JPH1026642A - Spectrum analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the frequency resolution of a spectrum analyzer in which a window function and a Fourier transform are used. SOLUTION: Zero-signal adders 1, 5 which extend a length in the direction of a time base when signals whose amplitude is zero are added to parts before and after a signal, π/2 phase shifters 3, 7 which cut a DC component, π/4 phase shifters 11, 12 which pass the DC component, multipliers 8, 13, Fourier transformers 9, 14, absolute-value circuits 10, 15 and a vibrator 16 are used. Thereby, the omission of a spectrum which is generated in an obsorvation method using a window function 4 is reduced, and the measuring resolution of the spectrum is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input signal spectrum analyzer.

[0002]

2. Description of the Related Art Conventionally, signal spectrum analysis methods include, for example, a window function and an FFT (Fast Fourier Transform).
m), which is widely used in FFT spectrum analyzers and the like. These are, for example, Reference 1: Image Analysis Handbook, Mikio Takagi et al., The University of Tokyo Press, 1991 and Reference 2: For scientific measurement No. 6, pp. 284-177, published by CQ Publishing, 1986.

In these disclosed techniques, in order to reduce distortion of the observed spectrum, a Fourier transform is performed by multiplying the input signal by a window function (see FIG. 9). However, there is a disadvantage that the resolution of measurement is reduced because the spectrum of the window function itself is widened. For example, when a Dorf-Chebyshev window is used as a window function, the resolution is less than half the theoretical resolution of the Fourier transform.

[0004]

The prior arts disclosed in the above-mentioned references 1 and 2 have a drawback that the spectral resolution is reduced due to the distortion of the spectrum caused by cutting out a part of the input signal as described above. Was. Therefore, an object of the present invention is to provide a spectrum analyzer in which the distortion of the spectrum is reduced and the resolution is improved.

[0005]

In order to achieve this object, a spectrum analyzer according to the present invention is arranged such that an input signal is cut into a finite length, and the amplitude of the cut signal is zero on both sides in time. And a first zero signal adder for extending the signal length by adding
A splitter; a first π / 2 phase shifter that cuts off a DC component of one of the output signals of the first two splitter to shift the phase by π / 2; a window function generator; A second method of adding a zero amplitude signal to both temporal sides of the window function signal generated by the generator.
A second signal divider for dividing the window function signal into two signals, and a second signal for cutting off the DC component of one of the output signals of the second signal divider to shift the phase by π / 2. a π / 2 phase shifter, a first multiplier for multiplying the outputs of the first and second π / 2 phase shifters, and a first Fourier for Fourier transforming the output signal of the first multiplier A first absolute value circuit for obtaining an absolute value of an output signal of the first Fourier transformer; and a π / 4 phase shifter for passing the other of the output signals of the first two divider through a DC component. The other of the output signals of the first π / 4 phase shifter and the second two-way splitter passes through a DC component and π / 4
A second π / 4 phase shifter for phase shifting, a second multiplier for multiplying the outputs of the first and second π / 4 phase shifters, and a Fourier transform of the output signal of the second multiplier. A second Fourier transformer for conversion, a second absolute value circuit for obtaining an absolute value of an output signal of the second Fourier transformer, and an output of the first absolute value circuit from an output signal of the second absolute value circuit And a subtracter for subtracting a signal.

[0006]

According to the apparatus of the present invention, the spectral distortion due to the window function can be reduced by signal processing, so that the resolution of spectrum observation can be improved. FIG. 2 is a block diagram showing an embodiment of the apparatus according to the present invention, which will be described in detail later.
7 can be easily understood by referring to FIG. These waveform diagrams are waveform diagrams when the input signal is a single sine wave, and the input signal and the window function signal are respectively π / 4.
The absolute value of the spectrum of the signal multiplied by the phase shift is equal to the spectrum of the window function signal (signal r). It can be intuitively understood that the absolute value of the spectrum is the absolute value of the spectrum (signal k) from which the center component of the spectrum of the window function signal has been removed. Accordingly, it can be understood that the difference between the two cancels out the degradation of the resolution due to the distortion of the spectrum due to the window function.

That is, in the present invention, when the spectrum of the input signal is originally as shown in FIG. 8, the conventional analysis method using a window function has a disadvantage that the spectrum of the window function itself is distorted and the measurement resolution is reduced. Improve what was,
Blocks 1, 2, 11, 13, 1 in FIG.
A spectrum (signal r, FIG. 7 (a)) having the same level of distortion as the conventional one is obtained through the paths 4 and 15 and blocks 1, 2 and 2 in FIG.
The components of the spectral distortion due to the window function are extracted along the paths 3, 8, 9, and 10 (signal k, FIG. 5A), and the difference between them is taken to offset the degradation of the resolution due to the window function. , An output signal (signal s, FIG. 7 (b)) having a higher resolution than when a normal window function is used.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a configuration block diagram according to an embodiment of the present invention.

An input signal a (FIG. 2A) is input to an input terminal. Here, for simplicity of explanation, the input signal a is treated as a single sine wave as shown in FIG. 2 (a), but generally an arbitrary waveform f (t)
Is input as a matter of course.

The input signal a is first cut into a finite length by the first zero signal adder 1, and a signal of zero amplitude is added to both sides of the cut signal in time to extend the signal length. A signal b (FIG. 2B) is obtained. The signal b is the first 2
The signal c and the signal 1 are split into two by the splitter 2, and one of the signals c is cut off the DC component of the signal by the first π / 2 phase shifter 3 and the signal d is shifted by π / 2. (Figure 2
(C)).

On the other hand, window function signal e
(FIG. 3 (a)) is generated, the signal e is input to the second zero signal adder 5, and a signal f (FIG. 3 (b) )) Is obtained.
The signal f is split into two by a second splitter 6 into a signal g and a signal n, and the signal g is cut off its DC component by a second π / 2 phase shifter 7 to be shifted by π / 2 and the signal h is shifted. (FIG. 3 (c))
Becomes

Next, the signal d and the signal h are multiplied by a first multiplier 8 to obtain a signal i (FIG. 4 (a)).
Is Fourier transformed by the Fourier transformer 9 of
(FIG. 4A shows the real part, and FIG. 4B shows the imaginary part.)
The signal k (FIG. 5A) is output from the first absolute value circuit 10.

On the other hand, the other signal 1 split into two by the first splitter 2 is converted into a signal m by the first π / 4 phase shifter 11 (FIG. 5).
(B)), and the other signal n split into two by the second splitter 6 is converted to a signal o by the second π / 4 phase shifter 12 (FIG. 5).
(C)). The signal m and the signal o are supplied to the second multiplier 13
Are multiplied by each other to obtain a signal p (FIG. 6 (a)). This signal p is Fourier-transformed by the second Fourier transformer 14, and a signal q (FIG. 6 (b) is its real part, FIG. 6 (c)) Obtains its imaginary part). The signal q is further output by the second absolute value circuit 15 as a signal r (FIG. 7A).

Finally, the signal k is subtracted from the signal r by the subtractor 16 to obtain an analysis spectrum signal s (FIG. 7B) for the input signal a according to the present invention. As described above, the signal r is equal to the spectrum of the window function signal, and the signal k is the absolute value of the spectrum obtained by removing the center component of the window function signal spectrum. It can be understood that the resolution is improved by canceling out the degradation of the resolution due to the spectrum distortion due to.

Here, the π / 2 and π / 4 phase shifters will be described. These phase shifters are devices for rotating the phase of π / 2 and π / 4 over the entire band for measuring the input signal under test. The filter whose impulse response has the characteristic of FIG. 10 is realized by hardware or software. can do. Here, FIG. 10 (a) shows an implementation of a π / 2 phase shifter, and FIG. 10 (b) shows an implementation of a π / 4 phase shifter. In FIG. 10, FT is Fourier Transformatio
n and FT ^-1 are inverse transforms thereof, and sgn (f) is a function sgn (f) = 1 (f> 0) = 0 (f = 0) =-1 (f <0) shown in FIG. The π / 2 phase shifter in the drawing is called a so-called Hilbert transform.

[0016]

As described above in detail, the use of the apparatus of the present invention makes it possible to reduce the distortion of the observed spectrum by multiplying the input signal by the window function. Since the spread of the spectrum can be suppressed and the degradation of the resolution can be offset, spectrum analysis with higher resolution than when a normal window function is used can be performed.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram according to an embodiment of a device of the present invention.

FIG. 2 (a) is a signal a, (b) is a signal b, (c)
FIG. 3 is a diagram showing time-amplitude characteristics of a signal d.

3A is a signal e, FIG. 3B is a signal f, and FIG.
FIG. 4 is a diagram showing time-amplitude characteristics of a signal h.

FIG. 4A shows a time-amplitude characteristic of a signal i,
FIG. 4B is a diagram illustrating frequency characteristics of a real part of a signal j, and FIG. 4C is a diagram illustrating frequency characteristics of an imaginary part of a signal j.

5A is a diagram illustrating frequency characteristics of a signal k, FIG. 5B is a diagram illustrating time-amplitude characteristics of a signal m, and FIG.

FIG. 6A shows a time-amplitude characteristic of a signal p,
FIG. 3B is a diagram illustrating frequency characteristics of a signal q real part, and FIG.

7A is a diagram illustrating a frequency characteristic of a signal r, and FIG. 7B is a diagram illustrating a frequency characteristic of a signal s.

FIG. 8 is an ideal spectrum characteristic diagram when the input signal is a single sine wave signal a.

FIG. 9 is a block diagram of a configuration example of an analyzer using a conventional window function.

FIG. 10 is a diagram for explaining a configuration of a π / 2 phase shifter and a π / 4 phase shifter.

[Explanation of symbols]

 1,5 first and second zero signal adder 2,6 first and second two divider 3,7 first and second π / 2 phase shifter 4 window function generator 8, 13 First and second multiplier 9,14 First and second Fourier transformer 10,15 First and second absolute value circuit 16 Subtractor

Claims (2)

[Claims] 1. A spectrum analyzing apparatus for analyzing a frequency spectrum of an input signal, the apparatus cuts an input signal into a finite length, and adds a signal of zero amplitude to both sides of the cut signal in time. To extend the signal length
, A first two-divider for dividing the signal into two, and a first for dividing one of the output signals of the first two-divider into a π / 2 phase by cutting off the DC component of the signal. a π / 2 phase shifter, a window function generator, a second zero signal adder for adding a signal of zero amplitude to both temporal sides of the window function signal generated by the window function generator, and the window function The second 2 that splits the signal into two
A divider, and a second π / 2 phase shifter that cuts off a DC component of one of the output signals of the second two divider and shifts the phase by π / 2.
First multiplying the outputs of the first and second π / 2 phase shifters;
, A first Fourier transformer for performing a Fourier transform on an output signal of the first multiplier, a first absolute value circuit for obtaining an absolute value of the output signal of the first Fourier transformer, The other of the output signals of the two dividers passes the DC component and
A first π / 4 phase shifter that shifts the phase by / 4, and a second π / 4 phase shifter that shifts the other output signal of the second splitter by π / 4 by passing a DC component. And the first and second π /
A second multiplier that multiplies the output of the four-phase shifter, a second Fourier transformer that performs a Fourier transform on the output signal of the second multiplier, and an absolute value of the output signal of the second Fourier transformer. A spectrum analyzer, comprising: a second absolute value circuit for taking the signal; and a subtractor for subtracting an output signal of the first absolute value circuit from an output signal of the second absolute value circuit. 2. The first and second π / 4 phase shifters include:
Fourier transformer and (1-jsgn (f)) / √2
2. The spectrum analysis apparatus according to claim 1, wherein the spectrum analysis apparatus comprises a circuit in which a circuit for multiplying a frequency characteristic and a Fourier inverse transformer are connected in series.