JPH0419570A - Frequency analyzing device - Google Patents

Abstract

PURPOSE:To reduce a time for analyzing frequencies in plural frequency ranges and to attain the analysis with high analytical resolution for frequency by accumulating the output results of a 1st digital high speed Fourier transforming device by an accumulator for every frequency range. CONSTITUTION:The input signal, the band of which is limited with passing through a low-pass filter 201, is subjected to A/D conversion 202. A waveform of this digital signal is chopped by the 1st preset high speed Fourier transforming device 203 for digital complex signal with a specified interval to make each of the parts to be overlapped and the subjected to Fourier transformation. Next, each waveform of them are accumulated by the data accumulator 204 for every frequency band. Then, this frequency band is selected by a 2nd high speed Fourier transforming device 205 for digital complex signal and also data for each waveform in the band are subjected to Fourier transformation to perform the frequency analysis for complex signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a frequency analysis device that analyzes and detects the frequency of a received signal buried in noise.

[Prior Art] FIG. 3 is a block diagram showing a conventional frequency analyzer disclosed in, for example, Japanese Patent Publication No. 53-2743.

In the figure, (101) is a pre-low-pass filter, (1
02) is an A/D converter, (103) is a digital complex signal frequency converter, (104) is a digital complex signal low-pass filter, (105) is a secondary sampling circuit, (10
B) is a digital complex signal fast Fourier transformer.

Next, the operation of the conventional frequency analyzer configured as described above will be explained. The input signal is pre-low-pass filtered (
through the A/D converter (101).
2) is converted into a digital signal.

Then, this digital signal is further put into a digital complex signal frequency converter (103) for frequency conversion, and then passed through a digital complex signal low-pass filter (104) to perform band limiting again, so that only the required band of the input signal is used. Take out. This extracted frequency band is sampled by a secondary sampling circuit (105) to reduce the number of samples,
When input into a digital complex signal fast Fourier transformer (10B), frequency analysis with high frequency resolution can be performed.

[Problem to be solved by the invention] However, with the conventional frequency analyzer as described above,
When attempting to perform frequency analysis for a plurality of different frequency bands, the processing after the digital complex signal frequency converter (103) must be repeated for each frequency band, which poses a problem in that the calculation process takes time.

The present invention was made in order to solve such problems, and an object of the present invention is to obtain a frequency analyzer that can perform high frequency analysis with a simple structure without spending time on calculation processing of frequency analysis for a plurality of different frequency bands. shall be.

[Means for Solving the Problems] The frequency analysis device according to the present invention cuts out the waveform of a digital signal at predetermined intervals, overlaps the cut out portions, and performs a Fourier transform on each of the overlapped waveforms. 1 digital fast Fourier transformer, an accumulator for accumulating each waveform obtained by the Fourier transform for each frequency band, a frequency band accumulated in the accumulator is selected, and each waveform data of the frequency band is Fourier-transformed. and a second digital fast Fourier transformer that performs frequency analysis of a complex signal.

[Function] In the present invention, the device is effective for analyzing sonar signals, seismic waves, brain waves, and the like. In this case, an analog signal whose band has been limited through a low-pass filter is transferred to an A/D
When the converter converts the digital signal into a digital signal and sends it to the first digital fast Fourier transformer, the first digital fast Fourier transformer cuts out the waveform of the digital signal at predetermined intervals and converts each of the cut out parts into overlap. Then, each of the overlapped waveforms is Fourier transformed and sent to the accumulator. The accumulator accumulates each waveform obtained by Fourier transform for each frequency band. The second digital fast Fourier transformer selects the frequency band stored in the accumulator, performs Fourier transform on each waveform data of the frequency band, and performs frequency analysis of the complex signal.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a conceptual diagram showing the input/output state of a data storage device.

In the figure, (201) is a low-pass filter, (202
) is an A/D converter, and (203) is a pre-digital complex signal fast Fourier transformer corresponding to the first digital fast Fourier transformer. are overlapped with each other, and then each of the overlapped waveforms is subjected to Fourier transformation.

(204) is a data accumulator that accumulates each waveform obtained by the Fourier transform for each frequency band; (205) is a digital complex signal fast Fourier transformer corresponding to the second digital fast Fourier transformer; ) is selected, and each waveform data in that frequency band is Fourier transformed to perform frequency analysis of the complex signal.

In the frequency analyzer configured as described above, an input signal that has passed through a low-pass filter (201) and has been band-limited is converted into a digital signal by an A/D converter (202), and then Digital complex signal fast Fourier transformer (
203).

By the way, the prefix digital complex signal fast Fourier transformer (
The output result of 203) is a spectral string with a frequency resolution determined by the order during Fourier transform and the sampling frequency of the input signal, and this spectral string is passed through multiple bandpass filters with a bandwidth corresponding to the frequency resolution described above. This can be considered as the output result on the frequency axis of the column. Therefore, in the present invention, a pre-digital complex signal fast Fourier transformer (20
3) is considered as a plurality of band-pass filter arrays, and the output results are accumulated in a data accumulator (204) for each frequency band.

Each waveform data for each frequency band accumulated in the data accumulator (204) is inputted to a digital complex signal fast Fourier transformer (205) as necessary and frequency-analyzed.

FIG. 2 is a conceptual diagram showing the input/output state of the data accumulator (204) as described above, where (f) is the frequency axis, (
t) is the time axis. Also, (301) is t.

(302) is a data string of time equal to the center frequency f
It is a data string of a frequency band having o and bandwidth W.

As mentioned above, the bandwidth W is exactly the frequency resolution of the pre-digital complex signal fast Fourier transformer (203). The output result of the pre-digital complex signal fast Fourier transformer (203) at time to is placed in the time domain corresponding to the data string (301). Now, the center frequency fo
To perform frequency analysis on digital complex signal fast Fourier transformer (205), (302
), enter the data for the corresponding area. If the final desired bandwidth is larger than the bandwidth W, frequency analysis of data strings in multiple bands may be performed.

As described above, the order of the Fourier transform in the pre-digital complex signal fast Fourier transformer (203), the data selection from the data accumulator (204), and the order of the Fourier transform in the digital complex signal fast Fourier transformer (205) are determined. It can be seen that by manipulating this, any frequency resolution and any bandwidth can be obtained. Furthermore, the frequency resolution can also be varied by manipulating the overlap rate of the input signal.

That is, now, the sampling frequency of the input signal is fs, the overlap rate of the input signal is θL1, and the order of the Fourier transform of the pre-digital complex signal fast Fourier transformer (203), which functions as a plurality of band-pass filter arrays, is SL ( If the order of the Fourier transform of the digital complex signal fast Fourier transformer (205) that performs frequency analysis is 52 (the number of points N2-2''), then the bandwidth W of the bandpass filter array is as follows. obtained from the formula, W-
fs/Nl The sampling frequency fsl of data input to the digital complex signal fast Fourier transformer (205) is obtained from the following equation.

fsl Castle 1- θ L fs I Nl 1 - θ L Furthermore, the frequency resolution W1 of the data output by the digital complex signal fast Fourier transformer (205) is sl l- fs 1 1 Nl 1-θL N2.

Furthermore, in order to obtain an arbitrary center frequency fO, on the frequency axis of the data accumulator (204), fo+fs/N
It is only necessary to select the first data string as the center, and in order to obtain an arbitrary bandwidth larger than the bandwidth W, the data accumulator (
It can be seen that it is sufficient to perform frequency analysis on a plurality of data strings on the frequency axis of 204).

By the way, in the present invention, the same Fourier transformer as the digital complex signal fast Fourier transformer (205) is used as the pre-digital complex signal fast Fourier transformer (203) which is a plurality of band-pass filter arrays. This consists of a pre-digital complex signal fast Fourier transformer (203) and a digital complex signal fast Fourier transformer (205) in the same Fourier transformer, and by using them in a time-division manner, the components when making a device. This is to reduce the number of points and provide a device that is small and lightweight and has a simple structure. Note that the pre-digital complex signal fast Fourier transformer (203) and the digital complex signal fast Fourier transformer (205) may be different Fourier transformers.

[Effects of the Invention] As described above, according to the present invention, the accumulator accumulates the output results of the first digital fast Fourier transformer, which functions as a plurality of band-pass filter arrays, for each frequency band. Since only frequency bands are subjected to frequency analysis, calculation time can be shortened when performing frequency analysis on multiple different frequency bands.In addition, by combining low-order Fourier transforms, it is possible to analyze frequencies with high frequency resolution. The effect is that analysis can be performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a conceptual diagram showing the input/output state of the data storage device (204), and FIG. 1 is a block diagram showing a conventional frequency analyzer. In the figure, (201) is a low-pass filter, (202
) is an A/D converter, (208) is a pre-digital complex signal fast Fourier transformer, (204) is a data accumulator, (2
05) is a digital complex signal fast Fourier transformer. Patent Applicant: Oki Electric Industry Co., Ltd. Block Diagram 3 of Phantom 1

Claims (1)

[Scope of Claims] A frequency analyzer comprising a low-pass filter that limits the band of an input analog signal and outputs it, and an A/D converter that converts the analog signal of the low-pass filter into a digital signal. , cutting out the waveform of the digital signal at predetermined intervals, and
a first digital fast Fourier transformer that overlaps the cut out portions and Fourier transforms each of the overlapped waveforms; an accumulator that accumulates each waveform obtained by the Fourier transform for each frequency band; a second digital fast Fourier transformer that selects a frequency band stored in the frequency band and Fourier transforms each waveform data of the frequency band to perform frequency analysis of a complex signal. .