JP5514240B2 - Signal analysis apparatus and signal analysis method - Google Patents

Description

  The present invention receives, for example, a wideband RF (Radio Frequency) signal distributed in a wide frequency band centered on a specific frequency used for mobile communication of a mobile communication device such as a mobile phone, and measures and analyzes its level. The present invention relates to a signal analysis apparatus and a signal analysis method.

  For example, a spectrum analyzer has been generally known as a signal analyzer that receives a wideband RF signal from a mobile communication device such as a mobile phone and accurately measures and analyzes a frequency component such as the level of the wideband RF signal. ing. In this spectrum analyzer, a wideband RF signal (signal under measurement) from a mobile communication device to be measured is mixed with a local signal and converted to an intermediate frequency signal, and the converted intermediate frequency signal is observed by an intermediate frequency circuit. The frequency component of only the signal band is allowed to pass through to limit the band, and then converted to a baseband signal to measure the frequency component such as the level of the wideband RF signal (signal under measurement), and the measurement result is displayed as a spectrum. .

  However, in the spectrum analyzer described above, level fluctuations (amplitude fluctuations) occur in the intermediate frequency band in the frequency conversion circuit and the intermediate frequency circuit, resulting in a level error. In recent mobile communication devices, the use band is further widened, and calibration of level fluctuations within this use band is desired.

  Patent Document 1 below discloses a signal analyzer that calibrates level fluctuations within the above-described use band. The signal analyzer disclosed in Patent Document 1 mixes the signal under measurement from the receiving end with the output of the local oscillator and converts it to an intermediate frequency signal, and then converts it into digital data at the A / D converter And a signal analysis system for obtaining a spectrum based on data output from the reception system. Also, a calibration RF signal that is FM-modulated over a predetermined band is generated and input in place of the signal under measurement at the receiving end, and output from the reception system when the calibration RF signal is input. A predetermined band detected by the detection unit, which is provided between the reception unit and the signal analysis system, and a detection unit that detects level fluctuation and phase fluctuation caused by the reception system within a predetermined band based on digital data And a filter unit that is corrected on the basis of the level fluctuation and the phase fluctuation.

  As a result, according to the signal analysis device disclosed in Patent Document 1, even if the frequency bandwidth (reception bandwidth) to be analyzed is wide, level fluctuations that occur in the reception system (high-frequency circuit portion) of the signal analysis device The phase fluctuation can be corrected and measured.

JP 2008-232807 A

  By the way, in this type of conventional signal analyzing apparatus, when the center frequency is changed, a phenomenon that the in-band frequency characteristics change with the change of the center frequency can be seen. FIG. 6 shows in-band frequency characteristics at 800 MHz and 5200 MHz as two different center frequencies. As is apparent from FIG. 6, it can be seen that the in-band frequency characteristics are different when the center frequency is different.

  And this in-band frequency characteristic may be influenced not only by the difference in the center frequency but also by the characteristic of the 1st mixer (corresponding to the mixing part of Patent Document 1) provided in the input stage of the signal analyzer. In a signal analyzer, it has been difficult to achieve high level accuracy at an arbitrary center frequency and an arbitrary bandwidth.

  Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a signal analysis apparatus and a signal analysis method capable of realizing high level accuracy at an arbitrary center frequency and an arbitrary bandwidth. It is said.

In order to achieve the above object, a signal analyzer according to claim 1 of the present invention includes a local signal generator 4 that generates a local signal,
A mixing unit 5 for mixing a signal under measurement input from an input terminal 7 with the local signal;
A correction circuit unit 2 for controlling the output frequency and outputting a signal corresponding to the intermediate frequency of the same frequency as the intermediate frequency signal output from the mixing unit;
A post-stage circuit unit 6 that processes the signal mixed in the mixing unit and measures the output level of the correction circuit unit by varying the output frequency of the local signal generation unit within a measurable frequency range. An analyzer 1 comprising:
The subsequent circuit unit includes a band frequency characteristic by the frequency characteristic of the output level of the correction circuit unit to which the subsequent circuit unit is measured, the frequency set central frequency to fixedly set the bandwidth of said local signal A correction value for the in-band frequency characteristic is calculated from a difference from the in-band frequency characteristic when the output frequency is varied in the frequency range.

The signal analysis method according to claim 2 is a signal analysis method using the signal analysis device 1 according to claim 1,
A first step of measuring an output level of the correction circuit unit 2 when the output frequency of the local signal generation unit 4 is varied in a measurable frequency range;
A second step of calculating an in-band frequency characteristic from the frequency characteristic of the output level of the correction circuit unit measured in the first step;
A frequency of the in-band frequency characteristic is calculated by fixing the frequency of the local signal generated by the local signal generation unit to a set center frequency and varying the output frequency of the correction circuit unit in a frequency range including a set bandwidth. Steps,
And a fourth step of calculating a difference between the in-band frequency characteristic calculated in the second step and the in-band frequency characteristic calculated in the third step as a correction value.

  According to the present invention, by changing the output frequency of the correction circuit unit of the apparatus main body, an RF signal having a known output power is output at an arbitrary frequency while fixing the center frequency of the local signal of the apparatus main body. Frequency information arbitrarily set, that is, a correction value of the in-band frequency characteristic in an arbitrary set center frequency and an arbitrary set bandwidth.

  And if the correction value of the in-band frequency characteristic at an arbitrary set center frequency and an arbitrary set bandwidth is stored in the storage unit, a correction signal at an arbitrary center frequency and an arbitrary bandwidth is provided in the apparatus body. Compared with the case of correcting the in-band frequency characteristics at each center frequency by using an external signal source calibrated in advance, it is possible to realize high level accuracy at an arbitrary center frequency and an arbitrary bandwidth. The correction time can be greatly shortened, and the capacity of the memory used for storing the correction value can be reduced.

It is a block diagram which shows schematic structure of the signal analyzer based on this invention. It is a figure which shows an example of the measurement data of the output level of the circuit part for correction | amendment in the signal analyzer which concerns on this invention. It is a figure which shows an example of the calculation result of the in-band frequency characteristic based on the measurement data of the output level of the circuit part for correction | amendment of FIG. The signal analyzer which concerns on this invention WHEREIN: The figure which shows an example of the calculation result of the in-band frequency characteristic when the output frequency of the circuit part for correction | amendment is varied in the range of a setting bandwidth with the center frequency of the preset frequency setting conditions It is. It is a figure which shows an example of the measurement result before and behind correction | amendment of the in-band frequency characteristic by frequency information in the signal analyzer which concerns on this invention. It is a figure which shows an example of the in-band frequency characteristic in two different center frequencies.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the present invention is not limited to this embodiment, and all other forms, examples, operation techniques, etc. that can be implemented by those skilled in the art based on this embodiment are included in the scope of the present invention. .

  The signal analysis apparatus 1 according to the present invention receives a wideband RF signal distributed in a wide frequency band centered on a specific frequency used for mobile communication of a mobile communication device such as a mobile phone, and analyzes the level thereof. As shown in FIG. 1, the correction circuit unit 2, the switching unit 3, the local signal generation unit 4, the mixing unit 5, and the subsequent circuit unit 6 are roughly configured.

  The correction circuit unit 2 is a circuit used when correcting in-band frequency characteristics at an arbitrary set center frequency and an arbitrary set bandwidth that are set in advance as frequency information by a user, and is an IF equivalent oscillation circuit. 11 and the output power control circuit 12.

  The IF equivalent oscillation circuit 11 includes a direct digital synthesizer (hereinafter abbreviated as DDS) 11a, which is an electronic circuit that digitally generates an arbitrary waveform or frequency from a single fixed oscillation source, A phase-locked loop (hereinafter abbreviated as PLL) 11b and a voltage-controlled oscillator 11c are configured. In the IF equivalent oscillation circuit 11, the oscillation frequency of the DDS 11a is variably controlled by a signal processing control unit 24, which will be described later, and the output frequency of the voltage controlled oscillator 11c is controlled by the voltage from the PLL 11b according to the variation of the oscillation frequency to lock the frequency. A signal corresponding to an intermediate frequency (IF) corresponding to a predetermined frequency is output from the voltage controlled oscillator 11c.

  The output power control circuit 12 includes a variable attenuator 12a, a mixer 12b, and a detector 12c. The output power control circuit 12 mixes the signal corresponding to the IF output from the voltage controlled oscillator 11c of the IF equivalent oscillation circuit 11 and the local signal output from the local signal generation unit 4 with the mixer 12b, and the signal analysis device 1 outputs a signal corresponding to an RF signal. The output power of the signal output from the mixer 12b is controlled by an ALC (automatic level control) loop composed of the variable attenuator 12a and the detector 12c.

  The switching unit 3 is composed of, for example, a high-frequency switch, and the contact 3a is connected to the input terminal 7 side or the correction circuit unit 2 side under the control of the signal processing control unit 24 based on an operation input from an operation panel (not shown) of the apparatus body. It has been switched to. By switching the contact 3a, a measurement mode in which the signal under measurement (RF signal) input from the input terminal 7 is received and measured by the mixing unit 5 or a correction for correcting the in-band frequency characteristics using the correction circuit unit 2 is performed. A mode is selected.

  The local signal generation unit 4 includes a local oscillator, and generates a local signal supplied to the mixing unit 5 and the mixer 12 b of the output power control circuit 12. In the local signal generation unit 4, the oscillation frequency of the local oscillator is variably controlled by the signal processing control unit 24.

  The mixing unit 5 is a 1st mixer provided between the switching unit 3 and the post-stage circuit unit 6, and the signal under measurement input from the input terminal 7 via the switching unit 3 or the correction circuit unit 2 to the switching unit 3. And the local signal from the local signal generator 4 are mixed, and the mixed intermediate frequency signal (IF signal) is output to the post-stage circuit unit 6.

  The post-stage circuit unit 6 processes the intermediate frequency signal from the mixing unit 5, and includes an intermediate processing unit 21, an A / D conversion unit 22, an IQ baseband processing unit 23, a signal processing control unit 24, a storage unit 25, and a display. The configuration includes the portion 26.

  The intermediate processing unit 21 has a bandpass filter whose band is variable, and passes the frequency component of only the signal band that the intermediate frequency signal from the mixing unit 5 is to be observed by the bandpass filter, and the band-limited intermediate frequency signal. Is output.

  The A / D conversion unit 22 converts the output from the intermediate processing unit 21 (band-limited intermediate frequency signal) into digital data using a clock from a clock generation unit (not shown).

  The IQ baseband processing unit 23 is a quadrature demodulating unit that obtains a baseband signal whose phase is orthogonal based on the digitized intermediate frequency signal, and generates a frequency signal having substantially the same frequency as the intermediate frequency signal. The signal is converted into two frequency signals whose phases are orthogonal to each other, and each of them is mixed by a mixer means to output an IQ baseband signal which is two orthogonal signals.

  The signal processing control unit 24 includes an FFT calculation unit, and converts all signals in the band of the IQ baseband signal from the IQ baseband processing unit 23 into data indicating a frequency domain spectrum. As a result, the horizontal axis is displayed on the display unit 26 as the frequency, and the vertical axis is displayed as the level (power value).

  Further, the signal processing control unit 24 calculates an in-band frequency characteristic in a correction mode described later. That is, the in-band frequency characteristic is calculated from the frequency characteristic based on the measurement data of the correction circuit unit 2. Further, the in-band frequency characteristic is calculated from the frequency characteristic based on the output level when the oscillation frequency of the local signal generation unit 4 is fixed to the set center frequency of the frequency information and the output frequency of the correction circuit unit 2 is varied. .

  Furthermore, the signal processing control unit 24 fixes the output signal from the voltage controlled oscillator 11c of the IF equivalent oscillation circuit 11 to the same frequency as the IF signal output from the mixing unit 5 in the correction mode described later, and the local signal generation unit 4 The oscillation frequency of the local oscillator is variably controlled at predetermined step intervals in the measurable frequency range.

  Further, the signal processing control unit 24 can change the output frequency of the correction circuit unit 2 at a predetermined step interval in a frequency range including the set bandwidth of the frequency information without changing the setting of the center frequency in the correction mode described later. I have control.

  The storage unit 25 stores measurement data measured by the signal processing control unit 24. The storage unit 25 stores the calculation result of the in-band frequency characteristic calculated by the signal processing control unit 24. Further, the storage unit 25 stores frequency information (set center frequency, set bandwidth) set by the user before correction.

  The display unit 26 is composed of a liquid crystal display, for example, and displays the spectrum waveform of the signal under measurement input from the input terminal 7 and the spectrum waveform of the signal when correcting the in-band frequency characteristics. This spectrum waveform is displayed with the horizontal axis broken down to frequency and the vertical axis broken down to that level.

  Next, as an operation of the signal analyzing apparatus 1 configured as described above, in-band frequency characteristics are corrected with frequency information (arbitrary setting center frequency and arbitrary setting bandwidth) preset by the user. A processing procedure will be described.

  The set center frequency (Center) and set bandwidth (Span) of the signal analyzer 1 are set as frequency information before correcting the in-band frequency characteristics by the operation of the operation panel (not shown) of the user. The center frequency is arbitrarily set within the measurable frequency range that represents the frequency range of the upper limit frequency and the lower limit frequency that can be measured by the signal analyzer 1. Here, it is assumed that the set center frequency (Center) = 1000 MHz and the set bandwidth (Span) = 125 MHz are set as frequency information. Further, it is assumed that a calibration signal (a sine wave signal with a known frequency) is input to the input terminal 7 from an external signal generator, and the level calibration of the main body of the signal analyzer 1 has already been performed.

  When the user selects a correction mode by operating an operation panel (not shown) in a state where the frequency information is set in advance, the contact 3a of the switching unit 3 is controlled by the signal processing control unit 24 of the post-stage circuit unit 6. Is switched from the input terminal 7 side to the correction circuit unit 2 side. In this state, the signal processing control unit 24 confirms the set center frequency from the frequency information set in advance in the signal analyzer 1. Here, since the set center frequency (Center) = 1000 MHz and the set bandwidth (Span) = 125 MHz are set as the frequency information, it is confirmed that the set center frequency is 1000 MHz.

  Next, when the signal processing control unit 24 finishes confirming the set center frequency described above, the signal processing control unit 24 measures the level of the output power of the signal output from the mixer 12b of the correction circuit unit 2. In measuring the output power level, the output signal from the voltage controlled oscillator 11 c of the IF equivalent oscillation circuit 11 is fixed to the same frequency as the IF signal output from the mixing unit 5, and the output signal from the local signal generating unit 4 is measured. The frequency is varied at predetermined step intervals in the measurable frequency range. Specifically, the frequency of the output signal from the local signal generator 4 is varied at 5 MHz step intervals in the range of 5 MHz to 6000 MHz.

  FIG. 2 is a diagram illustrating an example of measurement data of the output level of the correction circuit unit 2 in the signal analysis apparatus 1. In the example of FIG. 2, when the output level at the frequency of 5 MHz is -16.21 dBm, the output level at the frequency of 10 MHz is -16.25 dBm, the output level at the frequency of 15 MHz is -16.30 dBm, and the frequency is 5995 MHz. The output level is measured from a frequency of 5 MHz to a frequency of 6000 MHz at a 5 MHz step interval such that the output level is -18.17 dBm and the output level is -18.30 dBm. All the measurement data at this time is stored in the storage unit 25 as the frequency characteristics of the output power of the correction circuit unit 2.

Next, the signal processing control unit 24 variably controls the output frequency of the correction circuit unit 2 at a predetermined step interval in a frequency range including a set bandwidth of frequency information without changing the setting of the center frequency. For example, when the center frequency is 1000 MHz, the output frequency of the correction circuit unit 2 is varied at 5 MHz step intervals within a range of ± 65 MHz (> bandwidth (Span) / 2) with respect to the center frequency of 1000 MHz. Then, the signal processing control unit 24 calculates the in-band frequency characteristic at this time (calculation result A: second in-band frequency characteristic).

  FIG. 4 shows the calculation result A of the in-band frequency characteristics when the output frequency of the correction circuit unit 2 is varied within a range including the set bandwidth at the set center frequency of the preset frequency information (center frequency 1000 MHz ± 65 MHz). It is a figure which shows an example. In the example of FIG. 4, when the center frequency is 1000 MHz and the offset frequency is “0 MHz”, the calculation result A of the in-band frequency characteristic at the offset frequency of −65 MHz (935 MHz) is +0.20 dB, and the offset frequency is +15 MHz (1015 MHz). The calculation result A of the in-band frequency characteristic is −0.15 dB, and the calculation result A of the in-band frequency characteristic at the offset frequency +65 MHz (1065 MHz) is −0.25 dB. These calculation results A are stored in the storage unit 25.

  Next, the signal processing control unit 24 calculates an in-band frequency characteristic from the frequency characteristic of the output power of the correction circuit unit 2 acquired in advance and stored in the storage unit 25 (calculation result B: first band Internal frequency characteristics). FIG. 3 is a diagram showing an example of the calculation result B of the in-band frequency characteristic based on the output level measurement data of the correction circuit unit 2 of FIG. In the example of FIG. 3, for the center frequency 1000 MHz (offset frequency “0 MHz”), the calculation result B of the in-band frequency characteristic at the offset frequency −65 MHz (935 MHz) is +0.04 dB, and the offset frequency +15 MHz (1015 MHz). The calculation result B of the in-band frequency characteristic is -0.02 dB, and the calculation result B of the in-band frequency characteristic at the offset frequency +65 MHz (1065 MHz) is 0 dB. These calculation results B are stored in the storage unit 25.

Subsequently, the signal processing control unit 24 calculates A−B using the calculation results A and B of the in-band frequency characteristics described above. For example, in the example of FIGS. 2 and 3, when the offset frequency is −65 MHz, AB = 0.20−0.04 = 0.16 [dB] is calculated as the correction value. These calculation results are stored in the storage unit 25 as correction values of in-band frequency characteristics based on frequency information (set center frequency and set bandwidth) arbitrarily set by the user, and at the input terminal 7 in the measurement mode. To be reflected in the signal to be measured.

  Here, FIG. 5 is a diagram showing an example of in-band frequency characteristics before and after correction by frequency information in the signal analyzing apparatus 1. In the example of FIG. 5, 800 MHz is set as the set center frequency, and in-band frequency characteristics before and after correction when the set center frequency 800 MHz is set to the offset frequency “0 MHz” are shown. As is apparent from FIG. 5, in the state before correction, there is an error of −0.47 to 0.96 in the range of ± 60 MHz with respect to the offset frequency, whereas in the state after correction, the offset frequency is On the other hand, it can be seen that Error is approximately zero in the range of ± 60 MHz.

  In the above-described processing relating to the correction of the in-band frequency characteristics, for example, the oscillation frequency of the local signal generation unit 4 is variably controlled to measure the output level of the correction circuit unit 2 shown in FIG. The in-band frequency characteristics shown in FIG. 3 can be calculated from the characteristics, and the calculation results can be stored in the storage unit 25, and the processing procedure is not limited to the order described.

  As described above, according to the present invention, the correction circuit unit 2 of the apparatus main body is used and the output frequency of the correction circuit unit 2 is changed, so that the center frequency of the local signal of the apparatus main body is fixed and an arbitrary frequency is maintained. By outputting an RF signal having a known output power, frequency information arbitrarily set by the user, that is, a correction value of in-band frequency characteristics in an arbitrary set center frequency and an arbitrary set bandwidth can be obtained.

  And if the said correction value is preserve | saved in the memory | storage part 25, it will become possible to provide the apparatus main body with the correction signal in arbitrary center frequencies and arbitrary bandwidths, and it is high with arbitrary center frequencies and arbitrary bandwidths. Level accuracy can be realized, and the correction time can be greatly reduced and the correction value can be saved compared to correcting the in-band frequency characteristics at each center frequency using a pre-calibrated external signal source. The capacity of the memory to be used can be suppressed.

  By the way, in the above-described embodiment, the IF equivalent oscillation circuit 11 may be configured to output an arbitrary IF signal including the same frequency as the IF signal output from the 1st mixer as the mixing unit 5. It is not limited to.

DESCRIPTION OF SYMBOLS 1 Signal analyzer 2 Correction | amendment circuit part 3 Switching part 4 Local signal generation part 5 Mixing part 6 Subsequent circuit part 7 Input terminal 11 IF equivalent oscillation circuit 11a DDS
11b PLL
11c Voltage Control Oscillator 12 Output Power Control Circuit 12a Variable Attenuator 12b Mixer 12c Detector 21 Intermediate Processing Unit 22 A / D Converter 23 IQ Baseband Processing Unit 24 Signal Processing Control Unit 25 Storage Unit 26 Display Unit

Claims (2)

A local signal generator (4) for generating a local signal;
A mixing section (5) for mixing a signal under measurement input from an input terminal (7) with the local signal;
A correction circuit unit (2) for controlling the output frequency and outputting a signal corresponding to the intermediate frequency of the same frequency as the intermediate frequency signal output from the mixing unit;
A post-stage circuit unit (6) that processes the signal mixed by the mixing unit and measures the output level of the correction circuit unit by varying the output frequency of the local signal generation unit within a measurable frequency range. A signal analyzer (1) comprising:
The subsequent circuit unit includes a band frequency characteristic by the frequency characteristic of the output level of the correction circuit unit to which the subsequent circuit unit is measured, the frequency set central frequency to fixedly set the bandwidth of said local signal A signal analyzer that calculates a correction value of an in-band frequency characteristic from a difference from the in-band frequency characteristic when the output frequency is varied in a frequency range. A signal analysis method using the signal analysis device (1) according to claim 1,
A first step of measuring an output level of the correction circuit section (2) when the output frequency of the local signal generation section (4) is varied within a measurable frequency range;
A second step of calculating an in-band frequency characteristic from the frequency characteristic of the output level of the correction circuit unit measured in the first step;
A frequency of the in-band frequency characteristic is calculated by fixing the frequency of the local signal generated by the local signal generation unit to a set center frequency and varying the output frequency of the correction circuit unit in a frequency range including a set bandwidth. Steps,
A signal analysis method comprising: a fourth step of calculating, as a correction value, a difference between the in-band frequency characteristic calculated in the second step and the in-band frequency characteristic calculated in the third step.

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