JPH0577268B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field of the Present Invention> The present invention relates to a signal analysis device for analyzing and displaying waveform characteristics, spectrum characteristics, etc. of an input signal.

<Prior Art> (FIG. 8) As signal analysis devices of this type, there have conventionally been, for example, a spectrum analyzer that analyzes and displays the spectrum characteristics of an input signal, and a device that is a multi-channel spectrum analyzer.

In order to analyze a wideband signal, such a signal analyzer frequency-converts the input signal using a sweepable local oscillator signal and uses a band-pass filter (hereinafter referred to as
The spectral characteristics of the input signal are analyzed by detecting the signal that has passed through the BPF (denoted as BPF) and displaying this detected signal on a cathode ray tube in synchronization with the sweep cycle of the local signal.

FIG. 8 is a block diagram showing an example of a conventional signal analysis device for analyzing the spectrum characteristics of an input signal as described above.

In the figure, an input signal X ₀ is input to a frequency mixer (hereinafter referred to as mixer) 1 and frequency-converted by a local oscillator signal (its frequency is designated as f _L ) from a local oscillator 2 .

The output from mixer 1 has a predetermined bandwidth,
It is input to BPF3 with center frequency _fB .

The output signal of the BPF 3 is detected by a detector 4, and the detected signal is logarithmically compressed in a logarithmic compression amplifier 5 and sent to a display control section 6.

The display control section 6 amplifies this detected signal and supplies it to the Y axis of the cathode ray tube 7.

Therefore, the height of the spectrum of the input signal is logarithmically compressed and displayed on the Y axis.

Further, a sweep signal synchronized with the periodic signal from the control section 8 is supplied from the display control section 6 to the X axis of the cathode ray tube.

Here, when the local oscillator frequency f _L of the local oscillator 2 is swept over the range of f _L ±f _L ' by the frequency sweep signal (synchronized with the periodic signal) from the control unit 8, the frequency f _L − The spectral characteristics of the input signal in the range ±f _L ′ with f _B as the center are displayed on the cathode ray tube 7 .

Note that a diode has conventionally been used in the detector 4, and in order to prevent detection distortion of this diode, the operating point of the diode is adjusted in advance so that it is located on the linear part of its detection characteristic. .

<Problems to be Solved by the Present Invention> However, when a diode is used as the detector 4 as described above, the detection characteristics of each diode vary widely and are temperature dependent. It is necessary to set the operating point in consideration of the ambient temperature, etc. for each signal analyzer, and if this signal analyzer has multiple channels, it is necessary to match the detection characteristics of each channel, so this operation Setting the points involves very complicated work.

In addition, in the case of the detector 4 using a diode, the detection output is output via an integrating circuit (low-pass filter) of resistors and capacitors, so
When impulsive noise is added to the input signal, the level of the input signal's detection output fluctuates continuously due to the detection output of this noise, causing the waveform display to fluctuate, making it difficult to analyze (read) the input signal with high accuracy. The problem was that I couldn't do it.

<Means for solving the above problems> In order to solve the above problems, the signal analysis device of the present invention converts the frequency of an input signal using a local oscillation signal whose frequency can be changed and outputs a frequency. a conversion section; a bandpass filter that receives the output signal of the frequency conversion section and passes a predetermined frequency component;
A compressor that compresses the level of the signal that has passed through the bandpass filter based on predetermined compression characteristics and outputs this compressed signal, and a compressor that samples the signal from the compressor at a predetermined period and converts each into a digital signal. an analog-to-digital converter that outputs
A digital expander that digitally expands the digital signal from the analog-to-digital converter based on expansion characteristics corresponding to the compression characteristics of the compressor and outputs the expanded signal; and a digital arithmetic unit that performs digital arithmetic operations and calculates the characteristic value of the input signal.

<Operation> Therefore, among the input signals frequency-converted by the frequency converter, the signal that has passed through the band-pass filter is compressed by the compressor, and is converted at a predetermined period by the analog-digital converter. It is sampled, converted into a digital signal, and output. This digital signal is digitally expanded by a digital expander and output.

The signal output from the digital expander is input to a digital arithmetic unit, and the characteristic value of the input signal is calculated.

<One Embodiment of the Present Invention> (FIGS. 1 and 2) Hereinafter, one embodiment of the present invention will be described based on the drawings.

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

In the figure, 10 is a frequency conversion section of this device. Reference numeral 11 denotes a low pass filter (hereinafter referred to as LPF) for limiting the upper limit band of the input signal X ₀ (t) to prevent image interference, and its cutoff frequency is set to, for example, 1 GHz.

12 is a first frequency converter for converting the frequency of the input signal X ₀ (t) using the local oscillator signal from the first local oscillator 13
This first local oscillator 13 is a mixer of
The oscillation frequency f _L1 can be swept (for example, from 2 GHz to 3 GHz) by a frequency sweep signal from a control unit 28, which will be described later.

14 is a first BPF having a predetermined passband width f _W1 (for example, 20 MHz) centered on a predetermined frequency.

The first BPF 14 has a center frequency f _B1 set to be high (for example, 2 GHz) in order to prevent image formation of the input signal input to the first mixer 12 .

15 is the signal that passed through the first BPF 14,
A local oscillator signal from the second local oscillator 16 (e.g.
2040MHz).

Therefore, the 2 GHz signal that has passed through the band center of the first BPF 14 is converted into a 40 MHz signal by the second mixer 15 and output.

The output of the second mixer 15 is the second BPF 17
has been entered.

The second BPF 17 has a center f _B2 of its passband.
It is composed of a plurality of filters (not shown) so that the bandwidth f _W2 at 40 MHz can be varied in the range of, for example, several 100 Hz to several kHz.
Filter switching is performed by a band switching signal from the filter.

18 compresses the level of the signal that has passed through the second BPF 17 according to the magnitude of its input level, and compresses the level of the signal that has passed through the second BPF 17, and compresses the level of the signal that has passed through the second BPF 17.
This is a compressor for expanding the dynamic range of 19 (referred to as AD converter).

This compression characteristic is a logarithmic characteristic, for example, outputting a log{x(t)+1} output signal for the input signal level x(t) (however, when x(t) is a negative level, outputs −log{|x(t)|+1}).

In the following description, the characteristic of the compressor 18 with respect to the input signal x(t) will be denoted as A{x(t)}.

19 samples the compressed signal from the compressor using a sampling signal having a frequency at least twice that of the compressed signal, and converts the level value of the sampled signal into predetermined bits (e.g. 8 bits) in parallel. convert it into a digital signal and output it sequentially.
It is an AD converter.

20 is a digital expander that digitally expands the digital signal from the AD converter 19.

The expansion characteristic of this digital expander 20 corresponds to the compression characteristic A{x(t)} of the compressor 18,
10 ^X (t) for the input digital signal X(t)
-1 is digitally calculated and output sequentially (however, when X(t) is at a negative level, -10| ^X(t) |
+1).

Therefore, the digital signal output from the digital expander 20 is the same as the level value of the signal x(t) input to the compressor 18 which is directly converted into a digital signal by the AD converter 19.

In the following description, the expansion characteristic B of the digital expander 20 with respect to the input signal X(t) will be denoted as {X(t)}.

21 performs various digital operations based on the digital signal from the digital expander 20, and calculates characteristic values of the input signal, such as average detection output,
It is a digital arithmetic unit that calculates effective values, peak values, etc.

The digital arithmetic unit 21 performs various calculations in response to a calculation mode switching signal from a control section 28, which will be described later, and FIG. 2 shows a typical calculation mode in blocks.

In FIG. 2, the digital arithmetic unit 21 is set with four arithmetic modes selected by the mode selection section 22, and the first mode is a direct mode in which the digital signal from the digital expander 20 is output directly.

The second mode is an average detection mode 23 in which the arithmetic mean of the absolute values of digital signals that are sequentially input is calculated.

The third mode is an effective value mode 24 in which the square root of the summed average of the squares of the digital signals that are sequentially input is calculated.

The fourth mode is a peak value mode 25 in which the maximum value is selected from among the absolute values of digital signals that are sequentially input.

The digital values calculated by these calculation modes are selected by the mode selection section 22,
As shown in FIG. 1, the data are sequentially sent to the display control section 26.

The display control unit 26 controls the cathode ray tube 27 to display the digital values sequentially input from the digital calculator 21.

This display is synchronized with sequentially input digital values on the Y axis of the cathode ray tube 27, and on the X axis with a display synchronization signal of a predetermined period or a frequency sweep signal for sweeping the frequency of the first local oscillator 13. One of the display synchronization signals is supplied corresponding to the calculation mode of the digital calculator 21.

The control unit 28 controls the operation of the entire signal analysis device by sending control signals to each unit by external operation, etc. The control unit 28 controls the operation of the entire signal analysis device. The second BPF
At step 17, a band switching signal for varying the passband width and setting the display resolution is sent out.

Further, a calculation mode switching signal is sent to the digital calculation unit 21 to select the calculation mode for calculating the characteristic value of the input signal to be displayed.
A display synchronization signal synchronized with a predetermined period or a frequency sweep signal is sent to the display control unit 26 in order to make the X axis of the cathode ray tube 27 a time axis or a frequency axis.

<Operation of the above embodiment> (Figures 3 and 4) Next, the operation of the above embodiment will be explained.

First, the first local oscillator 1 is controlled by the control unit 28.
When the local oscillation frequency of 3 is set to 2.5GHz, the LPF
Among the signals x ₀ (t) input to the mixer 11 , a signal near 500 MHz is frequency-converted by the first mixer 12 and passes through the first BPF 14 .

The signal that has passed through the first BPF 14 is frequency-converted by a second mixer 15 using a local oscillator signal from a second local oscillator 16, and is input to a second BPF 17.

The bandwidth of the second BPF 17 is set in advance to, for example, ±1 kHz with respect to the center frequency by a band switching signal from the control unit 28.

Therefore, 500MHz±1k of the input signal x ₀ (t)
The Hz signal component passes through this second BPF 17.

For example, when the output signal x(t) shown in FIG. 3a passes through the second BPF 17, the output signal x
(t) is compressed by the compressor 18, as shown in FIG. 3b, and its output A{x(t)} is sent to the AD converter 19.

Compressed signal A {x(t)} input to AD converter 19
are sampled at a predetermined period, as shown in FIG. 3c, and the sample values A{x(t ₁ )}, A{x(t ₂ )},...
are respectively 8-bit digital signals X(t ₁ ),
X(t ₂ ), ... and sequentially digital expander 2
Output to 0.

The input digital signals X(t ₁ ), X(t ₂ ), ... into the digital expander 20 are respectively expressed as B{X
(t ₁ )}, B{X(t ₂ )},...
The signals are sequentially output to the digital arithmetic unit 21.

Here, when the calculation mode of the digital calculator 21 is selected as direct mode and the display control unit 26 receives a display synchronization signal of a predetermined period from the control unit 28, the X axis of the cathode ray tube 27 is used as a time axis. The swept and calculated values B{X(t ₁ )}, B{x(t ₂ )}, . The signals are sequentially plotted on the display screen, and the signals shown in FIG. 3d are displayed. this is,
It shows the waveform of the signal component that has passed through the second BPF 17.

Next, when the calculation mode of the digital calculator 21 is switched to the average detection mode 23 by the control unit 28, the signals B{X(t ₁ )}, B{X( t ₂ )}..., that is, P _o = 1/N _o 〓 ^j=n-N+1 |B{X(t _j )}| is performed, and this calculated value P _o is The signals are sequentially output every predetermined number of sampling times N in the AD converter 19.

Here, similarly to the above, the display control unit 26
When the X axis of the cathode ray tube 27 is swept at a predetermined period as a time axis, the calculated values P _o from the digital calculation section 21 are sequentially plotted on the display screen of the cathode ray tube 27.

As shown in Fig. 4, this indicates the average detection output of the 500MHz±1kHz signal component x(t) of the input signal x ₀ (t), and the change in this calculated value P _{o is}
It shows the amplitude fluctuation of this signal, that is, the modulated waveform.

Similarly, when the calculation mode of the digital calculator 21 is switched to the effective value mode 24 by the control section 28, the digital signals B{X(t ₁ )}, B{X(t ₂ ) from the digital expander 20 )},..., that is, R _o = [1/N _o 〓 ^j=n-N+1 B ² {X(t _j )}] ^1/2 is performed, and this calculated value R _o is the same as above. is sequentially outputted to the display control unit 26 every predetermined number of sampling times N,
500MHz±1K of input signal x ₀ (t) as shown in Figure 4
Displayed as an RMS waveform of the signal component in Hz.

Further, when the calculation mode of the digital calculator 21 is switched to the peak value mode 25, the digital signal B{X(t ₁ )} from the digital expander 20
A predetermined sampling circuit N of the absolute value of B{X(t ₂ )}),...
_{The maximum value of} |] are calculated and sequentially output to the display control unit 26, and as shown in _FIG .
Displayed as an envelope detection waveform of the Hz signal component.

Here, for example, the control unit 28 controls the second
When the passband width of the BPF 17 is set to 100Hz and the calculation mode of the digital calculator 21 is switched to the effective value mode, the local oscillation frequency of the first local oscillator 13 is changed by the frequency sweep signal of the control unit 28. , a predetermined number of sampling times N in the AD converter 19 in the range from 2.4 GHz to 2.6 GHz in 100 Hz steps.
When a display sweep signal synchronized with the frequency sweep is sent from the control section 28 to the display section 26, the digital arithmetic unit 21 receives the input signal x ₀
100Hz of signal components from 400MHz to 600MHz of (t)
The effective value is calculated for each time and outputted sequentially.

Also, according to the display sweep signal from the control unit 28, the X axis of the cathode ray tube 27 is set as a frequency axis.
Since it is swept sequentially, the cathode ray tube 27 has a fifth
As shown in the figure, the spectrum characteristics of the effective value level from 400MHz to 600MHz are displayed.

For example, when the digital calculator 21 performs detection in the average detection mode or the effective value mode, if the input signal includes an impulsive nozzle, the detection output due to the noise will be affected by the calculation. The data are averaged (averaged to 1/N or 1/√) and output within a period (that is, the time during which a predetermined number of samplings N are performed).

Note that this spectrum characteristic is displayed linearly on the Y axis, but the digital arithmetic unit 21
, the effective value R _o and the standard value R _p are calculated sequentially.
By performing a logarithmic calculation of the ratio, that is, 20log (R _o /R _p ), and outputting this to the display control unit 26, this spectrum characteristic will be displayed logarithmically (in decibels) on the cathode ray tube 27. .

<Other embodiments of the present invention> (FIGS. 6 and 7) In the above embodiments, the first local oscillator 13
However, the second local oscillator 1
6 is also configured to be sweepable, and when analyzing the spectrum near a specific frequency, the frequency of the first local oscillator 13 is fixed, and the local frequency of the second local oscillator 16 is swept in fine steps. You may also do so.

Furthermore, in the above embodiment, the frequency of the input signal is converted using two local oscillator signals, but as shown in FIG. 32 may be provided to lower the center frequency of the passband of the second BPF 17. Conversely, if the upper limit frequency of the analysis band of the input signal is low, it is also possible to analyze the signal with only one frequency conversion, as shown by the dotted line in FIG.

Further, in the above embodiment, the compression characteristic of the compressor 18 is logarithmic compression, but this characteristic is not limited to the above embodiment. A characteristic that follows the law or the μ law may be used, or a compressor with a polygonal characteristic may be used. In this case, the expansion characteristics of the digital expander 20 correspond to the compression characteristics of the compressor.

Further, in the above embodiment, the digital arithmetic unit 21
Although the various characteristic values calculated by are displayed as a continuous waveform, the calculated values may also be displayed numerically together with this waveform.

Furthermore, the operation mode of this digital arithmetic unit 21 is not limited to the above embodiment, and for example, the operation mode from the LPF 11 of the above embodiment to the digital expander 20 including the first and second local oscillators 13 and 16. The signal path is 1 channel, and the 7th
As shown in the figure, when a two-channel signal analyzer is configured, the phase difference between each input signal,
It is also possible to perform various calculations such as correlation using the digital calculator 21'.

Furthermore, the present invention can be applied in exactly the same way to a multi-channel signal analysis device.

<Effects of the present invention> Since the signal analysis device of the present invention is configured as described above, it eliminates the need for a detection diode whose detection characteristics vary and is temperature dependent.
Stable detection characteristics can be obtained without the complicated work of setting the operating point.

Furthermore, since the detection output of impulsive input noise is averaged within a predetermined period, signal analysis can be performed with high precision without display fluctuation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a block diagram showing the main parts of one embodiment. Figures 3a to 3d, 4 and 5
The figure is a signal waveform diagram showing the operation of one embodiment.
6 and 7 are block diagrams showing other embodiments of the present invention, and FIG. 8 is a block diagram showing a conventional device. 10... Frequency conversion section, 17... Second BPF,
18... Compressor, 19... AD converter, 20...
Digital expander, 21...Digital arithmetic unit.

Claims (1)

[Claims] 1. A frequency converter that converts the frequency of an input signal using a local oscillation signal with a variable frequency and outputs the resultant signal, and a band that receives the output signal of the frequency converter and passes a predetermined frequency component. a pass filter; a compressor that compresses the level of a signal that has passed through the band pass filter based on a predetermined compression characteristic and outputs the compressed signal; and a compressor that samples the compressed signal from the compressor at a predetermined period. an analog-to-digital converter that converts the sampled signals into digital signals and outputs them; and an analog-to-digital converter that converts the sampled signals into digital signals and outputs them; and a digital expander that digitally expands the input signal and outputs the expanded signal; and a digital arithmetic unit that performs a digital operation based on the signal from the digital expander to calculate a characteristic value of the input signal. A signal analysis device characterized by: