JPH0618573A - Spectrum analyzer - Google Patents

Abstract

PURPOSE:To extract a plurality of frequency components from input signal (signals to be measured) and, especially, continuously display the variation of the extracted frequency components on a time base. CONSTITUTION:A local oscillator 1 outputs a plurality of local oscillation signals LO having different frequencies by switching the signals LO at time intervals shorter than the hourly changing interval of signals to be measured. An RF is inputted to a mixer 5 and mixed with the signals LO from the oscillator 1 and a plurality of frequency components corresponding to the frequency of the signals LO are successively outputted from an IF 6 provided in the poststage of the mixer 5 at the switching time intervals by switching the signals LO and detected by means of a detection circuit 7. The output of the circuit 7 is displayed on, for example, a monitor, such as the CRT, etc., in real time or outputted to a printer, plotter, etc. Or, for example, the output of the circuit 7 is transferred to another processing system for various kinds of arithmetic processing or stored in a memory and the hourly changes of the frequency components are displayed on a monitor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectrum analyzer capable of extracting a plurality of frequency components from a signal under measurement and continuously capturing the signal change of the frequency components on a time axis.

[0002]

2. Description of the Related Art A spectrum analyzer is used to monitor a time change of an arbitrary frequency component included in an input signal (signal under measurement). The conventional spectrum analyzer is capable of monitoring on the time axis (that is, measurement by the zero span method) only for a single frequency. Therefore, in the case of monitoring or analyzing temporal changes of a plurality of frequency components using such a spectrum analyzer, a plurality of spectrum analyzers having different frequency settings are required.

FIG. 7 is a diagram showing an example of a measurement system used when performing noise analysis on a magnetic storage device (hard disk or the like). In the figure, the magnetic storage device 100
The signal f ₀₀ from the read / write circuit 101 is captured by _three spectrum analyzers (indicated by SA _{1 to} SA ₃ in the figure). At SA ₁ , the frequency f ₁₁ included in the noise of the disk sliding system is detected, and SA 1
_{In 2} , the frequency f ₁₂ included in the noise of the recording signal is detected, and in SA ₃ , f ₁₃ included in the sliding noise generated between the disk and the head is detected. SA ₁ , SA ₂ ,
SA ₃ has f ₁₁ ′, f as shown in parentheses in FIG.
The values ₁₂ ′ and f ₁₃ ′ are preset, and the frequency components f ₁₁ and f included in the measured signal f ₀₀ are preset.
The time change of ₁₂ and f ₁₃ is measured, and the start of noise generation,
The continuous state and the end state are monitored individually for each noise.

However, when using a plurality of spectrum analyzers as shown in FIG. 7, there are the following problems. That is, for example, (1) the number of frequencies to be analyzed (“3” in FIG. 7),
Generally, an expensive spectrum analyzer is required, and the measurement system becomes expensive. (2) It takes time and effort to prepare for measuring a plurality of frequency components to be analyzed under the same condition (for example, confirmation work of various measurement conditions and setting thereof). (3) The measurement result is an individual spectrum analyzer S
It is stored in A ₁ , SA ₂ , and SA ₃ , and these measurement results are displayed on a monitor such as a CRT of each spectrum analyzer. Therefore, analysis (display of measurement results,
Simultaneous use of marker function and calculation function) and simultaneous output of measurement results to a printer, etc. are difficult, and analysis efficiency and the like decrease. In addition, when mutually using each measurement data, data exchange between spectrum analyzers becomes complicated.

[0005]

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above problems, and extracts a plurality of frequency components from an input signal (signal to be measured). An object of the present invention is to provide a spectrum analyzer that can continuously display changes on a time axis.

[0006]

SUMMARY OF THE INVENTION The spectrum analyzer of the present invention is a local oscillation signal of different frequencies (hereinafter referred to as "local oscillation signal").
It is characterized in that it has a local oscillator for sequentially switching and outputting at fixed or arbitrary time intervals. For example,
The local oscillator is composed of a plurality of local oscillator signal sources, the setting values of these local oscillator signal sources are set to different frequencies, and the local oscillator signal from the local oscillator signal source is set at a constant or arbitrary time interval. By switching, it is possible to measure the time change of a plurality of frequency components included in the signal under measurement. In addition, the local oscillator is composed of a PLL synthesizer,
The set value of the output frequency of the L synthesizer may be switched at regular intervals or at regular time intervals to measure the time change of a plurality of frequency components contained in the signal under measurement. Further, the local oscillator may not be frequency swept (that is, zero span) or may be frequency swept in a narrow band.

The spectrum analyzer of the present invention is preferably used when the frequency to be measured is known in advance among the frequency components contained in the signal under measurement. The spectrum analyzer of the present invention is used in the same manner as the conventional spectrum analyzer, and the spectrum of the signal under measurement is displayed on the CRT.
It is also possible to display on a monitor such as, and then determine the frequency to be measured from this display. In the present invention, the local oscillator switches and outputs a plurality of local oscillation signals of different frequencies at short time intervals as compared with the time change of the signal under measurement. The signal under test is normally input to the mixer via the attenuator and mixed with the local oscillator signal from the local oscillator.By switching the local oscillator signal, the bandpass filter provided in the subsequent stage of the mixer responds to the frequency of the local oscillator signal. The plurality of frequency components are sequentially output at the switching time intervals and detected by the detection circuit.

The output from the detection circuit is displayed on a monitor such as a CRT or the like in real time, or output to a printer, a plotter, or the like, as described below. Further, for example, the data may be A / D converted to another processing system and then transferred to be subjected to various kinds of arithmetic processing, or may be sequentially stored in a memory, and time changes of frequency components may be displayed on a monitor. There is also.

In the present invention, either a so-called alternate method or a chop method can be adopted as a horizontal sweep (time axis sweep) method. That is, when the signal under measurement is periodic, the alternate system is preferably adopted, the local oscillation signal is switched for each horizontal sweep, and the predetermined frequency (frequency determined by the local oscillation signal) included in the measurement signal is changed. The level can be displayed. on the other hand,
When the signal under measurement is not periodic, the chopping method is preferably adopted, and by switching multiple local oscillator signals at high speed during one horizontal sweep period, multiple frequency components included in the input signal can be detected. It can be displayed simultaneously on the same monitor. Further, for example, when the change of the signal under measurement is slow compared with the horizontal sweep period and the change can be ignored,
Either the alternate method or the chop method can be adopted.

Usually, it takes a certain amount of time from the switching of the local oscillation signal until the outputs from the IF filter, the video filter and the like provided in the subsequent stage of the mixer settle to a stable value. This time depends on the rise time of the local oscillation signal, the characteristics of the above filters, the characteristics of the signal under measurement, and the like. In the alternate method, the local oscillation signal is switched for each horizontal sweep, so that the time required for the rise of the output from the filter or the like is guaranteed. However, in this case, since it takes a long time to measure (that is, a plurality of horizontal sweeps are required), for example, when the change of the signal under measurement is large compared with the horizontal sweep time, the measurement accuracy deteriorates. There may be cases.

On the other hand, in the chop method, a plurality of frequency levels can be measured by one horizontal sweep even if the signal under measurement does not change periodically. However, as described above, if the switching time of the local oscillator signal is set too short, the output from the above filters, etc., will not rise suddenly, resulting in unclear waveforms displayed on the monitor. Appears and the measurement accuracy deteriorates. In addition to this,
For example, when this method is used for a signal under measurement that changes periodically, the measurement cannot be performed in the same local time, so that the measurement accuracy may deteriorate.

In the present invention, in consideration of such a case,
It is possible to adopt a composite method of the alternate method and the chop method. For example, CR four frequency levels
When displaying on a T monitor or the like, it is also possible to display two frequency levels in one horizontal sweep and display the remaining two frequency levels in the next horizontal sweep. By doing so, it is possible to perform a measurement that combines the advantages of the alternate method and the chop method.

In the spectrum analyzer of the present invention, the frequency level measurement results (alternate method,
It is possible to perform A / D conversion of a chopping method and store it in a memory (for example, store time signal characteristics for each local oscillation signal). The frequency level sampling performed at this time can be performed only once for each frequency component to be measured, and this can be stored in memory. Alternatively, the switching of the local oscillator signal can be repeated and the measurement results can be displayed in time series. For each frequency component (ie
It can be stored in the memory for each local signal. In addition, when storing in the memory as described above,
Sampling is performed after the local signal rises.

The frequency level can be displayed on the monitor using the measurement result data stored in this memory.
For this display, a display method of a chop method or an alternate method is appropriately adopted. Furthermore, using the measurement data stored in the memory, it is possible to simultaneously display the level changes of a plurality of frequencies included in the signal under measurement over a long time (for example, minutes or hours), or to display a plurality of levels. Of the frequency levels, any frequency level can be selected and displayed.

[0015]

1 is a partial circuit diagram showing an embodiment of a spectrum analyzer of the present invention. The spectrum analyzer 01 in the figure uses a PLL synthesizer as the local oscillator 1, and the phase comparator 11 (PD) includes
A reference signal (REF) from the reference frequency oscillation source 12 and a signal (frequency f _N ) from the programmable divider (indicated by “÷ N”) 13 are input. Phase comparator 11
Mixes the signal of this frequency f _N with REF and sends it to the loop filter 14. Loop filter 1
4 removes noise and high frequency components from the input signal,
This is output to the voltage controlled oscillator (VCO) 15. The voltage controlled oscillator 15 outputs a signal having a frequency corresponding to the DC component of the input signal to the mixer 5 as a local oscillation signal LO and feeds it back to the phase comparator 11 via the programmable divider 13. A presetting switching means 16 is connected to the programmable divider 13 to switch the output frequency of the divider 13 at regular time intervals.

Since the local oscillator 1 is configured as described above, the output of the voltage controlled oscillator 15 (that is, the local oscillation signal L
O) The frequency is switched at regular time intervals or at arbitrary time intervals. Then, as described above, this local oscillation signal LO is output to the mixer 5. The mixer 5 mixes the output from the above-described filter of the local oscillation signal and the signal under measurement (RF) input via an attenuator (not shown) and outputs the mixed signal to the bandpass filter (IF) 6. After the signal from the bandpass filter 6 is input to the detection circuit 7, a CRT (not shown)
It is also possible to output in real time to a monitor or a printer or plotter. When displaying on the CRT monitor, a so-called chop method or alternate display method is appropriately adopted as a horizontal sweep method.
Further, the output from the detection circuit 7 can be A / D converted and then stored in a memory (not shown), and the frequency level can be displayed on the monitor using the measurement result data stored therein. Further, it can be transferred to another processing system (another computer or the like) and subjected to desired arithmetic processing and the like.

The spectrum analyzer 01 of FIG. 1 which uses a PLL synthesizer as a local oscillator has the advantages that the structure is relatively simple, the cost is low, and the handling is simple. In addition, the local oscillator 1
If the settling time of the PLL synthesizer is sufficiently large with respect to the time change of the signal under measurement, highly accurate measurement results can be obtained.

FIG. 2 is a partial circuit diagram showing another embodiment of the spectrum analyzer of the present invention. The local oscillator 2 of the analyzer 02 shown in the figure includes a plurality of local oscillator signal sources (there are four as 21a to 21d in the figure), and a semiconductor switch 22 for switching these outputs at regular time intervals or at arbitrary time intervals. It is composed by. Local signal source 21
The output frequency of the a~21d is programmable, it is used is preset to different frequencies _f 1 '~f _4'. In the analyzer 02 of this embodiment, the semiconductor switch 2
2 is switched at high speed, so that the local signal source 21a ...
The local oscillator signals LO _{1 to} LO ₄ from 21d are sequentially output to the mixer 5 at fixed time intervals or at arbitrary time intervals.
1 is output to the CRT monitor, other processing system, etc. through the band filter 6 and the detection circuit 7 as in the case of FIG.

In the local oscillator 2 using the plurality of local oscillator signal sources 21a to 21d, the overhead at the time of switching the local oscillator signal depends on the switching time of the semiconductor switch 22. Therefore, if a high-speed semiconductor switch 22 is used in accordance with the time change rate of the signal under measurement, the switching speed of the local oscillator signals LO _{1 to} LO ₄ is made to follow the time change of the signal under measurement. be able to. In addition, the frequency to be measured by the analyzer 02 (this should be f ₁ ~
f ₄ ) is only a specific frequency component included in the signal under measurement (RF). Therefore, unless other frequency components (close-in signals) near the specific frequencies f _{1 to} f ₄ to be measured are captured and measured as large values, the individual local oscillator signals LO _{1 to} LO ₄ have a very low purity. It doesn't have to be expensive. Since the above spectrum analyzer 02 uses a plurality of local signal sources 21a to 21d, its manufacturing cost is slightly higher than that of FIG. However, compared with the cost of preparing a plurality of conventional spectrum analyzers (four in this case), the cost is significantly reduced.

FIG. 3 is a partial circuit showing an example of design modification of the spectrum analyzer 02 shown in FIG. The spectrum analyzer of FIGS. 1 and 2 should be called a multi-span analyzer. On the other hand, the spectrum analyzer 03 in FIG. 3 should be called a 2-channel zero-span analyzer, and the local oscillator 3
A local signal source 23 outside the analyzer and a local signal source 2a inside the analyzer are connected to the switching terminal of the semiconductor switch 22 'of the above, and the local signal LO' from the external local signal source 23 and the local signal LO ' Local signal LO from the signal source 2a
The 2-channel signal ₁ is switched at a constant time or every arbitrary time. Of course, a semiconductor switch 22 'having three or more switching terminals is used, and signals from a plurality of external local oscillator signal sources or a plurality of internal analyzer local oscillator signals are input to these terminals, and three channels are provided. The above zero-span type spectrum analyzer can also be configured.

FIG. 4 shows an embodiment for measuring the predetermined frequency component contained in the signal under measurement with higher accuracy. In particular, when capturing a close-in signal near a certain frequency, it is necessary to set the resolution bandwidth (RBW) small. For example, the spectrum analyzer 04 of FIG. 7A can be used when the frequency to be captured and the frequency setting value of the local oscillator signal are slightly different from each other.
Used to capture the appropriate frequency component (ie, capture the optimum point). In the figure, the local oscillator 1'is the local oscillator 1 shown in FIGS.
1 to 3, the local oscillator signal LO from the local oscillator 1'is output to the mixer 5 via the sawtooth wave generator 8 for narrow band sweep. As shown in FIG. 3B, the sawtooth wave generator 8 has a frequency f _n ′ from the local oscillator 1 ′.
The local oscillation signal LO is output by sweeping in the range of ± Δf _n ′. By doing so, the frequency component existing in the vicinity of a certain frequency can be reliably captured.

In the spectrum analyzers 02 to 04 of FIGS. 2 to 4A, similarly to the spectrum analyzer 01 described in FIG. 1, when displaying on the CRT monitor, so-called chop system or alternate system display system is appropriately adopted. To be done. In addition, the output from the detection circuit 7
It is also possible to store the frequency level in a memory (not shown) and display the frequency level on the monitor using the stored measurement result data.

FIG. 5 exemplifies the measurement results obtained by the spectrum analyzer shown in FIGS. 1 to 4A. In the figure, the horizontal axis represents time and the vertical axis represents dB on a single monitor.
The time change of the signal level of the frequencies f _{1 to} f ₄ included in the signal under measurement is displayed. As described above, according to the present invention, it is of course possible to measure the time change of the signal level of the frequency component, but as will be described below, a non-linear device under test (for example, an amplifier, a mixer, etc.). The strain characteristics of can also be measured. That is, the frequency component due to the distortion in the nonlinear DUT is known. The values of these frequencies are preset in the switching means 16 shown in FIG. 1, the local oscillator signal sources 21a to 21d shown in FIG. 2, and the local oscillator signal sources 2a and 23 shown in FIG. The local oscillation signal is sequentially changed according to the change, and the measurement is performed. As a result, the input level of the DUT for a plurality of specific frequencies (shown as f _{1 to} f ₃ in the figure) as shown in FIG.
The distortion component characteristic can be monitored. The input level can be obtained by using the measurement value of a power meter or the like as the horizontal axis.

[0024]

According to the present invention, a single spectrum analyzer can measure a plurality of frequency components contained in the signal under measurement. As a result, the following effects can be further achieved. (1) Register the settings of the measurement parameters (measurement frequency, resolution bandwidth, video bandwidth, input attenuator rate, frequency measurement time, etc.) for each preset signal, and make these settings collectively during measurement. You can configure the settings. Moreover, since it is not necessary to exchange measurement signal data between a plurality of spectrum analyzers, the troublesomeness required for transferring the data is eliminated. Further, the calculation between each measurement signal data, the presence / absence of the display of the measurement result, the presence / absence of any combination thereof, and the like can be set as desired by the user. Also, when outputting to a printer or plotter, the user can select only the measurement result or calculation result desired. (2) Since it is not necessary to use a plurality of spectrum analyzers, the cost of equipment required for measurement can be significantly reduced. Also, the spectrum analyzer of the present invention can be easily manufactured by replacing only the local oscillator of the existing spectrum analyzer.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment in which a local oscillator of a spectrum analyzer of the present invention is configured by a PLL synthesizer.

FIG. 2 is a diagram showing an embodiment in which the local oscillator of the spectrum analyzer of the present invention is constituted by a plurality of local oscillator signal sources.

FIG. 3 is a diagram showing an example of design modification of the spectrum analyzer of FIG. 2, showing a case where a signal from an external signal source is used as a local oscillation signal.

FIG. 4 is a diagram showing an embodiment in which an oscillator that scans in a narrow band is provided between the local oscillator and the mixer in FIGS.

FIG. 5 is a diagram showing an example of measurement results by the spectrum analyzer of the present invention.

FIG. 6 is a diagram showing level-distortion component characteristics when the spectrum analyzer of the present invention is applied to the measurement of distortion characteristics of a nonlinear device under test.

FIG. 7 is an explanatory diagram of a conventional technique in the case of monitoring a time change of a plurality of arbitrary frequency components included in an input signal.

[Explanation of symbols]

 01 to 04 Spectrum analyzer 1 to 3, 1'Local oscillator 5 Mixer 6 Band filter 7 Detection circuit 8 Sawtooth wave generator

Claims (1)

[Claims] 1. A spectrum analyzer comprising a local oscillator that sequentially outputs local oscillation signals of different frequencies at fixed or arbitrary time intervals.