JP2002368640A - Fm receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an FM receiver that avoids the occurrence of malfunctions, caused when analog filters with different bandwidths to avoid crosstalks are switched for selection, when many broadcast stations exist adjacent to each other, as in various countries in Europe. SOLUTION: A mixer 24 is placed at a post-stage of a 1st stage IF filter 22 via a 2nd IF filter 26 to conduct frequency conversion into 450 kHz, and a main signal, from an analog/digital converter 25 for converting an analog signal into a digital signal, is given to a digital filter 30 via a delay circuit 27. An output signal from an analog/digital converter 28 is given via a digital filter 29, whose pass frequencies are 80 kHz-250 kHz to a digital signal processor DSP 31, which detects the level of spectrum for each adjacent circuit frequency, to select a coefficient of the digital filter 30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an FM receiver,
For example, the present invention relates to an IF filter used in an FM receiver that receives an FM-modulated broadcast signal.

[0002]

2. Description of the Related Art The FM (frequency modulation) system modulates the frequency of a carrier signal having a constant frequency according to a signal and transmits and receives the modulated signal. This FM modulation method uses AM (amplitude modulation).
Compared to the system, it has various advantages such as low noise and constant transmission power irrespective of the degree of modulation, and is widely used in music broadcasting and the like.

[0003] The prior art in this technical field is, for example, "FM interference detection method and apparatus" in JP-A-7-336246, "FM receiver" in JP-A-8-56168, and JP-A-4-265021. This is disclosed in "FM receiver" in Japanese Patent Laid-Open Publication, "FM Receiver" in JP-A-6-260951, and the like.

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, filter 4,
6, a changeover switch 11 for these filters 4 and 6, a limiter amplifier circuit (AMP) 5, a detection circuit 7, a band pass filter (BPF) 10, a detector 9 and a comparator 8. Then, the changeover switch 11 is switched by the output of the comparator 8, and the filters 4 or 6 having different bandwidths are provided.
Is configured to be selected.

A conventional F having the band switching circuit shown in FIG.
In the M receiver, a signal is transmitted via the front end 1 connected to the antenna A, for example, to a 10.7 MHz I
The frequency is converted to the F frequency and input to the IF filter 2. 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 a detection circuit 7 to obtain an audio signal.

[0006] Here, the broadcasting station desired to receive (desired station)
The case where there is another broadcasting station (adjacent station) adjacent to is described. In this case, the interference state at the time of receiving the desired station differs depending on the frequency difference to the adjacent station. Therefore, the level of the adjacent signal is usually detected using the band-pass filter 10 having the characteristics as shown in FIGS. The signal level is extracted by the bandpass filter 10 and the detector 9. If the signal level is equal to or higher than the threshold value set by the comparator 8, the switch 11 is switched to select the filter 4 having a narrow band. On the other hand, the comparator 8
Is smaller than the threshold value, the switch 11 selects the filter 6 having a wide band.

[0007]

In European countries and the like, FM broadcasting stations are set at 50 kHz, so that reception interference may occur due to interference in some areas. In order to perform good reception in the reception impairment area, the filter 4 having a narrow bandwidth and the filter 6 having a wide bandwidth are used as described above with reference to FIG.
Are switched by the switch 11. 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 the received FM signal is adjacent to a voice (audio) signal in a high frequency region. This spectrum is detected by the band-pass filter 10, and the output is switched to the filter 4 or 6 depending on whether the detection output is equal to or greater than the threshold.
It cannot be determined whether the neighboring station is at 100 kHz or 150 kHz.

For this purpose, a bandpass filter having characteristics as shown in FIGS.
At 100 kHz and 200 kHz on the basis of z, a frequent switching to a narrow bandpass filter is prevented. This suppresses a malfunction such as a change in sound quality and a change in sound due to switching more than necessary. However, since fine settings cannot be made with a conventional analog filter, malfunctions cannot be completely eliminated, and there are cases where functions do not function sufficiently in some areas.

[0009]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an FM receiver capable of more reliably eliminating a malfunction caused by an adjacent station.

[0010]

In order to solve the above-mentioned problems, an FM receiver according to the present invention employs the following characteristic configuration.

(1) The FM signal received by the antenna is
In an FM receiver which obtains an audio output signal by detecting an IF signal obtained through an F filter through an IF amplifier circuit and then amplifying the IF signal through a filter having a different bandwidth, the FM receiver is disposed downstream of the IF amplifier circuit and has a lower level than the first IF. Mixer for converting to frequency, and A / D for digitally converting an output signal of the mixer
An FM receiver comprising a converter, a DSP (Digital Signal Processor) for detecting a spectrum level for each adjacent center frequency, and a digital filter selected to have a coefficient adapted to a signal of a desired station.

(2) The FM receiver according to (1), wherein a second IF filter is provided between the IF amplifier circuit and the mixer.

(3) The FM receiver according to the above (1) or (2), wherein a delay circuit for compensating a processing time delay of the DSP is provided at a stage preceding the digital filter.

(4) The mixer operates at 10.7 MHz by 4
The FM receiver according to (1), (2) or (3), which converts the frequency to 50 kHz.

(5) A frequency of 80 kHz to 2 is set before the DSP.
The FM receiver according to (4), further including a digital filter for extracting a 50 kHz spectrum.

(6) 1 in the output signal of the IF amplifier circuit
The above (1) to (5) including a detector for detecting a 9 kHz component and an A / D converter for controlling the DSP by digitally converting an output signal of the detector to determine whether the signal is multipath or adjacent. Any of the FM receivers.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and operation of a preferred embodiment of an FM receiver according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the 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,
Mixer 24, analog-to-digital (A / D) converter 2
5, 28, 34, delay circuit 27, digital filters 29, 30, DSP (digital signal processor)
31, 32, digital-analog (D / A) converter 33
And a detector 35.

In the FM receiver of the present invention, a second IF filter and a mixer 24 are connected to the output of the IF amplifier circuit 23, in particular. Furthermore, A / D converters 25 and 28 are provided on the output side of the mixer 24, a delay circuit 27 connected to the output side of the A / D converter 25, and a digital circuit connected to the output side of the A / D converter 28. Filter 29, DSP 31 connected to the output side of this digital filter 29, digital filter 30 connected to this DSP 31 and delay circuit 27, and DSP 32 connected to the output side of this digital filter
It is characterized by having.

In the FM receiver according to the present invention, the IF amplifier circuit 2
The second IF filter 26 is connected to the third stage. After passing through the second IF filter 26, the signal is converted into, for example, 450 kHz by the mixer 24. The frequency-converted signal is converted into a digital signal by the A / D converter 25,
The signal is sent to the delay circuit 27. In the other A / D converter 28, the digital filter 29 controls the frequency from 80 kHz to 250 kHz.
Extract the spectrum in Hz.

Upon receiving the output signal from the digital filter 29, the DSP 31 outputs a signal of 450 kHz + 200 kHz, 45 kHz.
0kHz + 150kHz, 450kHz-100kHz
z, 450kHz-150kHz, 450kHz-20
The level of each frequency component is detected using a Hanning window function or the like centered on 0 kHz. When these detected values are equal to or higher than the respective set levels, the DSP 31 sends coefficients to the digital filter 30 in order to select a filter corresponding to the detected neighbor.

Here, the delay circuit 27 includes the A / D converter 2
5 to compensate for delays due to signal processing time by the DSP 31 and the like. In other words, the coefficients of the digital filter 30 are set by the DSP 31 before the delayed main signal is input to the digital filter 30. This ensures signal quality.

When the level of the above-mentioned frequency component simultaneously increases, the 19 kHz component shown in FIG.
F amplifier circuit 23 to detector 35 and A / D converter 34
Take out via monitor. Then, it is determined whether the signal is a multi-path or a multi-path based on the monitored signal level, so that the digital filter 30 does not malfunction due to the multi-path.

The output signal from the digital filter 30 is
The signal is processed through another DSP 32 and is further processed by the D / A converter 3
3 is converted into an analog signal. From the D / A converter 33, an audio output signal (Audio Out) of a desired broadcast station is output.
Is obtained. This audio output signal is connected to, for example, a speaker or headphones.

The configuration and operation of the preferred embodiment of the FM receiver according to the present invention have been described above in detail. However, such an embodiment is merely an example of the present invention and does not limit the present invention in any way. It can be easily understood by those skilled in the art that various modifications can be made according to the specific application without departing from the gist of the present invention.

[0026]

As will be understood from the above description, the FM receiver according to the present invention has the following remarkable practical effects. That is, as compared with the related art in which the analog filter is switched and used, the switching of the filter by the multipath of the adjacent interference detection circuit does not malfunction. In addition, the band can be switched smoothly, and reception of an uncomfortable interfering station can be suppressed as much as possible. Therefore, it is particularly effective in preventing interference when a large number of broadcast stations are 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.

FIG. 4 is a characteristic diagram of the bandpass filter shown in FIG.

[Explanation of symbols]

Reference Signs List 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 (6)

[Claims] 1. An FM receiver for obtaining an audio output signal by detecting an FM signal received by an antenna through an IF amplifier circuit, amplifying an IF signal obtained through an IF filter, and a filter having a different bandwidth. A mixer that is arranged at the subsequent stage of the amplifier circuit and converts the output signal of the mixer into a lower frequency than the first IF, an A / D converter that converts the output signal of the mixer into a digital signal, and a DSP that detects the level of the spectrum for each adjacent center frequency An FM receiver comprising: a digital signal processor); and a digital filter selected to have coefficients adapted to a signal of a desired station. 2. The FM receiver according to claim 1, wherein a second IF filter is provided between the IF amplifier circuit and the mixer. 3. The digital filter according to claim 1, wherein:
3. The FM receiver according to claim 1, further comprising a delay circuit that compensates for a processing time delay of P. 4. The mixer according to claim 1, wherein the frequency of 10.7 MHz is 450 k.
4. The FM receiver according to claim 1, wherein the frequency is converted to Hz. 5. A digital signal processing system in which a frequency of 80 kHz to 250 kHz is provided before the DSP.
The FM receiver according to claim 4, further comprising a digital filter that extracts a spectrum in Hz. 6. An output signal of the IF amplifier circuit, comprising: 19 kHz
2. A detector for detecting a z-component, and an A / D converter for controlling the DSP by digitally converting an output signal of the detector to determine whether the signal is multipath or adjacent. 6. The FM receiver according to any one of claims 1 to 5.