JPH0514937U - Spectrum analyzer - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a digital spectrum analyzer that has high resolution and can maintain consistency with a waveform when an analog filter is used. [Structure] A bandpass filter 16 for determining resolution is realized by using a digital filter bank capable of narrowing a band. This digital bandpass filter bank is formed, for example, by combining a lowpass filter and a highpass filter to construct a cascade tree structure. Since the processing is basically the same as that of the analog filter, the envelopes of the displayed waveforms are the same and the sameness can be maintained.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a spectrum analyzer for performing frequency spectrum analysis, and particularly to a high resolution digital spectrum analyzer.

[0002]

[Prior Art]

 A conventional spectrum analyzer converts an input signal into a low-frequency signal by mixing it with a local oscillation signal, and selects a frequency signal in a predetermined band with a variable bandwidth bandpass filter (analog filter that determines frequency resolution). After that, logarithmic compression is performed by the Log amp, the signal level is detected by the detector, and frequency analysis is performed.

[0003]

[Problems to be solved by the device]

 In the above-described conventional spectrum analyzer, the variable bandwidth bandpass filter that determines the resolution is an analog filter, and it is difficult to narrow the bandwidth above a certain level, so the resolution of the spectrum analyzer is limited.

In addition, in order to improve the resolution, there is a method in which an input signal is converted into a digital signal by using an A / D converter and then a frequency spectrum is analyzed by an FFT (fast Fourier transform) analyzer. . However, in this case, the value obtained by the FFT operation is a discrete value, so when the analysis waveform is displayed, the waveform and envelope when an analog filter that processes the input signal continuously is used. There is a problem that the waveforms may be different and the waveforms may not be consistent. In particular, in a device that has both analog / FFT functions in the same device, can perform analog analysis when low resolution is used, and can switch to FFT when high resolution is required, it can be used from analog to FFT. There is a big problem if the continuity of spectrum analysis results cannot be maintained when the resolution is switched.

The present invention has been made paying attention to such a problem, and its purpose is high resolution and can maintain consistency with a waveform when an analog filter is used. It is to provide a digital spectrum analyzer.

[0006]

[Means for Solving the Problems]

 In the present invention, a bandpass filter that determines the resolution is realized by using a digital filter bank. This digital bandpass filter bank is formed by, for example, combining a lowpass filter and a highpass filter to construct a cascade tree structure.

[0007]

[Action]

 The low-pass filter (LPF) and high-pass filter (HPF) that form the cascade tree are, for example, half-band filters (filters with a cutoff angular frequency of approximately π / 2), and by selecting a combination of these filters, A plurality of bandpass filters (bandpass filter banks) having different angular frequency bands can be configured. A digital filter can consist essentially of a delay element and an addition element, and LPF and HPF can be constructed with the slight modification of inverting and adding the polarities of signals of equal absolute value. That is, assuming that a is a coefficient and x is data, and the LPF is expressed as a0x0 + a1x1 + a2x2 + a3x3, the HPF only needs to invert the polarity every other term such as a0x0-a1x1 + a2x2-a3x3, which uses the two's complement. Can be easily achieved with. Therefore, the bandpass filter bank described above can be realized by using one digital filter in multiplex and passing the signal many times while considering the polarity of the signal, which is highly flexible and narrows the band. Easy to promote. Therefore, the resolution can be made higher than that when an analog filter is used.

Further, the digital filter basically performs a temporal process of adding various delays to an input wave and synthesizing them, and takes in all signals such as FFT to perform an operation. Unlike obtaining discrete values, it is basically the same as analog filter processing. Therefore, the envelopes of the displayed waveforms are the same, and the sameness can be maintained.

[0009]

【Example】

 Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. In this embodiment, in order to obtain a wide frequency band, it is divided into two frequency ranges by the switches 3 and 10 and has an internal configuration having a circuit for each, and the upper circuit is for the low frequency range and the lower circuit is for the lower frequency range. The side circuit is for high frequency range. Further, in this embodiment, a digital filter bank 16 is provided in the input section of the digital processing circuit 17, and the resolution is determined by this filter bank.

FIG. 2 is a diagram showing a configuration example of the bandpass filter bank 16. As shown, the filter bank 16 includes low-pass filters (LPF) 21, 25, 27, 33, 35, 37, 39, high-pass filters (HPF) 26, 28, 34, 38, 40, and signal transmission. It has a cascade tree structure in which the route switching means 20, 23, 24, 29, 30, 31, 32 are combined. This filter bank has 14 bands (pass frequency band, band nd00,01,10,11,12,13,20,21,22,23,24,25,26,27) every time the input signal passes. Are formed. Further, the characteristics of LPF and HPF are a half band filter as shown in FIGS. 3 (a) and 3 (b), respectively.

FIG. 4 is a diagram showing a hierarchical structure of selectable pass frequency bands in this embodiment. For example, in the case of band 10, either band 20 or 21 can be selected. In this way, the pass band can be appropriately narrowed down to obtain a signal in a desired band. That is, it becomes a bandpass filter with a variable bandwidth, and the resolution can be determined by this.

The input signal to be measured is level-adjusted by the attenuator 1 and passes through the limiter 2 for protection against excessive input. In the case of a low frequency range, after passing through the LPF 4, the variable frequency oscillator (local oscillator) 6 and the mixer 5 once mix up (convert to a high frequency) and separate the signal so that it does not overlap the original signal. After that, only the required pass band is selected by the BPF 7 (for example, only the right side of the difference signals existing on the left and right around the local oscillation frequency is selected). Next, mixing is performed by the fixed frequency oscillator 8 and the mixer 9 (conversion to low frequency). In the case of a high frequency range, only a predetermined pass band is selected by a pre-tuning BPF (pass band variable band pass filter) 42 and mixed down by a variable frequency oscillator 44 and a mixer 43. The low-frequency converted signal further passes through the BPF 11 and the amplifier 12, is mixed down by the fixed frequency oscillator 13 and the mixer 14, and after passing through the LPF 20, is A / D converted by the A / D converter 15 to perform digital signal processing. The signal is processed by the circuit 17 and displayed on the display device 18.

The variable frequency oscillators 6 and 44 are stepwise swept with a frequency width of 1/2 or less of the sampling frequency of the A / D converter 15. Within this range, real-time spectrum analysis function can be realized. Further, the operation of the entire circuit is controlled by the control circuit 19.

[0014]

[Effect of the device]

 As described above, according to the present invention, it is possible to provide a digital spectrum analyzer having a real-time spectrum analysis function, high resolution, and capable of maintaining consistency with a waveform when an analog filter is used.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a bandpass filter bank 16.

3 is an LPF used in the embodiment of FIG. 2,
It is a figure which shows the characteristic of HPF, (a) shows the characteristic of LPF, (b) shows the characteristic of HPF.

FIG. 4 is a diagram showing a hierarchical structure of selectable pass frequency bands in the embodiment of FIG.

[Explanation of symbols]

1 Attenuator 2 Limiter 3,10 High frequency range / low frequency range selector switch 4 LPF 5,9,14,43 Mixer 6,44 Variable frequency oscillator (local oscillator) 7 BPF 8,13 Fixed frequency oscillator (local oscillator) 11 BPF 12 Amplifier 15 A / D converter 16 Digital filter bank 17 Digital 111 Signal processing circuit 18 Display device 19 Control circuit 20 LPP 42 Pretune BPF

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Haruo Kobayashi 2-932 Nakamachi 2-chome, Musashino City, Tokyo Yokogawa Electric Co., Ltd.

Claims (1)

[Scope of utility model registration request] 1. A local oscillator (6), a mixer (5),
A digital signal processing circuit (17) including a filter circuit (20), an A / D converter (15), and a digital filter bank (16) is provided, and an input signal is locally oscillated by the local oscillator (6). The signal is frequency-converted by mixing with the signal, the frequency-converted signal is passed through the filter circuit (20), and then the A / D
A spectrum analyzer characterized by performing a frequency spectrum analysis by inputting it into a converter (15) to convert it into a digital signal, and passing this digital signal through the digital filter bank (16) that functions as a bandpass filter.