JP4108691B2 - Radio frequency spectrum calculation device - Google Patents

Description

  The present invention relates to a radio frequency spectrum calculation apparatus, and more particularly, to a radio frequency spectrum calculation apparatus that is used in a radio communication device, a radio signal measuring device, or the like and is suitable for expanding an observable frequency band by a factor of two.

  An example of the circuit configuration of a conventional well-known radio frequency spectrum calculation apparatus is shown in FIG. When the radio signal S1 to be observed or measured is received, the radio signal S1 is mixed and detected by the mixer 101 with the local signal (reference signal) S2 (frequency F0) supplied from the local oscillator 102, and the frequency of the difference is detected. The intermediate frequency signal is output. The mixer 101 converts the radio signal S1 into a lower frequency intermediate frequency signal S3 by the local signal S2. The mixer 101 functions as a frequency converter. A higher frequency component is removed from the intermediate frequency signal S3 by the low pass filter 103. The analog intermediate frequency signal output from the low-pass filter 103 is converted into a digital intermediate frequency signal by the AD converter 104. The digital intermediate-frequency signal is subjected to a fast Fourier transform processing by a fast Fourier transform unit (FFT) 105. Thereby, the calculation result regarding the frequency spectrum of the radio signal S1 is output from the output unit of the fast Fourier transform unit 105. The obtained calculation result relating to the frequency spectrum is displayed, for example, as a frequency spectrum distribution on the display unit of the radio signal measuring device.

  The sampling frequency at the previous stage in the AD converter 104 is expressed as “fs”. For example, the sampling frequency fs is set to 100 MHz in order to measure a wireless LAN or the like.

  An example of the frequency spectrum distribution obtained by the radio frequency spectrum calculation apparatus shown in FIG. 6 is as shown in FIG. According to this frequency spectrum distribution 106, only the frequency spectrum in the positive band can be observed.

  Furthermore, in recent years, there has also been proposed an apparatus for calculating the radio frequency spectrum by extracting the I signal (in-phase signal component) and the Q signal (quadrature signal component) from the radio signal S1 by synchronously detecting the radio signal S1. A circuit configuration example of this radio frequency spectrum calculation apparatus is shown in FIG. In FIG. 7, elements that are substantially the same as those described in FIG. 6 are given the same reference numerals.

  In the radio frequency spectrum calculation apparatus shown in FIG. 7, the radio signal S <b> 1 is input to the synchronous detection unit 201. The synchronous detection unit 201 is also supplied with a local signal S2 (frequency F0) from the local oscillator 102. In the synchronous detection unit 201, the radio signal S1 is branched into two parts, the local signal S2 is directly mixed for one radio signal, and the phase of the other radio signal is shifted by a 90 ° phase shifter 201a. The local signal S2 adjusted by 90 ° is mixed. As a result, the I and Q signals are extracted as shown in FIG. The I signal extracted by the synchronous detection unit 201 supplies data of the real part of the FFT operation in the fast Fourier transform unit (FFT) 105 via the low-pass filter 103a and the AD converter 104a. The Q signal extracted by the synchronous detection unit 201 supplies the data of the imaginary part of the FFT operation in the fast Fourier transform unit 105 via the low-pass filter 103b and the AD conversion unit 104b.

  As described above, the radio signal S1 to be measured is separated into an I signal and a Q signal by the synchronous detection unit 201, transmitted through independent signal processing channels, and subjected to FTT calculation processing by the fast Fourier transform unit 105. As a result, the frequency spectrum can be calculated by efficiently performing the calculation in the fast Fourier transform unit 105. When an FFT operation is performed using an A-D conversion value for the real part and “0” for the imaginary part, the result is symmetrical between the positive frequency component and the negative frequency component, and only the positive frequency component can be used. On the other hand, if an FFT operation is performed using an in-phase component for the real part and a quadrature component for the imaginary part, a positive frequency component and a negative frequency component can be obtained for the local signal (frequency F0).

  Compared with the radio frequency spectrum calculation apparatus shown in FIG. 7, in the case of the radio frequency spectrum calculation apparatus shown in FIG. 6, the data of the imaginary part of the FFT operation in the radio signal S1 is treated as zero. Therefore, as described above, in the radio frequency spectrum calculation apparatus shown in FIG. 6, the obtained frequency spectrum band is ½ of the sampling frequency fs, which is only the positive frequency component. In other words, the radio frequency spectrum calculation apparatus having the circuit configuration shown in FIG. 7 has the advantage that the observable frequency band is doubled.

  In the above sense, it is better to perform synchronous detection on the radio signal S1 to be measured to extract the I signal and the Q signal, and to perform FFT calculation processing using these signals and observe the frequency spectrum of the radio signal S1. The observation area is widened, which is desirable.

As a prior art related to the present invention, a noise generator described in Patent Document 1 is cited. This noise generator is a device suitable for testing a mobile communication device that supports the CDMA system in an anti-noise environment. This noise generator has a circuit configuration for generating an I signal and a Q signal, and the generated I signal and Q signal are quadrature-modulated by a quadrature modulator with a local signal to support a test under a CDMA anti-noise environment. A broadband noise signal is generated.
JP 2000-269745 A

  In order to actually realize the radio frequency spectrum calculation apparatus shown in FIG. 7, it is possible to read the I signal and the Q signal by the A / D converters 104a and 104b after synchronous detection of the radio signal S1. As shown in FIG. 8, amplifiers (amplifiers) 301a and 301b are required at the output stages of the I and Q signals of the synchronous detection unit 201. As these amplifiers 301a and 301b, since it is difficult to produce a DC amplifier (DC amplifier), an AC amplifier (AC amplifier) that is easy to produce is usually employed. However, this AC amplifier has a characteristic of cutting a DC component. This means that the component synchronized with the frequency (F0) of the local signal S2 is cut. Therefore, the distribution of the frequency spectrum output from the fast Fourier transform unit 105 of the radio frequency spectrum calculation apparatus having the configuration shown in FIG. 8 has a low signal level at the frequency F0 portion of the local signal S2, as shown in FIG. Problem arises.

  The configuration of the device disclosed in Patent Document 1 merely discloses a noise generation device for generating broadband noise provided on the device side that generates a radio signal.

  In view of the above problems, the object of the present invention is to measure the frequency spectrum of the radio signal using the I signal and the Q signal of the radio signal and double the observable band, and to improve the frequency spectrum of the DC component. An object of the present invention is to provide a radio frequency spectrum calculation apparatus intended to suppress attenuation.

  In order to achieve the above object, a radio frequency spectrum calculation apparatus according to the present invention is configured as follows.

A first radio frequency spectrum calculation device (corresponding to claim 1) synchronously detects a radio signal to be measured using a reference signal supplied from a local oscillator , and extracts an I signal and a Q signal of the radio signal. Detection means, first AC amplification means for amplifying the I signal, second AC amplification means for amplifying the Q signal, first AD converter means for converting the output signal of the first AC amplification means into a digital signal, and second AC amplification A second AD converting means for converting the output signal of the means into a digital signal; an output signal of the first AD converting means is input as real part data in the FFT operation; and an output signal of the second AD converting means is Fast Fourier transform calculation means for inputting as imaginary part data in FFT calculation, and signal giving means for giving a broadband noise signal to the reference signal supplied from the local oscillator to the synchronous detection means. Composed of Te.

  In the above-described radio frequency spectrum calculation apparatus, a wideband noise signal including the reference signal is superimposed on a reference signal (local signal) in advance, whereby each of the I signal and the Q signal is amplified by the AC amplifying means and is used as a reference. Even if the frequency component related to the signal is attenuated, it is possible to obtain a frequency spectrum distribution in which the frequency component of another band supplements the attenuated frequency component to suppress the frequency attenuation.

  The second radio frequency spectrum calculation device (corresponding to claim 2) is preferably characterized in that, in the first device configuration, the broadband noise signal is a white noise signal.

  In the third radio frequency spectrum calculation apparatus (corresponding to claim 3), in each of the apparatus configurations described above, the first and second A / D conversion means are preferably A / D conversion devices having two channel inputs. The fast Fourier transform calculation means is constituted by a DSP (digital signal processor). It is also possible to use an FPGA instead of the DSP (corresponding to claim 4).

  According to the present invention, an apparatus for calculating a radio frequency spectrum by extracting an I signal (in-phase signal component) and a Q signal (orthogonal signal component) from a radio signal by synchronously detecting the radio signal to be observed. In a radio frequency spectrum apparatus provided with AC amplifying means for amplifying each of the I signal and the Q signal, a broadband noise signal such as a white noise signal is used as a reference signal (local signal) added to each of the I signal and the Q signal. Since the frequency component corresponding to the frequency of the reference signal in the frequency spectrum distribution obtained as a result of the FFT operation processing can be suppressed, the I signal and the Q signal of the radio signal can be used. The frequency spectrum of the radio signal is measured and the observable band is doubled, and the frequency spectrum of the DC component is It is possible to suppress the attenuation of Le.

  DESCRIPTION OF EMBODIMENTS Preferred embodiments (examples) of the present invention will be described below with reference to the accompanying drawings.

  A radio frequency spectrum calculation apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 shows a block diagram of a basic circuit configuration of a radio frequency spectrum calculation apparatus, FIG. 2 shows a configuration of a signal applying unit, FIG. 3 shows a frequency spectrum of white noise, and FIG. 4 shows a calculated frequency spectrum. The distribution state of is shown.

  In FIG. 1, 11 is a local oscillator, 12 white noise adder, 13 is a synchronous detector, 14a and 14b are AC amplifiers (AC amplifiers), 15a and 15b are low-pass filters, 16a and 16b are A-D converters, 17 Is a fast Fourier transform (FFT). In this radio frequency spectrum calculation apparatus, the I signal (in-phase signal component) and the Q signal (quadrature signal component) are extracted from the radio signal S1 by synchronously detecting the radio signal S1 to be observed or measured, and I The radio frequency spectrum is calculated by performing a fast Fourier transform operation on the signal and the Q signal.

  The local oscillator 11 outputs a local signal S2 that is a sine wave signal having a frequency F0. The local signal S2 becomes a reference signal. Here, the frequency F0 is 2450 MHz, for example. The local signal S2 is supplied to the white noise adder 12. The white noise applicator 12 superimposes a white noise signal on the local signal S2.

  The configuration of the white noise applicator 12 is shown in FIG. In FIG. 2, the white noise adder 12 includes a signal synthesizer 21 and a white noise generator 22. The white noise generator 22 generates and outputs a white noise (White Noise) signal. As shown in FIG. 3, the “white noise” refers to noise having a characteristic that energy is generated almost uniformly over the entire frequency band 23 which is a wide band. The white noise signal output from the white noise generator 22 is superimposed on the local signal S2 by the signal synthesizer 21. Therefore, the local signal S2 becomes a local signal S2 'including a white noise signal. The local signal S2 'is a sinusoidal AC signal having a fundamental frequency of F0 which is the same as that of the local signal S2 and including a frequency component having a predetermined constant energy level over a wide frequency band. This local signal S2 'is supplied to the synchronous detector 13.

  In the above configuration, the white noise signal is added to the local signal S2, but the added signal is not limited to this. It may be a wideband noise signal similar to white noise, or a noise signal of a relatively wide frequency band including the frequency F0 of the local signal S2.

  For other circuit configurations, that is, the circuit configurations related to the synchronous detector 13, the AC amplifiers 14a and 14b, the low-pass filters 15a and 15b, the AD converters 16a and 16b, and the fast Fourier calculator 17, refer to FIG. This is the same as the configuration of the conventional radio frequency spectrum calculation apparatus described above.

  In the radio frequency spectrum calculation apparatus according to the present embodiment shown in FIG. 1, the radio signal S1 to be observed is input to the synchronous detection unit 13, and the local signal S2 ′ (frequency F0) supplied from the white noise adder 12 is further received. ) Is entered. The synchronous detection unit 13 branches the radio signal S1 into two parts and inputs them to the mixers 13a and 13b. For one radio signal S1, the mixer 13a mixes the local signal S2 'as it is. For the other radio signal S1, the local signal S2 'whose phase is adjusted by 90 ° by the 90 ° phase shifter 13c is mixed. With the circuit configuration of the synchronous detector 13, the I signal and the Q signal are extracted as shown in FIG.

  The I signal extracted by the synchronous detection unit 13 passes through the signal processing channels of the AC amplifier 14a, the low-pass filter 15a, and the A-D converter 16a, and is the real part of the FFT operation in the fast Fourier transform unit (FFT) 17. Supplied as data. Further, the Q signal extracted by the synchronous detection unit 13 passes through the signal processing channels of the AC amplifier 14b, the low-pass filter 15b, and the A-D conversion unit 16b as data of the imaginary part of the FFT operation in the fast Fourier transform unit 106. Supplied.

  As a result of the above processing, the radio signal S1 to be measured is separated into an I signal and a Q signal by the synchronous detection unit 13, transmitted through independent signal processing channels, and subjected to FTT calculation processing by the fast Fourier transform unit 17. . The calculation in the fast Fourier transform unit 106 is performed efficiently, and the frequency spectrum is calculated.

  Further, the frequency spectrum of the positive band and the frequency spectrum of the negative band are calculated from the I signal and the Q signal. As a result, as shown in FIG. 4, according to the radio frequency spectrum calculation apparatus according to the present embodiment, in addition to the positive band frequency spectrum, the negative band frequency spectrum is also obtained. Doubled.

  In particular, in the radio frequency spectrum calculation apparatus of this embodiment, as shown in FIG. 4, the attenuation of the portion corresponding to the frequency F0 of the local signal S2, that is, the frequency spectrum portion corresponding to the DC component is suppressed. The reason is that, as described above, the local signal S2 ′ is generated by superimposing the white noise signal on the local signal S2, and the synchronous detection of the radio signal S1 is performed using the local signal S2 ′. This is because the frequency component in the vicinity of the frequency F0 in the included white noise component acts to suppress the occurrence of the above-described conventional attenuation region.

  As described above, according to the radio frequency spectrum calculation apparatus according to the present embodiment, the white signal is added to the local signal S1 used in the synchronous detection by the synchronous detector 13 so as to have a band. In the frequency spectrum, attenuation of the frequency spectrum of the DC component can be suppressed.

  When the radio frequency spectrum calculation apparatus shown in FIG. 1 is actually manufactured, the apparatus configuration as shown in FIG. 5 is obtained. In this apparatus configuration, the synchronous detector 13 is configured as an IQ demodulator 31. The two A-D converters 16 a and 16 b are realized by a single chip (A-D conversion device) 32. The fast Fourier transform unit (FFT) 17 at the final stage is realized by a digital signal processor (DSP) 33. As the fast Fourier transform unit (FFT) 17, an FPGA (Field Programmable Gate Array) can be used instead of the DSP. The fast Fourier transform unit can also be realized by a dedicated chip. Other configurations are the same as those described in FIG. 1, and the same elements are denoted by the same reference numerals.

  The present invention is used for frequency spectrum analysis of radio waves.

It is a block block diagram which shows embodiment of the radio frequency spectrum calculation apparatus which concerns on this invention. It is a block diagram which shows the internal structure of a white noise applicator. It is a figure which shows the spectrum distribution of a white noise signal. It is a figure which shows an example of the frequency spectrum obtained with the radio frequency spectrum calculation apparatus which concerns on this embodiment. It is a block diagram which shows the actual structure of the radio frequency spectrum calculation apparatus which concerns on this invention. It is a block diagram which shows the 1st circuit example of the conventional radio frequency spectrum calculation apparatus. It is a block diagram which shows the 2nd circuit example of the conventional radio frequency spectrum calculation apparatus. It is a block diagram which shows the 3rd circuit example of the conventional radio frequency spectrum calculation apparatus. It is a figure which shows the frequency spectrum obtained with the radio frequency spectrum calculation apparatus of the conventional 1st circuit example. It is a figure which shows the frequency spectrum obtained with the radio frequency spectrum calculation apparatus of the conventional 3rd circuit example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Local oscillator 12 White noise imparting device 13 Synchronous detector 14a, 14b AC amplifier 15a, 15b Low-pass filter 16a, 16b A-D converter 17 Fast Fourier transform part 31 IQ demodulator 32 A-D conversion device 33 Digital signal processor ( DSP)

Claims (4)

A radio signal to be measured, and the synchronous detection means for synchronously detecting by using a reference signal supplied from the local oscillator, taking out I and Q signals of the radio signal,
First AC amplifying means for amplifying the I signal;
Second AC amplifying means for amplifying the Q signal;
First AD converting means for converting the output signal of the first AC amplifying means into a digital signal;
Second AD conversion means for converting the output signal of the second AC amplification means into a digital signal;
Fast Fourier transform operation means for inputting the output signal of the first A-D conversion means as real part data in FFT operation and inputting the output signal of the second A-D conversion means as imaginary part data in FFT operation; ,
Signal giving means for giving a broadband noise signal to the reference signal supplied from the local oscillator to the synchronous detection means;
A radio frequency spectrum calculation apparatus comprising:   2. The radio frequency spectrum calculation apparatus according to claim 1, wherein the broadband noise signal is a white noise signal.   3. The first and second A / D conversion means are constituted by an A / D conversion device having a two-channel input, and the fast Fourier transform calculation means is constituted by a DSP. Radio frequency spectrum calculation device.   4. The radio frequency spectrum calculation apparatus according to claim 3, wherein an FPGA is used instead of the DSP.

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