JP2017046199A - Filter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter device that can be simply configured while flexibly changing the characteristics thereof.SOLUTION: Plural first type filter units 40 are connected to one another in parallel. A selection unit 42 is connected to each of the plural first type filter units 40. A second type filter unit 44 is connected to the selection unit 42. The plural respective first type filter units 40 have different pass bands. The selection unit 42 selects one signal from respective signals passed through the plural first type filter units 40. The second type filter unit 44 inputs the signal selected in the selection unit 42.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a filter technique, and more particularly to a filter device that extracts a desired signal.

  The communication device is provided with a band pass filter. The band pass filter is configured by serially connecting a high pass filter and a low pass filter. A local oscillator signal generator and a frequency mixer are connected to the input end side of the high-pass filter, and the station is also connected between the output end side of the high-pass filter and the input end side of the low-pass filter. A signal generator and a frequency mixer are connected (for example, refer to Patent Document 1).

Japanese Patent Laid-Open No. 10-285063

  A band pass filter physically requires a large number of mounting components. Moreover, since the characteristic is fixed according to a physical mounting component, versatility is lowered.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique for easily configuring the apparatus while flexibly changing characteristics.

  In order to solve the above problems, a filter device according to an aspect of the present invention includes a plurality of first type filter units connected in parallel, a selection unit connected to each of the plurality of first type filter units, and a selection And a second type filter unit connected to the unit. Each of the plurality of first type filter units has a different pass band. The selection unit selects one of the signals that have passed through each of the plurality of first type filter units, and the second type filter unit inputs the signal selected by the selection unit.

  Another embodiment of the present invention is also a filter device. This device is a filter device mounted on one MCU (Micro Controller Unit), which receives an analog signal from the outside and converts the analog signal into a digital signal, and the digital signal converted in the ADC unit. A filter unit that performs a filtering process on the signal, and a DAC unit that converts the digital signal subjected to the filtering process in the filter unit into an analog signal and outputs the analog signal to the outside.

  Note that any combination of the above-described constituent elements and the expression of the present invention converted between a method, an apparatus, a system, a computer program, or a recording medium recording the computer program are also effective as an aspect of the present invention. is there.

  According to the present invention, it is possible to simplify the configuration while flexibly changing the characteristics.

It is a figure which shows the structure of the receiver apparatus based on the Example of this invention. It is a figure which shows another structure of the receiver apparatus based on the Example of this invention. It is a figure which shows another structure of the receiver concerning the Example of this invention. It is a figure which shows the structure of the filter part of FIGS. 1-3. FIGS. 5A to 5G are diagrams illustrating an outline of processing of the first type filter unit of FIG. It is a figure which shows the structure of the 1st type filter part of FIG. It is a figure which shows the filter characteristic of the 1st type filter part of FIG. It is a figure which shows the output characteristic of the 1st type filter part of FIG. It is a figure which shows the filter characteristic of the 2nd type filter part of FIG. It is a figure which shows the output characteristic of the 2nd type filter part of FIG. It is a flowchart which shows the filtering procedure by the filter part of FIGS.

  Before specifically describing the embodiments of the present invention, an outline of the embodiments will be described. The embodiment relates to a frequency filter used for a voice call and using a general-purpose microcomputer. With the recent enhancement of communication infrastructure, calls using a mobile phone network have become natural in mobile vehicles. These calls are often made in a noisy environment, and therefore a technique is required to make it easier to hear the other party's voice. Up to now, for example, a low-pass filter is inserted into the audio line, and a dedicated IC having an equalizer function is also inserted. The low-pass filter reduces high-frequency noise, and the dedicated IC amplifies the volume of the human voice frequency band. In the low-pass filter, a circuit is constituted by discrete components. Further, in order to use the equalizer function, it is necessary to separately install an IC having the function or to use a DAC with a built-in equalizer function. For this, the system becomes expensive and the substrate area becomes large, and it becomes difficult to reduce the size of the system. Moreover, it is not preferable also in terms of occurrence of failure.

  In recent years, it can be said that there is no case where a general-purpose microcomputer not equipped with an ADC (Analog to Digital Converter) / DAC (Digital to Analog Converter) is used. Not many. An object of the present embodiment is to solve the problems in terms of price and area in the prior art, and to change the filter constant dynamically according to the characteristics of the voice of the speaker to correct the sound volume to the optimum level. For this purpose, the present embodiment realizes the low-pass filter that has been realized by the discrete components and the equalizer function that has been realized by the dedicated IC by the calculation capability of the ADC (DAC) and the CPU of the MCU (Micro Controller Unit). To do.

  FIG. 1 shows the configuration of a receiver 100 according to an embodiment of the present invention. The receiving device 100 includes a communication module 10, an MCU 12, an amplifier 14, and a speaker 16. The MCU 12 includes an ADC unit 20, a filter unit 22, and a DAC unit 24.

  The communication module 10 is compatible with a wireless communication system such as a mobile phone network, and executes communication with a communication device (not shown). Since a known technique may be used for the communication module 10, description thereof is omitted here. For example, the communication module 10 outputs the received signal to the MCU 12 as an analog signal. The analog signal corresponds to an audio signal generated by a user who uses the communication device.

  The MCU 12 corresponds to the above-described general-purpose microcomputer. One of the interfaces provided in the MCU 12 is an ADC unit 20, and the ADC unit 20 inputs an analog signal from the communication module 10. The ADC unit 20 converts an analog signal into a digital signal and outputs the digital signal to the filter unit 22. Here, the sampling frequency in the ADC unit 20 is set to 6.8 kHz or more, for example, 8.0 kHz. This is because the frequency band used for the audio signal is 0.3 to 3.4 kHz and the sampling theorem is taken into consideration. Further, the resolution of the ADC unit 20 is set to 10 bits or 8 bits. For example, since IP (Internet Protocol) telephone mainly uses 8-bit quantization, 8 bits or more are required.

  The filter unit 22 is a filter device mounted on the MCU 12 and is configured to be rewritable by a program. The filter unit 22 receives the digital signal from the ADC unit 20. The filter unit 22 performs a filtering process on the digital signal. Although details of the filtering process will be described later, for example, a high frequency band component is reduced and an audio frequency band component is amplified. If the sampling frequency of the ADC unit 20 is 8 kHz, the filter unit 22 should perform the filtering process at a period of 125 μsec. The filter unit 22 outputs the digital signal subjected to the filtering process to the DAC unit 24.

  The DAC unit 24 receives the digital signal subjected to the filtering process from the filter unit 22. The DAC unit 24 converts the digital signal into an analog signal and outputs the analog signal to the amplifier 14. Therefore, the DAC unit 24 is also one of the interfaces provided in the MCU 12. Here, the update rate of the DAC unit 24 is set in the same manner as the ADC unit 20. Further, the resolution of the DAC unit 24 is set to 8 bits.

  The amplifier 14 receives the analog signal from the DAC unit 24 and amplifies the analog signal. The amplifier 14 outputs the amplified analog signal to the speaker 16. The speaker 16 receives an analog signal from the amplifier 14 and outputs the analog signal as sound. A known technique may be used for the amplifier 14 and the speaker 16.

  FIG. 2 shows another configuration of the receiver 100 according to the embodiment of the present invention. The receiving device 100 includes a communication module 10, an MCU 12, an amplifier 14, a speaker 16, and a DAC 30. The communication module 10 here performs the same processing as the communication module 10 of FIG. 1, but outputs a digital signal instead of an analog signal. The output destination of the digital signal is the DAC 30. The DAC 30 converts the digital signal into an analog signal and outputs the analog signal to the MCU 12. Processing in the MCU 12, the amplifier 14, and the speaker 16 is the same as that in FIG.

  FIG. 3 shows still another configuration of the receiver 100 according to the embodiment of the present invention. The receiving device 100 includes a communication module 10, an MCU 12, an amplifier 14, a speaker 16, and a DAC 30. The MCU 12 includes an ADC unit 20, a filter unit 22, a DAC unit 24, and a packet processing unit 26.

  The signal received by the communication module 10 here is a signal corresponding to the IP phone. The communication module 10 outputs the IP packet to the MCU 12. The packet processing unit 26 of the MCU 12 inputs the IP packet from the communication module 10. The packet processing unit 26 extracts a voice signal included in the IP packet by executing reception processing on the IP packet. The audio signal corresponds to the digital signal in FIG. The packet processing unit 26 outputs a digital signal to the DAC 30. Processing in the DAC 30, the ADC unit 20, the filter unit 22, the DAC unit 24, the amplifier 14, and the speaker 16 is the same as that in FIG.

  FIG. 4 shows the configuration of the filter unit 22. The filter unit 22 includes a first type first filter unit 40a, a second first type filter unit 40b, a third first type filter unit 40c, a selection unit 42, and a second type filter collectively referred to as a first type filter unit 40. Part 44 is included.

  The first first type filter unit 40a, the second first type filter unit 40b, and the third first type filter unit 40c are connected in parallel. The number of first type filter units 40 connected in parallel is not limited to “3”. Each first type filter unit 40 is a band pass filter. Here, the frequency of the voice is generally assumed to be 100 to 1000 Hz, but the frequency having a peak among them varies depending on the person. Therefore, the first type filter units 40 have different passbands so that voices having different frequencies at the peak are extracted by any of the first type filter units 40. Here, FIGS. 5A to 5G are used to explain the difference in pass band from the first first-type filter unit 40a to the third first-type filter unit 40c.

  FIGS. 5A to 5G show an outline of processing of the first type filter unit 40. FIG. FIG. 5A shows the frequency characteristics of the digital signal input to each first type filter unit 40. The horizontal axis indicates the frequency, and the vertical axis indicates the amplitude. FIG. 5B shows the frequency characteristic of the first first-type filter unit 40a, FIG. 5C shows the frequency characteristic of the second first-type filter unit 40b, and FIG. 3 shows frequency characteristics of the first type filter unit 40c. As shown in FIGS. 5B to 5D, the frequency characteristics of the first-type filter units 40 are different from each other. The digital signal shown in FIG. 5A is input to each of the first type filter units 40 as described above. The result is shown as FIG. 5 (e)-(g). FIG. 5E shows an output signal from the first first-type filter unit 40a, FIG. 5F shows an output signal from the second first-type filter unit 40b, and FIG. The output signal from the 3rd 1st type filter part 40c is shown. Since the frequency characteristics of the first type filter units 40 are different, the amplitudes of the output signals are also different. Returning to FIG.

  Each first-type filter unit 40 is configured by a finite impulse response (FIR) filter. FIG. 6 shows the configuration of the first type filter unit 40. The first type filter unit 40 includes a first delay unit 50a, a second delay unit 50b, a third delay unit 50c, an Nth delay unit 50n, and a first tap unit collectively referred to as a delay unit 50. 52a, second tap section 52b, third tap section 52c, fourth tap section 52d, N + 1 tap section 52n + 1, first adder 54a, second adder 54b, and third adder 54c, collectively referred to as adder 54. , An Nth adder 54n.

  The first type filter unit 40 captures a digital signal by a timer interrupt that occurs at the same cycle as the sampling frequency. The plurality of delay units 50 are configured in a one-dimensional array, and delay the digital signal by operating or acting like a barrel shifter. Further, a tap coefficient is set for each tap unit 52. The tap coefficient is set so as to pass the band having the frequency characteristics shown in any of FIGS. 5B to 5D. Each tap unit 52 receives the digital signal or the digital signal delayed by the delay unit 50, and executes multiplication of the digital signal and the tap coefficient.

  The adding unit 54 adds the multiplication results from the tap unit 52. The addition unit 54 outputs the addition result to the selection unit 42 (not shown). Here, as the number of stages of “N”, the minimum number of stages is determined according to the frequency to be passed. Further, the number of stages is infinite when the function of the first-type filter unit 40 is realized by a software program as long as the memory and the computing capability allow. When the sampling frequency is 8 kHz, for example, “N” of the first-type filter unit 40 is set to 15 in order to extract a human voice around 0.48 kHz to 0.8 kHz.

  FIG. 7 shows the filter characteristics of the first type filter unit 40. The horizontal axis indicates the frequency, and the vertical axis indicates the amplitude. This corresponds to the frequency characteristic of any of the first first type filter unit 40a to the third first type filter unit 40c. FIG. 8 shows the output characteristics of the first type filter unit 40. As illustrated, the amplitudes at 0.8 kHz, 2.4 kHz, and 4.0 kHz increase in accordance with the frequency characteristics of the first type filter unit 40. Returning to FIG.

  The selection unit 42 is connected to each of the plurality of first type filter units 40 and inputs a digital signal that has passed through each first type filter unit 40. This digital signal corresponds to the addition result described above. The selection unit 42 selects one of the digital signals that have passed through each of the plurality of first type filter units 40. Specifically, the selection unit 42 calculates the average value of the amplitude of the digital signal for each first-type filter unit 40 over a certain period. Here, the predetermined period is set in advance. The selection unit 42 compares the calculated average values, selects the maximum average value, and selects the first type filter unit 40 that outputs a digital signal having the maximum average value.

  Note that the magnitude may be used instead of the amplitude, or another statistical value such as a median value may be used instead of the average value, and the selection unit 42 performs the same processing on them. The selection unit 42 outputs the digital signal input from the selected first type filter unit 40 to the second type filter unit 44. Such selection by the selection unit 42 may be made not only at the timing when the call is started but also during the call. At that time, hysteresis may be set in the first type filter unit 40 in order to suppress occurrence of a situation in which the first type filter unit 40 is frequently switched. For example, the selection unit 42 adds a predetermined value to the average value from the first type filter unit 40 selected once. The selection unit 42 outputs the selected digital signal to the second type filter unit 44.

  The second type filter unit 44 is connected to the selection unit 42 and inputs the digital signal selected by the selection unit 42. The second type filter unit 44 is a low-pass filter and reduces high-frequency noise components in the input digital signal. Similar to the first type filter unit 40, the second type filter unit 44 is composed of an FIR filter. On the other hand, as described above, the second type filter unit 44 is a low-pass filter and the first type filter unit 40 is a band-pass filter. The type 1 filter unit 40 has different coefficients and the number of stages.

  If it demonstrates concretely, the 2nd type filter part 44 will be comprised by 3 taps or 5 taps. When the frequency characteristic of the low-pass filter is attenuated from 0 kHz, the first type filter unit 40 is configured with 3 taps, and after the frequency characteristic of the low-pass filter maintains a gain of 1.0 until about 1.2 kHz. In the case of attenuation, the first type filter unit 40 is configured with 5 taps. For example, in the case of 3 taps, the tap coefficient is (1, 2, 1), and in the case of 5 taps, the tap coefficient is (-1, 3, 8, 3, -1). As described above, the number of taps of the second type filter unit 44 is made smaller than the number of taps of the plurality of first type filter units 40.

  FIG. 9 shows the filter characteristics of the second type filter unit 44. The horizontal axis indicates the frequency, and the vertical axis indicates the amplitude. This corresponds to a frequency characteristic that attenuates after maintaining a gain of 1.0 up to about 1.2 kHz. FIG. 10 shows the output characteristics of the second type filter unit 44. As shown in the figure, the amplitude in the vicinity of 0,8 kHz is larger than the others in accordance with the voice of the person, so that the user can output a low hearing noise.

  This configuration can be realized in terms of hardware by a CPU, memory, or other LSI of any computer, and in terms of software, it can be realized by a program loaded in the memory, but here it is realized by their cooperation. Draw functional blocks. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms only by hardware, or by a combination of hardware and software.

  The operation of the filter unit 22 configured as above will be described. FIG. 11 is a flowchart showing a filtering procedure by the filter unit 22. The filter unit 22 takes in the digital signal from the ADC unit 20 (S10). Each of the multiple first type filter units 40 performs FIR filter processing (S12). The selection unit 42 determines an optimum filter from the plurality of first type filter units 40 (S14). The second type filter unit 44 executes FIR filter processing (S16). The second type filter unit 44 outputs a digital signal to the DAC unit 24 (S18).

  According to the present embodiment, since one of the plurality of first type filter units is selected, it is possible to use filters adapted to voices having various characteristics. In addition, since a filter matched to voices with various characteristics is used, a desired component can be extracted. Further, since the second filter unit is disposed at the rear of the first type filter unit, the noise component can be reduced. In addition, since the noise component is reduced, the quality of voice can be improved. Further, since the two types of filters are combined, the voice component can be extracted by the band pass filter, and the noise component can be extracted by the low pass filter. Further, since only two types of filters are combined, the configuration can be simplified.

  In addition, since each of the plurality of first type filter units has different frequency characteristics, it can be adapted to various voice characteristics. Further, since the number of taps of the second type filter unit is made smaller than the number of taps of the plurality of first type filter units, the amount of calculation can be reduced. Further, since the number of taps of the second type filter unit is made smaller than the number of taps of the plurality of first type filter units, the scale of the program can be reduced. Moreover, since the number of taps of the second type filter unit is made smaller than the number of taps of each of the plurality of first type filter units, the amount of memory can be reduced.

  In addition, since the filter device is mounted on the MCU including the ADC unit and the DAC unit, the filter device can be configured by a software program. Moreover, since the filter device is configured by a software program, the filter configuration can be flexibly changed. Further, since the filter device is constituted by a software program, it is possible to rewrite later. In addition, since it is possible to rewrite later, it is possible to easily execute a trial manufacture of the filter. In addition, since later rewriting becomes possible, the version of the filter can be easily upgraded. Further, since the ADC unit and the DAC unit are provided in the MCU, they can be used until the MCU fails. Moreover, since the ADC unit, the filter unit, and the DAC unit are provided in the MCU, it is possible to suppress an increase in size of the apparatus even when a low frequency is used.

  In the above, this invention was demonstrated based on the Example. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to each of those constituent elements or combinations of processing processes, and such modifications are also within the scope of the present invention. .

  The outline of one embodiment of the present invention is as follows. A filter device according to an aspect of the present invention includes a plurality of first type filter units connected in parallel, a selection unit connected to each of the plurality of first type filter units, and a second type connected to the selection unit. And a filter unit. Each of the plurality of first type filter units has a different pass band. The selection unit selects one of the signals that have passed through each of the plurality of first type filter units, and the second type filter unit inputs the signal selected by the selection unit.

  According to this aspect, since the second type filter unit is used after selecting one of the plurality of first type filter units, a desired component can be extracted in accordance with voices having various characteristics.

  Each of the plurality of first type filter units may be a band pass filter, and the second type filter unit may be a low pass filter. In this case, since two types of filters are combined, a voice component can be extracted with a band-pass filter, and a noise component can be extracted with a low-pass filter.

  Each of the plurality of first type filter units may have different frequency characteristics. In this case, since they have different frequency characteristics, they can be adapted to various voice characteristics.

  The plurality of first type filter units and the second type filter unit are finite impulse response (FIR) filters, and the number of taps of the second type filter unit is smaller than the number of taps of the plurality of first type filter units. . In this case, since the number of taps of the second type filter unit is made smaller than the number of taps of the plurality of first type filter units, the amount of calculation can be reduced.

  Another embodiment of the present invention is also a filter device. This device is a filter device mounted on one MCU (Micro Controller Unit), which receives an analog signal from the outside and converts the analog signal into a digital signal, and the digital signal converted in the ADC unit. A filter unit that performs a filtering process on the signal, and a DAC unit that converts the digital signal subjected to the filtering process in the filter unit into an analog signal and outputs the analog signal to the outside.

  According to this aspect, since the filter device is mounted on the MCU including the ADC unit and the DAC unit, the filter configuration can be flexibly changed.

  The filter unit includes a plurality of first type filter units connected in parallel, a selection unit connected to each of the plurality of first type filter units, and a second type filter unit connected to the selection unit. Also good. Each of the plurality of first type filter units may have different passbands. The selection unit may select one of the digital signals that have passed through each of the plurality of first type filter units, and the second type filter unit may input the digital signal selected by the selection unit.

  In the present embodiment, the first type filter unit 40 includes two types of filters: a plurality of first type filter units 40 and a selection unit 42. However, the present invention is not limited to this. For example, the first type filter unit 40 may include only one type of filter, or may include three or more types of filters. According to this modification, the degree of freedom of configuration can be expanded.

  In the present embodiment, the first type filter unit 40 is a band pass filter, and the second type filter unit 44 is a low pass filter. However, the present invention is not limited to this. For example, the types of filters used for the first type filter unit 40 and the second type filter unit 44 may be different. According to this modification, the degree of freedom of configuration can be expanded.

  In the present embodiment, the first type filter unit 40 and the second type filter unit 44 are configured by FIR filters. However, the present invention is not limited to this. For example, an FIR filter may not be used for the first type filter unit 40 and the second type filter unit 44, and an infinite impulse response (IIR) filter may be used. According to this modification, the degree of freedom of configuration can be expanded.

  10 communication modules, 12 MCUs, 14 amplifiers, 16 speakers, 20 ADC units, 22 filter units, 24 DAC units, 26 packet processing units, 30 DACs, 40 first type filter units, 42 selection units, 44 second type filter units , 50 delay unit, 52 tap unit, 54 adder unit, 100 receiver.

Claims (6)

A plurality of first-type filter units connected in parallel;
A selection unit connected to each of the plurality of first type filter units;
A second type filter unit connected to the selection unit,
Each of the plurality of first type filter units has a different pass band,
The selection unit selects one from the signals that have passed through each of the plurality of first type filter units,
The second type filter unit inputs a signal selected by the selection unit. Each of the plurality of first type filter units is a bandpass filter,
The filter device according to claim 1, wherein the second type filter unit is a low-pass filter.   The filter device according to claim 2, wherein each of the plurality of first type filter units has different frequency characteristics. The plurality of first type filter units and the second type filter unit are finite impulse response (FIR) filters,
4. The filter device according to claim 1, wherein the number of taps of the second type filter unit is smaller than the number of taps of the plurality of first type filter units. 5. A filter device mounted on one MCU (Micro Controller Unit),
An ADC unit for inputting an analog signal from the outside and converting the analog signal into a digital signal;
A filter unit that performs a filtering process on the digital signal converted in the ADC unit;
A DAC unit that converts the digital signal subjected to the filtering process in the filter unit into an analog signal and outputs the analog signal to the outside;
A filter device comprising: The filter unit is
A plurality of first-type filter units connected in parallel;
A selection unit connected to each of the plurality of first type filter units;
A second type filter unit connected to the selection unit,
Each of the plurality of first type filter units has a different pass band,
The selection unit selects one from the digital signals that have passed through each of the plurality of first type filter units,
The filter device according to claim 5, wherein the second type filter unit inputs the digital signal selected by the selection unit.

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