JP3789318B2 - FM receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an FM receiver, for example, an IF filter used in an FM receiver that receives FM-modulated broadcast signals.
[0002]
[Prior art]
The FM (Frequency Modulation) system modulates the frequency of a carrier wave signal having a constant frequency according to the signal and transmits / receives it. This FM modulation method has various advantages such as less noise and constant transmission power regardless of the modulation degree compared to the AM (amplitude modulation) method, and is therefore widely used for music broadcasting and the like. Yes.
[0003]
Prior art in such a technical field includes, for example, “FM interference detection method and apparatus” in JP-A-7-336246, “FM receiver” in JP-A-8-56168, and “FM receiver” in JP-A-4-265021. FM receiver "and" FM receiver "of JP-A-6-260951.
[0004]
FIG. 2 is a block diagram showing a configuration of a typical conventional FM receiver. Antenna A, front end (RF amplification and frequency conversion circuit) 1, first stage IF (intermediate frequency) filter 2, IF amplification circuit 3, filters 4 and 6, changeover switch 11 of these filters 4 and 6, limiter amplification circuit (AMP) ) 5, a detection circuit 7, a band pass filter (BPF) 10, a detector 9 and a comparator 8. The changeover switch 11 is switched by the output of the comparator 8 and is configured to select the filter 4 or 6 having a different bandwidth.
[0005]
In the conventional FM receiver having the band switching circuit shown in FIG. 2, the signal is converted to an IF frequency of 10.7 MHz, for example, via the front end 1 connected to the antenna A, and input to the IF filter 2. The The IF signal that has passed through the first-stage IF filter 2 is amplified by the IF amplifier circuit 3 with a predetermined gain. Thereafter, the signal passes through the IF filter 6 having a wide band and is input to the limiter amplifier circuit 5. The IF signal output from the limiter amplifier circuit 5 is detected by the detection circuit 7 to obtain an audio signal.
[0006]
Here, the case where there is another broadcast station (adjacent station) adjacent to the broadcast station (desired station) desired to be received will be described. In this case, the interference state received when receiving the desired station differs depending on the frequency difference to the adjacent station. For this reason, the level of the adjacent signal is detected by using the band-pass filter 10 having the characteristics shown in FIGS. 4A to 4C. The signal level is taken out by the band pass filter 10 and the detector 9. If this signal level is equal to or higher than the threshold set by the comparator 8, the switch 11 is switched to select the filter 4 having a narrow band. On the other hand, when it is smaller than the threshold value of the comparator 8, the switch 11 selects the wide band filter 6.
[0007]
[Problems to be solved by the invention]
In European countries and the like, since FM broadcasting is installed at 50 kHz, reception interference due to interference may occur depending on the region. In order to perform good reception in this reception failure area, the filter 4 with the narrow bandwidth and the filter 6 with the wide bandwidth are switched by the switch 11 as described above with reference to FIG. At this time, when the received FM signal is detected by the detection circuit 7, a spectrum component as shown in FIG. 3 appears when it is adjacent to a voice (audio) signal and a high frequency region. This spectrum is detected by the band pass filter 10 and switched to the filter 4 or 6 depending on whether the detected output is greater than or less than the threshold value, but it cannot be determined whether the adjacent station is 100 kHz or 150 kHz.
[0008]
Therefore, the bandpass filter having the characteristics shown in FIGS. 4A to 4C is prevented from being frequently switched to a narrow bandpass filter at 100 kHz and 200 kHz with reference to 150 kHz. Thereby, malfunctions such as a change in sound quality and a change in sound due to switching more than necessary are suppressed. However, since the conventional analog filter cannot be set finely, malfunctions cannot be completely eliminated, and there are cases where the function does not function sufficiently depending on the region.
[0009]
OBJECT OF THE INVENTION
Accordingly, an object of the present invention has been made in view of the above-described problems of the prior art, and is to provide an FM receiver that can more reliably eliminate malfunctions caused by adjacent stations.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problems, the FM receiver according to the present invention employs the following characteristic configuration.
[0011]
(1) the FM signal received by the antenna, detects through the first digital filter the IF signal obtained through the IF filter after amplification by IF amplifier, an FM receiver for obtaining an audio output signal, the IF amplifier circuit A mixer that is disposed downstream of the IF filter and converts the frequency of the IF filter to a lower frequency than the intermediate frequency of the IF filter, a first A / D converter that digitally converts an output signal of the mixer, and a first A / D converter A DSP (digital signal processor) that detects a spectrum level for each adjacent center frequency from the output , and the first digital filter is selected as a coefficient adapted to the signal of the desired station according to the instruction of the DSP FM receiver.
[0012]
(2) between the first A / D converter and said first digital filter, FM receiver (1) providing a delay circuit for compensating the DSP processing time delay.
[0013]
(3) The FM receiver according to (1) or (2), wherein the mixer performs frequency conversion from 10.7 MHz to 450 kHz.
[0014]
(4) The FM receiver according to (3), wherein a second digital filter for extracting a spectrum of 80 kHz to 250 kHz is provided between the first A / D converter and the DSP.
[0015]
(5) the IF output signal of the detector and該検wave for detecting a 19kHz component in the output signal of the amplifier circuit multipath (Multipath) or adjacent or determined by digital conversion, a second to control the DSP The FM receiver according to any one of (1) to (4), comprising an A / D converter.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration and operation of a preferred embodiment of an FM receiver according to the present invention will be described in detail with reference to the accompanying drawings.
[0018]
FIG. 1 is a block diagram showing a configuration of a preferred embodiment of an FM receiver according to the present invention. This FM receiver includes an antenna 20, a front end 21, a first IF filter 22, an IF amplifier circuit 23, a second IF filter 26, a mixer 24, analog-digital (A / D) converters 25, 28, and 34, a delay (Delay). ) Circuit 27, digital filters 29 and 30, DSP (digital signal processor) 31 and 32, digital-analog (D / A) converter 33, and detector 35.
[0019]
The FM receiver of the present invention connects the second IF filter and the mixer 24 particularly to the output of the IF amplifier circuit 23. Further, the A / D converters 25 and 28 are connected to the output side of the mixer 24, the delay circuit 27 is connected to the output side of the A / D converter 25, and the digital is connected to the output side of the A / D converter 28. A filter 29, a DSP 31 connected to the output side of the digital filter 29, a digital filter 30 connected to the DSP 31 and the delay circuit 27, and a DSP 32 connected to the output side of the digital filter are provided.
[0020]
In the FM receiver of the present invention, the second IF filter 26 is connected to the subsequent stage of the IF amplifier circuit 23. After passing through the second IF filter 26, the mixer 24 converts it to 450 kHz, for example. The frequency-converted signal is converted into a digital signal by the A / D converter 25 and sent to the delay circuit 27. In the other A / D converter 28, the spectrum of 80 kHz to 250 kHz is extracted by the digital filter 29.
[0021]
In response to the output signal from the digital filter 29, the DSP 31 detects the level of each frequency component using a Hanning window function centered on 450 kHz + 200 kHz, 450 kHz + 150 kHz, 450 kHz-100 kHz, 450 kHz-150 kHz, 450 kHz-200 kHz. . When these detected values are equal to or higher than the set levels, the coefficients are sent from the DSP 31 to the digital filter 30 in order to select a filter corresponding to the detected adjacency.
[0022]
Here, the delay circuit 27 delays the main signal passing through the A / D converter 25 and compensates for a delay due to a signal processing time or the like by the DSP 31. In other words, before the delayed main signal described above is input to the digital filter 30, the coefficient of the digital filter 30 is set by the DSP 31. This ensures signal quality.
[0023]
When the level of the frequency component described above rises simultaneously, the 19 kHz component shown in FIG. 3 is extracted from the IF amplifier circuit 23 via the detector 35 and the A / D converter 34 and monitored. Then, based on the monitored signal level, it is determined whether it is multipath or adjacent, and the digital filter 30 is prevented from malfunctioning due to multipath.
[0024]
The output signal from the digital filter 30 is processed through another DSP 32 and further converted into an analog signal by the D / A converter 33. From the D / A converter 33, an audio output signal (Audio Out) of the desired broadcast station is obtained. This audio output signal is connected to, for example, a speaker or headphones.
[0025]
The configuration and operation of the preferred embodiment of the FM receiver according to the present invention have been described in detail above. However, such an embodiment is merely an example of the present invention and does not limit the present invention. Those skilled in the art can easily understand that various modifications and changes can be made according to a specific application without departing from the gist of the present invention.
[0026]
【The invention's effect】
As understood from the above description, according to the FM receiver of the present invention, the following significant effects can be obtained. That is, compared with the prior art that uses an analog filter by switching, the filter switching by the multipath of the adjacent disturbance detection circuit does not malfunction. Also, smooth band switching is possible, and reception of unpleasant disturbing stations can be suppressed as much as possible. Therefore, it is particularly effective for blocking interference when there are many broadcasting stations adjacent to each other as in European countries.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a preferred embodiment of an FM receiver according to the present invention.
FIG. 2 is a block diagram showing a configuration of a typical conventional FM receiver.
FIG. 3 shows a frequency spectrum obtained by detecting an FM signal.
4 is a characteristic diagram of the bandpass filter shown in FIG. 2. FIG.
[Explanation of symbols]
20 antenna 21 front end 22 first (first stage) IF filter 23 IF amplifier circuit 24 mixer 25, 28, 34 A / D (analog / digital) converter 26 second IF filter 27 delay circuit 29, 30 digital filter 31, 32 DSP (Digital signal processor)
33 D / A (digital / analog) converter 35 detector

Claims (5)

The FM signal received by an antenna, detects through the first digital filter the IF signal obtained through the IF filter after amplification by IF amplifier, an FM receiver for obtaining an audio output signal, to a subsequent stage of the IF amplifier circuit And a mixer that converts the IF filter to a frequency lower than the intermediate frequency of the IF filter, a first A / D converter that digitally converts the output signal of the mixer, and an adjacent output from the output of the first A / D converter A DSP (digital signal processor) that detects a spectrum level for each center frequency of the signal , and the first digital filter is selected to have a coefficient adapted to a signal of a desired station according to the instruction of the DSP. A featured FM receiver. Said 1 A / D converter and the first 1 The FM receiver according to claim 1, further comprising a delay circuit for compensating a processing time delay of the DSP between the digital filters. The FM receiver according to claim 1, wherein the mixer performs frequency conversion from 10.7 MHz to 450 kHz. Said 1 4. The FM receiver according to claim 3, further comprising: a second digital filter that extracts a spectrum of 80 kHz to 250 kHz between the A / D converter and the DSP. 5. A detector that detects a 19 kHz component in the output signal of the IF amplifier circuit, and the output signal of the detector is converted into a multipath ( Multipath The FM receiver according to any one of claims 1 to 4, further comprising a second A / D converter that determines whether the signal is adjacent to each other and controls the DSP.

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