JPH0247563A - Spectrum analyzer - Google Patents

Abstract

PURPOSE:To measure the spectrums of signals from a low frequency region to a high frequency region in high resolution at a high speed by synthesizing the spectrums obtained by discrete Fourier transform and analog spectrum analysis, and forming a series of the spectrum. CONSTITUTION:The low-frequency component lower than a specified frequency in an input signal is sent into a Fourier transformation device 12 from a signal distributing device 11. The high frequency signal component higher than a specified frequency is sent into a high frequency spectrum analyzer 13. The Fourier transformation device 12 generates and sends the low frequency spectrum signal into a spectrum synthesizer 14 by the discrete Fourier transformation. The high frequency spectrum analyzer 13 generate and sends the high frequency spectrum signal into the spectrum synthesizer 14. The spectrum signal which is continued from the low frequency to the high frequency is synthesized with an arbitrarily set boundary frequency as a boundary. In this way, the spectrums of the signals from the low frequency region to the high frequency regions can be measured in high resolution at a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Fields] The present invention is a method for transmitting the spectrum of signals from low frequency ranges to high frequency ranges ranging from several hertz to megahertz or gigahertz at high speed.
The present invention also relates to a spectrum analyzer that can perform measurements with high resolution.

[Prior Art] Spectrum analyzers can be broadly classified into the following two types based on their methods.

(a) Fast Fourier transform (1,1sj F□urie
A real-time spectrum analyzer (hereinafter referred to as "rFFT spectrum analyzer") using the rTrans-form (hereinafter referred to as "rFFT") method.The basic configuration example of an FFT spectrum analyzer is shown in Part 6.
As shown in the figure. In FIG. 6, the input signal is filtered through a low-pass filter 6.
1 and is converted into a digital signal by an A/D converter 62. An A/D converter usually has a sample and hold circuit at its front stage. It is not possible to process a signal with a frequency higher than the frequency of the sampling clock given to the sample and hold circuit. The output signal of the A/D converter 62 is decomposed into a spectrum by discrete Fourier transform in a Fourier transformer (FFT) 63 and guided to a display 64. The display 64 displays the spectrum of the input signal, with the horizontal axis representing frequency and the vertical axis representing amplitude.

The FFT spectrum analyzer has the feature of being able to Fourier transform even a low frequency signal such as voice at high speed and displaying the spectrum. However, since the input signal is directly A/D converted, the conversion speed of the A/D converter determines the upper limit frequency of the analyzer, making it impossible to analyze high frequency signals.

Furthermore, if an attempt is made to expand the dynamic range of the amplitude axis, the number of bits of the A/D converter will increase and the conversion speed will become slower, which will further reduce the upper limit frequency of the analyzer.

(b) Sweep type spectrum analyzer using heterodyne method (hereinafter referred to as "analog spectrum analyzer") A basic configuration example of an analog spectrum analyzer is shown in FIGS. 7(a) and 7(b). In FIG. 7(a), the input signal is mixed with the output signal of the local oscillator 75 in a mixer 71 and converted into an intermediate frequency signal. The intermediate frequency signal passes through an analysis filter 72 and is detected by a detector 35. The output signal of the detector 35 is guided to the display 74 as a vertical axis signal. The sweep controller 76 is a local oscillator 75
The horizontal axis signal is supplied to the display 74 while controlling the sweep of the horizontal axis. The display 74 displays the spectrum of the input signal, with the horizontal axis representing frequency and the vertical axis representing amplitude.

The example shown in FIG. 7(b) is the same as the example shown in FIG. 7(a).
/D converter 77 and memory 78 are added.

The analog output signal of the wave detector 35 is converted into a digital signal by an A/D converter 77 and stored in a memory 78.

Similar to the example shown in FIG. 7(a), the display 79 displays the spectrum of the input signal with the horizontal axis representing the frequency and the vertical axis representing the amplitude. The one shown in FIG. 7(b) is sometimes called a digital storage type spectrum analyzer.

Analog spectrum analyzers have features that enable spectrum analysis of high frequency signals in the gigahertz band. However, spectrum analysis of low frequency signals such as audio has a disadvantage in that it takes several 10 seconds to several 100 seconds to obtain one spectrum image on a display.

Therefore, when analyzing a signal that includes a wide spectrum from low frequencies to high frequencies, it has conventionally been necessary to use both the FFT spectrum analyzer (a) and the analog spectrum analyzer (b).

However, when trying to analyze the spectrum of a low-frequency signal such as voice with high resolution and high accuracy using an analog spectrum analyzer, there is a disadvantage that the processing time is extremely long as described above. , it has been impossible to analyze the spectrum of high-frequency signals that span the gigahertz band.

[Problem to be Solved by the Invention] In the conventional technology, the problem would be solved if high resolution/high speed processing in the low frequency range of an analog spectrum analyzer was realized, but this is theoretically impossible. This is because in order to perform spectrum analysis with high resolution, the band of the analysis filter must be narrowed, and as a result, the sweep time becomes longer in inverse proportion to the square of the analysis filter bandwidth. In addition, raising the upper limit frequency of the FFT spectrum analyzer to the gigahertz band would solve the problem, but it is also possible to directly
This is because D conversion is impossible with current technology.

Therefore, when analyzing signals that include a wide spectrum from low frequencies to high frequencies, we prepare an FFT spectrum analyzer for analyzing low frequency signals and an analog spectrum analyzer for analyzing high frequency signals, and take advantage of the characteristics of each analyzer. However, it was considered to measure the low frequency signal and high frequency signal separately. However, this also has the following issues to be resolved.

(a) Spectrum analyzers of different types must be prepared, making the device extremely expensive.

(1)) Spectra obtained by each analyzer are displayed on separate screens, and therefore cannot be observed as a series of spectrum data.

[Means for Solving the Problems] In order to solve the above problems, the present invention obtains the spectrum of a low frequency signal by discrete Fourier transform on the one hand, and the spectrum of a high frequency signal through analog spectrum analysis on the other hand, The respective spectra are combined by a spectrum synthesizer to form a series of spectra.
I am trying to obtain the spectrum of a signal ranging from low frequencies to high frequencies. Furthermore, the spectrum can be displayed on a single screen or used for other purposes as needed. Several inventions have been created based on the mode of operation of this spectrum synthesizer. That is, in the above invention, a frequency converter that converts an input signal to an intermediate frequency, a second A/l) converter that converts the output of the detector into a digital value, and a spectrum of the low frequency signal of the Fourier transformer. and a spectrum synthesizer that stores the spectrum of the high-frequency signal of the second A/D converter, reads out the stored values in association with the input signal frequency, and outputs the stored values as a series of spectrum data. Featured.

Furthermore, a changeover switch that switches between the output of the low-pass filter and the output of the detector, and an A/D that receives the output selected by the changeover switch and converts it into a digital value.
When the converter and the selector switch are switched to the low-pass filter side, the digital output of the A/D converter is subjected to discrete Fourier transform to output a spectrum of the low frequency signal, and the digital output of the A/D converter is subjected to discrete Fourier transform. When the changeover switch is switched to the detector side, the output of the A/D converter is stored as the spectrum value of the high frequency signal, and each of the above It is characterized by comprising a data processing circuit that reads out stored values in association with input signal frequencies and outputs them as a series of spectrum data.

[Embodiment] 1 above Ω 1 above l FIG. 1 shows a block diagram of a first embodiment of the present invention. A first embodiment of the present invention will be described using FIG.

The input signal is guided to a signal splitter (11). The signal splitter (11) sends low frequency signal components below a predetermined frequency (f,) to the Fourier transformer (12), and converts them to a desired frequency (f,).
fn) or higher are sent to a high frequency spectrum analyzer (13). Here, the predetermined frequency (fL)
The relationship between fn and desired frequency (fn) will be explained.

(i) In the case of fl>fH (see Fig. 8(a)), the frequencies fL and fH overlap, and the signal components from f to fH in the input signal are transferred to the Fourier transformer 1.
2 and a high frequency spectrum analyzer 13 for processing.

(ii) In the case of fiefH (see Figure 8(b)), there is a gap between frequencies fL and fn, and the signal components from fL to fn in the input signal are processed by the Fourier transformer 12 and the high frequency spectrum analyzer. 13. This frequency setting is effective when there is an extremely large signal component between fH and fH that saturates the subsequent circuit and interferes with spectrum analysis below L and above 11. It is.

In the present invention, the frequency relationship (i) or (ii) above may be arbitrarily selected.

Although various combinations of the signal distributor (11) are possible, typical ones are shown below.

(A) A combination of a low-pass filter for separating low-frequency signal components below a predetermined frequency and a high-pass filter for separating high-frequency signal components above a desired frequency.

(B) Analyzer input terminal and Fourier transformer (1
2) and a high frequency spectrum analyzer (13) that divides the input signal while matching the impedance of the lever. Note that a typical signal divider is one in which resistors are connected in a T-shape.

The Fourier transformer 12 performs discrete Fourier transform on the signal received from the signal distributor 11 to generate a low frequency spectrum signal, and sends the spectrum signal to the spectrum synthesizer 14 . For details on the technology for converting analog signals into spectrum signals using discrete Fourier transform, please refer to
JP-A-53-132958 and JP-A-56-10816
4 is disclosed.

The high frequency spectrum analyzer 13 converts the signal received from the signal distributor 11 into an intermediate station signal, generates a high frequency spectrum signal by detecting and A/D converting the signal, and transmits the spectrum signal to the spectrum synthesizer. 14. A typical example of the high frequency spectrum analyzer 13 is one in which the display 74 is removed from the configuration shown in FIG. 7(a).

The spectrum synthesizer 14 generates a low-frequency spectrum signal below the low-frequency boundary value (Heshi) and a high-frequency spectrum signal above the high-frequency boundary value (AH) based on a boundary value related to an arbitrarily set boundary frequency. and synthesize them as a series of spectral signals.

As a result, the low frequency spectrum signal obtained by discrete Fourier transform and the high frequency spectrum signal obtained by analog spectrum analysis become continuous spectrum signals from low frequency to high frequency with the boundary frequency as a boundary. This continuous spectrum signal can be displayed on a display, etc.

An example of spectrum synthesis will be explained using FIG. 9. Memory addresses are divided based on the boundary value, and the spectrum data of the low frequency signal is stored in the F address, and the spectrum data of the high frequency signal is stored in the upper address.

(i) In the example shown in FIG. 8(a) (fL>fn), each frequency of the signal distributor II and the spectrum synthesizer 14
The relationship with the boundary value given to (f H< A t =
Set so that A H<fc). Figure 9(a)
As shown in , the amplitude data of the low frequency spectrum is stored from address "0" in the memory to address rn-IJ, and the amplitude data of the high frequency spectrum is stored from address rnJ to address rN-IJ.

(ii) In the example shown in FIG. 8(b), each frequency of the signal distributor 11 and the spectrum synthesizer 1 are
The relationship with the boundary value given to 4 is (fL≧Ac, f+≦
AH). As shown in FIG. 9(b), the amplitude data of the low frequency spectrum is transferred from memory address "0" to address rnJ, and the amplitude data of the high frequency spectrum is transferred from address rmJ to address rN-.
Stored in IJ. Although the area from address rn+IJ to address rm-IJ is an empty area, as shown in FIG. You may provide a blank space when using it.

Figure 2 shows a block diagram of a second embodiment of the present invention. A second embodiment of the present invention will be described using FIG. The difference between the second embodiment and the first embodiment is that a display 15 is added to the configuration shown in FIG. 1, and a continuous spectrum from low frequency to high frequency is displayed! This is the point shown in 5. The operation is the same as in the first embodiment.

A display example is shown in FIG. In this example, the horizontal axis (frequency axis) is graduated on a logarithmic scale, and a spectrum ranging from several tens of hertz to a gigahertz band is displayed on one screen.

FIG. 3 shows a block diagram of a third embodiment of the present invention. A third embodiment of the present invention will be described using FIG.

The input signal is directed to a low pass filter 3I and a frequency converter 34. The low-pass filter 31 passes low-frequency signals below a predetermined frequency (fL). The first A/D converter 32 is
The analog signal passed through the low-pass filter 31 is converted into a digital signal. The Fourier transformer 33 converts the digital output signal of the first A/D converter 32 into a spectrum of a low frequency signal by discrete Fourier transform, and sends the data to the spectrum synthesizer 37. The frequency converter 34 is
Mixer 34a, analysis filter 34b, local oscillator 34c
and a sweep controller 34d, which converts the input signal into a predetermined intermediate frequency signal. The detector 35 detects the intermediate frequency output signal of the frequency converter 34. 20th)
The A/D converter 36 converts the analog output signal of the wave detector 35 into a digital signal, and outputs the signal to the spectrum synthesizer 37 as spectrum data of a high frequency signal. Generally, in the frequency converter 34, the lower limit frequency (fH) that can be analyzed is often limited by the input circuit or the local oscillation frequency. The spectrum synthesizer 37 extracts spectrum data below a preset low frequency boundary value (A) from the spectrum data of the low frequency signal sent from the Fourier transformer 33, and further extracts spectrum data below a preset low frequency boundary value (A).
From the spectrum data of the high frequency signal sent from the D converter 36, spectrum data above the high frequency boundary value (AH) is extracted, and each extracted data is synthesized,
A series of spectrum data from low frequency to high frequency is generated and the data is output to the display 15. Display 15
displays a series of spectra from low frequencies to high frequencies on one screen. An example of the display is shown in FIG.

As for the boundary between the low frequency signal (f [below)] and the high frequency signal (above fn) and the spectrum synthesis, those explained in the first embodiment may be applied (see FIGS. 8 and 9).

Figure 4 shows a block diagram of a fourth embodiment of the present invention. A fourth embodiment of the present invention will be described using FIG. 4. The fourth embodiment differs from the third embodiment in that the A/D converter is shared.

The input signal is directed to a low pass filter 31 and a frequency converter 34. The low-pass filter 31 passes low-frequency signals below a predetermined frequency ([L). Frequency change 1g! The I device 34 is
Converts an input signal into a predetermined intermediate frequency signal.

The detector 35 detects the intermediate frequency signal of the frequency converter 34.

When processing low frequency signals, the changeover switches 40, 43, and 44 are set to the a side. A/D converter 41 converts the analog signal that has passed through low-pass filter 31 into a digital signal, and sends the signal to data processing circuit 42 . The data processing circuit 42 includes changeover switches 43 and 44, a Fourier transformer 46, and a spectrum synthesizer 45. The Fourier transformer 46 converts the digital output signal of the A/D converter 41 into a spectrum of a low frequency signal by discrete Fourier transform, and sends the data to the spectrum synthesizer 45.

When processing high frequency signals, the changeover switches 40, 43 and 44 are set to the b side. The A/D converter 41 converts the analog intermediate frequency signal frequency-converted by the frequency converter 34 into a digital signal, and sends the signal to the data processing circuit 42 as spectrum data of the high frequency signal.

The spectrum synthesizer 45 extracts a preset low frequency boundary value (AL) from the spectrum data of the low frequency signal.
) The following spectrum data is extracted, and from the spectrum data of the high frequency signal, the spectrum data above the preset high frequency boundary (1α (AH)) is extracted,
The extracted data are combined to generate a series of spectrum data ranging from low frequencies to high frequencies. Spectrum synthesizer 45 sends the synthesized spectrum data to display 38. The display 38 displays a series of spectra from low frequencies to high frequencies on one screen.

An example of the display is shown in FIG. Note that it is not necessarily necessary to display the above series of spectra on the display. It is also possible to record data and retrieve it when necessary.

[Effects of the Invention] The spectrum analyzer according to the present invention obtains the spectrum of a low frequency signal by discrete Fourier transform, and obtains the spectrum of a high frequency signal by analog spectrum analysis, so that the following effects can be obtained. .

(1) The spectrum of signals ranging from low frequencies to high frequencies can be observed on a single screen.

(2) Since the low frequency signal component and the high frequency signal component are processed simultaneously, the overall processing speed becomes faster.

(3) Since there is no need to prepare spectrum analyzers of different types, the cost of the device becomes extremely low.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention;
The figure is a block diagram showing a second embodiment of the present invention, FIG.
FIG. 4 is a block diagram showing a fourth embodiment of the present invention, FIG. 5 is a display example by the spectrum analyzer of the present invention, and FIG. 6 is a conventional display example. FIG. 7 is a block diagram of an FFT spectrum analyzer, FIG. 7 is a block diagram of a conventional analog spectrum analyzer, FIG. 8 is a diagram showing frequency boundaries, and FIG. 9 is a memory map for spectrum synthesis. In the figure, 11 is a signal splitter, 12 is a Fourier transformer, 1
3 is a high frequency spectrum analyzer, 14 is a spectrum synthesizer, I5 is a display, 31 is a low pass filter, 32 is a first
33 is a Fourier transformer, 34 is a frequency converter, 35 is a detector, 36 is a second A/D converter, 3
7 represents a spectrum synthesizer, 40 represents a changeover switch, and 42 represents a data processing circuit.

Claims (1)

[Scope of Claims] 1) A signal splitter (11) that receives an input signal and outputs a low frequency signal component below a predetermined frequency and a high frequency signal component above a desired frequency, and receives the low frequency signal component. A Fourier transformer (1
2), a high frequency spectrum analyzer (13) that receives the high frequency signal component, converts it into a frequency spectrum, and outputs a high frequency spectrum signal; and a high frequency spectrum analyzer (13) that receives the low frequency spectrum signal and the high frequency spectrum signal and converts it into a frequency spectrum, and A spectrum analyzer comprising a spectrum synthesizer (14) that performs spectrum synthesis in a band. 2) Receiving the output signal of the spectrum synthesizer (14),
The spectrum analyzer according to claim 1, further comprising a display (15) for displaying the low frequency spectrum and the high frequency spectrum on one screen. 3) A low-pass filter (31) that passes a low-frequency signal below a predetermined frequency among the input signals, and a first A/D converter (32) that A/D-converts the signal that has passed the low-pass filter. and a Fourier transformer (33) that outputs the spectrum of the low frequency signal by performing discrete Fourier transform on the digital output of the first A/D converter, and setting a high frequency signal higher than a desired frequency of the input signal. a frequency converter (34) that converts the frequency to an intermediate frequency while sweeping the frequency with the specified sweep time; a detector (35) that detects the output of the frequency converter; and a detector (35) that converts the output of the detector into a digital value; a second A/D converter (36) that outputs a spectrum of the high-frequency signal; a spectrum of the low-frequency signal of the Fourier transformer and a spectrum of the high-frequency signal of the second A/D converter are respectively stored; A spectrum analyzer comprising a spectrum synthesizer (37) that reads out the stored value in association with the input signal frequency and outputs it as a series of spectrum data. 4) A low-pass filter (31) that passes a low-frequency signal below a predetermined frequency among the input signals, and a low-pass filter (31) that passes a low-frequency signal below a predetermined frequency of the input signal, and sweeps the high-frequency signal above the desired frequency of the input signal to an intermediate frequency while sweeping the frequency over a set sweep time. a frequency converter (34) for converting, a detector (35) for detecting the output of the frequency converter, a changeover switch (40) for switching between the output of the low-pass filter and the output of the detector; receiving said output selected by a switch;
an A/D converter (41) that converts into a digital value; and when the changeover switch is switched to the low-pass filter side, the digital output of the A/D converter is converted into the low-frequency signal by discrete Fourier transform; outputs the spectrum of the discrete Fourier-transformed low-frequency signal, stores the spectrum value of the low-frequency signal that has been subjected to the discrete Fourier transform, and converts the output of the A/D converter to the high-frequency signal when the changeover switch is switched to the detector side. A data processing circuit (4) stores the data as a spectrum value, reads out each stored value in association with the input signal frequency, and outputs the data as a series of spectrum data.
2) A spectrum analyzer comprising: