JPH0228568A - Spectrum analyzer - Google Patents

Abstract

PURPOSE:To easily and accurately display the electric power value of a signal to be measured together with normal spectrum distribution data by distributing the signal to be measured to a signal processing part and a power sensor through a signal branching circuit. CONSTITUTION:The input signal from an input terminal IN is branched by the signal branching circuit 105. Then one is processed by the signal processing part 101 with the sweep signal from a sweep signal generation part 100 and the signal corresponding to the spectrum is outputted. This is A/D-converted 102 and stored on a memory 103. The power sensor 106, on the other hand, detects the power of the signal to be measured and the detected power is A/D- converter 107 and stored on a memory 108. The data read out of the memories 103 and 108 are displayed together on the same screen of a display part 104.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of a spectrum analyzer that performs frequency analysis of a signal under test.

[Conventional technology]

Conventionally, as is well known, spectrum analyzers are capable of measuring frequencies ranging from several 10 kHz to several 10 to several 100 kHz.
The characteristics of a high-frequency signal under test in a relatively high range of GHz are measured, and the spectrum intensity at each frequency is displayed on the clear display section, with the horizontal axis as the frequency axis. For example, as shown in FIG. 10, the spectrum analyzer configured in this manner includes an RF section (high frequency circuit) 1, an IF section (intermediate frequency circuit) 2, a detection NJ, an A/D conversion section 4, a digital memory 5, and a Display section 6, sweep signal generation section 7 and f-
It is composed of an evening processing/control section 8, etc.

In such a circuit configuration, the high frequency measured signal & inputted from the input terminal 9 is transmitted to the RF section consisting of a mixer and a local oscillator! is input to. In this RF section 1, the input signal under test a is a local oscillation signal (local signal) of a local oscillator whose missed frequency changes according to the signal level of the sweep signal outputted from the sweep signal generation section 7. The frequency is converted into an intermediate frequency signal C by mixing the signal C with the intermediate frequency signal C. The intermediate frequency signal C output from the RF section 1 is input to IFF 2O, which has a built-in band pass filter (BPF). Then, only the frequency component that matches the pass frequency of the band pass filter passes through this IFF 20, is input to the next detection section 3, and is output as a DC detection signal d corresponding to the magnitude thereof. This detection signal d is the following A/
The D conversion unit 4 converts the sampling signal e outputted from the data processing/control unit 8, which is made up of, for example, a microprocessor, into digital data by converting it into digital data. The data is stored in the memory 5.

The digital data for each sampling period of the detected signal d stored in the digital memory 5 is read out in a certain order in response to the successive signal f of a certain period outputted from the data processing/control section 8. and sent to the display section 6.

This display section 6 has, for example, an image memory for one screen that can be displayed at a time on the display screen, and after storing each data value input sequentially in the image memory, it stores the image memory for the one screen. Display image information on the display screen. Thus, spectrum distribution data as shown in FIG. 11 is displayed on the display screen of the display unit 6.

Each squictor in FIG. 11 is shown as an ideal line having no area. However, in reality, it is displayed as a squictor having a width corresponding to the bandwidth of the IFF2O bandpass filter.

The data processing/control unit 8 controls the sweep interval and sweep speed of the sweep signal generation unit 7 so that the spectrum distribution data shown in FIG. 11 is displayed on the display unit 6, and
A sampling signal f is sent to the A/D converter 4, and a read signal f is sent to the digital memory 5. Further, necessary arithmetic processing is executed so that the spectrum value of the desired frequency value is displayed on the solution display section 6.

[Problem to be solved by the invention]

However, the spectrum analyzer configured as shown in FIG. 10 still has the following problems. In other words, in order to investigate the properties of the signal under test a, it is necessary to accurately grasp the distribution data of the spectrum values of each frequency included in the signal, and to calculate the sum of each spectrum value, that is, the power value of the input signal under test a. There are many cases where it is necessary to understand both at the same time.

Is this input signal under test a a spectrum component that spreads beyond the bandwidth of the IFF2O bandpass filter? In order to measure the power value of the hot water contained in the current using a conventional spectrum analyzer as shown in Fig.
For example, the data values obtained in each period of each sampling signal e in the converting section 4 may be integrated in the f-tar/control section 8.

In order to accurately integrate the power value of the input signal under test 1, it is necessary to
It is assumed that each spectrum value is measured accurately. However, it is generally difficult to predict in advance the spread of spectrum components included in the input noise signal under test. Also,
IFF of the spectrum measured as described above
Complicated correction calculations are required when all errors are corrected and integrated according to the bandwidth of the 2O bandpass filter. Therefore, it is almost impossible to accurately measure the power value using the above-mentioned integration method.

In addition, in such a spectrum analyzer,
Only signal components in a specific frequency sweep range selected and set by the f-event processing/control section 8 are displayed on the bot display section 6. In reality, high-level spectrum values (frequency components) may exist in frequency regions outside of this frequency sweep range.However, there are many cases where the operator is unaware of the existence of such high-level frequency components. do. In addition, the RF section 1
In this case, there is a concern that the user may not notice that saturation has occurred and may perform measurements with many errors. Also, due to excessive input, RF
There is also a concern that Part 1 may be damaged. In particular, noisy signals and RF
When measuring a signal such as a pulse signal in which the spectrum is distributed over a wide band, the above-mentioned problem is likely to occur because the total power value and Nockle peak power are much larger than the individual spectrum values.

Furthermore, like a continuous wave (CW) signal, the entire spectrum falls within the passband of the IFF2O bandpass filter, r
Even when it is possible to measure the power value, there is usually a large error due to the complicated signal circuits in the RF section 1 and IF'F2O3. Therefore, in order to accurately measure the power value even for continuous wave signals, input a signal whose power value is accurately determined in advance as a reference signal, and then adjust the indicated value of the spectrum analyzer at the frequency used. I had to proofread it. However, this calibration work is extremely time-consuming and greatly reduces measurement work efficiency. In addition, as a real problem, it is almost impossible to always have a signal whose power value is known accurately at the frequency to be measured, and it is difficult to measure the power value with insufficient measurement accuracy. There is an unavoidable problem.

Therefore, an object of the present invention is to provide a spectrum analyzer that can easily and accurately display power values along with normal spectrum distribution data.

[Means to solve the problem]

In order to achieve the above object, a spectrum analyzer according to one aspect of the present invention includes means for substantially guiding an input signal to a first path and a second path, and an input signal guided to the first path. means for generating a power value corresponding to the input signal directed to the second path; and display means.

Further, the spectrum analyzer according to another aspect of the present invention includes an RF section that mixes the signal to be measured input from the input terminal with a local excavation signal whose frequency is swept by a sweep signal from the gold sweep signal generating section and converts the frequency. , an IF section that extracts a predetermined frequency component of the output signal of this RF section, a detection section that detects the output signal of this IF section, and an A/D conversion section that converts the detected signal of this detection section into a digital value at a constant cycle. a display unit that displays each digital value converted by the A/D conversion unit as a spectrum value at each frequency; a signal branching or switching circuit inserted between the input terminal and the RF unit; The apparatus is equipped with a power detector that detects the power value of the signal under test multi-branched by the signal branching circuit and sends it to the display section for display together with the spectrum value.

[Effect]

According to the spectrum analyzer according to one aspect as described above, by distributing the signal under measurement to the spectrum-2-mura data generation unit and the power value detection unit, measurement can be easily and accurately performed without increasing measurement time. It can display the power value along with the spectrum data.

Further, according to another aspect of the spectrum analyzer configured as described above, the signal under test inputted from the input terminal is inputted to the RF section via the signal branch or switching circuit, and is also inputted to the power detector. Ru. The measured signal line input to the RF section, this RF section, the next IF section, the detection section, and the A/D conversion section decompose the signal into spectrum values corresponding to each frequency, which are displayed on the W display section.

On the other hand, the power value of the signal under measurement input to the power detector is detected by the power detector as an average value or a peak value. Then, the detected total power value is displayed on the square display section together with each of the spectrum values.

Therefore, each spectrum value and the total power value at each frequency of the signal under test are simultaneously displayed on the harm display section.

〔Example〕

First, an overview of the present invention will be explained.
As shown in the figure, a signal processing section 101 processes the signal under test using a sweep signal from a full sweep signal generation section 100 inputted from an input terminal IN, and outputs a signal corresponding to the spectrum of the signal under test; a first A/D converter 10 that converts the corresponding signal into first digital data;
2, a first memory 103 that stores the first digital data, and a display section 104 that displays the first digital data.

According to the present invention, the input terminal IN and the signal processing section 10
a signal dividing circuit (or signal switching circuit) 105 inserted between the signal dividing circuit (or signal switching circuit) 105 and a power sensor 106 that detects the power of the signal under test; and converts the output of the power sensor 106 into second digital data. It is equipped with a second A/D converter 107 and a second memo IJ 10B that stores the output of the second A/D converter 107, and displays the second digital data and the second memo on the display. A spectrum analyzer with a unique configuration is provided, which is characterized in that it displays both digital data of 1 and 1 on the same screen of the display unit 104.

Further, according to the present invention, in addition to the above-mentioned unique configuration, the first
Note I) Correction of detecting the difference between the first digital data stored in the LOS and the second digital data stored in the second memory 108 as correction data. a data detection section 109; a third memory 110 that stores correction data that is the difference between the first and 27' digital data detected by the correction data detection section 109; A spectrum analyzer is provided, comprising a correction section 111 that corrects all the f digital data of Ml stored in a first memory based on correction data that is a difference between data, and displays the corrected data on the display section 104. Ru.

In FIG. 1, a correction data detection section 109, a third memory 110, and a correction section 111 are constructed in a data processing/control section 112 similar to that in FIG.

Furthermore, according to the present invention, in addition to the above-described unique configuration, the first A/D converter 102 and the second A/D converter 107 are configured by a common A/D converter 102. and the signal from the signal processing section and the nine power sensor 10
6 and all the signals are switched to the one A/D converter 10.
2, and controls the switching unit 113 in synchronization with the sweep period and reset period of the sweep signal. In this aspect, the first memory 103 and the second memory 108
should be understood as separate memory areas within the same memory.

105 and a variable attenuator 114 for varying the input dredge, which is provided between the input signal processing section 101 and the signal processing section 101, and adjusts the attenuation value of the attenuator to a desired value based on the second digital data. A spectrum analyzer is provided to control the With this, the excessive input level can be suppressed to an appropriate level.

Next, some embodiments of the present invention based on one or more outlines will be described with reference to the drawings.

FIG. 2 is a block diagram showing a schematic configuration of the spectrum analyzer of the first embodiment. The same parts as in the conventional spectrum analyzer shown in FIG. 10 are given the same reference numerals. In this embodiment, input terminal 9 and mixer 1
A signal branching circuit 11 is interposed between the RFF 1a and the RFF 1a consisting of the RFF 1a and the local oscillator 1b. The RF section 1 is connected to one output terminal of this signal branch circuit 11, and the power detector 12 is connected to the other output terminal. The signal branching circuit 11 is composed of, for example, a resistor dividing type divider, and divides the measured signal a input from the input terminal 9 into a power distribution ratio (for example, 1:1) determined in advance by the voltage division ratio of the resistors.
Accordingly, it is distributed to the RFF 1a and the power detector 12.

The power detector 12 is composed of a normal high-frequency power detector using a thermocouple element, a diode element, an averaging circuit, etc., or a power detector using a broadband amorphous power sensor technique, and can detect a wide range from direct current to high frequency. It is possible to accurately detect the power value of a signal including frequency.

As the latter power detector, all the power measuring devices disclosed in the international patent application PCT/JP8710 O812 by the same applicant as the present application can be used. A DC power value signal g output from the power detector 12 is input to the A/D converter 4 via the switching circuit 13. The detection signal d from the detection section 3 is also input to this switching circuit 13 . Then, the signal input to the A/D conversion section is switched to the detection signal d or the power value signal g using a switching signal sent from the data processing/control section 8'.

It is assumed that the digital memory 5' has first and second memory areas corresponding to the first and second memories 103 and 108 in FIG.

Other configurations of the RFF1aIF section 2, the detection section 3, the A/D conversion section 4, the display section 6, and the sweep signal generation section 7 are the same as in FIG. The f-event processing/control section 8' differs in control of each section from that shown in FIG. 10, as will be described later.

A variable attenuator 114 similar to that of FIG.
It is controlled by the control section 8.

Next, the operation of the spectrum analyzer configured as described above will be explained with reference to a complete time chart of a general sweep signal outputted from the sweep signal generator 7 shown in FIG. That is, time 1. The sweep signal for sweeping the frequency of the local oscillation signal l output from the RFF1a local oscillator 1b starts increasing from the lowest value corresponding to the measured lowest frequency, and reaches the measured maximum at time tl after the sweep period A has elapsed. When the signal level reaches the maximum value corresponding to the frequency, the signal level decreases, and from time t1 after the reset period B has elapsed, the sweep for the next sweep period A is started from the minimum value corresponding to the original lowest measurement frequency.

Then, the data processing/control unit 8' sends a switching signal h2 to the switching circuit 13 to input the detected signal d to the A/D converter 4 within the sweep period A, and conversely, the switching signal h2 is sent to the switching circuit 13 to input the detected signal d to the A/D converter 4 within the reset period B. Power value signal gtA/D to circuit 13
A switching signal is sent to be input to the converter 4.

Thus, during the sweep period A, the high frequency measured signal a input from the input terminal 9 is input to the RFF 1a mixer 1a, and is mixed with the local oscillation signal l whose frequency is swept by the sweep signal. The frequency is converted into an intermediate frequency signal C. From the intermediate frequency signal C outputted from the RFF 1a, only the frequency component matching the passing frequency of the band pass filter (BPF) is extracted in the next IF circuit 2 and input to the next detection section 3. Then, it is converted into a DC detection signal d corresponding to the magnitude thereof, and is input to the A/D converter 4 via the switching circuit 13.

The detected signal d is sent to the A/D converter 4 and the data processing/control unit 8'.
The data is converted into digital data according to the period of the sampling signal 6 output from the snack digital memory 5'.
is stored in the first memory area of.

The τ digital data for each sampling period of the detected signal d stored in the first memory area of the digital memory 5' is also generated in response to the read signal f of a constant period outputted from the data processing/control section 8'. , are read out in a fixed order and sent to the m display section 6. As shown in FIG. 4, spectrum values at each frequency, that is, spectrum distribution data DI, are displayed on the customary display section 6. Note that this spectrum distribution data ends at the next reset period B! is retained.

Also, during the reset period B, the power value signal g output from the power detector 12 is sent to the A/D via the switching circuit 13.
The conversion unit 4 converts it into a digital value. This digital value is stored in the second memory area, which is a dedicated area for power values in the digital sled 5', and then read out from the digital memory 5' and converted into numerical character data as shown in FIG. Then, the average power value P is displayed in an empty area of the spectrum distribution data on the CRT display section 6. This numerical character data of the power value is held until the end of the next sweep period A.

Thus, the spectrum distribution data and the power value are displayed on the same screen on the snow display section 6 as shown in FIG. In this way, the signal branch circuit 11 and the power detector 12
By providing this, it has become possible to simultaneously obtain each spectrum value and power value at each frequency of the signal under test a.

Further, as described above, the signal branching circuit 11 and the power detector 12 have a simple structure, are inexpensive, and can have wide frequency characteristics. Therefore, compared to the conventional spectrum analyzer shown in FIG. 10, manufacturing costs will not increase significantly.

Furthermore, the measurement accuracy can be significantly improved compared to the case where the power value is calculated by adding each spectrum value.

Furthermore, in the WJ1 embodiment shown in FIG. 2, the power value is measured using the reset period Bi of the sweep signal K.
Therefore, by measuring the power value,
Compared to a conventional spectrum analyzer that only obtains all spectrum distribution data, the overall measurement time is not extended. That is, the power value is also measured within the conventional measurement time.

FIG. 5 is a block diagram showing a spectrum note analyzer according to a second embodiment of the present invention. The same parts as in the first embodiment shown in FIG. 2 are given the same reference numerals.

In this second embodiment, an RF (high frequency) switch circuit 11hf is used as a signal switching circuit inserted between the input terminal 9 and the RFF 1a.

Then, by this RF switch circuit 11&, the signal under test a inputted from the input terminal 9 is sent to the FR section 1, or
It is possible to switch whether the signal is sent to the power detector 12 or to the power detector 12 by a switching signal from the data processing/control unit 8'. and,
This switching timing is synchronized with the switching timing of the switching circuit 13.

That is, during the sweep period A of the sweep signal shown in FIG.
The F switch circuit 11*f is switched to the RF section 1 side, and the switching circuit 13 is switched to the detected signal d side. Furthermore, during the reset period B, the RF switch circuit 11hf is switched to the power detector 12 side, and the switching circuit 13 is switched to the power value signal g side.

Then, each spectrum value is measured during the sweep period A, and the power value is measured during the reset period B. Therefore, in this second embodiment as well, the spectrum distribution data and power value of the signal under test a can be measured and displayed on the m display unit 6 on the same screen. As a result, the first
Almost the same effects as in the embodiment can be obtained.

Furthermore, an RF switch circuit 11hf is added as a signal branch circuit.
Compared to other signal branch circuits that use the resistor divider type divider or directional coupler mentioned above, the loss of the signal under test is lower due to the insertion of the signal branch circuit. This can prevent the overall sensitivity of the spectral analyzer from decreasing.

FIG. 6 is a block diagram showing a sictrum analyzer according to a third embodiment of the present invention. The same parts as in the embodiment of FIG. 2 are given the same reference numerals.

In this third embodiment, the switching circuit 1 in FIG.
3 is removed, and the detected signal d outputted from the detection section 3 is input directly to the A/D conversion section 4.

Further, the power value signal ge output from the power detector 12 is input to each A/D converter 4a. And each A/D
The digital data obtained by the conversion section 4.4a is written into the first and second memory areas of the digital memory 5'. Although the same sampling signal e is input to the A/D converter 4.4, it is not necessary that they match. Even with such a configuration, the spectral distribution data of the signal under test a Since it is possible to find the power value and
It is possible to obtain almost the same effect as the embodiment shown in FIG.

Furthermore, in this third embodiment, by converting the detection signal d and the power value signal g into digital data values using dedicated A/D converters 4.41, the third
It is also possible to measure the power value during the sweep period A in the figure. Therefore, even when the sweep period A for spectrum measurement is long, the power value of the input signal under test 1 can be monitored in real time on the display screen of the m display section 6. In this way, the power value of the measured signal a can be constantly monitored not only during the trap and reset period B but also during the sweep period A, so that when excessive power is input, an alarm output is immediately generated, and a warning display and alarm sound are generated. be able to. Further, as in FIG. 2, it is also possible to use the power value signal g so that the input attenuator 114 inserted before the RF section 1 can be fully automatically adjusted to obtain a correct display value. That is, the spectrum analyzer can be protected from damage caused by excessive signal input.

Furthermore, in each of the embodiments shown in FIGS. 2, 5, and 6, a specific operation of the operation unit OP (calibration command CALIB)
Accordingly, each data value obtained from the signal under test a and displayed on the end display section 6 is calculated using a calibration signal in which the relationship between the detection signal d and the power value signal g is accurately determined in advance. It is possible to calibrate each f-ta value using the data processing/control unit 8' so that it becomes a correct value. In this case, when a continuous wave (CW) signal is used as the calibration signal, the power value thereof does not need to be known in advance.

In this case, the data processing/control unit 8' includes the correction data detection unit 109 shown in FIG.
Calibration (correction) can be performed using O and the correction unit 111.

In the above description, it has been assumed that the power detector 12 is configured to detect the entire average power. However,
In particular, when it is necessary to detect the peak power in pulse full wave spectrum measurement, as shown in FIG.
Or a diode element Jffia that detects the input signal from the signal switching circuit JJ&, and this diode element 12
Peak hold circuit J, ? which holds the peak compensation of the detected output of 1? This peak hold circuit Jjb may be provided with a reset signal from the data processing/control section 8/ at every measurement cycle. In addition, the power detector 1 in Fig. 7
2 is an averaging circuit 1 which averages the detection output from the diode element JJa in order to detect the nine-average power value as described above.
2e is provided. The power detector 12 also includes a switch J, ? for switching the outputs of the averaging circuit 12c and the peak hold circuit Jjb according to the purpose of use 4'C. d
are also provided.

FIG. 8 shows a display example of the spectral distribution data D2 and peak power (P2) of the Noyals modulated wave.

FIG. 9 shows a professional configuration applied to an optical sic tract analyzer as a fourth example. In FIG. 9, the same parts as in FIG. 2 are given the same reference numerals, and their explanation will be omitted.

That is, the optical signal a' to be measured inputted to the optical signal input end 9' is branched into two by an optical signal branching section 11' formed of, for example, a half mirror. One of the optical signals enters the half mirror 1m' of the RF section 1'. This half mirror J
An optical local excavation signal from an electro-optical converter 11 (such as a light emitting diode) that responds to the electrical sweep signal from the sweep signal generator 7 is incident on a'. ' performs a mixer action equivalent to an electric mixer and outputs an optical intermediate frequency signal. This optical intermediate frequency signal is converted into an electrical intermediate frequency signal by a photoelectric converter 1c such as a photodiode. Therefore, the processing from here on is similar to that in FIG.

The other optical signal from the optical signal branching section 11' is sent to an optical power sensor J2' including a light receiving element such as a photodiode.
At the same time as the photoelectric conversion is performed, the optical power is detected. Therefore, from now on, the power value signal g in FIG. 2 is read as the optical power value signal g and the same processing is performed.

Therefore, according to this fourth embodiment, FIG.
As in the figure, optical spectrum distribution data and optical power values are displayed on the same screen.

The embodiments shown in FIGS. 5 to 7 can be similarly applied to the optical spectrum analyzer in accordance with the embodiment shown in FIG. 9.

Note that this is a programmable optical attenuator controlled by the 1dij data processing/control unit 8' of FIG.

This optical attenuator 1d, like the variable attenuator 114 in FIG. 1, suppresses the excessive input level to an appropriate level.

〔Effect of the invention〕

As explained above, according to the present invention, the signal under test is distributed to the signal processing section and the power detection section through the signal branching section. It is possible to provide a spectrum analyzer that can easily and accurately display signals and can be applied to a wide range of fields including electrical signals and optical signals.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an overview of a spectrum analyzer according to the present invention, FIG. 2 is a block diagram showing a spectrum analyzer according to a first embodiment of the present invention, and FIG. 3 is a time diagram showing the operation of the same embodiment. Chart, Figure 4 is a diagram illustrating the display screen of the same embodiment, Figures 5 and 6 are
The figures are block diagrams showing spectrum analyzers according to the second and third embodiments of the present invention, FIG. 7 is a diagram showing a specific example of a power detector used in each embodiment, and FIG. 8 is a block diagram showing the power detector of FIG. FIG. 9 is a block diagram showing an optical spectrum analyzer according to a fourth embodiment of the present invention; FIG. 10 is a block diagram showing a conventional spectrum analyzer; FIG. 11 is a diagram showing general spectrum distribution data displayed on the display section. 1...RF section, 2...IF section, 3...detection section, 4
．． 4m...A/D conversion unit, 5...Digital memory, 6...Display unit, 7,100...Sweep signal generation unit, 8,112...Data processing/control unit, 9... - Input terminal, 11, 105... Signal branch circuit (or signal switching circuit), l1m... RF switch circuit (signal switching circuit), 12... Power detector, 12'... Optical power sensor, 106...Glow sensor, 13...Switching circuit, a...Measurement signal, b...Sweep signal, d...
・Detection signal, g...Power value signal.

Claims (1)

[Claims] 1. Means for substantially directing an input signal to a first path and a second path; and means for generating spectrum data corresponding to the input signal guided to the first path; A spectrum analyzer comprising: means for detecting a power value corresponding to an input signal guided into said second path; and means for displaying said spectrum data together with said power value. 2. The spectrum analyzer according to claim 1, further comprising means for correcting said spectrum data according to a difference signal between said spectrum data and said power value. 3. The spectrum analyzer according to claim 1, further comprising means for attenuating an input signal guided to said first path according to said power value. 4. A signal processing unit that processes the signal under test input from the input terminal using a sweep signal and outputs a signal corresponding to the spectrum of the signal under test; and a signal processing unit that converts the corresponding signal into first digital data. 1 A/D converter; a first memory that stores the first digital data; a signal branch or switching circuit inserted between the input terminal and the signal processor; and the signal branch. or a power sensor that detects the power of the signal under measurement from the switching circuit; a second A/D converter that converts the output of the power sensor into second digital data; and the second A/D converter. A spectrum analyzer comprising: a second memory for storing the output of the section; and a display section for displaying the second digital data together with the first digital data. 5. detection means for detecting a difference between the first digital data stored in the first memory and the second digital data stored in the second memory; and the detection means a third memory for storing the difference between the digital data detected by the third memory, and correcting the first digital data stored in the first memory based on the difference between the digital data and displaying the corrected data on the display section. 5. The spectrum analyzer according to claim 4, further comprising a correction means. 6. The first A/D converter and the second A/D converter are composed of one common A/D converter, and the signal from the signal processing unit and the signal from the power sensor and a control means for controlling the switching means in synchronization with a sweep period and a reset period of the sweep signal.
Spectrum analyzer as described. 7. A variable attenuator for varying the input level provided between the input terminal and the signal processing section, and a control section for controlling the attenuator to a desired value based on the second digital data. The spectrum analyzer according to claim 4, further comprising: