JP4682851B2 - Squelch circuit and radio - Google Patents

Description

  The present invention relates to a squelch circuit that controls an audio output level in accordance with a noise level in an output of a detection circuit in a wireless device or the like.

  In general, FM radios are provided with a squelch circuit to prevent a loud noise from being output from a speaker based on unnecessary radio waves having a low signal level. The squelch circuit converts a noise component extracted from the FM detection signal by a band-pass filter into a DC voltage (hereinafter referred to as “squelch voltage”) having a value corresponding to the level using a rectifier circuit. Based on whether or not the value is equal to or greater than a predetermined threshold, this is a mechanism for stopping the output of the audio signal obtained by the detection to the speaker and releasing the stopped state (see, for example, Patent Document 1).

  FIG. 12 is a circuit diagram showing a squelch circuit of a radio device according to a conventional example. In this squelch circuit, a noise component included in the output of the detection circuit 11 is extracted by the bandpass filter 12, rectified by the rectifier circuit 13, and further smoothed by the capacitor C2, thereby obtaining the squelch voltage sp. I am doing so. The squelch voltage sp is supplied to the ADC input terminal 14 a of the microcomputer 14.

  The microcomputer 14 converts this squelch voltage sp into digital data by an AD converter and compares it with a predetermined threshold value. Then, an ON signal is sent to the amplifier 16 as an amplifier control signal ac if the squelch voltage sp is less than the threshold, and an OFF signal is sent if it is greater than or equal to the threshold. The amplifier 16 amplifies the output of the detection circuit 11 and supplies it to the speaker 17 only when the amplifier control signal ac is on. This prevents strong noise from being output from the speaker 17 when a valid signal (desired wave) is not included in the reception channel and the level of the noise component is high.

  Detection of whether or not the squelch voltage is equal to or higher than a predetermined threshold is generally performed in the microcomputer based on a value obtained by digitizing the squelch voltage with an AD converter as described above. However, the voltage output from the rectifier circuit of the squelch circuit is accompanied by a very high level noise component. For this reason, normally, as described above, a capacitor is inserted in front of the AD converter to remove the noise component, and only the DC component is taken out as a squelch voltage.

  On the other hand, the wireless device is provided with a function called scanning as a unique function. This function sequentially receives two or more set channels from among a plurality of channels each assigned a different frequency, and if there is no desired wave in the channel being received, receives the next channel, If there is no desired wave, repeat the operation of receiving the next channel, and if there is a desired wave in the channel being received, stay in that channel, detect the received signal and output the sound from the speaker Is.

  In addition to this, a desired wave is transmitted to a specially set channel (hereinafter referred to as “priority channel”) while detecting a received signal in a certain normal channel and outputting sound from a speaker. If the desired wave does not exist, return to the normal channel and continue detection, but if the desired wave exists, stay in the priority channel and start the new channel. There is a function called priority scan that starts detection at.

Japanese Patent No. 2998450

  However, according to the above-described prior art, the smoothing capacitor inserted in front of the AD converter causes a response delay in the squelch voltage with respect to fluctuations in the noise level. FIG. 13 shows the waveform of the squelch voltage input to the AD converter when the reception frequency is changed. In the figure, 131 is a squelch voltage waveform, and 132 is a UL (unlock) voltage waveform. The UL voltage is based on the operation of the local oscillator of the radio. At 3.3 [V], the reception frequency is fixed and the radio is receiving, and the voltage is 0.0 [V]. The reception frequency is being changed and is not fixed (unlocked), indicating that nothing is being received.

  As shown in the figure, the UL voltage is changed from 3.3 [V] to 0.0 [V] when the change of the reception frequency is started, and is changed to 3.3 [V] again when the change of the reception frequency is completed. Return. During this time, the squelch voltage has a value of about 3.3 [V] before the start of the change of the reception frequency. However, after the change of the reception frequency is completed, the squelch voltage is changed from a value of about 3.3 [V] to the original value after the change. It converges to a value of about 1 [V]. This convergence requires about 50 [msec]. Therefore, after the reception frequency is changed, it is necessary to provide a waiting time of about 50 [msec] until the microcomputer can determine the squelch voltage.

  In particular, when switching the reception frequency, no reception is performed during the transition period from the frequency before switching to the frequency after switching, so the noise level of the detection signal is maximized and the squelch voltage output by the rectifier circuit is the highest. Raised to a high level. For this reason, it takes a remarkable time for the squelch voltage to converge to the original DC voltage corresponding to the low noise level when receiving the desired wave from the high level due to the influence of the capacitor.

  Also, at the time of scanning or priority scanning, a squelch voltage is used to determine the presence or absence of a desired wave, but as described above, a smoothing capacitor is used to obtain a squelch voltage. Even after starting, the original squelch voltage cannot be obtained. Therefore, it is necessary to provide a predetermined waiting time from the start of reception until the presence / absence of a desired wave is determined. For this reason, since a certain time is required when scanning a channel having no desired wave, the scanning speed cannot be improved. Further, during priority scanning, the reception sound of the normal channel is interrupted when there is no desired wave in the priority channel.

  In particular, according to the IMBE (Multi-Band Excitation) vocoder (speech encoder / decoder) adopted by the radio equipment compliant with the APCO P25 (ACPO project 25) method, even when the received signal no longer exists, If it is within a certain time from that time, for example, 38 [msec], the output of the received sound can be continued in a pseudo manner by performing prediction and interpolation based on the audio signal before that time. Therefore, even when priority scanning is performed, if there is no desired wave in the priority channel and if the time to return to the normal channel being received is 38 [msec] or less, the normal channel sound is not interrupted. Output from the speaker can be continued. However, in practice, due to the waiting time required due to the smoothing capacitor of the squelch circuit, the state in which the reception signal is interrupted continues for 38 [msec] or more, so that the sound output of the normal channel is interrupted.

  FIG. 14 is a timing chart showing this situation. Until a time t1, a certain normal channel is received. During this time, sound based on the sound signal 141 obtained by decoding the received signal is output from the speaker. When the priority scan is started at time t1, the UL voltage becomes 0.0 [V] and nothing is received, so that the noise level at the output of the detection circuit becomes the highest value and the squelch voltage is the highest. Raised to level.

  When 13 [msec] elapses from time t1 and reaches time t2, the change to the priority channel is completed, the UL voltage becomes 3.3 [V], and the reception operation in the priority channel is started. Thereafter, the squelch voltage spends 50 [msec] and converges to the original value at time t4. In this case, since this value is larger than the predetermined threshold, it is determined that there is no valid received signal in the priority channel, and the change to the normal channel is started.

  When the change to the normal channel is started at time t4, the squelch voltage is similarly raised to the highest level. When 13 [msec] elapses and the change to the normal channel is completed at time t5, the audio output based on the audio signal 144 obtained by decoding the received signal in the normal channel is started, the priority scan is completed, Thereafter, the squelch voltage similarly converges to the original value.

  During the period from time t1 to time t5, reception on the normal channel cannot be performed. For this reason, during the period from time t1 to time t3 after 38 [msec] has elapsed, audio output based on the audio signal 142 interpolated by the vocoder described above is performed. In the subsequent period from time t3 to t5, since 38 [msec] has elapsed since the reception of the normal channel was stopped, the voice signal is not interpolated by the vocoder, and the voice is interrupted 143.

  An object of the present invention is to make it possible to more quickly determine a squelch voltage after changing a reception channel in view of the problems of the conventional technology.

  To achieve the above object, the first invention provides a rectifier circuit that rectifies a noise component based on an output of a detector circuit of a receiver, a smoothing capacitor that uses the rectified noise component as a smoothed DC voltage, The present invention relates to a squelch circuit including control means for performing on / off control of an audio output based on an output of a detection circuit based on a comparison result between a voltage value of a DC voltage and a predetermined threshold voltage value. This squelch circuit comprises voltage fixing means for fixing the voltage value of the DC voltage to a predetermined voltage level from the start of the change of the reception frequency in the receiver or a predetermined time thereafter until the change is completed. Features. Here, the receiver corresponds to, for example, a receiver constituting an FM radio. For example, a frequency discriminator corresponds to the detection circuit.

  In this configuration, in the conventional case where there is no voltage fixing means, when the change of the reception frequency in the receiver is started, no signal is received, and the noise level at the output of the detection circuit becomes the maximum value. Therefore, the voltage value of the smoothed DC voltage is also raised to the highest level. When the change of the reception frequency is completed, if there is a reception signal at the reception frequency, the noise level at the output of the detection circuit is lowered, so that the voltage value of the smoothed DC voltage is also lowered correspondingly. Because of the action of the smoothing capacitor, a value corresponding to the noise level cannot be taken immediately, and a predetermined period is required until it converges to its original value. For this reason, the determination about a squelch voltage cannot be performed rapidly. Therefore, the receiver cannot quickly determine the presence or absence of a valid received signal whose sound output is turned on by the control means after the reception frequency is changed.

  On the other hand, according to the present invention, the voltage value of the DC voltage is fixed at a predetermined voltage level from the start of the change of the reception frequency in the receiver or a predetermined time thereafter until the change is completed. After completion of the change of the reception frequency, convergence is performed from the fixed voltage level to the DC voltage level corresponding to the noise level after completion of the change. Therefore, by appropriately setting the predetermined voltage level, it is possible to shorten the period until convergence and quickly determine the squelch voltage. Therefore, the receiver can more quickly determine whether there is a valid received signal after changing the reception frequency.

  The squelch circuit according to a second invention is characterized in that, in the first invention, the predetermined voltage level is equal to the threshold voltage value.

  The squelch circuit according to a third invention is the squelch circuit according to the first or second invention, wherein the voltage fixing means is based on a signal indicating start and completion of change of the reception frequency obtained based on the operation of the local oscillator of the receiver. The voltage value is fixed during a period from the change start time to the completion time.

  The squelch circuit according to a fourth invention is the squelch circuit according to any one of the first to third inventions, wherein the voltage fixing means is a voltage supply means for supplying a voltage of the predetermined voltage level, and between the voltage supply means and the smoothing capacitor. The voltage value is fixed by turning on the switch. Here, the switch includes, for example, a switch using a transistor and a relay switch.

  A squelch circuit according to a fifth aspect of the present invention is the squelch circuit according to any one of the first to third aspects, provided between the microcomputer having the ADC input terminal and the DAC output terminal, and between the DAC output terminal and the smoothing capacitor. The microcomputer functions as the control means based on the smoothed DC voltage applied to the ADC input terminal, and outputs the voltage of the predetermined voltage level from the DAC output terminal. It functions as the voltage fixing means by controlling.

  A squelch circuit according to a sixth aspect of the present invention is the squelch circuit according to any one of the first to third aspects, comprising a microcomputer having terminals that are used for both ADC input and DAC output, and the microcomputer inputs the terminals to the ADC. Functioning as the control means by accepting the input of the smoothed DC voltage from the terminal, and outputting the voltage of the predetermined voltage level from the terminal using the terminal as a DAC output. It functions as the voltage fixing means.

  The squelch circuit according to a seventh invention is the squelch circuit according to any one of the first to third inventions, wherein the voltage fixing means is based on a predetermined power supply voltage, a forward voltage of the diode, a pinch-off voltage of the Zener diode, or an output voltage of the shunt regulator. The voltage value is fixed.

  A radio device according to an eighth aspect of the present invention includes any one of the first to seventh squelch circuits, and after the reception frequency is changed, the squelch circuit receives an effective signal whose sound output is turned on. It is characterized by comprising means for judging whether or not based on the smoothed DC voltage in the squelch circuit, and having a function of performing scanning using this judgment means. As the scan, for example, if there is a channel in which two or more channels set in advance are sequentially received and a valid signal is received, scanning that switches to reception of that channel and priority scanning are applicable.

  According to the present invention, the voltage value of the smoothed DC voltage (squelch voltage) is fixed to a predetermined voltage level from the start of the change of the reception frequency in the receiver or a predetermined time thereafter until the change is completed. Since it did in this way, the determination about this DC voltage after the change of a receiving channel can be performed more rapidly. Therefore, in the receiver provided with the squelch circuit of the present invention, it is possible to quickly determine the presence or absence of a valid received signal after changing the reception frequency, and to improve the scanning operation speed. In addition, sound interruption during priority scanning can be prevented.

  FIG. 1 is a circuit diagram showing a configuration of a squelch circuit in a wireless device according to the first embodiment of the present invention. In the figure, 11 is a detection circuit that detects a signal from an antenna and outputs a demodulated audio signal sd, 12 is a bandpass filter that extracts a noise component based on the output of the detection circuit 11, and 13 is a bandpass filter 12. A rectifier circuit that rectifies the output of the rectifier circuit, C2 is a smoothing capacitor that smoothes the output of the rectifier circuit 13, 14 is a microcomputer that controls each part of the apparatus based on the output sp of the smoothed rectifier circuit 13, and 15 is a microcomputer 14 A switch provided between the ADC input terminal 14a and the DAC output terminal 14b, 16 an audio amplifier that amplifies the audio signal sd from the detection circuit 11, and 17 a speaker that converts the audio signal from the audio amplifier 16 into a sound wave signal. It is.

  The rectifier circuit 13 includes two diodes D1 and D2 connected in series between the ADC input terminal 14a and the ground, a resistor R1 connected in parallel to the series circuit, and a connection point and a band of the diodes D1 and D2. The capacitor C1 provided between the pass filter 12 is provided. The diodes D1 and D2 are provided in the forward direction toward the ADC input terminal 14a.

  This wireless device is compliant with the APCO P25 (ACPO project 25) system, and includes an IMBE (Multi-Band Excitation) system vocoder (speech encoder / decoder). This vocoder performs prediction and interpolation processing on the interrupted signal portion based on the previous audio signal even if the received signal is instantaneously interrupted within a certain time, for example, 38 [msec]. It has a function that can continue to output the audio signal without interruption.

  In this configuration, when the reception signal of the designated channel is supplied to the detection circuit 11, the detection circuit 11 performs detection based on the reception signal and outputs the obtained audio signal sd to the amplifier 16. The amplifier 16 amplifies the audio signal sd and supplies it to the speaker 17. On the other hand, the bandpass filter 12 extracts a noise component based on the output sd of the detection circuit 11 and supplies it to the rectifier circuit 13. The rectifier circuit 13 outputs a squelch voltage sp as a DC voltage according to the level of the noise component. The squelch voltage sp is smoothed by the capacitor C2 and supplied to the microcomputer 14 through the ADC input terminal 14a.

  The microcomputer 14 AD-converts the squelch voltage sp, compares it with the determination threshold voltage, for example, 1 [V], and sends the amplifier control signal ac to the amplifier 16 based on the comparison result. That is, in this example, an off signal is sent to the amplifier 16 when the squelch voltage sp is 1 [V] or more, and an on signal is sent to the amplifier 16 when it is less than 1 [V]. The amplifier 16 outputs the amplified audio signal sd to the speaker 17 when the amplifier control signal ac is on, and does not output it when it is off. Further, the microcomputer 14 always outputs 1 [V] equal to the determination threshold voltage after DA conversion from the DAC output terminal 14b.

  The radio unit observes the operation of a local oscillator that generates a local oscillation frequency to be used for frequency conversion of a received signal. When receiving any channel, 3.3 V is received. If not, 0.0 [V] is given to the microcomputer 14 as a UL signal. The microcomputer 14 outputs a switch control signal sc for opening the switch 15 when the UL signal is 3.3 [V] and closing when the UL signal is 0.0 [V].

  FIG. 2 shows a waveform example of the voltage applied to the ADC input terminal 14a and the UL signal when the reception frequency is changed. In the figure, 21 is the waveform of the voltage applied to the ADC input terminal 14a, and 22 is the waveform of the UL signal. This figure shows a case where the squelch voltage before changing the reception frequency is about 3.5 [V] and the squelch voltage after changing the reception frequency is 1 [V]. Before the change of the reception frequency is started, the UL signal is 3.3 [V], and the microcomputer 14 opens the switch 15. Therefore, the squelch voltage before changing the reception frequency is applied to the ADC input terminal 14a as it is.

  When the change of the reception frequency is started, nothing is received, so the UL signal becomes 0.0 [V]. In response to this, the microcomputer 14 closes the switch 15. As a result, the voltage 1 [V] at the DAC output terminal 14b is applied to the ADC input terminal 14a as it is.

  Thereafter, when the reception frequency is determined and the reception operation is started, the UL signal becomes 3.3 [V]. In response to this, the microcomputer 14 opens the switch 15. Then, the voltage of the ADC input terminal 14a starts from 1 [V] and converges to the squelch voltage after changing the reception frequency. However, in the example of FIG. 2, since the squelch voltage after changing the reception frequency is just 1 [V], it converges immediately.

  FIG. 3 shows a waveform 31 of the voltage at the ADC input terminal 14a and a waveform 32 of the UL signal in the same case as in the example of FIG. 2 except that the squelch voltage after changing the reception frequency is 0.7 [V]. . The waveform 32 of the UL signal is the same as in FIG. The waveform 31 of the voltage at the ADC input terminal 14a is the same as that in FIG. 2 until the change is completed, but the change is completed, the reception frequency is determined, the reception operation is started, and the switch 15 is closed. When the open state is changed from 1 to V, it converges to a squelch voltage of 0.7 [V] starting from 1 [V]. However, since 1 “V” as the base point is the same as the determination threshold voltage 1 [V] for the squelch voltage, the microcomputer 14 immediately determines that the squelch voltage is less than 1 [V], and changes the value after the change. It is possible to recognize that there is an audio signal effective in frequency, or to enable listening after changing the reception frequency by turning on the amplifier control signal ac.

  FIG. 4 shows the voltage waveform 41 of the ADC input terminal 14a and the waveform 42 of the UL signal in the same case as in the example of FIG. 2 except that the squelch voltage after changing the reception frequency is 1.5 [V]. . The waveform 42 of the UL signal is the same as in FIG. The waveform 41 of the voltage at the ADC input terminal 14a is the same as that in FIG. 2 until the change is completed. However, the change is completed, the reception frequency is determined, the reception operation is started, and the switch 15 is closed. When the open state is set to 1, the voltage converges to a squelch voltage of 1.5 [V] starting from 1 [V]. However, since 1 “V” as the base point is the same as the determination threshold voltage 1 [V] for the squelch voltage, the microcomputer 14 immediately determines that the squelch voltage is 1 [V] or more, and the amplifier control signal It is possible to turn off ac to prevent noise from being output from the speaker 17 or to recognize that there is no effective audio signal at the changed frequency.

  FIG. 5 is a timing chart showing the operation during priority scanning in the apparatus of FIG. In the figure, the waveforms of the UL voltage, the switch control signal sc, the squelch voltage sp, and the audio signal output to the speaker 17 are shown in order from the top. The period up to time T1 is the period for receiving the normal channel, the period from time T1 to T2 is the period for switching from the normal channel to the priority channel, and the period from time T2 to T3 is the effective reception in the priority channel. A period for confirming the presence or absence of a signal, a period from time T3 to T4, is a period for switching from the priority channel to the normal channel, and a period after time T4 is a period for receiving the normal channel.

  Since the UL voltage is 3.3 [V] during the period up to T1 during which the normal channel is received, the microcomputer 14 opens the switch 15. Therefore, during this period, the squelch voltage sp is applied to the ADC input terminal 14a of the microcomputer 14. During this time, if the squelch voltage is less than 1 [V], the microcomputer 14 sends an ON signal to the amplifier 16 because the level of the noise component is low. In response to this, the amplifier 16 amplifies the audio signal from the detection circuit 11 and supplies it to the speaker 17. That is, since the audio signal 51 obtained by decoding the received signal in the normal channel is supplied to the speaker 17, the user can listen to the received voice in the normal channel.

  When the time T1 for starting the switching to the priority channel arrives, since the UL voltage is changed from 3.3 [V] to 0.0 [V], the microcomputer 14 switches the switch 15 to the ON state. Thereby, the voltage of the ADC input terminal 14a is fixed to the voltage 1 [V] of the DAC output terminal 14b. Thereafter, when the switching to the priority channel is completed at time T2, the UL voltage becomes 3.3 [V], so the microcomputer 14 switches the switch 15 to the OFF state. In response to this, the voltage at the ADC input terminal 14a starts to converge toward the original squelch voltage in the priority channel, starting from 1 [V]. Therefore, as shown in the figure, if the squelch voltage is 1 [V] or higher, the microcomputer 14 can immediately determine that.

  If it is determined that the squelch voltage is 1 [V] or higher, this means that there is no valid signal in the priority channel, and there is only a large noise. Control to return to the normal channel. As a result, switching to the normal channel starts. Accordingly, since the UL voltage becomes 0.0 [V], the microcomputer 14 turns on the switch 15 and fixes the squelch voltage to 1 [V]. When the channel switching is completed at time T4, since the UL voltage becomes 3.3 [V], the microcomputer 14 turns off the switch 15. In response to this, the squelch voltage starts to converge from 1 [V] to its original value. If the squelch voltage is less than 1 [V], the microcomputer 14 determines that immediately after time T4 and sends an ON signal to the amplifier 16. As a result, the supply of the audio signal 53 obtained by decoding the reception signal through the normal channel is started again to the speaker 17.

  During this period, since the normal channel cannot be received during the period from time T1 to time T4, the radio apparatus supplies the speaker 17 with the audio signal 52 predicted and interpolated by the decoder.

  According to the present embodiment, the squelch voltage is fixed to be the same voltage value as the determination threshold for the squelch voltage during the switching of the reception channel. This determination can be made immediately. Therefore, the presence / absence of an effective received signal on each channel in the scan operation can be determined in a short time. For this reason, the priority channel can be checked in a short time during the priority scan, so that it is possible to prevent the interruption of sound that has conventionally occurred from the start of the scan to the return to the reception of the original normal channel.

  For example, if 13 [msec] is required from time T1 to T2 (t1 to t2 in FIG. 14), according to the conventional example of FIG. 14, the change of the reception frequency is completed and the UL voltage is 3.3 [ V], and since it takes 50 [msec] for the squelch voltage to converge to 1 [V] which is the determination threshold voltage from the high voltage value at that time, a total of 63 [msec] is required for one channel scan And That is, the number of channels that can be referred to in one second is 15 channels. In the priority scan, the time required to refer to the priority channel away from the normal channel is 76 (= 13 + 50 + 13) [msec]. Since this time exceeds 38 [msec] that can be predicted and interpolated by the IMBE vocoder, the reception voice is interrupted.

  On the other hand, according to the present embodiment, since the squelch voltage is fixed at 1 [V] when the change of the reception frequency is completed, the microcomputer 14 can determine the squelch voltage almost without waiting. it can. For example, if it takes 10 [msec] to read and determine the squelch voltage, the time required to scan one channel is 23 (= 13 + 10) [msec]. 43 channels can be referenced per second. In the priority scan, the time for referring to the priority channel away from the normal channel is 36 (= 13 + 10 + 13) [msec] as shown in FIG. This is shorter than 38 [msec] in which the sound of the normal channel can be predicted and interpolated by the IMBE vocoder, and therefore, the priority channel is observed without causing any interruption in the received voice using the vocoder. be able to.

  FIG. 6 is a circuit diagram showing a squelch circuit of a radio device according to the second embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same elements. In FIG. 6, Tr is a field effect transistor as a switching element connected between the ADC input terminal 14a and the DAC output terminal 14b, R2 is a discharge resistor connected between the gate and source of the transistor Tr, and D3 is This is a diode whose anode side is connected to the gate of the transistor Tr.

  In the embodiment of FIG. 1, on / off of the connection between the ADC input terminal 14a and the DAC output terminal 14b is controlled by the switch 15, in the present embodiment, this control is performed by the transistor Tr. ing. A switch control signal sc for controlling on / off of the transistor Tr is given through a diode D3. Other points are the same as those in the embodiment of FIG.

  FIG. 7 is a circuit diagram showing a squelch circuit of a radio device according to the third embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same elements. In FIG. 7, reference numeral 71 denotes a relay connected between the ADC input terminal 14a and the DAC output terminal 14b. In the embodiment of FIG. 1, on / off of the connection between the ADC input terminal 14a and the DAC output terminal 14b is controlled by the switch 15, whereas in the present embodiment, the connection is controlled by the relay 71. Yes. Other points are the same as those in the embodiment of FIG.

  FIG. 8 is a circuit diagram showing a squelch circuit of a radio device according to the fourth embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same elements. In FIG. 8, reference numeral 81 denotes a local oscillation circuit for frequency conversion included in the wireless device. The local oscillation circuit 81 has a function of outputting the above-described UL signal, and supplies the UL signal to the switch 15. That is, in the embodiment of FIG. 1, the microcomputer 14 controls the switch 15 based on the UL signal, whereas in the present embodiment, the switch 15 is directly controlled by the UL signal from the local oscillation circuit 81. I have to. Other points are the same as those in the embodiment of FIG.

  FIG. 9 is a circuit diagram showing a squelch circuit of a radio device according to the fifth embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same elements. In FIG. 9, 91 is a terminal used for both ADC input and DAC output. In the embodiment of FIG. 1, on / off of the connection between the ADC input terminal 14a and the DAC output terminal 14b is controlled by the switch 15, in the present embodiment, a function similar to this is achieved by the terminal 91. Is switched to ADC input or DAC output.

  That is, a microcomputer in which one terminal can be arbitrarily switched and used for DAC output and ADC input is well known. In this embodiment, such a microcomputer 14 is used. According to this, the terminal 91 is used for ADC input at the same timing as when the switch 15 is turned off, and is used to input a squelch voltage, and the terminal 91 is output as a DAC at the same timing as when the switch 15 is turned on. For use, the same function as in the embodiment of FIG. 1 can be performed by using it to output 1 [V]. In this case, the squelch circuit itself is the same as the conventional squelch circuit in FIG. Other points are the same as those in the embodiment of FIG.

  FIG. 10 is a circuit diagram showing a squelch circuit of a radio device according to the sixth embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same elements. In FIG. 10, D4 is a diode whose anode side is connected to the ADC input terminal 14a. In the embodiment of FIG. 1, 1 [V] of the same level as the determination threshold voltage for the squelch voltage is output from the DAC output 14b. However, in this embodiment, the DAC output is not used as this voltage. In addition, other fixed voltages are used.

  That is, a control signal cs based on the UL voltage is applied to the cathode side of the diode D4, a reverse bias is applied when the UL voltage is 3.3 [V], and a forward direction when the UL voltage is 0.0 [V]. A bias is applied. While the forward bias is applied, the forward voltage of the diode D4 is applied as a fixed voltage to the ADC input terminal 14a. About another point, it is the same as that of the case of embodiment of FIG.

  FIG. 11 is a circuit diagram showing a squelch circuit of a radio device according to the seventh embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same elements. In the embodiment of FIG. 1, 1 [V] of the same level as the determination threshold voltage for the squelch voltage is output from the DAC output 14b. However, in this embodiment, the DAC output is used as this voltage. Instead, other fixed voltages are used.

  That is, a series circuit of a switch SW and a Zener diode D5 is provided between the ADC input terminal 14a of the microcomputer 14 and the ground, and the switch SW is turned on when the UL voltage is 0.0 [V]. V] is controlled to be turned off. While the switch SW is on, the voltage of the ADC input terminal 14a is controlled to 1 [V] by the pinch-off voltage of the Zener diode D5. Other points are the same as those in the embodiment of FIG. In addition, as a method for applying a fixed voltage to the ADC input terminal 14a of the microcomputer 14, a method using a shunt regulator or the like is also conceivable.

It is a circuit diagram which shows the structure of the squelch circuit in the radio | wireless machine which concerns on the 1st Embodiment of this invention. It is a figure which shows the waveform example of the voltage applied to the ADC input terminal of a microcomputer when a receiving frequency is changed in the radio | wireless machine of FIG. 1, and UL signal. 1 shows the waveform of the voltage at the ADC input terminal and the waveform of the UL signal in the same case as in the example of FIG. 2 except that the squelch voltage after changing the reception frequency is 0.7 [V] in the wireless device of FIG. FIG. 1 shows the waveform of the voltage at the ADC input terminal and the waveform of the UL signal in the same case as in the example of FIG. 2 except that the squelch voltage after changing the reception frequency is 1.5 [V] in the wireless device of FIG. FIG. 3 is a timing chart showing an operation during priority scanning in the apparatus of FIG. 1. It is a circuit diagram which shows the squelch circuit of the radio | wireless machine which concerns on the 2nd Embodiment of this invention. It is a circuit diagram which shows the squelch circuit of the radio | wireless machine which concerns on the 3rd Embodiment of this invention. It is a circuit diagram which shows the squelch circuit of the radio | wireless machine which concerns on the 4th Embodiment of this invention. It is a circuit diagram which shows the squelch circuit of the radio | wireless machine which concerns on the 5th Embodiment of this invention. It is a circuit diagram which shows the squelch circuit of the radio | wireless machine which concerns on the 6th Embodiment of this invention. It is a circuit diagram which shows the squelch circuit of the radio | wireless machine which concerns on the 7th Embodiment of this invention. It is a circuit diagram which shows the squelch circuit of the radio | wireless machine which concerns on a prior art example. FIG. 13 shows a waveform of a squelch voltage input to the AD converter when the reception frequency is changed in the wireless device of FIG. FIG. 13 is a timing chart showing a situation in which interruptions occur in normal channel audio output in the wireless device of FIG. 12.

Explanation of symbols

11: detector circuit, 12: band pass filter, 13: rectifier circuit, 14: microcomputer, 14a: ADC input terminal, 14b: DAC input terminal, 15: switch, 16: amplifier, 17: speaker, 21, 31, 41, 131: ADC input voltage waveform, 22, 32, 42, 132: UL signal waveform, 51-53, 141, 142, 144: Audio signal waveform, 71: Relay, 81: Local oscillator circuit, 91: Terminal, 143: State in which sound is interrupted, C1, C2: Capacitor, D1 to D4: Diode, D5: Zener diode, R1, R2: Resistance, SW: Switch, Tr: Transistor

Claims (7)

A noise extracting means for extracting a noise component based on an output of a detector circuit of the receiver; a rectifying circuit for rectifying the extracted noise component; a smoothing capacitor for converting the rectified noise component into a smoothed DC voltage; In a squelch circuit comprising control means for performing on / off control of audio output based on the output of the detection circuit based on a comparison result between a voltage value of a DC voltage and a predetermined threshold voltage value,
A squelch comprising voltage fixing means for fixing a voltage value of the DC voltage to the threshold voltage value from a start time of a change of the reception frequency in the receiver or a predetermined time after that to a time when the change is completed. circuit. The voltage fixing means fixes the voltage value during a period from the reception frequency change start time to the completion time based on a signal indicating the start and completion of the change of the reception frequency obtained based on the operation of the local oscillator of the receiver. The squelch circuit according to claim 1, wherein: The voltage fixing means includes a voltage supply means for supplying a voltage of the threshold voltage value , and a switch provided between the voltage supply means and the smoothing capacitor, and the voltage value is fixed by turning on the switch. The squelch circuit according to claim 1 or 2 , wherein A microcomputer having an ADC input terminal and a DAC output terminal; and a switch provided between the DAC output terminal and the smoothing capacitor, wherein the microcomputer is applied to the ADC input terminal. It functions as the control means based on a DC voltage, and also functions as the voltage fixing means by outputting the voltage of the threshold voltage value from the DAC output terminal and controlling the switch. The squelch circuit according to claim 1 or 2 . A microcomputer having a terminal for both ADC input and DAC output, the microcomputer using the terminal for ADC input and receiving the smoothed DC voltage input from the terminal; functions as means, with the terminal for the DAC output, in claim 1 or 2, characterized in that functions as the fixed voltage means by outputting a voltage of the threshold voltage from the terminal The squelch circuit described. It said voltage clamp means comprises a predetermined power supply voltage, the forward voltage of the diode, the pinch-off voltage of the zener diode, or the output voltage of the shunt regulator according to 1 or 2, characterized in that performs a fixing of the voltage value Squelch circuit. A squelch circuit according to any one of claims 1 to 6 , wherein after the reception frequency is changed, whether or not an effective signal whose sound output is turned on is received by the squelch circuit is smoothed by the squelch circuit. A wireless device comprising means for making a determination based on the converted DC voltage, and having a function of performing a scan using the determination means.

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