JP2012191337A - Am/fm receiver and noise reduction method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a pulse noise removal performance.SOLUTION: An AM/FM receiver for detecting pulse noise in reception signals and reducing the pulse noise includes: a noise removal method selection unit 31 for outputting selection signals for selecting one of a plurality of noise removal steps on the basis of a level difference between a reception signal level of an adjacent station adjacent, by a frequency, to a reception target station and a reception signal level of the reception target station; noise gates 33, 34 for respectively executing noise removal by the plurality of noise removal steps of respectively different processes to detection signals of the reception signals; and a noise removal result switching unit 32 for selecting one noise removal step from the noise gates 33, 34 by the selection signals outputted by the noise removal method selection unit 31 and obtaining output signals.

Description

  The present invention relates to an AM / FM receiver, and more particularly to a technique for reducing pulse noise during reception.

  In recent years, with the spread of AM / FM receivers using digital signal processing, noise applied in pulses, such as ignition noise, door mirror opening / closing noise, wiper motor noise (operation noise), etc., in vehicles where products are frequently installed However, there is an increasing number of cases that are included in the demodulated output (output after detection) as disturbance. In this case, since the signal to be listened to is disturbed by the pulse noise, there is an increasing demand for a technique for improving the ability to remove the pulse noise.

  FIG. 8 is a block diagram showing the configuration of the FM receiver described in Patent Document 1. In FIG. In FIG. 8, the FM receiver includes an IF filter (intermediate frequency filter) 11, an MPC (multipath scancerer) 12 composed of an automatic gain controller (AGC) 121 and an adaptive equalizer 122, and outputs of the MPC 12 and the IF filter 11. Switch 14 for switching, FMDET (detector) 15 comprising a Hilbert transformer 151 and ArcTan calculator 152, VAR (envelope dispersion detector immediately before detection) 16, and ADJ / ALT (adjacent station detector) 17 An S-meter (signal meter, electric field strength detection unit) 18, an adaptive equalizer (Control Sequencer) 19, a DIP (IF signal dent detection unit) 20, and a 19K AM Mod (envelope waviness detection unit) 21 , Stereo (stereo deco It comprises a da) 23, a USN (ultrasonic component detecting unit) 24, and DEV (overmodulation detector) 25, a. Further, the FM receiver includes a PN (pulse noise detection unit) 26, a noise removal unit 22, and a delay amount control unit 13.

  The intermediate frequency filter 11 selectively passes a frequency in a predetermined band in the received signal. The multipath scan cell 12 has an adaptive equalizer 122 for removing the influence of multipath from the received signal output from the intermediate frequency filter 11. The detector 15 detects the received signal from the multipath scan 12. The pulse noise detection unit 26 detects noise from the detection signal output by the detector 15 and generates a corresponding control signal. The noise removing unit 22 removes noise from the detection signal output from the detector 15 according to the control signal. The delay amount control unit 13 controls the operation timing of the noise removal unit 22 via the pulse noise detection unit 26 according to the delay amount of the adaptive equalizer 122.

  The center tap position detection unit 131 finds the maximum coefficient corresponding to the center tap from the coefficients input to the adaptive equalizer 122, and calculates the delay amount from the position and size. By adjusting the timing of the gate signal for enabling the noise removing unit 22 based on the calculated delay amount, the noise removing unit 22 can be effectively operated.

  Relatedly, Patent Documents 2 and 3 disclose techniques for reducing noise by controlling an intermediate frequency signal.

JP 2010-093695 A Japanese Patent Laid-Open No. 08-307289 JP 2010-098413 A

  The following analysis is given in the present invention.

  In the FM receiver described in Patent Document 1, when an adjacent station near the desired station exists at the same level of intensity as the desired station, the output (demodulated signal) of the FM receiver is disturbed by the adjacent station, and distortion is caused. growing. Alternatively, since the demodulated signal is subjected to adjacent station interference mixed with the contents of neighboring stations, when the noise elimination section is interpolated at two points, both the start point and / or the end point are affected by the adjacent station. For this reason, when there is interference by an adjacent station, noise may not be sufficiently reduced even though noise removal (noise canceller) processing is performed.

  Next, an example of such a case will be described. 9 and 10 show noise when an FM unmodulated signal is input to the IF filter (intermediate frequency filter) 11 shown in FIG. 8, pulse noise is mixed at intervals of 2 msec, and interference from an adjacent station of 200 kHz is received. It is a figure which shows the waveform of the demodulation output after performing the demodulation output before removing, and noise removal. 9 and 10, the vertical axis indicates the magnitude of the amplitude of the output signal, and when the signal of FM 100% modulation is demodulated, the maximum value of the amplitude is normalized to be ± 0.25, and the horizontal axis is Indicates the output time of the demodulated signal. Here, a demodulated output in a 5 msec period from 225 msec to 230 msec is shown.

  FIG. 9A shows a demodulated output when there is no adjacent station. Since it is a demodulated output of an FM non-modulated signal, when there is no influence of pulse noise, the output is near 0 with no amplitude. Here, since the pulse noise is added, the demodulated output indicates that noise having a triangular shape is mixed at intervals of 2 msec due to the influence of the pulse noise mixed at intervals of 2 msec.

  FIG. 9B shows the result of removing the pulse noise by the conventional noise removing method under the same input conditions as in FIG. 9A. It is shown that the triangular amplitude of 2 msec interval described in FIG. 9A has been removed by the linear interpolation process.

  FIG. 10A shows a demodulated output when the same pulse noise is mixed as in FIG. 9A and the signal levels of the desired station and the adjacent station are close to each other. As in FIG. 9A, a noise having a triangular amplitude is shown in the demodulated output at intervals of 2 msec, but the width of the pulse expands to about twice that of FIG. 9A depending on the signal level of the adjacent station. Yes.

  FIG. 10B shows the result of removing the pulse noise by the conventional noise removal method under the same input conditions as those in FIG. As described above, the conventional pulse noise removal method is configured for the purpose of removing the noise having the triangular amplitude shown in FIG. 9A, and the removal time is fixed in the triangular amplitude period. Therefore, it is shown that it is difficult to remove noise having a triangular amplitude in which the width of the noise is widened.

  An AM / FM receiver according to one aspect of the present invention is an AM / FM receiver that detects pulse noise in a received signal and reduces pulse noise, and is adjacent to a reception target station in frequency. A noise removal technique selection unit that outputs a selection signal for selecting one of a plurality of noise removal means based on a level difference between a reception signal level of an adjacent station and a reception signal level of a reception target station; and a reception signal A noise gate group that performs noise removal by a plurality of noise removal means with different processing and a selection signal output by the noise removal method selection unit selects one noise removal means from the noise gate group. And a noise removal result switching unit for obtaining an output signal.

  An AM / FM receiver noise reduction method according to another aspect of the present invention is a method in which an AM / FM receiver detects pulse noise in a received signal to reduce the noise, and the reception target station The step of comparing the level difference between the reception signal level of the adjacent station adjacent to the frequency and the reception signal level of the reception target station, and noise removal by a plurality of noise removal means having different processes for the detection signal of the reception signal Respectively, a step of selecting one of a plurality of noise removing means based on the level difference, and a step of obtaining an output signal through the noise removing means selected for the detection signal of the received signal; ,including.

  According to the present invention, since a plurality of noise removal methods for removing pulse noise due to adjacent station interference are selected based on the signal level of the adjacent station, the pulse noise removal performance can be improved.

It is a block diagram which shows the structure of the FM receiver which concerns on 1st Example of this invention. It is a flowchart showing operation | movement of the pulse noise removal part of 1st Example of this invention. It is a figure which shows the example of the combination of the noise removal system in the pulse noise removal part of 1st Example of this invention. It is a figure which shows the example of the waveform from which the noise was reduced by the pulse noise removal part of 1st Example of this invention. It is a block diagram which shows the structure of the FM receiver based on 2nd Example of this invention. It is a flowchart showing operation | movement of the pulse noise removal part of 2nd Example of this invention. It is a figure which shows the example of the combination of the noise removal system in the pulse noise removal part of 2nd Example of this invention. It is a block diagram which shows the structure of the conventional FM receiver. It is a figure which shows the waveform by which noise reduction was carried out by the noise removal process in the conventional FM receiver. It is a figure which shows the waveform in which noise reduction is inadequate by the noise removal process in the conventional FM receiver.

  Hereinafter, an embodiment for carrying out the present invention will be outlined. Note that the reference numerals of the drawings attached to the following outline are only examples for facilitating understanding, and are not intended to be limited to the illustrated embodiments.

  An AM / FM receiver according to an embodiment of the present invention is an AM / FM receiver that detects pulse noise in a received signal and reduces pulse noise. A noise removal technique selection unit (31 in FIG. 1) for outputting a selection signal for selecting one of a plurality of noise removal means based on the level difference between the reception signal level and the reception signal level of the reception target station; A noise gate group (33, 34 in FIG. 1) that performs noise removal by a plurality of noise removal means having different processes on the detection signal of the received signal, and a selection signal output by the noise removal technique selection unit A noise removal result switching unit (32 in FIG. 1) that selects one noise removal unit from the gate group and obtains an output signal.

  In the AM / FM receiver, it is preferable that the plurality of noise removing units have a function of extending a noise removal period that is a target of noise removal.

  In the AM / FM receiver, one of a plurality of noise removing means (corresponding to 33 in FIG. 1) is a function of linearly interpolating signal levels at the start point and end point of the noise removal period and outputting an interpolated signal in the noise removal period. It is preferable to have.

  In the AM / FM receiver, another one of the plurality of noise removing means (corresponding to 34 in FIG. 1) has a function of holding and outputting the signal level at the start point of the noise removing period over the noise removing period. It is preferable.

  In the AM / FM receiver, the signal that does not remove the high band and the signal that suppresses the high band are added to the output signal of the noise removal result switching unit at a ratio corresponding to the received signal level of the adjacent station. A high frequency processing unit (corresponding to 35 in FIG. 5) may be further provided.

  According to the AM / FM receiver as described above, the type of noise removal processing is selected from the detected level by combining the level detection processing of the adjacent station and a plurality of noise removal methods, and the adjacent station interference is detected in the demodulated signal. Even if there is an influence, the noise removal effect can be improved.

  Hereinafter, it will be described in detail with reference to the drawings in accordance with embodiments.

  FIG. 1 is a block diagram showing the configuration of an FM receiver according to the first embodiment of the present invention. In FIG. 1, the same reference numerals as those in FIG. The FM receiver of the present embodiment includes a pulse noise removal unit 30 and a pulse noise detection unit 26a instead of the noise removal unit 22, the pulse noise detection unit 26, and the delay amount control unit 13 of FIG. The pulse noise removal unit 30 includes a noise removal method selection unit 31, a noise removal result switching unit 32, and noise gates 33 and 34.

  The noise gates 33 and 34 are blocks for performing different noise removal processing on the detection signal output from the FMDET (detector) 15, for example, previous value interpolation, linear interpolation, zero insertion, band limitation by a filter, etc. To remove pulse noise. The noise removal technique selection unit 31 is a signal for selecting an optimum processing method from the plurality of noise processes based on the signal level of the adjacent station output from the ADJ / ALT (adjacent station detection unit) 17. Is output to the noise removal result switching unit 32 and the noise gates 33 and 34. The pulse noise detection unit 26a sets the operation timing of the noise gates 33 and 34, that is, the noise removal interval, based on the detection signal output from the FMDET (detector) 15 and the signal output from the DIP (IF signal dent detection unit) 20. To do. The noise removal result switching 32 has a switching function for switching the noise-processed signal output from the noise gates 33 and 34 in accordance with the processing result of the noise removal method selection unit 31, and is a signal with reduced noise. Is output to Stereo (stereo decoder) 23.

  Next, operations of the pulse noise detection unit 26a and the pulse noise removal unit 30, which are main parts of the present invention, will be described. FIG. 2 is a flowchart showing the operation of the pulse noise removal unit of the first exemplary embodiment of the present invention.

  FIG. 3 is a diagram illustrating a specific example of a combination of noise determination and a noise removal method in the flowchart of FIG. In FIG. 3, the vertical axis represents the type of the detected adjacent station, and the horizontal axis represents the level difference from the detected adjacent station and the corresponding noise removal method. Then, in accordance with the contents of the vertical and horizontal axes, a threshold used for processing determination used by the noise removal technique selection unit 31, and noise removal methods such as linear interpolation and pre-interpolation used by the noise gates 33 and 34 The combination determined by the specific name is exemplified.

  In FIG. 2, the ADJ / ALT (adjacent station detection unit) 17 first measures the signal level of the reception target station (desired station) and the signal level of the adjacent station (step S101).

  The noise removal technique selection unit 31 determines a station having a higher level among the adjacent stations (step S102). If the station having a higher level is a station having a frequency higher than the desired station frequency, the process proceeds to step S103, and the frequency from the desired station frequency is determined. If the station has a low frequency, the process proceeds to step S105.

  When it is determined that the station with the higher level is a station having a frequency higher than the desired station frequency (YES in step S102), the desired station level is compared with the adjacent station level (step S103), and the signal level of the desired station is obtained. On the other hand, when the signal level of the adjacent station is larger than the threshold value 1 (YES in step S103), the noise removal result switching 32 selects a method (previous value interpolation) for holding the previous value in the noise removal section expanded by the noise gate 34. The process is terminated (step S104).

  In step S103, if the signal level of the adjacent station is smaller than the threshold 1 with respect to the signal level of the desired station (NO in step S103), the threshold 2 is set to determine whether the signal level of the desired station and the signal level of the adjacent station are close to each other. It judges using (step S110).

  When it is determined that the signal level of the adjacent station is close (YES in step S110), the noise removal result switching 32 selects a method of linear interpolation after extending the noise removal section twice with the noise gate 33. Then, the process ends (step S111).

  If it is determined in step S110 that the signal level of the desired station is not close to the signal level of the adjacent station (NO in step S110), it indicates that the signal level of the adjacent station is smaller than the signal level of the desired station. In the noise removal result switching 32, the method of linear interpolation in the noise removal section by the noise gate 33 is selected, and the process ends (step S112).

  If it is determined that the adjacent station has a frequency lower than the desired station frequency (NO in step S102), the desired station level is compared with the adjacent station level (step S105).

  When the signal level of the adjacent station is greater than the threshold value 1 or more than the signal level of the desired station (YES in step S105), the noise removal result switching 32 is a method of holding the previous value in the noise removal section expanded by the noise gate 34 (before Value interpolation) is selected and the process is terminated (step S106).

  In step S105, when the signal level of the adjacent station is smaller than the threshold value 1 with respect to the signal level of the desired station (NO in step S105), the threshold value 2 is set to determine whether the signal level of the desired station and the signal level of the adjacent station are close. It judges using (step S107).

  When it is determined that the signal levels of adjacent stations are close (YES in step S107), the noise removal result switching 32 selects a method of linear interpolation after extending the noise removal section by a noise gate 33 twice. Then, the process ends (step S108).

  If it is determined in step S107 that the signal level of the desired station is not close to the signal level of the adjacent station (NO in step S107), it indicates that the signal level of the adjacent station is smaller than the signal level of the desired station. In the noise removal result switching 32, the method of linear interpolation in the noise removal section by the noise gate 33 is selected, and the process ends (step S109).

  Next, the effect of noise reduction in the FM receiver that operates as described above will be described. FIG. 4 is a diagram illustrating an example of a waveform whose noise has been reduced by the pulse noise removing unit 30. This is a result of removing the pulse noise having the same input conditions as in FIG. 10A by the noise removal method selected by the above-described processing flowchart.

  In the flowchart of FIG. 2, a 200 kHz adjacent station is selected as the determination in step S101. Next, in step S102, since the station with a higher level among the adjacent stations is a station having a frequency higher than the desired station frequency, the process proceeds to step S103. Since the 200 kHz adjacent station is selected in step S101, the threshold value of the determination process in step S103 is selected to be +6 dB or more in FIG. 3, but the determination condition in step S103 is not satisfied, and the process proceeds to step S110.

  Here, since the 200 kHz adjacent station is selected in step S101, the threshold value for the determination process in step S110 is selected from +6 dB to -6 dB. Since this matches the input condition of FIG. 10A, step S111 is executed as a noise removal method. Step S111 is a linear interpolation method in which the noise removal interval in FIG. 3 is doubled, and it is shown that triangular noise having a wide pulse width that could not be removed by the conventional noise removal method is removed.

  FIG. 5 is a block diagram showing a configuration of an FM receiver according to the second exemplary embodiment of the present invention. In FIG. 5, the same reference numerals as those in FIG. The FM receiver of the present embodiment is an example in which a plurality of noise removal methods selected according to the adjacent station level are applied to the first embodiment.

  The FM receiver of FIG. 5 includes a pulse noise removing unit 30a instead of the pulse noise removing unit 30 of FIG. The pulse noise removing unit 30a includes, in the pulse noise removing unit 30, a noise gate 35 (corresponding to a high frequency processing unit) including a blend processing signal creation unit 36, a high frequency suppression processing unit 37, and a blend processing unit 38. Prepare to add.

  The high frequency suppression processing unit 37 is an LPF (low pass filter) that removes the high frequency of the output signal of the stereo (stereo decoder) 23. The blend processing signal creation unit 36 suppresses the signal from which the high frequency is not removed and the high frequency processed by the high frequency suppression processing unit 37 according to the signal level of the adjacent station output by the noise removal technique selection unit 31. The ratio of adding the received signals is calculated and output to the blend processing unit 38. The blend processing unit 38 adds the output signal from which the high frequency is not removed and the signal in which the high frequency processed by the high frequency suppression processing unit 37 is suppressed at the ratio calculated by the blend processing signal creation unit 36. And output.

  Next, the operation of the pulse noise removing unit 30a, which is the main part of the present invention, will be described. FIG. 6 is a flowchart showing the operation of the pulse noise removing unit 30a of the second embodiment. In FIG. 6, steps with the same reference numerals as in FIG. 2 perform the same processing. FIG. 7 is a diagram showing an example of a combination of noise determination and noise removal method in the flowchart of FIG. 6, and the format is the same as FIG.

  In step S201 following YES in step S105, and in S204 following YES in step S103, the pulse noise removing unit 30a selects a method (previous value interpolation) for holding the previous value in the noise removal section expanded by the noise gate 34, and A method of performing high-frequency suppression processing with the noise gate 35 is selected, and the processing ends.

  In step S202 following YES in step S107, and in S205 following YES in step S110, the pulse noise removing unit 30a selects a method of linear interpolation in which the noise removal section is doubled by the noise gate 33, and further the noise gate 35. The method for performing the high-frequency suppression process is selected with, and the process ends.

  In step S203 following NO in step S107 and in S206 following NO in step S110, the signal level of the adjacent station is smaller than the signal level of the desired station, and the pulse noise removal unit 30a performs noise gate as a noise removal method. In 33, a method of linear interpolation is selected and the process is terminated.

  According to the FM receiver as described above, by removing two types of noise removal methods, either the noise gates 33 and 34 and the noise gate 35, in series under a condition where noise is increased, pulse noise removal performance is achieved. Can be further enhanced.

  In each of the above embodiments, the FM receiver has been described. However, the AM receiver can be configured to include a similar pulse noise removing unit.

  It should be noted that the disclosures of the aforementioned patent documents and the like are incorporated herein by reference. Within the scope of the entire disclosure (including claims) of the present invention, the embodiments and examples can be changed and adjusted based on the basic technical concept. Various combinations and selections of various disclosed elements are possible within the scope of the claims of the present invention. That is, the present invention of course includes various variations and modifications that could be made by those skilled in the art according to the entire disclosure including the claims and the technical idea.

11 IF Filter (intermediate frequency filter)
12 MPC (Multipath Scancera)
14 Switch 15 FMDET (detector)
16 VAR (envelope dispersion detector immediately before detection)
17 ADJ / ALT (adjacent station detector)
18 S-meter (signal meter, electric field strength detector)
19 Adaptive Equivalent (Control Sequencer)
20 DIP (IF signal dent detector)
21 19K AM Mod (envelope swell detector)
22 Noise Gate (noise removal unit)
23 Stereo (stereo decoder)
24 USN (Ultrasonic Component Detection Unit)
25 DEV (overmodulation detector)
26a PN (pulse noise detector)
30, 30a Pulse noise removal unit 31 Noise removal method selection unit 32 Noise removal result switching unit 33 to 35 Noise gate 36 Blend processing signal creation unit 37 High frequency suppression processing unit 38 Blend processing unit 121 AGC (Automatic Gain Controller)
122 Adaptive Equalizer 151 Hilbert Transformer 152 ArcTan Operation Unit

Claims (7)

An AM / FM receiver that detects pulse noise in a received signal and reduces pulse noise,
A selection signal for selecting one of a plurality of noise removing means is output based on a level difference between a reception signal level of an adjacent station adjacent to the reception target station in frequency and a reception signal level of the reception target station. A noise removal method selection unit;
A noise gate group that performs noise removal by a plurality of the noise removal units having different processes on the detection signal of the reception signal, and
A noise removal result switching unit that selects one of the noise removal units from the noise gate group according to the selection signal output by the noise removal method selection unit, and obtains an output signal;
An AM / FM receiver comprising:   The AM / FM receiver according to claim 1, wherein the plurality of noise removing units have a function of extending a noise removal period that is a target of noise removal.   The one of the plurality of noise removing means has a function of linearly interpolating a signal level at a start point and an end point of the noise removal period and outputting an interpolated signal in the noise removal period. AM / FM receiver.   4. The AM / according to claim 3, wherein the other one of the plurality of noise removing means has a function of holding and outputting a signal level at a start point of the noise removing period over the noise removing period. FM receiver.   A high output signal that adds a signal that does not remove a high frequency band and a signal that suppresses the high frequency band at a ratio corresponding to the received signal level of the adjacent station with respect to the output signal of the noise removal result switching unit. The AM / FM receiver according to claim 3 or 4, further comprising a region processing unit. A method in which an AM / FM receiver detects pulse noise in a received signal and reduces the noise,
Comparing the level difference between the reception signal level of the adjacent station adjacent to the reception target station in frequency and the reception signal level of the reception target station;
A step of performing noise removal by a plurality of noise removal units having different processes, respectively, on the detection signal of the received signal;
Selecting one of the plurality of noise removing means based on the level difference;
Obtaining an output signal through the selected noise removing means for the detection signal of the received signal;
The noise removal processing method characterized by including.   The method further includes the step of adding a signal that does not remove a high frequency band to the output signal and a signal that suppresses the high frequency band at a ratio corresponding to the received signal level of the adjacent station and outputting the signal. The noise removal processing method according to claim 6.

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