Patent Publication Number: US-10778192-B2

Title: Filter coefficient calculation device, signal generation device including the same, filter coefficient calculation method, and signal generation method

Description:
TECHNICAL FIELD 
     The present invention relates to a filter coefficient calculation device calculating a filter coefficient of a finite impulse response (FIR) filter, a signal generation device including the filter coefficient calculation device, a filter coefficient calculation method, and a signal generation method. 
     BACKGROUND ART 
     Finite Impulse Response (FIR) filters have been used in circuits in various fields such as digital communication, sound processing, and image processing. For example, in a field of digital communication, an emphasis optimization device that optimizes a setting value of an emphasis function to be added to an input digital signal is known (see Patent Document 1). Meanwhile, the emphasis function refers to a function of correcting a waveform in order to cancel the amount of deterioration of the waveform because the waveform may deteriorate due to frequency characteristics of a transmission line, a circuit, and the like in high-speed data communication. 
     The emphasis optimization device disclosed in Patent Document 1 includes inverse characteristic calculation means for calculating an inverse characteristic of an amplitude characteristic of a transmission line, inverse Fourier transform means for performing inverse Fourier transform on the inverse characteristic of the amplitude characteristic of the transmission line to obtain an optimal impulse response, impulse response cutout means for cutting out the number of taps necessary for an emphasis function from the impulse response, and optimal setting value calculation means for converting the cut-out impulse response into a value of an emphasis function to calculate an optimal setting value. 
     With such a configuration, the emphasis optimization device disclosed in Patent Document 1 can obtain an optimal setting value of an emphasis function without troublesome work. 
     RELATED ART DOCUMENT 
     Patent Document 
     [Patent Document 1] JP-A-2013-201661 
     DISCLOSURE OF THE INVENTION 
     Problem that the Invention is to Solve 
     However, in the emphasis optimization device disclosed in Patent Document 1, it is possible to suitably cope with a case where the number of taps of the FIR filter is approximately 2 and a transmission speed is approximately 25 Gbit/sec, but it is difficult to cope with the demand for an increase in functionality in recent years, and thus there is a desire for improvement. 
     Specifically, in the emphasis optimization device disclosed in Patent Document 1, it is necessary to perform troublesome processing to calculate a filter coefficient in a case where an ultra high speed digital signal of 30 Gbit/sec is processed, for example, by an FIR filter having 10 taps, and thus it is difficult to calculate a filter coefficient within a practical time. 
     In addition, there are various functions for performing predetermined processing on an input signal by an FIR filter as disclosed in Patent Document 1 and a device is independent for each function in the related art, and thus there has been a desire to realize a plurality of functions in a switching manner by one FIR filter. 
     The invention is contrived in view of the above-described situations, and an object thereof is to provide a filter coefficient calculation device capable of calculating a filter coefficient of an FIR filter having a relatively large number of taps at high speed and realizing a plurality of functions, a signal generation device including the filter coefficient calculation device, a filter coefficient calculation method, and a signal generation method. 
     Means for Solving the Problem 
     According to an aspect of the invention, there is provided a signal generation device comprising a filter coefficient calculation device, signal generation means for generating a signal for testing a test target device, and a finite impulse response filter which has a plurality of predetermined functions executable by the finite impulse response filter depending on a filter coefficient, for setting a filter coefficient calculated by the filter coefficient calculation device, receiving the signal from the signal generation means, performing one or some functions on the signal, and outputting the signal to the test target device, in which the filter coefficient calculation device comprises a plurality of transfer function calculation means for calculating transfer functions of the finite impulse response filter, each of the plurality of transfer function calculation means corresponds to each of the plurality of predetermined functions of the finite impulse response filter, selection means for selecting one or some of the transfer functions in the plurality of the transfer function calculation means, and the filter coefficient calculation means for performing inverse Fourier transform on the transfer function selected by the selection means or a product of the transfer functions selected by the selection means to obtain an impulse response of the finite impulse response filter as the filter coefficient. 
     With such a configuration, the signal generation device according to the aspect of the invention can perform inverse Fourier transform on the transfer function in one function selected by the selection means or a product of the transfer functions in the plurality of functions selected by the selection means to obtain the impulse response of the finite impulse response filter, and can calculate the impulse response as the filter coefficient. 
     That is, the signal generation device according to the aspect of the invention does not require complicated processing to calculate the filter coefficient, and can realize the plurality of functions by one FIR filter. 
     Therefore, the signal generation device according to the aspect of the invention can calculate the filter coefficient of the FIR filter having a relatively large number of taps at high speed and can realize the plurality of functions. 
     In the signal generation device according to the aspect of the invention, the function designation means may comprise at least one of an emphasis function unit that adds an emphasis function to the signal generated by the signal generation means, a channel emulator function unit that adds a function of simulating a channel through which the signal passes to the signal output to the test target device, and an intersymbol interference function unit that adds a function of exerting influence of intersymbol interference on the signal output to the test target device. 
     With such a configuration, the signal generation device according to the aspect of the invention can realize at least one of the emphasis function, the channel emulator function, and the intersymbol interference function by one FIR filter. 
     In the signal generation device according to the aspect of the invention, the channel emulator function unit may add the function of simulating the channel on the basis of scattering parameters of the test target device. 
     With such a configuration, the signal generation device according to the aspect of the invention can add the function of simulating the channel on the basis of the scattering parameters of the test target device. 
     The signal generation device according to the aspect of the invention may further comprise a display device that comprises an operation unit for detecting a selection operation of causing a user to select one or the plurality of functions, in which the operation unit may output a signal indicating one or the plurality of functions selected by the selection operation of the user to the selection means. 
     With such a configuration, the signal generation device according to the aspect of the invention comprises the display device comprising the operation unit for detecting the selection operation of causing the user to select one or the plurality of functions from among the plurality of functions, and thus it is possible to cause the user to intuitively ascertain that the signal generation device has the plurality of functions and any functions can be synthesized. 
     In the signal generation device according to the aspect of the invention, the display device may comprise a display unit that displays a setting state of one or the plurality of functions selected by the selection operation of the user. 
     With such a configuration, the signal generation device according to the aspect of the invention can cause the user to intuitively ascertain the setting state of one or the plurality of functions. 
     According to another aspect of the invention, there is provided a signal generation method comprising a filter coefficient calculation step for a finite impulse response filter that has a plurality of predetermined functions executable by the finite impulse response filter depending on a filter coefficient, a signal generation step of generating a signal for testing a test target device, a filter coefficient setting step of setting a filter coefficient calculated by the filter coefficient calculation step in the finite impulse response filter, and a signal output step of causing the finite impulse response filter to perform the predetermined function or functions on the signal generated in the signal generation step and outputting the signal to the test target device, in which the filter coefficient calculation step comprises a transfer function calculation step of calculating a plurality of transfer functions, each of the plurality of the transfer functions corresponds to each of the plurality of the predetermined functions of the finite impulse response filter, a selection step of selecting one or some transfer functions in the plurality of the transfer functions, and a filter coefficient calculation step of performing inverse Fourier transform on the transfer function in the function selected in the selection step or a product of the some transfer functions selected in the selection step to obtain an impulse response of the finite impulse response filter as the filter coefficient. 
     With such a configuration, in the signal generation method according to the aspect of the invention, it is possible to perform inverse Fourier transform on the transfer function in one function selected in the selection step or a product of the transfer functions in the plurality of functions selected in the selection step to obtain the impulse response of the finite impulse response filter, and to calculate the impulse response as the filter coefficient. 
     That is, in the signal generation method according to the aspect of the invention, complicated processing is not required to calculate the filter coefficient, and it is possible to realize the plurality of functions by one FIR filter. 
     Therefore, in the signal generation method according to the aspect of the invention, it is possible to calculate the filter coefficient of the FIR filter having a relatively large number of taps at high speed and to realize the plurality of functions. 
     With such a configuration, the signal generation method according to the aspect of the invention includes the filter coefficient calculation method, and thus it is possible to calculate the filter coefficient of the FIR filter having a relatively large number of taps at high speed and to realize the plurality of functions. 
     The signal generation method according to the aspect of the invention may further include at least one of an emphasis function step of adding emphasis function to the signal, a channel emulator function step of adding a function of simulating a channel through which the signal passes to the signal output to the test target device, and an intersymbol interference function step of adding a function of exerting influence of intersymbol interference on the signal output to the test target device. 
     In the signal generation method according to the aspect of the invention, the channel emulator function step may add the function of simulating the channel on the basis of scattering parameters of the test target device. 
     The signal generation method according to the aspect of the invention may further comprise a display step of detecting a selection operation of causing a user to select one or the plurality of functions to display the detected selection operation, in which a signal indicating one or the plurality of functions selected by the selection operation of the user may be output to the selection step. 
     In the signal generation method according to the aspect of the invention, the display step may display a setting state of one or the plurality of functions selected by the selection operation of the user. 
     Advantage of the Invention 
     The invention can provide a filter coefficient calculation device having an effect of making it possible to calculate a filter coefficient of an FIR filter having a relatively large number of taps at high speed and realize a plurality of functions, a signal generation device comprising the filter coefficient calculation device, a filter coefficient calculation method, and a signal generation method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a configuration diagram of an FIR filter in an embodiment of the invention. 
         FIG. 2  is a diagram illustrating functions in the embodiment of the invention. 
         FIG. 3  is a functional configuration diagram of a signal generation device in the embodiment of the invention. 
         FIG. 4  is a diagram illustrating an emphasis function screen in the embodiment of the invention. 
         FIG. 5  is a diagram illustrating a channel emulator function in the embodiment of the invention. 
         FIG. 6  is a diagram illustrating an ISI function screen in the embodiment of the invention. 
         FIG. 7  is a flowchart of the signal generation device in the embodiment of the invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Outline of this Embodiment 
     First, an outline of a signal generation device in this embodiment will be described with reference to  FIGS. 1 and 2 . 
     The signal generation device in this embodiment is a device that includes an FIR filter capable of executing three functions and outputs a test signal to a test target device (DUT). 
     As illustrated in  FIG. 1 , an FIR filter  12  included in the signal generation device in this embodiment includes a delay device  12   a , a multiplier  12   b , and an adder  12   c . In the drawing, hN denotes a filter coefficient, and N denotes the number of taps. 
     In  FIG. 1 , when an input signal is denoted by x(n), an output signal is denoted by y(n), and an impulse response of the FIR filter  12  is denoted by φ, the impulse response φ is represented by [Expression 1] and the output signal y(n) is represented by [Expression 2]. Meanwhile, n denotes a time, ω denotes a frequency, and a sign * denotes a convolution integral. 
     
       
         
           
             
               
                 
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     It is assumed that the signal generation device in this embodiment realizes the following three functions by the FIR filter  12  having 10 taps. 
     (1) Emphasis Function 
     (2) Channel Emulator Function 
     (3) ISI (intersymbol interference) Function 
     As described in Background Art, an emphasis function is a function of correcting a waveform in order to cancel the amount of deterioration of the waveform. A channel emulator function is a function of adding a function of simulating a channel through which a signal to be output to a DUT passes to the signal. An Inter Symbol Interference (ISI) function is a function of adding a function of exerting the influence of intersymbol interference on the signal to be output to the DUT. 
     As illustrated in  FIG. 2 , the signal generation device in this embodiment is configured such that three functions are arranged in series and one or a plurality of functions can be selected from among the three functions. For example, in the signal generation device, the emphasis function is turned on so as to be in a selected state, and the channel emulator function and the ISI function are turned off so as to be in an unselected state. In addition, for example, in the signal generation device, the emphasis function and the ISI function are turned on so as to be in a selected state and synthesized, and the channel emulator function is turned off so as to be in an unselected state. In addition, for example, in the signal generation device, the three functions can also be turned on so as to be in a selected state and synthesized. 
     (Method of the Related Art) 
     Here, a case where the above-described three functions are realized by the FIR filter  12  will be described using a method of the related art. 
     (1) Emphasis Function 
     When a filter coefficient is set to be hEk, an input signal is set to be xE(n), an output signal is set to be yE(n), and an impulse response is set to be φE in the emphasis function, the impulse response φE is represented by [Expression 3] and the output signal yE(n) is represented by [Expression 4]. 
     
       
         
           
             
               
                 
                   
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     (2) Channel Emulator Function 
     When a filter coefficient is set to be hVk, an input signal is set to be xV(n), an output signal is set to be yV(n), and an impulse response is set to be φV in the channel emulator function, the impulse response φV is represented by [Expression 5] and the output signal yV(n) is represented by [Expression 6]. 
     
       
         
           
             
               
                 
                   
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     Since xV(n)=yE(n), [Expression 6] is represented by [Expression 7]. 
     
       
         
           
             
               
                 
                   
                     
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     (3) ISI Function 
     When a filter coefficient is set to be hIk, an input signal is set to be xI(n), an output signal is set to be yI(n), and an impulse response is set to be φI in the ISI function, the impulse response φI is represented by [Expression 8] and the output signal yI(n) is represented by [Expression 9]. 
     
       
         
           
             
               
                 
                   
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     When there is an attempt to synthesize the above-described three functions by the FIR filter  12  having 10 taps, an FIR filter having 30 taps is required. However, as described in the [Problem that the Invention is to Solve] column, complicated processing is required to calculate a filter coefficient, and it is difficult to calculate the filter coefficient within a practical time, which is impractical. 
     (Method of this Embodiment) 
     In a field of digital signal processing, it is known that a product of transfer functions (frequency characteristics of impulse responses) is equivalent to a convolution integral. The inventor of the invention has solved the problem focusing on this point. Hereinafter, a specific description thereof will be given. 
     In  FIG. 2 , when a transfer function in the emphasis function is set to be ΦE(ω), a transfer function in the channel emulator function is set to be ΦV(ω), and a transfer function in the ISI function is set to be ΦI(ω), the output signal y(n) is represented by [Expression 11].
 
 y ( n )=Ø E *Ø V *Ø I   *X   I   [Expression 11]
 
     When Fourier transform is performed on [Expression 11], [Expression 12] is obtained.
 
 Y (ω)=Φ E (ω)·Φ V (ω)·Φ I (ω)· X (ω)  [Expression 12]
 
     Here,
 
Φ(ω)=Φ E (ω)·Φ V (ω)·Φ I (ω)  [Expression 13]
 
is established.
 
     As described above, a product of transfer functions (frequency characteristics of impulse responses) is equivalent to a convolution integral, and thus it is possible to obtain an impulse response φ(n) by performing inverse Fourier transform on [Expression 13]. That is, the signal generation device in this embodiment can obtain the impulse response φ(n) by simple calculation using a product of transfer functions without performing complicated calculation of a convolution integral, and thus it is possible to calculate a filter coefficient of the FIR filter  12  having a relatively large number of taps at high speed and to realize a plurality of functions. 
     Meanwhile, in [Expression 13], in a case where there is an unselected function from among the three functions, the transfer function thereof is set to 1. For example, in a case where the emphasis function is not selected, the transfer function thereof ΦE(ω) is set to 1. 
     In addition, a frequency characteristic (transfer function) of the FIR filter  12  can be obtained as follows on the basis of [Expression 14]. Meanwhile, T denotes the number of pieces of data, and m denotes a numerical range from 0 to (T−1).
 
Z=e j2πm/T   [Expression 14]
 
     The transfer function ΦE(ω) in the emphasis function is obtained by substituting [Expression 14] for the right side of [Expression 3]. In addition, the transfer function ΦV(ω) in the channel emulator function is obtained by substituting [Expression 14] for the right side of [Expression 5]. In addition, the transfer function ΦI(ω) in the ISI function is obtained by substituting [Expression 14] for the right side of [Expression 8]. 
     [Description of Configuration] 
     Next, a configuration in an embodiment of a signal generation device  10  according to the invention will be described. 
     As described in  FIG. 3 , the signal generation device  10  in this embodiment includes a signal generation unit  11 , the FIR filter  12 , a display device  20 , and a filter coefficient calculation device  30 . The signal generation device  10  includes a microcomputer including a CPU, a ROM, a RAM, an input and output circuit to which various interfaces are connected, and the like. The signal generation device  10  causes the microcomputer to function as each function unit  40  of the signal generation device  10  by causing the ROM to execute a control program stored in advance. 
     A DUT  1  as a test target device is connected to the signal generation device  10 , and an error detector  2  is connected to the DUT  1 . The signal generation device  10  outputs an ultra high speed digital signal having a transmission speed of, for example, 30 Gbit/sec to the DUT  1  as a test signal, and the error detector  2  detects an error rate of the DUT  1  on the basis of the test signal from the signal generation device  10 . 
     The signal generation unit  11  generates a digital signal of a pulse pattern based on a communication standard or any pulse pattern on the basis of a control signal received from an operation unit  21  (to be described later) of the display device  20 , and outputs the generated digital signal to the FIR filter  12 . The signal generation unit  11  is an example of signal generation means. 
     As illustrated in  FIG. 1 , the FIR filter  12  includes the delay device  12   a , the multiplier  12   b , and the adder  12   c , and has 10 taps. A filter coefficient calculated by the filter coefficient calculation device  30  is set for the multiplier  12   b  of the FIR filter  12 , and the FIR filter  12  performs predetermined processing on an input digital signal and outputs the processed signal to the DUT  1 . Meanwhile, in this embodiment, the number of taps of the FIR filter  12  is set to 10, but the invention is not limited thereto. 
     The filter coefficient calculation device  30  includes the function unit  40  and a filter coefficient synthesis unit  50 . The function unit  40  includes an emphasis function unit  41 , a channel emulator function unit  42 , and an ISI function unit  43 . A signal indicating a function selected by a user and various parameters for executing functions are input to the function unit  40  from the operation unit  21 . Meanwhile, in this embodiment, an example in which three functions are realized by one FIR filter  12  is described, but the invention is not limited to the realization of the three functions. In addition, the function unit  40  is an example of functional means. 
     The emphasis function unit  41  includes a first transfer function calculation unit  41   a . The first transfer function calculation unit  41   a  calculates the transfer function ΦE(ω) in the emphasis function on the basis of [Expression 3] and [Expression 14]. Meanwhile, the first transfer function calculation unit  41   a  is an example of transfer function calculation means. 
     The channel emulator function unit  42  includes a second transfer function calculation unit  42   a  and an S parameter (Scattering parameter) storage unit  42   b.    
     The second transfer function calculation unit  42   a  calculates the transfer function ΦV(ω) in the channel emulator function on the basis of [Expression 5] and [Expression 14]. Here, the second transfer function calculation unit  42   a  converts an S parameter of the DUT  1  which is stored in the S parameter storage unit  42   b  into the FIR filter  12  having 10 taps to calculate the transfer function ΦV(ω). Meanwhile, the second transfer function calculation unit  42   a  is an example of transfer function calculation means. 
     The S parameter storage unit  42   b  stores the S parameter of the DUT  1  which is acquired in advance using, for example, a network analyzer. 
     The ISI function unit  43  includes a third transfer function calculation unit  43   a . The third transfer function calculation unit  43   a  calculates the transfer function ΦI(ω) in the ISI function on the basis of [Expression 8] and [Expression 14]. Meanwhile, the third transfer function calculation unit  43   a  is an example of transfer function calculation means. 
     The filter coefficient synthesis unit  50  includes a function selection unit  51  and a filter coefficient calculation unit  52 . 
     The function selection unit  51  selects one or more functions from among the three functions and inputs the selected transfer function on the basis of a function selection signal (to be described later) from the operation unit  21 , and thus the function selection unit  51  selects at least one from among the emphasis function unit  41 , the channel emulator function unit  42 , and the ISI function unit  43 . The function selection unit  51  is an example of selection means. 
     The filter coefficient calculation unit  52  performs inverse Fourier transform on a transfer function in one function input by the function selection unit  51  or a product of transfer functions in a plurality of functions on the basis of [Expression 13] to obtain an impulse response of a finite impulse response filter, and calculates the impulse response as a filter coefficient. For example, in a case where a plurality of functions are selected by the operation unit  21 , the filter coefficient calculation unit  52  calculates a filter coefficient obtained by synthesizing the functions. In addition, the filter coefficient calculation unit  52  sets the calculated filter coefficient in the FIR filter  12 . Meanwhile, the filter coefficient calculation unit  52  is an example of filter coefficient calculation means. 
     The display device  20  includes the operation unit  21  which includes, for example, a touch panel and outputs an operation signal in accordance with a user&#39;s touch operation, and a display unit  22  which is disposed so as to overlap the operation unit  21  and includes a liquid crystal display. 
     The operation unit  21  is operated by the user and inputs various parameters for executing functions of the function unit  40 . In addition, the operation unit  21  detects a selection operation for causing the user to select one or a plurality of functions from among the three functions, and outputs a function selection signal. Further, the operation unit  21  instructs the signal generation unit  11  to generate a signal. 
     The display unit  22  includes a display control circuit and displays a predetermined image. In addition, the display unit  22  can display a setting state of one or a plurality of functions selected by the operation unit  21  on the basis of the function selection signal output from the operation unit  21 . Further, the display unit  22  is configured to be capable of monitoring an output signal of the FIR filter  12  on the basis of a control signal received from the operation unit  21 . 
     An example of the function of the display unit  22  will be described with reference to  FIGS. 4 to 6 .  FIGS. 4 to 6  respectively illustrate display screens of the display unit  22  in a case where an emphasis function, a channel emulator function, and an ISI function are selected. 
       FIG. 4  illustrates an example of an emphasis function screen  60 . The emphasis function screen  60  is provided with a function display region  61  schematically showing configurations and selected states of functions, and a setting state display region  62  showing a setting state of the emphasis function. 
     The signal generation device  10  can cause a user to intuitively ascertain that there are three functions of the emphasis function, the channel emulator function, and the ISI function as functions incorporated into the signal generation device  10  by providing the function display region  61  in the emphasis function screen  60 , and it is possible to synthesize any functions by touching selection buttons  61   a  to  61   c . In the example illustrated in  FIG. 4 , the selection button  61   a  is turned on by the user, and the emphasis function is selected. 
     In addition, the setting state display region  62  is provided with a form setting portion  62   a  for setting any one form of pre-emphasis or de-emphasis in the emphasis function, and an amplitude setting portion  62   b  for setting an amplitude of a signal. Further, the setting state display region  62  is provided with an output monitoring region  62   c . In the output monitoring region  62   c , an emphasis function based on 10 taps can be set by the voltage setting portion  62   d  of va to vj, and a waveform set by the voltage setting portion  62   d  can be monitored. Meanwhile, the selection buttons  61   a  to  61   c , the form setting portion  62   a , the amplitude setting portion  62   b , the voltage setting portion  62   d , and the like illustrated in  FIG. 4  are examples of the operation unit  21 . 
     Similarly to  FIG. 4 ,  FIG. 5  illustrates an example of a channel emulator function screen  70 . The channel emulator function screen  70  is provided with a function display region  61  schematically showing configurations and selected states of functions, and a setting state display region  71  showing a setting state of a channel emulator function. In the example illustrated in  FIG. 5 , a selection button  61   b  is turned on by a user in the function display region  61 , and the channel emulator function is selected. 
     The setting state display region  71  is provided with a file open button  71   a  for opening a file of the S parameter of the DUT  1  which is stored in advance in order to realize the channel emulator function. In addition, the setting state display region  71  is provided with a bit rate setting portion  71   b  for setting a bit rate, and a graph display region  71   c  for displaying a graph indicating a relationship between a frequency and power. Meanwhile, the file open button  71   a , the bit rate setting portion  71   b , and the like illustrated in  FIG. 5  are examples of the operation unit  21 . 
       FIG. 6  illustrates an example of an ISI function screen  80 . Similarly to  FIG. 4 , the ISI function screen  80  is provided with a function display region  61  schematically showing configurations and selected states of functions, and a setting state display region  81  showing a setting state of an ISI function. In the example illustrated in  FIG. 6 , a selection button  61   c  is turned on by a user in the function display region  61 , and the ISI function is selected. 
     The setting state display region  81  is provided with a test standard setting portion  81   a  for setting a test standard to be applied, a Nyquist frequency setting portion  81   b  for setting a Nyquist frequency, an insertion loss setting portion  81   c  for setting an insertion loss, an amplitude setting portion  81   d  for setting an amplitude, a graph display region  81   e  for displaying a graph indicating a relationship between a frequency and an insertion loss, and the like. Meanwhile, the test standard setting portion  81   a , the Nyquist frequency setting portion  81   b , the insertion loss setting portion  81   c , the amplitude setting portion  81   d , and the like illustrated in  FIG. 6  are examples of the operation unit  21 . 
     [Description of Operation] 
     Next, the operation of the signal generation device  10  in this embodiment will be described with reference to  FIG. 7 .  FIG. 7  is a flowchart illustrating a filter coefficient calculation method and a signal generation method in this embodiment. 
     The signal generation unit  11  generates a predetermined signal on the basis of a control signal received from the operation unit  21  of the display device  20  (step S 11 ), and outputs the generated signal to the FIR filter  12 . 
     The operation unit  21  outputs a function selection signal indicating one or a plurality of functions selected by a user&#39;s operation to the function unit  40  and the function selection unit  51  of the filter coefficient synthesis unit  50  (step S 12 ). 
     The function selection unit  51  selects one or a plurality of functions from among three functions on the basis of the function selection signal output from the operation unit  21  (step S 13 ). 
     The function unit  40  selects a transfer function of the FIR filter  12  in one or a plurality of functions selected in step S 13  (step S 14 ). Specifically, for example, in a case where an emphasis function and an ISI function are selected in step S 13 , the emphasis function unit  41  calculates a transfer function ΦE(ω) on the basis of [Expression 3] and [Expression 14], and the ISI function unit  43  calculates a transfer function ΦI(ω) on the basis of [Expression 8] and [Expression 14]. 
     The filter coefficient calculation unit  52  calculates a filter coefficient in one or a plurality of functions selected in step S 13  (step S 15 ). Specifically, the filter coefficient calculation unit  52  performs inverse Fourier transform on a transfer function in one function or a product of transfer functions in a plurality of functions selected in step S 13  to obtain an impulse response of the FIR filter  12 , and calculates the impulse response as a filter coefficient. 
     For example, in a case where the emphasis function and the ISI function are selected in step S 13 , the filter coefficient calculation unit  52  performs inverse Fourier transform on a product of ΦV(ω) and ΦI(ω) to obtain an impulse response of the FIR filter  12  as a transfer function ΦV(ω)=1 in a channel emulator function which is not selected, and calculates the impulse response as a filter coefficient. 
     The filter coefficient calculation unit  52  sets the calculated filter coefficient in the FIR filter  12  (step S 16 ). 
     The FIR filter  12  inputs the signal generated in step S 11 , performs predetermined processing (processing for adding a selected function) on the signal, and outputs the processed signal to the DUT  1  (step S 17 ). 
     As described above, the filter coefficient calculation device  30  in this embodiment can perform inverse Fourier transform on a transfer function in one function selected by the function selection unit  51  or a product of transfer functions in a plurality of functions selected by the function selection unit  51  to obtain an impulse response of the FIR filter  12 , and can calculate the impulse response as a filter coefficient. 
     That is, the filter coefficient calculation device  30  in this embodiment does not require complicated processing to calculate a filter coefficient, and can realize a plurality of functions by one FIR filter  12 . 
     Therefore, the filter coefficient calculation device  30  in this embodiment can calculate a filter coefficient of the FIR filter  12  having a relatively large number of taps at high speed and can realize a plurality of functions. 
     In addition, the signal generation device  10  in this embodiment includes the filter coefficient calculation device  30 , and thus it is possible to calculate a filter coefficient of the FIR filter  12  having a relatively large number of taps at high speed and to realize a plurality of functions. 
     As described above, the filter coefficient calculation device, the signal generation device including the filter coefficient calculation device, the filter coefficient calculation method, and the signal generation method according to the invention are useful as a filter coefficient calculation device having an effect of making it possible to calculate a filter coefficient of an FIR filter having a relatively large number of taps at high speed and realize a plurality of functions and calculating a filter coefficient of a finite impulse response filter, a signal generation device including the filter coefficient calculation device, a filter coefficient calculation method, and a signal generation method. 
     DESCRIPTION OF REFERENCE NUMERALS AND SIGNS 
       1  DUT (test target device) 
       2  Error detector 
       10  Signal generation device 
       11  Signal generation unit (signal generation means) 
       2  FIR filter (finite impulse response filter) 
       20  Display device 
       21  Operation unit 
       22  Display unit 
       30  Filter coefficient calculation device 
       40  Function unit (functional means) 
       41  Emphasis function unit 
       41   a  First transfer function calculation unit (transfer function calculation means) 
       42  Channel emulator function unit 
       42   a  Second transfer function calculation unit (transfer function calculation means) 
       42   b  S parameter storage unit 
       43  ISI function unit (intersymbol interference functional means) 
       43   a  Third transfer function calculation unit (transfer function calculation means) 
       50  Filter coefficient synthesis unit 
       51  Function selection unit (selection means) 
       52  Filter coefficient calculation unit (filter coefficient calculation means) 
       60  Emphasis function selection screen 
       70  Channel emulator function selection screen 
       80  ISI function selection screen