JP4519451B2 - Receiver and gain adjustment method - Google Patents

Description

  The present invention relates to a receiver and a gain adjustment method, and more particularly to a receiver including an AGC (Automatic Gain Control) circuit that controls the gain of an amplifier in accordance with the signal level of a received radio wave, and a gain adjustment method thereof.

  FIG. 5 shows a configuration of an FM receiver 100 as a conventional general receiver. A conventional FM receiver 100 shown in FIG. 5 includes an antenna 101, an RF (Radio Frequency) amplifier 102, a first band pass filter 103, a mixer 104, a local oscillation circuit 105, a second band pass filter 106, and an IF (Intermediate Frequency). An amplifier 107, an electric field strength detector 108, an FM detection circuit 109, an RF_AGC circuit 110, and the like are provided.

  The FM signal received by the antenna 101 is first amplified by the RF amplifier 102, and only the signal in the band including the signal of the desired channel is extracted by the first bandpass filter 103. The signal of the band including the signal of the desired channel is mixed with the local oscillation signal output from the local oscillation circuit 105 by the mixer 104 and converted into a signal centered on the intermediate frequency of 10.7 MHz.

  From the signal output from the mixer 104, only the signal of the desired channel is extracted by the second band pass filter 106 and amplified by the IF amplifier 107. The signal output from the IF amplifier 107 is FM detected by the FM detection circuit 109 and output as an audio signal.

  In addition, the RF_AGC circuit 110 receives the output signal of the RF amplifier 102 and the output signal of the first bandpass filter 103 and detects the signal level of the signal output from the RF amplifier 102. An AGC voltage capable of adjusting the gain of the RF amplifier 102 is output to the RF amplifier 102 in accordance with the detected signal level. That is, when the signal level of the radio wave received from the antenna 101 becomes higher than a predetermined level, the RF_AGC circuit 110 lowers the gain of the RF amplifier 102 and attenuates the signal level of the input radio wave.

  The electric field strength detection circuit 108 detects the electric field strength of the signal of the desired channel amplified by the IF amplifier 107. The electric field strength detection circuit 108 outputs a voltage signal (hereinafter referred to as S meter voltage) corresponding to the electric field strength of the signal of the desired channel to the RF_AGC circuit 110.

  The field strength detection circuit 108 and the RF_AGC circuit 110 will be described by taking, as an example, a case where a jamming station whose frequency is close to the frequency of the desired channel is nearby and the field strength of the jamming radio wave is stronger than the field strength of the desired channel.

  When the received radio wave of the desired channel is significantly smaller than the radio wave from the interfering station, the radio wave from the desired station cannot be received. In order to improve such a situation, the S-meter voltage corresponding to the radio wave of the desired channel is detected by the electric field intensity detection circuit 108 and input to the RF_AGC circuit 110. The RF_AGC circuit 110 controls the gain of the RF amplifier 102 based on the value of the S meter voltage.

  When the radio wave of the desired channel is small according to the measurement result of the S meter voltage and the signal level itself output from the RF amplifier 102 is high (the signal level of the disturbing wave is high), the AGC operation is performed by the RF_AGC circuit 110, and the RF amplifier Control to lower the gain of 102 is performed.

  However, simply lowering the gain of the RF amplifier 102 weakens the signal level of the desired channel, causing a problem that the user's desired broadcast cannot be heard.

  Patent Document 1 is known as a technique for solving the problem that the sensitivity of a receiver is suppressed by the operation of an AGC circuit in an environment in which radio waves from a jamming station are received. In Patent Document 1, an attenuator and an FET are provided in a receiving circuit, and the operation order of the FET and the attenuator is controlled by a control unit according to the level of an input signal.

JP 2001-168747 A

  However, in Patent Document 1, since the attenuator and the FET are provided in the receiving circuit and two-stage control is performed, the configuration becomes complicated.

  The present invention has been made in view of the above circumstances, and provides a receiver and a gain adjustment method capable of obtaining a good reception state with a simpler configuration even in an environment where an interference wave exists. With the goal.

In order to achieve such an object, the receiver of the present invention includes an amplifier that amplifies an input signal and an automatic signal that adjusts the gain of the amplifier by outputting a control signal corresponding to the level of the signal output from the amplifier to the amplifier. A gain adjusting circuit; an electric field intensity detecting circuit for detecting an electric field intensity at a desired frequency using a signal amplified by the amplifier; and the electric field intensity is less than a first threshold value and the voltage of the control signal Control the automatic gain adjustment circuit to output to the amplifier a control signal that increases the gain of the amplifier when the signal intensity exceeds a fourth threshold, and the electric field strength exceeds the second threshold; The automatic gain adjustment circuit is controlled to output a control signal for lowering the gain of the amplifier to the amplifier when the voltage of the control signal is lower than a third threshold value, and the electric field strength is Shiki In a predetermined range determined by a value and the second threshold value, or in a predetermined range determined by the third threshold value and the fourth threshold value. And a control unit that does not control the automatic gain adjustment circuit , wherein the first threshold value is smaller than the second threshold value and the third threshold value is set. The value is smaller than the fourth threshold value .

  The automatic gain adjustment circuit is controlled according to the electric field intensity detected by the electric field intensity detection circuit and the control signal from the automatic gain adjustment circuit to optimize the control signal. Accordingly, it is possible to optimally adjust the gain of the amplifier with a simple configuration of controlling the automatic gain adjustment circuit according to the electric field strength and the control signal, and to receive a signal of a desired frequency satisfactorily.

  In the receiver having the above-described configuration, the control means may compare the control signal and the electric field strength value with respective threshold values, and change the voltage value of the control signal according to the comparison result.

  The control signal and the electric field strength are compared with respective threshold values to determine the control signal and the electric field strength, and a control signal having a voltage value corresponding to the determination result is generated. Therefore, the voltage value of the control signal can be set to an optimum value according to the value of the control signal and the electric field strength. Further, by inputting this control signal to the amplifier, a signal having a desired frequency can be received satisfactorily.

  In the receiver configured as described above, the automatic gain adjustment circuit may output the control signal according to a set value, and the control means may change the set value according to the control signal and the electric field strength.

The automatic gain adjustment circuit outputs the control signal according to a set value, and the control means controls the automatic gain adjustment circuit by changing the set value. Therefore, the value of the control signal for controlling the gain of the amplifier can be set to a value corresponding to the control signal and the electric field strength.

  In the receiver configured as described above, the control means may optimize the control signal based on a state of the control signal and the electric field strength in a predetermined period.

  The control signal is optimized based on the state of the control signal and the electric field strength in a predetermined period. Therefore, it is possible to reduce the influence of noise generated instantaneously and to receive a signal of a desired frequency satisfactorily.

The gain control method of the present invention includes a step of adjusting a gain of the amplifier by outputting a control signal corresponding to a level of a signal output from an amplifier that amplifies an input signal to the amplifier, and after amplification by the amplifier Detecting the electric field strength of a signal having a desired frequency using a signal, and when the electric field strength is less than a first threshold value and the voltage of the control signal exceeds a fourth threshold value, Controlling the automatic gain adjustment circuit to output a control signal for increasing the gain of the amplifier to the amplifier, the electric field intensity exceeds a second threshold value, and the voltage of the control signal is a third threshold value; The automatic gain adjustment circuit is controlled to output a control signal for lowering the gain of the amplifier to the amplifier when the electric field intensity is less than the first threshold value and the second threshold value. Within a predetermined range That case, or if the voltage of the control signal is within a predetermined range defined by said third threshold and the fourth threshold value, does not control for the automatic gain control circuit processes If, have a, the first threshold value, the smaller than the second threshold, the third threshold is characterized in that less than the fourth threshold value .

  The control signal is optimized according to the electric field intensity detected by the electric field intensity detection circuit and the control signal generated according to the signal level of the signal output from the amplifier, and the optimized control signal is input to the amplifier. Yes. Therefore, it is possible to optimally adjust the gain of the amplifier by a simple procedure of optimizing the control signal according to the electric field strength and the control signal, and to receive a signal of a desired frequency satisfactorily.

  The present invention can receive a signal of a desired frequency satisfactorily by optimizing the gain of the amplifier even under the influence of a radio wave from a jamming station.

  Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows an embodiment in which the present invention is applied to an FM receiver. As shown in FIG. 1, the FM receiver 1 of this embodiment includes an antenna 2, an RF amplifier 3, a first bandpass filter 4, a mixer 5, a local oscillation circuit 6, and a second bandpass filter 7. An IF amplifier 8, an electric field strength detection circuit 9, an FM detection circuit 10, a control unit 11, a memory unit 12, and an RF_AGC circuit 13.

  The RF amplifier 3 amplifies the RF signal received via the antenna 2.

  The first band pass filter 4 selectively extracts only the signal in the band including the signal of the desired channel from the RF signal amplified by the RF amplifier 3.

  The mixer 5 receives the output signal of the first bandpass filter 4, mixes this signal and the local oscillation signal from the local oscillation circuit 6, and determines a predetermined IF frequency (for example, 10.7 MHz). Generate a signal.

  The second band pass filter 7 selectively passes only the signal of the desired channel from the IF frequency signal output from the mixer 5.

  The IF amplifier 8 amplifies the signal of the desired channel output from the second band pass filter 7.

  The FM detection circuit 10 performs FM detection on the signal of the desired channel amplified by the IF amplifier 8 and extracts a voice signal.

  The electric field strength detection circuit 9 detects the electric field strength of the signal of the desired channel based on the output signal of the IF amplifier 8. The electric field strength detection circuit 9 outputs a voltage signal (hereinafter referred to as S meter voltage) corresponding to the electric field strength of the signal of the desired channel. The S meter voltage value is output to the control unit 11.

  The RF_AGC circuit 13 receives the output signal of the RF amplifier 3 and the output signal of the first bandpass filter 4 and detects the signal level of the signal output from the RF amplifier 3. An AGC voltage capable of adjusting the gain of the RF amplifier 3 is output to the RF amplifier 3 and the control unit 11 in accordance with the detected signal level. Here, the AGC voltage and the gain of the RF amplifier 3 will be described. The gain of the RF amplifier 3 can be increased by setting the value of the AGC voltage small, and conversely the RF amplifier 3 that sets the value of the AGC voltage large. The gain can be reduced.

  The control unit 11 is composed of a microcomputer or the like, and controls the RF_AGC circuit 13 using the S meter voltage value detected by the electric field strength detection circuit 9 and the AGC voltage from the RF_AGC circuit 13. The control unit 11 inputs an AGC setting signal to the RF_AGC circuit 13 and controls the RF_AGC circuit 13. The voltage value of the AGC setting signal takes a discrete value, and the value of the AGC voltage that is the output of the RF_AGC circuit 13 can be reduced by setting the voltage value of the AGC setting signal large. Further, by reducing the voltage value of the AGC setting signal, the value of the AGC voltage that is the output of the RF_AGC circuit 13 can be increased. In this embodiment, three types of voltage values 6, 9, and 12 mV of the AGC setting signal are prepared.

  The memory unit 12 includes a non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read-Only Memory), and records a determination threshold value used by the control unit 11.

  In this embodiment, the value of the AGC voltage output from the RF_AGC circuit 13 and the value of the S meter voltage output from the electric field strength detection circuit 9 are used as parameters, and the RF_AGC circuit 13 is controlled by these values, so that RF The gain of the amplifier 3 is optimally controlled.

  A threshold value is provided for determining whether or not the AGC voltage output from the RF_AGC circuit 13 and the S meter voltage output from the electric field strength detection circuit 9 are within a predetermined range. The S meter voltage includes an S meter upper limit threshold (hereinafter abbreviated as S upper threshold) 20 that defines the upper limit value of the S meter voltage, and an S meter voltage that defines the lower limit value of the S meter voltage. The lower threshold (hereinafter abbreviated as S lower threshold) 21 is set. In this embodiment, 1.758 V is set as the S upper limit threshold 20, and 1.563 is set as the S lower limit threshold 21. Similarly, the AGC voltage also includes an AGC voltage upper limit threshold value (hereinafter abbreviated as AGC upper limit threshold value) 22 that defines the upper limit value of the AGC voltage, and an AGC voltage limit value that defines the lower limit value of the AGC voltage. A lower threshold (hereinafter abbreviated as AGC lower threshold) 23 is set. In the present embodiment, 0.43V is set as the AGC upper limit threshold 22, and 0.313V is set as the AGC lower limit threshold 23. These values are recorded in the memory unit 12. This determination threshold value is merely an example, and can be changed according to the receiver.

  When the value of the S meter voltage output from the electric field intensity detection circuit 9 is between the S upper threshold 20 and the S lower threshold 21 (for example, at T2 shown in FIG. 2), the control unit 11 Determines that the S meter voltage is within the normal range and does not perform control. Similarly, when the AGC voltage output from the RF_AGC circuit 13 is between the AGC upper limit threshold value 22 and the AGC lower limit threshold value 23 (at T2 shown in FIG. 2), the control unit 11 also sets the AGC voltage. Is determined to be within the normal range and control is not performed.

  However, when the value of the S meter voltage is lower than the value of the S lower limit threshold value 21 and the value of the AGC voltage exceeds the value of the AGC upper limit threshold value 22 (T1 shown in FIG. 2), the control unit 11 determines that it is abnormal, and switches the voltage value of the AGC setting signal. Similarly, when the value of the S meter voltage exceeds the value of the S upper limit threshold 20 and the value of the AGC voltage falls below the value of the AGC lower threshold 23 (T5 shown in FIG. 2), The control unit 11 determines that there is an abnormality and switches the voltage value of the AGC setting signal.

  When the value of the S meter voltage falls below the value of the S lower limit threshold value 21 and the value of the AGC voltage exceeds the value of the AGC upper limit threshold value 22, the electric field strength level of the desired channel is small, and the gain of the RF amplifier 3 Can also be determined to be small. Therefore, the control unit 11 performs control to change the voltage value of the AGC setting signal to a large value and increase the gain of the RF amplifier 3. However, if the voltage value of the AGC setting signal has already been set to the highest value before switching, the voltage value of the AGC setting signal is not changed.

  Further, when the value of the S meter voltage exceeds the value of the S upper limit threshold value 20 and the value of the AGC voltage falls below the value of the AGC lower limit threshold value 23, the electric field strength level of the desired channel is large and the RF amplifier 3 It can be determined that the gain is large. Therefore, the control unit 11 changes the voltage value of the AGC setting signal to a small value and performs control so as to lower the gain of the RF amplifier 3. However, if the voltage value of the AGC setting signal has already been set to the minimum value before switching, the voltage value of the AGC setting signal is not changed.

  Next, the operation of this embodiment will be described with reference to FIG. FIG. 2 shows the transition of the S meter voltage and the AGC voltage over time. When the electric field intensity level of the signal of the desired channel decreases due to movement or the like, this decrease in electric field intensity level is detected by the S meter voltage of the electric field intensity detection circuit 9. The RF_AGC circuit 13 increases the value of the AGC voltage and controls the gain of the RF amplifier 3 to be small since the value of the S meter voltage has decreased.

  Here, when T1 shown in FIG. 2 is reached, the value of the S meter voltage falls below the S lower limit threshold value 21 and the value of the AGC voltage exceeds the value of the AGC upper limit threshold value 22. Increase the voltage value. For example, the voltage is changed from 6 mV to 9 mV. Increasing the voltage value of the AGC setting signal increases the gain of the RF amplifier 3. Accordingly, since the signal level of the desired channel also increases, the value of the S meter voltage also increases, and the AGC voltage decreases (T2).

  At T3, the value of the S meter voltage again falls below the S lower limit threshold value 21, and the value of the AGC voltage exceeds the value of the AGC upper limit threshold value 22. Therefore, the control unit 11 increases the voltage value of the AGC setting signal. This time, change from 9mV to 12mV.

  Increasing the voltage value of the AGC setting signal increases the gain of the RF amplifier 3. Then, the signal level of the desired channel gradually increases, the value of the S meter voltage also increases, and the value of the AGC voltage decreases.

  At T5 shown in FIG. 2, since the value of the S meter voltage exceeds the S upper limit threshold value 20 and the value of the AGC voltage falls below the value of the AGC lower limit threshold value 23, the control unit 11 reduces the voltage value of the AGC setting signal. Lower. Change from the previously set 12 mV to 9 mV.

  In this manner, this embodiment can optimally set the gain of the RF amplifier 3 according to the values of the S meter voltage and the AGC voltage, and can satisfactorily receive the signal of the desired channel.

  The operation procedure of the control unit 11 will be described with reference to the flowchart shown in FIG. The control unit 11 inputs the S meter voltage of the signal of the desired channel from the electric field intensity detection circuit 9, and also inputs the AGC voltage from the RF_AGC circuit 13, and obtains an average value of these at predetermined intervals (step S1). By optimizing the AGC voltage in accordance with the state of the AGC voltage and the S meter voltage in a predetermined period, it is possible to reduce the influence of noise generated instantaneously.

  When the average value is obtained, the obtained S meter voltage and AGC voltage are compared with respective determination threshold values (step S2). First, it is compared whether or not the calculated average value of the S meter voltage is smaller than the S lower threshold 21 of the S meter voltage (step S3). If the average value of the S meter voltage is smaller than the S lower limit threshold value 21 (step S3 / YES), then whether or not the average value of the AGC voltage is larger than the AGC upper limit threshold value 22 of the AGC voltage. Determine. When the average value of the AGC voltage is larger than the AGC upper limit threshold 22 (step S4 / YES), when the set value of the AGC setting signal is not the maximum value (step S5 / NO), the AGC setting is made. The set value of the signal is changed to one larger AGC set value (step S6).

  When the average value of the S meter voltage is larger than the S lower limit threshold value 21 of the S meter voltage (step S3 / NO), or when the average value of the AGC voltage is smaller than the AGC upper limit threshold value 22 of the AGC voltage (Step S4 NO), the process proceeds to the next determination step. In this step, first, it is compared whether or not the average value of the S meter voltage is larger than the S upper limit threshold 20 of the S meter voltage (step S7). If the average value of the S meter voltage is larger than the S upper limit threshold 20 (step S7 / YES), then whether or not the average value of the AGC voltage is smaller than the AGC lower limit threshold 23 of the AGC voltage. Determine. When the average value of the AGC voltage is smaller than the AGC lower threshold 23 (step S8 / YES), when the set value of the AGC setting signal is not the minimum value (step S9 / NO), the AGC setting is made. The signal set value is changed to one smaller AGC set value (step S10).

  When the average value of the S meter voltage is smaller than the S upper limit threshold value 20 of the S meter voltage (step S7 / NO), or when the average value of the AGC voltage is larger than the AGC lower limit threshold value 23 of the AGC voltage (Step S8 NO), it is determined that the radio wave is received from the desired station at a desired level.

  FIG. 4 shows the value of the S meter voltage and the output of the FM receiver 1 when the receiving station is fixed and the signal level of the radio wave from the jamming station is increased.

  The value of the S meter voltage (dBuV) is shown on the left side of the graph shown in FIG. 4, and the output (dB) of the FM receiver 1 is shown on the right side. Further, the electric field strength level (dBuV) of the disturbing station increases from the left to the right in FIG.

  First, a case where the control of the present embodiment by the control unit 11 is not performed will be described. A broken line 50 shown in FIG. 4 indicates the value of the S meter voltage when the control operation by the control unit 11 is not performed, and a broken line 51 indicates an output of the FM receiver when the operation by the control unit 11 is not performed. . When the value of the S meter voltage decreases as shown in FIG. 4, the gain of the RF amplifier 3 is lowered by the AGC function of the RF_AGC circuit 13. By the gain control of the RF amplifier 3 by the RF_AGC circuit 13, the output itself of the FM receiver 1 is rapidly lowered as shown in FIG.

  In contrast, the present embodiment will be described. A broken line 52 shown in FIG. 4 indicates the value of the S meter voltage when the control operation by the control unit 11 is performed, and a broken line 53 indicates the operation by the control unit 11. The output of the FM receiver when doing is shown. When the value of the S meter voltage decreases and falls below the S lower limit threshold 21 and the value of the AGC voltage of the RF_AGC circuit 13 exceeds the AGC upper limit threshold 22, the control unit 11 controls the AGC setting signal. Change the voltage value to a larger value. Thereby, compared with the case where the control mentioned above is not performed, the sudden fall of the output of FM receiver 1 is prevented. Accordingly, the signal level of the desired channel can be kept good.

  The above-described embodiment is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention. For example, although the FM receiver is taken as an example in the above-described embodiments, an AM receiver may be used.

2 is a block diagram showing a configuration of an FM receiver 1. FIG. It is a figure which shows the change of the S meter voltage when not controlling, and the case where AGC voltage is controlled by the control part 11 using the determination threshold value. 4 is a flowchart showing an operation procedure of the control unit 11. It is a figure which shows the value of the S meter voltage when the receiving station is fixed and the signal level of the radio wave from the jamming station is raised, and the output of the FM receiver. It is a block diagram which shows the structure of the conventional FM receiver 100. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 FM receiver 2 Antenna 3 RF amplifier 4 1st band pass filter 5 Mixer 6 Local oscillation circuit 7 2nd band pass filter 8 IF amplifier 9 Electric field strength detection circuit 10 FM detection circuit 11 Control part 12 Memory part 13 RF_AGC circuit

Claims (4)

An amplifier for amplifying the input signal;
An automatic gain adjustment circuit for adjusting a gain of the amplifier by outputting a control signal according to a level of a signal output from the amplifier to the amplifier;
An electric field strength detection circuit for detecting an electric field strength at a desired frequency using a signal amplified by the amplifier;
The automatic gain to output a control signal for increasing the gain of the amplifier to the amplifier when the electric field strength is below a first threshold value and the voltage of the control signal exceeds a fourth threshold value. A control signal for controlling the adjustment circuit to lower the gain of the amplifier when the electric field strength exceeds a second threshold and the voltage of the control signal is lower than a third threshold; The automatic gain adjustment circuit is controlled to output and the electric field strength is within a predetermined range determined by the first threshold value and the second threshold value, or the voltage of the control signal is Control means that does not control the automatic gain adjustment circuit when it is within a predetermined range determined by the third threshold value and the fourth threshold value ;
Have,
The receiver , wherein the first threshold value is smaller than the second threshold value, and the third threshold value is smaller than the fourth threshold value . The automatic gain adjustment circuit outputs the control signal according to a set value,
The control means, by changing the pre SL setpoint, the receiver of claim 1, wherein the controller controls the automatic gain control circuit. The receiver according to any one of claims 1 to 3, wherein the control unit optimizes the control signal based on a state of the control signal and the electric field strength in a predetermined period. Outputting a control signal corresponding to the level of a signal output from an amplifier for amplifying an input signal to the amplifier, and adjusting a gain of the amplifier;
Detecting the electric field strength of a signal having a desired frequency using the signal amplified by the amplifier;
The automatic gain to output a control signal for increasing the gain of the amplifier to the amplifier when the electric field strength is below a first threshold value and the voltage of the control signal exceeds a fourth threshold value. A control signal for controlling the adjustment circuit to lower the gain of the amplifier when the electric field strength exceeds a second threshold and the voltage of the control signal is lower than a third threshold; The automatic gain adjustment circuit is controlled to output and the electric field strength is within a predetermined range determined by the first threshold value and the second threshold value, or the voltage of the control signal is A step of not controlling the automatic gain adjustment circuit when it is within a predetermined range determined by the third threshold and the fourth threshold ;
I have a,
The gain adjustment method , wherein the first threshold value is smaller than the second threshold value, and the third threshold value is smaller than the fourth threshold value .

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