JPH0980092A - Method for automatically setting parameter of spectrum analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically determine the pass band width(RBW) or the like of a spectrum analyzer by determining RBW of BPF on the basis of the frequency interval of a waveform to be displayed, the noise level or the like. SOLUTION: RBW of BPFs 19, 24 of a spectrum analyzer 15 is made a parameter, and RBW is determined from the frequency interval of the waveform to be displayed so as to satisfy the relation with the frequency interval of the waveform to be displayed and the noise level or the dynamic range of an input signal. In other words, a control part 31 reads the spectrum of the input signal from a buffer memory 29, detects a frequency with its maximum value and makes it a central frequency. The central frequency is stored in a parameter value storing part 36. When the central frequency is determined, the input signal is measured again so that the central frequency may be in the center of a display scope and stored in a buffer memory 29. A noise part to be measured is made an offset value, three times thereof a frequency span, and RBW of BPFs 19, 24 is determined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a spectrum analyzer to measure a ratio of a carrier signal level of an input signal to a noise level, so-called C / N,
The ratio of the signal level of the input signal to the noise level, so-called S / N measurement, generated based on two fundamental wave inputs,
When measuring the amount of intermodulation distortion that is input at the same time as these, the bandwidth RBW of the bandpass filter that extracts the frequency-converted signal of the input signal, and the low frequency band that extracts the display signal from the detection output as necessary. The present invention relates to a spectrum analyzer parameter automatic setting method for automatically setting parameters such as a bandwidth VBW of a pass filter, a center frequency of a display screen, and a frequency span displayed on the display screen.

[0002]

2. Description of the Related Art FIG. 4 shows a general configuration example of a spectrum analyzer. The output signal of the object 11 is input to the spectrum analyzer 15 as an input signal. In the spectrum analyzer 15, the input signal is supplied to the frequency mixer 17 through the input variable attenuator 16, and the frequency sweep oscillator 1
8 is frequency-mixed with the local signal, the mixed output is supplied to the bandpass filter 19, the output of the filter 19 is amplified by the amplifier 21, and the amplified output is the frequency mixer 2
At 2, the frequency is mixed with the local signal from the local oscillator 23,
The intermediate frequency signal is taken out by the bandpass filter 24, the output of the filter 24 is detected by the detector 26,
The detected output is passed through the low pass filter 27, and then A
The signal is converted into a digital signal by the / D converter 28 and stored in the buffer memory 29. The control unit 31 is a so-called CPU, and sets the amount of attenuation of the attenuator 16 according to the parameter set by the parameter setting means 32, and controls the ramp voltage generator 34 through the timing controller 33 so as to control the sweep frequency oscillator 18. Control, that is, setting of the sweep frequency band, setting of the bandwidth RBW of the filters 19 and 24, setting of the bandwidth VBW of the filter 27, setting of the sampling period of the A / D converter 28, etc. Display control of the stored data on the display 35 is performed.

When measuring the C / N of an input signal using this spectrum analyzer, the following operation was performed. 1. Press the frequency button to set the center frequency. 2. The frequency interval (offset value) between the signal to be measured (carrier wave) and noise is set.

3. Press the frequency span button to set the frequency span (frequency range displayed on the display screen). 4. Match the carrier peak with the center frequency of the screen. 5. Match the carrier level with the reference level. 6. Align the marker with the peak point of the signal in peak search.

7. Make the marker a delta marker. 8. Match the delta marker to the noise band being measured. 9. Select noise measurement. Ten. Read the displayed value of the noise level. When setting the frequency span by this operation, the bandwidth RBW of the band-pass filters 19 and 24 (usually the settable width thereof is predetermined) is set by trial and error so that the signal portion and the noise portion are separated from each other. The waveform was displayed correctly.

Also in the measurement of the intermodulation distortion contained in the input signal, the two input fundamental waves and the two input fundamental waves, for example, 3
The RBW was set by trial and error so that the following four distortions were clearly displayed. In other measurements using a spectrum analyzer, RBW was set by trial and error when performing waveform display in the frequency domain. R
Conventionally, other parameters of the BW, that is, the bandwidth VBW of the low-pass filter 27, the center frequency of the display screen, the frequency range (frequency span) displayed on the display screen, and the like have been set manually.

[0007]

Conventionally, various parameters in the spectrum analyzer are manually set, and in particular, the setting of the bandwidth RBW that determines the resolution is made by trial and error by setting various parameters. Because
The setting took a relatively long time, and the operation was troublesome. Further, conventionally, S / N is not measured by a spectrum analyzer, and there has been a demand for S / N measurement.

[0008]

According to the invention of claim 1, the pass band width RBW of the band pass filter of the spectrum analyzer is used as a parameter, and the frequency interval of the waveform to be displayed and the noise level or the dynamic range of the input signal are set. The RBW is determined from the frequency interval of the displayed waveform so as to satisfy the relational characteristic, and the RBW is automatically set in the band pass filter.

In the following, on the premise of the invention of claim 1, according to the invention of claim 2, the bandwidth VBW of the low-pass filter is obtained.
Is RBW / 10. In the third aspect of the invention, the frequency span is three times the frequency interval. In the invention of claim 4, the peak level of the input signal is the center frequency. In S / N measurement, the difference between the center frequency of the signal part and the frequency at one end of the noise part is the frequency interval, in C / N measurement the difference between the carrier frequency and the measured noise frequency is the frequency interval, and the intermodulation distortion amount measurement Then, the difference between both fundamental wave frequencies is defined as the frequency interval.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is applied to S / N measurement will be described. For example, as shown in FIG. 1A, in the waveform display in the frequency domain displayed on the display screen, the minimum frequency f _SL and the maximum frequency f _{SH of} the signal portion to be measured,
Further, the maximum frequency f _NH and the minimum frequency f _{NL of the} noise portion (measurement bandwidth) are manually set, as in the conventional case.
Determination of Center Frequency In the spectrum analyzer shown in FIG. 4, the control unit 31 reads the spectrum of the input signal from the buffer memory 29, detects the frequency f _C having the maximum value, and sets it as the center frequency. The center frequency f _C is stored in the parameter value storage unit 36. When the center frequency or carrier frequency of the signal output from the object 11 is known in advance, the frequency is set to the center frequency f.
_It may be manually set as _C. When the center frequency f _C is determined, the input signal is re-acquired and stored in the buffer memory 29 so that it becomes the center of the display screen.
Frequency span determination Noise part to be measured (frequency band)
One end, for example, and f _NH, frequency interval f _NH -f _C of the center frequency (peak frequency) f _C of the signal portion Yes is manually set as the offset value f _of, 3 of the offset value
The frequency span is set to 3f _of times. This frequency span is stored in the parameter value storage unit 36. RBW Determination Next, the pass band width RBW of the band pass filters 19 and 24 is determined.

In this case, the frequency interval of the waveform to be displayed is the offset value f _of , and R is set so that the bottom of the spectrum of the signal portion does not affect the end of the noise portion to be measured.
Determine BW. This is uniquely determined from FIG. 2A showing the relationship characteristic between the dynamic range with RBW as a parameter and the offset value f _of . That is, FIG.
Due to the influence of 4, the measurement target, that is, the skirt of the signal part spectrum, represents the limit where the end of the noise part is not applied. The value on the vertical axis indicates the noise level when the peak value of the signal portion is 0 dB. Therefore, the absolute value of this vertical axis is the dynamic range. Dynamic range and offset value f _of
Given the bandwidth RB of the characteristic curve near this point
Select the smaller W. For example, the noise level is -10
0 dBc / Hz, that is, the dynamic range is 100 d
When B and the offset value f _of are 40 kHz, the point is point A in the figure, and the bandwidth 3 kHz of the characteristic curve on the left side of the figure from this point A is RBW. If the RBW is smaller than 3 kHz, the problem of spectrum overlap does not occur, but the frequency sweep time (measurement time) becomes long. Therefore, the bandwidth of the curve on the left side as close as possible to the point A is set.

Further, the dynamic range is determined as follows. When the dynamic range is increased, that is, when the noise level is decreased, distortion and spurious are generated due to the influence of the frequency mixers 17 and 22 inside the spectrum analyzer. Normally, the limit of the maximum value (minimum value of noise level) of the dynamic range that does not cause such distortion and spurious is obtained by measurement in advance, and a margin is added to the limit value and stored in the spectrum analyzer.
This is given, for example, by the dashed curve in Figure 2A. The measurable range is the range above this dashed curve in FIG. 2A. For example, if the offset value is 40 kHz, 40
The dynamic range is smaller than the value (point B) 113 dB on the broken line curve at kHz, that is, the noise level is -11.
It is necessary to set it to 3 dBc / Hz or more.

When the RBW is large, the noise level becomes large and the dynamic range becomes small. When the noise generated in the spectrum analyzer is N _S and the attenuation amount of the input attenuator 16 is ATT, the noise level NL can be expressed by the following equation. _{NL = N S +10 log (RBW} ) + and detection limit of the maximum signal level that can be ATT input and SL is a SL-NL. This limit line is shown by a dotted line in the noise level-offset value characteristic diagram of FIG. 2B. If the absolute value of the dynamic range is larger than this, the signal is distorted or the peak protrudes from the display surface. Thus the dynamic range DR becomes _{DR <SL-N S -10 log} (RBW) -ATT. From this, the set value of RBW and the settable range of the dynamic range (however, the vertical axis represents the noise level value which is the inverted value of the dynamic range) are shown in FIG. 2B. As the internally generated noise level N _S increases, the lower limit value also increases, so the dotted line of the noise level moves upward, and when N _S decreases, the lower limit value decreases, and the dotted line of the noise level moves downward. The range in which the dynamic range can be set for the offset value f _of is the range shaded in FIG. 2B, and the dynamic range can be set. If the dynamic range is set in this range, the RBW value will be uniquely determined.

The RBW value thus obtained is also stored in the parameter value storage unit 36. The lower limit value of the bandwidth VBW of the low pass filter (video filter) 27 is set to VBW = RBW / 10 according to an empirical rule. Further, as the reference level, the input attenuator 16 is controlled so that the maximum peak value matches the upper end of the display surface. The VBW and the reference level are also stored in the parameter value storage unit 36.

After the various parameter values are automatically determined as described above, these parameter values are set in the corresponding parts by the control unit 31, respectively, and the sweep time T _S is the frequency span (Hz) / { RBW (Hz) x min
(RBW, VBW) (Hz) x 0.5} (sec) is determined and set. min (RBW, VBW) is RBW
And VBW, whichever is smaller.

Thereafter, the input signal is fetched and stored in the buffer memory 29, and each data between the minimum frequency f _SL and the maximum frequency f _SH of the signal portion is fetched from the buffer memory 29 and each level value thereof is fetched. All (linear values, that is, not dB values) are added, and the added value is divided by the number of data. In order to make this division result G _S have the size of the signal band, the following calculation is performed to perform the level L _{s of the} signal part.
And

L _s = 10 log G _S +10 log ((f _SH −f _SL ) /
(1.2 × RBW) +2.5 RBW is multiplied by 1.2 by the bandpass filters 19 and 2
Correction based on 4 being a Gaussian characteristic, 2.5
Is added in order to correct the level drop due to logarithmic amplification performed in the previous stage of the detector 26. Further, each data in the measurement frequency band, that is, between the lowest frequency f _{NL of the} noise band and the lowest frequency f _SN of the signal part, and between the highest frequency f _{SH of the} signal part and the highest frequency f _NH of the noise band is buffer memory. 29, all level values (linear values) are added, and the added value is divided by the number of data. In order to make this division result G _N the size of the noise band, the following calculation is performed to obtain the level L _{N of the} noise part.

L _N = 10 log G _N +10 log ((f _SL −f _NL +
f _NH − f _SH ) / (1.2 × RBW)) + 2.5 L _S / L _N is displayed on the display screen as the measured S / N.
Similarly, in S / N measurement of burst waves, parameters are automatically set. In this case, the sweep frequency is fixed to capture the center frequency of the input signal, and the signal is captured.
This is read out from the buffer memory 29, and the trigger signal synchronized with the input burst signal as shown in FIG.
B) is created, a burst waveform is displayed on the display screen in the time domain as shown in FIG. 3D by using this trigger signal.
With respect to the displayed waveform, the range 41 to be measured is designated by a marker, and the gate signal 42 corresponding to this is generated as shown in FIG. 3C. Repetition period T of this input burst signal
_{The r} and the pulse width T _w are known to the user in advance. The inputs of the frequencies f _NL and f _NH indicating the measurement band and the frequencies f _SL and f _SH indicating the signal part are the same as in the S / N measurement of the continuous wave signal, and in the automatic setting of various parameters, the low pass filter is used. S / of the continuous wave input signal described above except that the bandwidth VBW of 27 is 1 / T _G (T _G is the pulse width of the gate signal 42 for extracting from the input burst signal).
The same is done as in the case of N measurement.

Next, the case where the present invention is applied to the measurement of the ratio of the carrier level to the noise level, so-called C / N, will be described. In this case, the center frequency f _C is determined by S /
The same is done as for the measurement of N. Also in this case, if the carrier frequency is known, that value may be manually input as the center frequency f _C. Furthermore, the noise frequency f _N is generally defined by how far away from the carrier the noise is to be measured, depending on the type of modulation signal to be measured, and the noise frequency f _N to be measured.
The frequency interval between _N and the carrier frequency f _C is the offset value f
It is input set as _of. In this case, the two frequencies to be displayed in waveform are the carrier frequency and the noise frequency.

The frequency span is 3f _of as in the S / N measurement.
It is said. RBW, VBW, and reference level S / S
It is performed in the same manner as the N measurement. In the measurement, each determined parameter value is set in the corresponding portion, the input signal is captured, and the data level L _C of the carrier frequency f _c in the buffer memory 29 and the noise frequency f _N (f in this example, f _c +
The level L _N of the data of f _0f ) is taken out and the ratio L _C / L _{N of them} is displayed on the display screen. The waveform display in the frequency domain in this case is as shown in FIG. 1C, for example.

The C / N measurement of the burst signal can also be measured by taking out a part of the burst waveform and determining the parameters in the same manner as the S / N measurement of the burst signal described above. The determination of RBW and VBW according to the present invention described above can also be applied when two fundamental waves and their intermodulation waves, for example, a third-order distorted wave are input and the third-order distorted wave level is measured. In this case, the frequencies f of the two fundamental waves
₁ and f ₂ are the frequencies of the two display waveforms, and therefore the frequency interval f ₂ −f ₁ may be used as the above-mentioned offset value f _of .

As shown in FIG. 1B, a signal portion is displayed in the frequency domain on the left half of the display screen, and a specific frequency of the noise portion, for example, f _NH noise is displayed in the time domain on the right half of the display screen. Is also done. This signal is taken into the buffer memory 29 for frequency domain display and the noise is taken into the buffer memory 29 for time domain display alternately. In this case, the frequency span in capturing the signal portion is the offset value f _of, and RBW is the S /
Determine as for N measurements, making VBW equal to RBW.

The frequency span in capturing noise for time domain display is zero, and the oscillation frequency of the sweep oscillator 18 is fixed so as to capture only the instructed frequency component, in this example f _NH component, and RBW is the signal. VBW is equal to RBW, with the same as part capture. This noise data is captured at least to the extent that it can be displayed for each point on the time axis in the right half of the display screen, the level values (linear values) of all data displayed on this display screen are added, and the added value is the number of data. Divide by and the result of this division G _N1
The noise level L _N is calculated by the following equation, assuming that the noise of is uniformly distributed in the noise portion.

L _N = 10 log G _N1 +10 log ((f _SL − f _NL +
f _NH − f _SH ) / RBW)) +2.5 The signal level L _S is determined as described above and L
_{Calculate S} / L _N. In such a measurement, VBW is shown in FIG.
The display measurement is 10 times as large as the display measurement shown in (3), and therefore the sweep time (measurement time) becomes 1/10 as is clear from the calculation formula of the sweep time.

The display measurement shown in FIG. 1B is also applied to the measurement of C / N. Furthermore, S / N and C / N of burst wave
VBW in these cases is 1 /
It is T _G and does not reduce the measurement time. The above-described automatic determination of parameters and automatic setting of the determined parameters can be generally applied to measurement using a spectrum analyzer.

[0026]

As described above, according to the present invention, various parameters of the spectrum analyzer are automatically determined, and in particular, the RBW is automatically determined, compared with the conventional case where it is determined by trial and error. , It can be decided in a short time, and the user does not need to perform troublesome operations. Moreover, S / N can be measured using a spectrum analyzer.

[Brief description of drawings]

FIG. 1A is a diagram showing a display example of a display screen during S / N measurement, B is a diagram showing an example in which a signal portion is displayed in a frequency domain and noise is displayed in a time domain, and C is a diagram showing C / N measurement. It is a figure which shows the example of a display of a display screen.

FIG. 2 is a diagram showing a relationship characteristic between a noise level and an offset value with RBW as a parameter.

FIG. 3A is a diagram showing a waveform example of a burst signal, B is a diagram showing a trigger synchronized with this burst signal, C is a diagram showing an example of a gate signal for extracting a part of the burst signal, and D is a diagram. It is a figure which shows the time domain display example of a burst signal.

FIG. 4 is a block diagram showing a configuration example of a spectrum analyzer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Aoyama 1-32-1, Asahimachi, Nerima-ku, Tokyo Within Advantest, Inc. In Stock Company Advantest (72) Inventor Yoshiaki Miyamae 1-32-1 Asahi-cho, Nerima-ku, Tokyo Stock Company Advantest (72) Inventor Toshiharu Kasahara 1-32-1 Asahi-cho, Nerima-ku, Tokyo Stock Association Company Advantest (72) Inventor Hiroaki Takaoku 1-32-1, Asahi-cho, Nerima-ku, Tokyo Stock company Advantest

Claims (8)

[Claims] 1. A method for setting a parameter when a waveform is displayed in a frequency domain by a spectrum analyzer, wherein a pass band width RBW of a band pass filter of the spectrum analyzer is used as a parameter, and a frequency interval of a waveform to be displayed and a noise level or an input. Automatic setting of parameters of spectrum analyzer, characterized in that the RBW is determined from the frequency interval of the displayed waveform so as to satisfy the relation characteristic with the dynamic range of the signal, and the RBW is automatically set in the band pass filter. Method. 2. The bandwidth VBW of the low-pass filter through which the detector output of the spectrum analyzer is passed is RBW.
10. The automatic parameter setting method for a spectrum analyzer according to claim 1, wherein the parameter is set to / 10. 3. The automatic parameter setting method for a spectrum analyzer according to claim 1, wherein a frequency span of three times the frequency interval is spanned. 4. The automatic parameter setting method for a spectrum analyzer according to claim 1, wherein the peak level frequency of the input signal is used as the display center frequency. 5. The spectrum according to claim 1, wherein a center frequency of a signal portion and a frequency at one end of a noise portion are set to the frequency interval when measuring S / N. Analyzer automatic parameter setting method. 6. The parameter of the spectrum analyzer according to claim 1, wherein an interval between an input signal carrier frequency and a measurement noise frequency is set to the frequency interval when measuring C / N. Automatic setting method. 7. When measuring the amount of intermodulation distortion, the difference between the frequencies of the two fundamental waves of the input signal and the frequencies of the intermodulation waves adjacent thereto is set as the frequency interval. The automatic parameter setting method of the spectrum analyzer according to claim 1 or 2. 8. A dynamic range of an input signal is smaller than both a dynamic range determined by a limit where distortion and spurious noise generated in the spectrum analyzer are not a problem and a limit dynamic range determined by a noise level and a maximum input signal level. The automatic parameter setting method for a spectrum analyzer according to any one of claims 1 to 7, wherein