JP2008294790A - Receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiver capable of reducing dissonant noise generated in non-input even when an antenna amplifier is used. <P>SOLUTION: In the receiver 1, received frequencies are searched from an upper limit to a lower limit, the minimum voltage level among voltage levels of an S meter signal output from an intermediate frequency amplifier circuit 6 is stored in a memory of a microcomputer 13, the optimal curve is selected from a plurality of mute curves stored in the memory of the microcomputer 13 based on the minimum voltage level and a mute circuit 8 is operated based on the curve. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a receiving apparatus that receives a broadcast wave, converts it into an audio signal, and outputs it, and more particularly to a receiving apparatus that includes an antenna amplifier.

  FIG. 1 shows a configuration of a receiving apparatus that receives a conventional radio broadcast. 1 includes an antenna 101, an antenna amplifier 102, an RF amplification circuit 103, a front end 104, an intermediate frequency amplification circuit 105, a detection circuit 106, a mute circuit 107, and a stereo separation circuit 108. An audio amplifier 109, a speaker 110, a PLL circuit 111, and a microcomputer 112.

  The antenna amplifier 102 amplifies the received signal to a predetermined level and outputs the amplified signal to the RF amplifier circuit 103 in order to increase the sensitivity of the received signal received by the antenna 101.

  The RF amplifier circuit 103 selects and amplifies a desired station from the input received signal and outputs it to the front end 104.

  The front end 104 converts the received signal of the desired station input from the RF amplifier circuit 103 from the frequency of the carrier wave to a constant frequency (intermediate frequency) using the signal input from the PLL circuit 111, and the intermediate frequency amplifier circuit 105. Output to.

  The intermediate frequency amplification circuit 105 amplifies the signal converted to the intermediate frequency by the front end 104 to a level that can be demodulated by the detection circuit 106 and outputs the amplified signal to the detection circuit 106. Further, the intermediate frequency amplifier circuit 105 generates an S meter signal that is a signal representing the intensity of the received electric field from the signal converted to the intermediate frequency and outputs the S meter signal to the mute circuit 107.

  The detection circuit 106 demodulates the signal converted to the intermediate frequency into an audio signal and outputs it to the mute circuit 107.

  The mute circuit 107 mutes (attenuates the signal) the audio signal input from the detection circuit 106 based on the voltage level of the S meter signal input from the intermediate frequency amplifier circuit 105, and supplies it to the stereo separation circuit 108. Output.

  The stereo separation circuit 108 separates the audio signal input from the mute circuit 107 into a right channel (Rch) and a left channel (Lch), and outputs the separated signal to the audio amplifier 109.

  The audio amplifier 109 amplifies the audio signal separated into Rch and Lch by the stereo separation circuit 108 to a predetermined level. The audio signal amplified by the audio amplifier 109 is output from the speaker 110 as audio.

  The PLL circuit 111 is a phase synchronization circuit, and outputs a signal for converting a received signal of a desired station to an intermediate frequency to the front end 104 according to an instruction from the microcomputer 112.

  The microcomputer 112 is a microcomputer having a CPU and a memory (not shown) incorporated therein, and instructs the PLL circuit 111 to output a signal for controlling the entire receiving apparatus 100 and converting the carrier frequency of the desired station into an intermediate frequency. .

  When the receiving device 100 having the above-described configuration is mounted on a vehicle or the like as a radio receiver, for example, when the electric field strength of a broadcast wave received through a tunnel or the like decreases, the receiving device 100 mutes based on the S meter signal indicating the electric field strength. The level of the audio signal input to the circuit 107 is attenuated to reduce annoying noise (noise) that occurs when there is no input (when a broadcast wave cannot be received).

  In particular, in the receiving device 100 mounted on a moving body such as a vehicle, the antenna amplifier 102 is used to improve the sensitivity because the sequential reception situation changes. However, when the antenna amplifier 102 is used, there is a problem that the noise floor of the received signal increases due to the residual noise of the antenna amplifier 102 and the CN (ratio of carrier wave to noise) decreases.

For such a problem, a receiving device described in Patent Document 1 has been proposed. The receiving apparatus described in Patent Literature 1 includes a desired station level detection unit 4 that detects a signal level of a desired station, a lower level detection unit 5 that detects a signal level of a frequency band adjacent to the lower side of the desired station, An upper level detection unit 6 that detects a signal level in a frequency band adjacent to the upper side of the desired station, and a frequency characteristic control unit 8 that controls the frequency characteristic of the frequency characteristic variable unit 7 according to the detected level. The CN of the input signal is detected according to the level, and when CN is lowered, the amount of attenuation of the high frequency component of the frequency characteristic of the frequency characteristic variable unit 7 is increased to reduce the sense of harshness on hearing.
JP 2006-253886 A

  However, the receiving device described in Patent Document 1 is effective in reducing noise when there is an adjacent station in the desired station. However, when there is no input such as when the vehicle enters a tunnel, the signal level of the desired station is obtained. However, since the signal levels of adjacent stations are equal, the effect of reducing noise cannot be obtained. In addition, when an antenna amplifier is connected, there is no effect to make the noise at the time of no input equal to that when there is no antenna amplifier, so there is an annoying noise due to the residual noise of the antenna amplifier generated at the time of no input. There was a problem that it could not be reduced.

  Therefore, an object of the present invention is to provide a receiving apparatus that can reduce annoying noise that occurs when no input is used, for example, even when an antenna amplifier is used.

  In order to solve the above-described problem, a receiving device according to claim 1 is an antenna amplifier that amplifies a received signal received by an antenna, receiving means that selects a received signal of a specified frequency, and demodulates the received signal. The demodulating means for outputting the audio signal, the electric field intensity detecting means for detecting the electric field intensity of the selected received signal from the received signal selected by the receiving means, and the output level of the audio signal demodulated by the demodulating means And attenuating means for attenuating based on the electric field strength detected by the electric field strength detecting means, in order to cause the electric field strength detecting means to detect the electric field strength in a predetermined predetermined frequency band. A search means for searching for a frequency band in a predetermined range; and a minimum electric power detected by the electric field strength detection means in the frequency band of the predetermined range searched by the search means. A minimum electric field strength storage means for storing the strength; and an attenuation amount changing means for changing the attenuation amount of the attenuation means based on the minimum electric field strength stored by the minimum electric field strength storage means. Yes.

  Hereinafter, a receiving apparatus according to an embodiment of the present invention will be described. In the receiving apparatus according to the embodiment of the present invention, the search means searches for a predetermined frequency band within a predetermined range, and the minimum electric field strength detected as a result of the search is stored and stored in the minimum electric field strength storage means. The attenuation amount changing means changes the attenuation amount of the attenuation means based on the minimum electric field strength. By doing this, if the minimum electric field strength (the electric field strength at the time of no input) is increased due to the influence of noise or the like by the antenna amplifier, it can be changed to increase the amount of attenuation. The annoying noise that sometimes occurs can be reduced.

  Further, the attenuation amount changing means may be selected from a plurality of preset attenuation patterns based on the minimum electric field intensity stored in the minimum electric field intensity storage means. By doing in this way, annoying noise can be reduced by an appropriate attenuation pattern according to the electric field strength at the time of no input.

  The plurality of attenuation patterns may be configured such that the attenuation amount when the electric field strength detected by the electric field strength detecting unit decreases as the minimum electric field strength stored in the minimum electric field strength storing unit increases. Good. In this way, when the electric field strength at the time of no input is high due to noise or the like, when the electric field strength becomes low during actual reception, the attenuation means is changed to increase the attenuation amount. Can do.

  Further, the range from the upper limit to the lower limit of the frequency that can be received by the receiving means may be searched. By doing in this way, the electric field strength detection means can detect the electric field strength at the frequency where there is no broadcast wave or the like in the range from the upper limit to the lower limit of the receivable frequency (when no input), and store it as the minimum electric field strength Even if the noise level is increased due to the influence of an antenna amplifier or the like, it can be changed so as to increase the amount of attenuation, so it is possible to reduce annoying noise that occurs when there is no input.

  Further, the search means may perform a search including at least a frequency that is not input from the antenna. By doing this, the electric field strength at the frequency at which there is no input, that is, the frequency at which there is no broadcast wave can be detected and stored as the minimum electric field strength by the electric field strength detection means. Even if it is raised, it can be changed so as to increase the amount of attenuation, so it is possible to reduce annoying noise that occurs when there is no input.

  An embodiment of the present invention will be described with reference to FIGS. A receiving apparatus 1 according to an embodiment of the present invention includes an antenna 2, an antenna amplifier 3, an RF amplifier circuit 4, a front end 5, an intermediate frequency amplifier circuit 6, a detection circuit 7, a mute circuit 8, The apparatus includes a stereo separation circuit 9, an audio amplifier 10, a speaker 11, a PLL circuit 12, and a microcomputer 13, and is a device that is attached to a vehicle and receives a radio broadcast, for example.

  The antenna amplifier 3 amplifies the received signal to a predetermined level and outputs it to the RF amplifier circuit 4 in order to increase the sensitivity of the received signal received by the antenna 2.

  The RF amplifier circuit 4 as a receiving means selects and amplifies a desired station from the input received signal and outputs it to the front end 5.

  The front end 5 as a search means converts the received signal of the desired station input from the RF amplifier circuit 4 from a carrier frequency to a constant frequency (intermediate frequency) using a signal input from the PLL circuit 12, Output to the intermediate frequency amplifier circuit 6.

  The intermediate frequency amplification circuit 6 as the electric field strength detection means amplifies the signal converted to the intermediate frequency by the front end 5 to a level that can be demodulated by the detection circuit 7 and outputs the amplified signal to the detection circuit 7. Further, the intermediate frequency amplifier circuit 6 generates an S meter signal that is a signal representing the electric field strength of the received signal from the signal converted to the intermediate frequency, and outputs the S meter signal to the mute circuit 8.

  The detection circuit 7 as a demodulating means demodulates the signal converted to the intermediate frequency into an audio signal and outputs it to the mute circuit 8.

  The mute circuit 8 serving as an attenuating means mutes (attenuates the signal) the stereophonic sound signal input from the detection circuit 7 based on the voltage level of the S meter signal input from the intermediate frequency amplifier circuit 6. Output to the separation circuit 9.

  The stereo separation circuit 9 separates the audio signal input from the mute circuit 8 into a right channel (Rch) and a left channel (Lch) and outputs the separated signal to the audio amplifier 10.

  The audio amplifier 10 amplifies the signals separated into Rch and Lch in the stereo separation circuit 9 to respective predetermined levels. The audio signal amplified by the audio amplifier 10 is output from the speaker 11 as audio.

  The PLL circuit 12 as search means is a phase synchronization circuit, and outputs a signal for converting the received signal of the desired station to an intermediate frequency to the front end 5 in accordance with an instruction from the microcomputer 13.

  The microcomputer 13 as a minimum electric field strength storage means and attenuation amount changing means is a microcomputer having a CPU and a memory (not shown) incorporated therein, and controls the entire receiving apparatus 1 and intermediates the carrier frequency of the desired station selected to the PLL circuit 12. Instructing the output of a signal for conversion to frequency and setting the mute control curve for the mute circuit 8.

  Next, in the receiving apparatus 1 having the above-described configuration, the noise reduction operation when there is no input will be described with reference to the flowchart shown in FIG. The flowchart shown in FIG. 3 is executed by the CPU of the microcomputer 13.

  First, in step S1, a search is performed from the upper limit to the lower limit of the reception frequency of the receiving apparatus 1, and the process proceeds to step S2. Specifically, first, the reception upper limit frequency in the receiver 1 is set in the RF amplifier circuit 4 and the PLL circuit 12 is made to output a signal necessary for converting the upper limit frequency into an intermediate frequency. Then, the front end 5 outputs a signal obtained by converting the upper limit frequency into an intermediate frequency, and the intermediate frequency amplification circuit 6 outputs an S meter signal corresponding to the intermediate frequency. Next, the frequency to be selected is changed to a lower limit side by a predetermined interval (this interval is shorter than the interval at which the broadcasting station exists), and the changed frequency is converted to an intermediate frequency for the PLL circuit 12 The signal necessary to do the output is output. Then, the front end 5 outputs a signal obtained by converting the changed frequency into an intermediate frequency, and the intermediate frequency amplification circuit 6 outputs an S meter signal corresponding to the intermediate frequency. This is repeated up to the lower limit of the reception frequency. That is, a predetermined frequency band within a predetermined range is searched.

  Next, in step S2, the voltage level of the minimum S meter signal output from the intermediate frequency amplifier circuit 6 when searching from the upper limit to the lower limit of the reception frequency of the receiver 1 in step S1 is detected to detect the internal level of the microcomputer 13. Store in the memory and proceed to step S3. That is, the minimum electric field intensity detected by the electric field intensity detecting means in the searched frequency band is stored.

  Next, in step S3, a mute control curve stored in advance in the memory of the microcomputer 13 is selected based on the minimum voltage level of the S meter signal stored in the memory, and the mute pattern of the mute circuit 8 is set. A mute control curve is shown in FIG. FIG. 4 is a curve representing the output level of the mute circuit 8 with respect to the electric field level, with the vertical axis indicating the output level of the mute circuit 8 and the horizontal axis indicating the electric field level (voltage level of the S meter signal). In the case of FIG. 4, a plurality of curves (patterns) from curve 00 to curve 10 are set, and from a plurality of curves from curve 00 to curve 10 based on the voltage level of the minimum S meter signal as shown in FIG. select. Then, the mute circuit 8 operates based on the selected curve. That is, the attenuation amount of the attenuation unit is changed by selecting from a plurality of preset attenuation patterns based on the minimum electric field intensity stored in the minimum electric field intensity storage unit.

  From FIG. 4 and FIG. 5, in this embodiment, a mute curve is selected that sharply lowers the output level when the electric field is low as the voltage level of the S meter signal at no input is high. That is, when the voltage level of the S meter signal at the time of no input is high due to residual noise of the antenna amplifier 3 or the like, a curve is selected that lowers the output level as the electric field level decreases. That is, as the minimum electric field intensity stored in the minimum electric field intensity storage means increases, the attenuation when the electric field intensity detected by the electric field intensity detection means decreases is increased.

  According to the present embodiment, a search is performed from the upper limit to the lower limit of the reception frequency, the minimum voltage level of the voltage level of the S meter signal output from the intermediate frequency amplifier circuit 6 is stored, and the minimum voltage level is stored. By selecting the optimum curve from a plurality of mute curves based on this, it is possible to select a curve that lowers the output level as the electric field level decreases when the voltage level of the minimum S meter signal is high. The annoying noise due to the residual noise of the antenna amplifier 3 when there is no input can be reduced.

  Also, since a plurality of mute curves are selected based on the voltage level of the S meter signal when there is no input, an appropriate mute curve can be obtained even if the antenna amplifier 3 is replaced or removed with another circuit characteristic. The annoying noise can be reduced by selecting.

  Here, the inventors measured the input / output characteristics and compared them in an example to which the present invention was applied and a comparative example. The compared graph is shown in FIG. FIG. 6 shows input / output characteristics when a 98.1 MHz carrier wave subjected to 30% FM modulation is used as an input signal. In the comparative example, two types are displayed: the case where the antenna amplifier 3 is provided (Comparative Example 1) and the case where the antenna amplifier 3 is not provided (Single receiver: Comparative Example 2).

  In FIG. 6, the vertical axis represents the output level of the mute circuit 8, and the horizontal axis represents the electric field level of the input signal. Also, the thick line S1 indicates the audio signal level in the example, the thick line N1 indicates the noise level in the example, the dotted line S2 indicates the audio signal level in the comparative example 1, the dotted line N2 indicates the noise level in the comparative example 1, and the thin line S3 compares. The audio signal level in Example 2 and the thin line N3 indicate the noise level in Comparative Example 2.

  According to FIG. 6, the output level of Comparative Example 1 is higher than that of Comparative Example 2 even when the same electric field level is provided. For example, the audio signal output level when the electric field level is 5 dBμV is approximately −6 dB in Comparative Example 2 and approximately 0 dB in Comparative Example 1. That is, the sensitivity is improved by providing the antenna amplifier 3.

  However, when the electric field level with almost no input is −20 dBμV, Comparative Example 2 has an output level of about −20 dB, whereas Comparative Example 1 has −10 dB. It was an annoying noise.

  According to FIG. 6, it is clear that the output level of the embodiment to which the present invention is applied can be reduced to the same level as that of the comparative example 2 while maintaining the same sensitivity as that of the comparative example 1, but without any input.

  That is, by selecting a mute curve that can reduce this value to −20 dB based on the minimum level (−10 dB) at the time of no input, it is possible to obtain a receiving device with high sensitivity and low noise.

  It should be noted that the present invention is preferably applied to a receiving apparatus whose reception situation changes sequentially, for example, a receiving apparatus mounted on a mobile object such as an in-vehicle radio or a portable device such as a portable radio that is easy to carry. be able to.

  Further, in the above-described embodiment, the electric field strength at the time of no input is detected by searching from the upper limit to the lower limit of the frequency that can be received by the receiver 1, but it is only necessary to detect the electric field strength at the time of no input. A range narrower than the lower limit from the upper limit may be searched as long as the frequency includes no stations, that is, a frequency that includes no frequency.

  According to the embodiment described above, the following receiving apparatus 1 is obtained.

(Supplementary note 1) An antenna amplifier 3 for amplifying a reception signal received by the antenna 2, an RF amplifier circuit 4 for selecting a reception signal of a designated frequency, and a detection circuit 7 for demodulating the reception signal and outputting an audio signal The intermediate frequency amplifier circuit 6 detects the S meter signal from the received signal selected by the RF amplifier circuit 4 and the output level of the audio signal demodulated by the detector circuit 7 based on the S meter signal detected by the intermediate frequency amplifier circuit 6. In the receiving device 1 including the mute circuit 8 that attenuates
A front end 5 and a PLL circuit 12 that search for a predetermined frequency band in order to cause the intermediate frequency amplifier circuit 6 to detect an S meter signal in a predetermined predetermined frequency band;
A microcomputer 13 for storing the voltage level of the minimum S meter signal detected by the intermediate frequency amplifier circuit 6 in a predetermined frequency band searched by the front end 5 and the PLL circuit 12;
A microcomputer 13 for changing the attenuation of the mute circuit 8 based on the voltage level of the minimum S meter signal stored by the microcomputer 13;
A receiving device 1 comprising:

  According to this receiving apparatus 1, when the voltage level of the minimum S meter signal is increased due to the influence of noise or the like by the antenna amplifier 3, it can be changed so as to increase the attenuation amount. It can reduce annoying noise.

  In addition, the Example mentioned above only showed the typical form of this invention, and this invention is not limited to an Example. That is, various modifications can be made without departing from the scope of the present invention.

It is a block diagram of the receiver in a prior art. It is a block diagram of the receiver concerning one Example of this invention. 3 is a flowchart showing noise reduction operation when the receiving apparatus shown in FIG. It is an example of a plurality of mute curves. It is a correspondence table of the mute curve with respect to the voltage level of the S meter signal at the time of no input. It is an input-output characteristic figure which compared the Example and the comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Receiver 2 Antenna 3 Antenna amplifier 4 RF amplifier circuit (reception means)
5 Front end (search means)
6 Intermediate frequency amplifier (electric field strength detection means)
7 Detection circuit (demodulation means)
8 Mute circuit (attenuation means)
12 PLL circuit (search means)
13 Microcomputer (Minimum electric field strength storage means, attenuation change means)

Claims (5)

An antenna amplifier that amplifies the received signal received by the antenna, a receiving unit that selects a received signal of a specified frequency, a demodulating unit that demodulates the received signal and outputs an audio signal, and a reception selected by the receiving unit Electric field strength detection means for detecting the electric field strength of the selected received signal from the signal, and attenuation means for attenuating the output level of the audio signal demodulated by the demodulation means based on the electric field strength detected by the electric field strength detection means In a receiving device comprising:
Search means for searching the frequency band of the predetermined range in order to cause the electric field strength detection means to detect the electric field strength of a predetermined frequency band of the predetermined range;
Minimum electric field strength storage means for storing the minimum electric field intensity detected by the electric field intensity detection means in the frequency band of the predetermined range searched by the search means;
Attenuation amount changing means for changing the attenuation amount of the attenuation means based on the minimum electric field strength stored in the minimum electric field strength storage means;
A receiving apparatus comprising:   2. The reception according to claim 1, wherein the attenuation amount changing unit selects from a plurality of preset attenuation patterns based on the minimum electric field intensity stored in the minimum electric field intensity storage unit. apparatus.   In the plurality of attenuation patterns, as the minimum electric field intensity stored in the minimum electric field intensity storage unit increases, the attenuation amount when the electric field intensity detected by the electric field intensity detection unit decreases becomes larger. The receiving device according to claim 2.   The receiving device according to any one of claims 1 to 3, wherein the search unit searches a range between an upper limit and a lower limit of frequencies that can be received by the receiving unit.   5. The receiving apparatus according to claim 1, wherein the search unit performs a search including at least a frequency at which an input from the antenna is not input. 6.

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