JP3670902B2 - Noise reduction device for radio receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for removing noise from a composite signal in a radio receiver, for example, an FM tuner in a car radio.
[0002]
[Prior art]
A high-frequency pulse signal in a wide frequency range that interferes with the ignition spark of an internal combustion engine and the reception of radio broadcasts can be detected. This high frequency pulse is superimposed as noise on the composite signal. In a radio receiver such as an FM tuner, it is necessary to detect this noise and remove the noise.
[0003]
Japanese Patent Laid-Open No. 7-154277 (H04B 1/10) proposes a circuit for removing pulse noise from a composite signal for a digital radio receiver. In this conventional technique, pulse noise is detected by comparing a signal subjected to high-frequency filtering and squared with a temporal average value. When this pulse noise is detected, control is performed so that the composite signal is replaced by a sample value generated during the preceding pilot tone period while the pulse noise is being detected, thereby removing noise.
[0004]
[Problems to be solved by the invention]
As described above, usually, when the pulse noise detects the occurrence by performing the forward processing had use a delay circuit and a low pass filter (LPF), but to remove pulse noise, the forward process If it does, it will become a waveform as shown by the continuous line of FIG. When the pulse noise is generated, the pulse noise is removed. However, if the forward processing is performed as it is, the influence of the pulse noise is generated so as to be surrounded by B in the figure.
[0005]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a noise removing device capable of shortening the time affected by noise such as pulse noise and generating a good audio signal. .
[0006]
[Means for Solving the Problems]
The present invention includes a noise detection means for detecting noise, a forward processing means for performing forward signal processing, a backward processing means for performing backward signal processing, a signal from the noise detection means, a signal of the forward processing means, Data switching processing means for inputting a signal from the backward processing means and switching the signal from the forward processing means and the signal from the backward processing means to output as an audio signal based on the signal from the noise detection means; And the data switching processing means selects the signal of the forward processing means when the signal from the noise detection means indicates that noise is not detected, and the signal indicating that the noise detection means has detected noise. From the time of output, the signal processed by the backward processing means is selected and output, and it takes time to eliminate the influence of noise. If that, and outputs switch signals from the backward processing means on a signal from the forward process.
[0007]
The signal processing may be configured to perform LPF processing.
[0008]
By configuring as described above, it is possible to select and output each of the processes having almost no influence of noise such as pulse noise, so that the influence can be effectively reduced.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
In FIG. 1, a composite signal is supplied to the input terminal 1 by a demodulator not shown. This composite signal has a sampling frequency of 228 kHz. This sampling frequency is a multiple of the 19 kHz pilot tone frequency.
[0010]
The composite signal supplied to the input terminal is supplied to the noise detection circuit 1, the forward processing circuit 2, and the backward processing circuit 3 that detect noise such as pulse noise. Signals from the noise detection circuit 1, the forward processing circuit 2, and the backward circuit 3 are given to the data switching processing circuit 4. Based on the signal from the noise detection circuit 1, the data switching processing circuit 4 switches the signal from the forward processing circuit 2 which is normal forward LPF processing and the signal from the backward processing circuit 3 which is backward LPF processing to switch the audio signal. Output as.
[0011]
FIG. 2 is a block diagram showing a specific example of the noise detection circuit 1 and includes a high-pass filter (HPS) 11, a squaring circuit 12, a time averaging circuit 13, and a comparison circuit 14 .
[0012]
The high-pass filter 11 suppresses insignificant components of the composite signal against noise such as pulse noise and gives the signal to the squaring circuit 12. The square circuit 13 performs square evaluation and rectification, and forms an absolute value of the composite signal filtered by the high-pass filter 2.
[0013]
The output signal of the squaring circuit 12 is given to the time averaging circuit 13 and the comparison circuit 14.
[0014]
The time averaging circuit 13 calculates a time average value of the signal from the squaring circuit 12, and gives the value to the comparison circuit 14 as a threshold value.
[0015]
The comparison circuit 14 compares the signal for determining the cutoff frequency from the time averaging circuit 13 with the signal from the squaring circuit 12 to detect noise. That is, when the signal from the squaring circuit 12 is larger than the signal from the time averaging circuit 14, it is determined that noise has occurred, and a signal is given to the data switching circuit 4 and the like.
[0016]
In the above-described embodiment, the square calculation is performed after the high-pass filter 11, but an absolute value calculation process may be performed instead of the square calculation.
[0017]
FIG. 3 is a block diagram showing a specific example of the forward processing circuit 2 and includes a low-pass filter (LPF) 21 and a delay circuit 22 as signal processing. The composite signal is supplied to a low pass filter (LPF) 21. The signal filtered by the low-pass filter 21 is given to the delay circuit 22. The delay circuit 22 obtains a signal from the noise detection circuit 1 and supplies the filtered composite signal to the data switching circuit 4 when no pulse signal is detected. When the noise detection circuit 1 detects noise, the composite signal delayed by the pilot tone period by the delay circuit 22 is supplied to the data switching circuit 4. While detecting the noise, the composite signal is controlled so as to be replaced by the sample value generated during the preceding pilot tone period, thereby performing noise removal. That is, the forward processing circuit 2 predicts and outputs data preceding the noise while the noise is occurring.
[0018]
The forward processing circuit 2 shown in FIG. 3 uses LPF as signal processing. However, forward processing is not limited to this, and data is predicted by data interpolation processing, signal processing using BPF, or the like. May be output.
[0019]
FIG. 4 is a block diagram showing a specific example of the backward processing circuit 3. The composite signal is stored in the buffer memory 31, the signal from the noise detection circuit 1 is obtained, and the signal stored in the buffer memory 31 by a predetermined amount is inverted by the time axis inversion processing circuit 32 to perform the signal processing. To the low pass filter (LPF) 33. Then, the composite signal filtered by the low-pass filter 33 is inverted by the time axis inversion processing circuit 34 and given to the data switching circuit 4.
[0020]
When the noise detection circuit 1 detects noise, the backward processing circuit 3 performs noise removal by controlling the composite signal so that it can be replaced with the sample value by going back in time on the time axis.
[0021]
FIG. 5 is a block diagram showing another specific example of the backward processing circuit 3. The composite signal is stored in the buffer memory 31, the signal from the noise detection circuit 1 is obtained, the signal stored in the buffer memory 31 by a predetermined amount is inverted by a coefficient in the circuit 35, and the signal processing is performed by a low-pass filter (LPF). To wave. Then, the composite signal whose coefficient has been inverted is inverted by the time axis inversion processing circuit 34 and supplied to the data switching circuit 4.
[0022]
When the noise detection circuit 1 detects a pulse, the backward processing circuit 3 also controls the composite signal so that it can be replaced with the sample value by going back the time axis backward.
[0023]
The backward processing circuit 3 shown in FIG. 4 and FIG. 5 uses LPF as signal processing. However, the backward processing is not limited to this, and composite processing is performed by data interpolation processing, signal processing using BPF, and the like. The signal may be output so as to be retroactively replaced with the sample value.
[0024]
The data switching circuit 4 inputs signals from the noise detection circuit 1, the forward processing circuit 2, and the backward circuit 3, and combines normal forward signal processing and backward signal processing based on the signals from the noise detection circuit 1. The output is to eliminate the influence of the rear part of the pulse generation interval of the signal processing. That is, as shown in FIG. 6 described above, when forward processing is performed, as indicated by the solid line in FIG. Further, the case where the backward processing is performed is indicated by a broken line in the figure. As shown in the area surrounded by A in FIG. 6, the influence of noise occurs before the occurrence of noise. Therefore, in the present invention, until the noise is detected, the data switching circuit 4 selects and outputs the signal from the forward processing so that the composite signal processed by the forward processing circuit 2 is output.
[0025]
When a pulse is detected by the noise detection circuit 1, in the forward processing, as described above, the influence of the pulse noise occurs. The data switching circuit 4 selects and outputs a signal from the backward processing so as to output it.
[0026]
When a predetermined time elapses by the backward processing circuit 3, that is, when the time for eliminating the influence of noise has passed, the data switching circuit 4 selects and outputs a signal from the forward processing.
[0027]
With this configuration, as apparent from FIG. 6, the influence of noise can be effectively eliminated.
[0028]
In the present invention, the circuit indicated by the block may be realized by using individual circuits. However, the present invention is realized by using a digital signal processor that performs the process indicated by the block circuit by appropriate programming. It may be realized.
[0029]
【The invention's effect】
As described above, according to the present invention, the time during which noise such as pulse noise is affected can be shortened, and the influence can be effectively reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment according to the present invention.
FIG. 2 is a block diagram showing a specific example of a pulse noise detection circuit used in the present invention.
FIG. 3 is a block diagram showing a specific example of a forward processing circuit used in the present invention.
FIG. 4 is a block diagram showing a specific example of a backward processing circuit used in the present invention.
FIG. 5 is a block diagram showing a specific example of another backward processing circuit used in the present invention.
FIG. 6 is a waveform diagram when forward processing and backward processing are performed.
[Explanation of symbols]
1 pulse noise detection circuit 2 forward processing circuit 3 backward processing circuit 4 data switching processing circuit

Claims (2)

Noise detection means for detecting noise, forward processing means for performing forward signal processing, backward processing means for performing backward signal processing, a signal from the noise detection means, a signal of the forward processing means, and a backward processing means And a data switching processing means for switching the signal from the forward processing means and the signal from the backward processing means to output as an audio signal based on the signal from the noise detection means, The data switching processing unit selects the signal of the forward processing unit when the signal from the noise detection unit indicates that noise is not detected, and from the time when the noise detection unit outputs a signal indicating that the noise has been detected. When the signal processed by the backward processing means is selected and output, and after the time when the influence of noise disappears, Noise removal device according to a radio receiver and outputs switch to a signal from the forward process signals from the filtrate orientation processing means.   2. The noise removal device for a radio receiver according to claim 1, wherein LPF processing is performed as the signal processing.

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