band filter 6 into a DC voltage.

  The output of the electric field intensity detection circuit 9 is a signal meter, and the comparison between the signal meter and the reference voltage is performed by the comparison circuit 10, and the attenuation amount of the attenuator 11 is adjusted according to the magnitude relationship. The output signal of the attenuator 11 is amplified by the AGC detection signal amplifier 12, and when the output signal of the AGC detection signal amplifier 12 exceeds a predetermined signal level, the gain of the RF circuit 2 becomes small. By switching the amplification factor of the AGC detection signal amplifier 12 with the changeover switch 15 via the amplification factor controller 13, the AGC amount is adjusted, and the optimum AGC sensitivity corresponding to the radio wave condition is set.

FIG. 8 is a graph showing changes in AGC sensitivity with respect to the signal meter. In the definition of AGC sensitivity in the present invention, a case where AGC operates at a low level is expressed as “high sensitivity”. Due to the operation of the attenuator 11, the AGC sensitivity decreases as the signal meter becomes smaller. Further, the AGC sensitivity changes in the entire signal meter by switching the amplification factor of the AGC detection signal amplifier 12. The AGC sensitivity characteristics of g, h, and i shown in FIG. 8 are changes in sensitivity characteristics due to switching of the amplification factor. Further, Vmax in FIG. 8 indicates a dynamic range that can be handled by the circuit.
JP-A-4-65907

  However, since a signal exceeding Vmax cannot be processed, there is no AGC sensitivity in a region exceeding Vmax. As indicated by i in FIG. 8, when the gain of the AGC detection signal amplifier 12 is switched and the AGC sensitivity is set to a low state as a whole, an AGC dead zone occurs in a region where the signal meter is small. Since the AGC does not operate in the dead zone region, the disturbing wave input to the first mixer 3 is not suppressed, and there is a problem that voice deterioration is caused by the disturbing wave.

  The present invention is directed to solving the problems of the prior art. In the AGC function in the FM radio receiver, the AGC sensitivity is changed according to the signal meter of the antenna reception electric field strength of the desired signal, and the signal meter It is an object of the present invention to provide an FM radio receiver that prevents the deterioration of the sound quality due to the influence of an interfering signal due to the decrease in the AGC dead zone.

  In order to achieve the above object, an FM radio receiver according to claim 1 according to the present invention includes an RF gain control function for an antenna input signal, and a conversion function for the antenna input signal to a first intermediate frequency signal. A function of detecting sound from the first intermediate frequency signal, a function of outputting a signal meter indicating the electric field strength of the antenna input signal, and an AGC function of reducing the RF gain when the antenna input signal is larger than a predetermined AGC detection signal FM radio receiver having an attenuator for attenuating the AGC detection signal from the first intermediate frequency signal and a plurality of comparators having different attenuation characteristics for the signal meter, and comparing the signal meter and the reference voltage by the comparator A comparison circuit for controlling the attenuation amount of the attenuator, an AGC detection signal amplifier for amplifying the output signal of the attenuator, and AG Amplification rate controller for switching the amplification factor of the detection signal amplifier, and a switch for simultaneously switching a plurality of comparators of the comparison circuit and the amplification factor controller, and switching the amplification factor of the comparator and operating the AGC function It is characterized by making it.

  The FM radio receiver according to claim 2 is a function of controlling an RF gain with respect to an antenna input signal, a function of converting the antenna input signal into a first intermediate frequency signal, and a function of detecting sound from the first intermediate frequency signal. And an FM radio receiver having a function of outputting a signal meter indicating the electric field strength of the antenna input signal and an AGC function of reducing the RF gain when the antenna input signal is larger than a predetermined AGC detection signal. A voltage shift circuit that converts and outputs a voltage so that the shift amount increases when the signal meter increases and decreases when the signal meter increases, an attenuator that attenuates the AGC detection signal from the first intermediate frequency signal, and a voltage shift circuit A comparison circuit that controls the attenuation of the attenuator by comparing the output voltage of the An AGC detection signal amplifier that amplifies the signal; an amplification factor controller that switches the amplification factor of the AGC detection signal amplifier; and a switch that simultaneously switches the voltage conversion of the voltage shift circuit and the amplification factor of the amplification factor controller. The AGC function is operated by switching the amplification factor.

  According to the above configuration, the AGC function can be operated even when the signal meter is zero.

  According to the present invention, even when the signal meter is zero, the AGC function operates, and it is possible to prevent the sound quality from being deteriorated due to the interference signal.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of an FM radio receiver according to Embodiment 1 of the present invention. Here, components corresponding to the constituent elements described in FIG. 7 showing the conventional example and having equivalent functions are denoted by the same reference numerals, and the same applies to the following drawings.

  As shown in FIG. 1, the FM radio receiver includes an antenna 1, an RF circuit 2, a first mixer 3, a local oscillator 4, an IFT 5, a narrow band filter 6, an IF unit 7, a detection circuit 8, and an electric field strength detection circuit 9. , A comparison circuit 10, an AGC detection signal attenuator 11, an AGC detection signal amplifier 12, an amplification factor controller 13, an AGC control circuit 14, and a changeover switch 15.

  In FIG. 1, the FM modulated signal received by the antenna 1 is gain-controlled by the RF circuit 2 and converted to a first intermediate frequency (IF signal) by the first mixer 3. The output signal of the first mixer 3 is input as two systems of an AGC detection signal and an IF processing signal. The AGC detection signal is input to the attenuator 11. On the other hand, the IF processing signal converts the current output of the first mixer 3 into a voltage by the IFT 5. The IFT 5 has a sufficiently wide pass band as compared with the band of the FM receiving station, and its output signal passes through a narrow band filter 6 close to the bandwidth of the FM receiving station, and performs IF and signal processing for amplification and filtering. Then, the detection circuit 8 converts the signal into an FM audio signal.

  The electric field strength detection circuit 9 converts the electric field strength of the signal that has passed through the narrow band filter 6 into a DC voltage. The output of the electric field intensity detection circuit 9 is a signal meter, and the comparison between the signal meter and the reference voltage is performed by the comparison circuit 10, and the attenuation amount of the attenuator 11 is adjusted according to the magnitude relationship, and the signal meter is small. In such a case, the amount of attenuation is increased. On the other hand, if it is large, the amount of attenuation is decreased.

  The output signal of the attenuator 11 is amplified by the AGC detection signal amplifier 12, and when the output signal of the AGC detection signal amplifier 12 exceeds a predetermined signal level, the gain of the RF circuit 2 becomes small. Further, the AGC amount is adjusted by switching the amplification factor of the AGC detection signal amplifier 12 through the amplification factor controller 13 by the changeover switch 15, and the optimum AGC sensitivity corresponding to the radio wave condition is set. The comparison circuit 10 for controlling the attenuator 11 is composed of a plurality of comparators (first to Nth comparators) having different attenuation amounts with respect to the signal meter, and an optimum comparison circuit (comparator) is selected by the changeover switch 15. .

FIG. 2 is a circuit diagram showing an embodiment of the comparison circuit (comparator) and the attenuator described in FIG. As shown in FIG. 2, the comparison result output terminal 100, the switch signal input terminal 101, the signal meter input terminal 102, the input terminal 104 of the attenuator 11, the output terminal 105 of the attenuator 11, transistors Q _{1 to} Q _M , and the resistance R _{1 to} R _N , a constant current source I 0, a diode D ₁ , and a resistor R _Z1 .

Signal meter input from signal meter input terminal 102 is first input to the base of the transistor Q _2. Reference voltage Vref is input to the base of the transistor Q _1. A resistor R ₁ is connected between the emitters of the transistors Q ₁ and Q ₂ . Here, this resistance is called a comparator resistance. Switch is provided at both ends of the resistor R _1, is connected at both ends of R ₁ to the constant current sources I0 when this switch is turn ON. The reference voltage Vref is approximately half the maximum value Vmax of the signal meter. The collector of the transistor Q ₂ is connected to the power supply VCC, and the collector of the transistor Q ₁ is the output terminal of the comparison circuit 10.

  In the operation of the comparison circuit 10, the output current changes depending on the potential difference between the reference voltage Vref and the signal meter. The output current Iout is (Equation 1)

に従い、シグナルメーターが大きいほど出力電流Ｉoutが小さくなる。シグナルメーターに対する出力電流特性は１／Ｒ_１の傾きを持つ特性となる。

Accordingly, the larger the signal meter, the smaller the output current Iout. Output current characteristics for signal meter is a characteristic having a slope of 1 / R _1.

  In this comparison circuit 10, the output terminals of a plurality of comparators in which only the comparator resistance is changed become the comparison result output terminal 100 of the comparison circuit 10, and only the comparator selected by the switch signal input terminal 101 operates. .

Attenuator 11 drives the diode D ₁ by the output current of the selected comparator. Diode D ₁ is to lower impedance each time the current increases, the attenuation amount of the attenuator 11 is determined by the relative ratio of the impedance of R _Z1 and D _1. Because when signal meter is sufficiently small large output current of the comparator circuit 10 lowers the impedance of the diode D _1, the attenuation amount increases. Conversely when signal meter is sufficiently large has a small output current of the comparator circuit 10, the attenuation amount not reduced impedance of the diode D ₁ is smaller.

  FIG. 3 is a graph showing the AGC sensitivity with respect to the signal meter in the FM radio receiver shown in FIG. The horizontal axis represents the signal meter, and the vertical axis represents the AGC sensitivity. Vmax is the dynamic range of the circuit. As shown in FIG. 3, when the maximum sensitivity is switched between g, h, and i, the comparators are also switched at the same time, and each minimum sensitivity does not exceed Vmax.

(Embodiment 2)
FIG. 4 is a block diagram showing a configuration of an FM radio receiver according to Embodiment 2 of the present invention. The second embodiment is an example in which the signal meter is changed by the voltage shift circuit 16 and the control of the attenuator 11 is realized by the single comparison circuit 10.

  As shown in FIG. 4, the FM radio receiver includes an antenna 1, an RF circuit 2, a first mixer 3, a local oscillator 4, an IFT 5, a narrowband filter 6, an IF unit 7, a detection circuit 8, and an electric field strength detection circuit 9. , A comparison circuit 10, an AGC detection signal attenuator 11, an AGC detection signal amplifier 12, an amplification factor controller 13, an AGC control circuit 14, a changeover switch 15, and a voltage shift circuit 16.

  In FIG. 4, the FM modulated signal received by the antenna 1 is gain-controlled by the RF circuit 2 and converted to the first intermediate frequency (IF signal) by the first mixer 3. The output signal of the first mixer 3 is input as two systems of an AGC detection signal and an IF processing signal. The AGC detection signal is input to the attenuator 11. On the other hand, the IF processing signal converts the current output of the first mixer 3 into a voltage by the IFT 5. The IFT 5 has a sufficiently wide pass band as compared with the band of the FM receiving station, and its output signal passes through a narrow band filter 6 close to the bandwidth of the FM receiving station, and performs IF and signal processing for amplification and filtering. Then, the detection circuit 8 converts the signal into an FM audio signal.

  The electric field strength detection circuit 9 converts the electric field strength of the signal that has passed through the narrow band filter 6 into a DC voltage. The output of the electric field strength detection circuit 9 is a signal meter and is input to the voltage shift circuit 16. In the voltage shift circuit 16, although the shift amount is zero and the output voltage does not change at the maximum value of the signal meter, the shift amount is increased as the signal meter becomes smaller, and output is performed by shifting the voltage. This shift amount is switched by the changeover switch 15.

  The comparison between the output voltage of the voltage shift circuit 16 and the reference voltage is performed by the comparison circuit 10, and the attenuation amount of the attenuator 11 is adjusted according to the magnitude relationship. When the signal meter is small, the attenuation is increased. Conversely, when the signal meter is large, the attenuation is decreased. The output signal of the attenuator 11 is amplified by the AGC detection signal amplifier 12, and when the output signal of the AGC detection signal amplifier 12 exceeds a predetermined signal level, the gain of the RF circuit 2 becomes small.

FIG. 5 is a circuit diagram showing an embodiment of the voltage shift circuit shown in FIG. As shown in FIG. 5, the switch signal input terminal 101, signal meter input terminal 102, the shift voltage output terminal 103 of the signal meter, is a transistor _Q 7 to Q _M, resistors _R 1 0 to R _M, resistors _{R Z2} Prefecture The

A signal meter input from the signal meter input terminal 102 is input to the bases of the transistors Q ₇ and Q ₈ . The emitter of the transistor _{Q 7} is connected via a resistor _{R 10} and inter-GND. A secondary current source having a polarity different from that of the primary current source by a mirror circuit including transistors Q ₉ and Q ₁₀ and a resistor R _{11 using} a collector current of the transistor Q ₇ determined by the signal meter and the resistor R ₁₀ as a primary current source. I ₁₀ is generated.

Also, signal meter is connected to the base of the transistor _Q 12 to Q _M. The emitter of the transistor _Q 12 to Q _M - power between, and connect different resistor _R 12 to R _M of each value, to generate the different current sources _I 12 ~I _M of a current value to the signal meter. Current source _{I 10, I} 12 ~I _M are switched by respective switches, the difference between the primary current source by connecting a resistor _{R Z2} to flow in the resistor _{R Z2,} one end of the resistor _{R Z2} is connected to the signal meter The

Signal meter against by the primary current source and a similar current becomes zero flowing through the resistor R _Z2 If current source I ₁₀ showing the current characteristics is selected, the output voltage becomes similar to the signal meter. Conversely, when the signal meter is reduced and the current sources I _{12 to} I _M that increase the current are selected, the current flowing through the resistor R _Z2 increases, and the output voltage increases with respect to the signal meter as the signal meter decreases. . This output voltage can be changed according to each signal meter by a combination of switches for switching the current sources I ₁₀ and I _{12 to} I _M described above.

  FIG. 6A is a characteristic diagram of the voltage shift circuit. In FIG. 6A, g ′ is a characteristic when the signal meter is used as it is as a comparison voltage. When the maximum sensitivity of the gain controller 13 of the AGC detection signal amplifier 12 is increased by the switch 15, the voltage is shifted by the voltage shift circuit 16 even when the signal meter is zero, such as h 'or i'. Increasing the attenuation of the attenuator 11 makes the slope of the AGC sensitivity relative to the signal meter gentle. FIG. 6B is a characteristic diagram of AGC sensitivity with respect to the signal meter, and shows the same sensitivity characteristic as the characteristic of FIG. 3 described in the first embodiment.

  The FM radio receiver according to the present invention is useful as an FM receiver having an AGC function because the AGC operates even when the signal meter is zero, can prevent deterioration in sound quality due to an interference signal.

The block diagram which shows the structure of the FM radio receiver in Embodiment 1 of this invention 1 is a circuit diagram showing an embodiment of the comparison circuit (comparator) and attenuator shown in FIG. Characteristic diagram of AGC sensitivity for signal meter in embodiment 1 The block diagram which shows the structure of FM radio receiver in Embodiment 2 of this invention 4 is a circuit diagram showing an embodiment of the voltage shift circuit shown in FIG. (A) in the second embodiment is a characteristic diagram of a voltage shift circuit with respect to a signal meter, and (b) is a characteristic diagram of AGC sensitivity with respect to the signal meter. The block diagram which shows the structure of the conventional FM receiver AGC sensitivity characteristics for conventional signal meters

Explanation of symbols

1 Antenna 2 RF Circuit 3 First Mixer 4 Local Oscillator 5 IFT
6 Narrow band filter 7 IF section 8 Detection circuit 9 Electric field intensity detection circuit 10 Comparison circuit 11 Attenuator 12 AGC detection signal amplifier 13 Amplification rate controller 14 AGC control circuit 15 Switch 16 Voltage shift circuit 100 Comparison result output terminal 101 Switch signal Input terminal 102 Signal meter input terminal 103 Shift voltage output terminal 104 Input terminal 105 Output terminal

Claims (2)

An RF gain control function for an antenna input signal, a function for converting the antenna input signal to a first intermediate frequency signal, a function for voice detection from the first intermediate frequency signal, and a signal indicating the electric field strength of the antenna input signal In an FM radio receiver having a function of outputting a meter and an AGC function for reducing the RF gain when the antenna input signal is larger than a predetermined AGC detection signal,
An attenuator for attenuating the AGC detection signal from the first intermediate frequency signal and a plurality of comparators having different attenuation characteristics with respect to the signal meter, and comparing the signal meter with a reference voltage by the comparator A comparison circuit for controlling the attenuation amount of the attenuator, an AGC detection signal amplifier for amplifying the output signal of the attenuator, an amplification factor controller for switching the amplification factor of the AGC detection signal amplifier, and a plurality of comparators of the comparison circuit And a switch for simultaneously switching the amplification factor of the amplification factor controller, and the AGC function is operated by switching the comparator and the amplification factor. An RF gain control function for an antenna input signal, a function for converting the antenna input signal to a first intermediate frequency signal, a function for voice detection from the first intermediate frequency signal, and a signal indicating the electric field strength of the antenna input signal In an FM radio receiver having a function of outputting a meter and an AGC function for reducing the RF gain when the antenna input signal is larger than a predetermined AGC detection signal,
When the signal meter is small, the shift amount is increased, and when the signal meter is large, the voltage shift circuit that converts the voltage so that the shift amount is small and outputs, and the attenuation that attenuates the AGC detection signal from the first intermediate frequency signal A comparison circuit that controls an attenuation amount of the attenuator by comparing an output voltage of the voltage shift circuit with a reference voltage, an AGC detection signal amplifier that amplifies the output signal of the attenuator, and the AGC detection signal An amplification factor controller that switches the amplification factor of the amplifier; and a switch that simultaneously switches the shift amount of the voltage shift circuit and the amplification factor of the amplification factor controller, and the AGC function is switched by switching the shift amount and the amplification factor. FM radio receiver characterized by operating.

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