CN101520500A - System and method for executing external calibration - Google Patents
System and method for executing external calibration Download PDFInfo
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- CN101520500A CN101520500A CN200810088186A CN200810088186A CN101520500A CN 101520500 A CN101520500 A CN 101520500A CN 200810088186 A CN200810088186 A CN 200810088186A CN 200810088186 A CN200810088186 A CN 200810088186A CN 101520500 A CN101520500 A CN 101520500A
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Abstract
The invention relates to a system and method for executing external calibration. The invention provides a system which is used for executing the external calibration to reduce or eliminate the frequency correlation response which is associated with the external equipment for receiving the analog signals. The system comprises an ADC and a spectrum processor which is used for transforming the digital data of time domain into the spectrum. The external calibrator is used for reducing or eliminating the frequency correlation response between the ADC and the spectrum processor which is associated with the external equipment. The corresponding method comprises the following steps of determining the frequency response of the external equipment, determining the gain of the central frequency, determining the standardized frequency response, configuring the inverse filter and applying the filter to the digital data of time domain and computing the result before any transformation or transforming to frequency domain.
Description
Technical field
The present invention relates to adopt external unit to receive the measurement and the proving installation of measurement and test signal.
Background technology
Test and measurement mechanism, for example oscillograph, spectrum analyzer or a testing apparatus rely on external unit to measure or test to obtain signal usually.These external units, for example antenna, cable, prime amplifier or probe have the frequency dependence frequency response usually.This frequency response is heterogeneous, and the meaning is exactly that amplitude gain changes with frequency is different.Therefore, signal distortion after of device reception by the external unit in the receiver channel.The distorted signals compensation is useful for obtaining correct signal.This compensation relates to external calibration.
In the example of spectrum analyzer 10, shown in accompanying drawing 1 (prior art), external calibration is carried out after frequency spectrum processing, in this process the time-domain digital conversion of signals is arrived frequency domain.Input signal is at first by external unit 12, and it can be for example antenna, prime amplifier or probe.After external unit 12, signal enters the RF input end of spectrum analyzer 10.External unit can comprise a plurality of external units, and for example antenna was connected with prime amplifier by cable before being input to device.As shown in Figure 1, input signal enter the RF input end and by frequency selective filter 14, frequency mixer 16 and frequency overlapped-resistable filter (antialias filter) 18 to provide intermediate frequency (IF) to analog to digital converter (ADC) 20.Although only show a frequency mixer, also can use the multi-frequency switching stage in some applications.IF can equal base band in some applications.After ADC produced digital signal, digital intermediate frequency (DIF) module 22 became base band homophase (I) and quadrature (Q) data with digital IF conversion of signals.Frequency spectrum processing module 24 will become the frequency spectrum of frequency domain data for the IQ data-switching of time domain data.Frequency spectrum processing module 24 can utilize Fast Fourier Transform (FFT) (FFT) to be accomplished to the conversion of frequency domain.In the spectrum analyzer shown in the accompanying drawing 1, after frequency spectrum processing, adopt software to carry out external calibration, as s/w external calibration module 26 show on the display that is shown in 28 before the frequency spectrum.External calibration is by before being sent to display with frequency spectrum, and the inverse of the frequency response of (scale) spectrum results that converts and external unit is realized.Spectrum analyzer 10 also comprises additional reservoir and processor, comprises CPU, be provided with and control to provide, and the operation external calibration shows with generating.Because the fine understanding of reservoir and processor does not need additional description here.
Because the utilization of the system and method shown in the accompanying drawing 1 external calibration is up to the end of processing chain, so there are a plurality of shortcomings in it.When implementing additional the measurement, for example by upgrading, external calibration may also need expansion or revise.Simultaneously, because externally proofreading and correct, phase information loses before, so it can not be used for for example Modulation analysis of vector analysis in conjunction with the phase response of external unit.In addition, when resolution bandwidth (RBW) be big and with amplitude variations cycle of external unit be comparable, the system and method shown in the accompanying drawing 1 causes coarse spectral line waveform.If input signal is the frequency that continuous wave (CW) signal and spectrum analyzer are adjusted to this signal, frequency spectrum should show the waveform of RBW wave filter.Yet the final frequency spectrum of attached system shown in Figure 1 has shown the inverse of the frequency response at RBW filter shape peak.
Summary of the invention
Therefore, one embodiment of the invention are shown in Figure 2.This embodiment used external calibration before frequency spectrum processing.And in certain embodiments, system also can implement to proofread and correct in time domain before other handles as trigger processing or digital phosphor demonstration.In a further embodiment, external calibration adopts hardware to realize.
Description of drawings
Accompanying drawing 1 (prior art) illustrates the spectrum analyzer with rearmounted frequency spectrum processing external calibration.
Accompanying drawing 2 explanations had the spectrum analyzer of external compensation before frequency spectrum processing.
Accompanying drawing 3 provides the process flow diagram of the embodiment of external compensation method.
Accompanying drawing 4 provides the process flow diagram of the embodiment of the external compensation method that is connected with the stepping centre frequency.
Accompanying drawing 5 explanations comprise the embodiment of the system of external calibration device.
Accompanying drawing 6 explanations comprise the embodiment of the system of external calibration device.
Accompanying drawing 7 explanations comprise the embodiment of the system of external calibration device.
Embodiment
First embodiment of native system 100 is shown in Figure 2.System 100 is and similar spectrum analyzer shown in the accompanying drawing 1, but provided external calibration device 126 before frequency spectrum processing module 24.In addition, as shown in Figure 2, the output of external calibration device 126 pulse producer 130 that also can be triggered, and digital phosphor video-stream processor 132 uses.The digital phosphor display relates to a kind of display that is used in the digital fluorescence oscilloscope for example, and for example those use the look and feel that quick rasterizing and attenuation processing show with analogue simulation fluorescence, for example by changing intensity.Alternatively, pseudo-color or thermocolour coloured silk are used to obtain based on the demonstration of impacting and decay is provided with.
The frequency response of given external unit, it can provide with the form of corrected value form in certain embodiments, the following structure of digital filter h (n):
Wherein H (w) is the frequency response of digital filter, and D (w) is the frequency response of external unit, and BW is that DIF acquisition bandwidth and wc are centre frequencies.In one embodiment of the invention, the frequency response of external unit (D (w)) is provided as the combination frequency response of all external units in the signalling channel.D (w) is as not only comprising the amplitude response but also comprise phase response, only comprising the amplitude response in more embodiment, and the function of a complex variable that perhaps only comprises phase response provides.
The embodiment of a method 200 that external calibration is provided is shown in Figure 3.The frequency response D1 (w) of external unit is determined, as shown in the step 210.In certain embodiments, the frequency response of external unit covers the frequency range of whole care.In other embodiment, extrapolation can be used to from the initial value of providing extended frequency range.In a further embodiment, wherein frequency response is not can obtain in the frequency range of whole care, indicates normal mistake to the user.
In an embodiment of method, frequency response is determined according to the acquisition bandwidth (BW) in given adjusting centre frequency (wc), makes and determines during frequency response is from wc-BW/2 to wc+BW/2.In certain embodiments, external unit is made up of a plurality of external units, the antenna that for example links together, cable and prime amplifier.The frequency response of combination external unit can be from based on determining the single external calibration form of the feature description of whole combination external unit.In other embodiments, constitute each external unit that makes up external unit and have the external calibration form of himself.Combination external calibration form obtains by making up each correction form.In certain embodiments, for example, when all forms were not shared same frequency, interpolation method was used so that make up a plurality of external calibration forms to obtain the combination frequency response.But when the response of definite combination frequency, in a lot of embodiment the combination frequency response comprise all external units of forming this external unit will be preferred, it is just enough only to make up most important external unit in certain embodiments.
As shown in the step 220, the gain G (wc) at centre frequency wc place is determined.The combination frequency response is divided into two parts: frequency-independent constant gain and frequency dependence response.The normalized response D2 (w) of centre frequency is determined in step 230.The gain that combination frequency response D1 (w) uses the centre frequency place by standardization to obtain normalized response D2 (w), D2 (w)=D1 (w)/G (wc).In certain embodiments, this will reduce or eliminate the quantization error of filter coefficient, and this is because the point of fixity operation is finished on hardware usually.
The digitizing time domain data that provided by ADC is provided the inverse filter that the external calibration module provides now, as shown in the step 250.In certain embodiments, the digitizing time domain data is further handled by the DIF processing module, and it can provide for example baseband I Q data.
The result of external calibration module is converted, as providing in step 260.This conversion is based on predetermined gain G (wc).In certain embodiments, after the frequency spectrum processing module converts, converting occurs in the frequency domain.In other embodiments, time domain data is converted.In a further embodiment, converting may be provided in the time domain to be used for some processing, for example triggers, and is provided in the frequency domain to be used for other processing.
Another embodiment of accompanying drawing 4 explanation this method will be used for example when spectrum analyzer moves with step mode it.In step mode, use a plurality of collection values that are adjusted to different center frequency with this frequency spectrum with combine from the frequency spectrum that measures.In step mode, by regulating centre frequency in step, the embodiment of this method can provide external unit to proofread and correct, as providing in step 300, and to each centre frequency re-treatment step 220 to 260.At some embodiment, step 220 will only be reused the previous foreign frequency response of determining.In other embodiments, step 210 also will be repeated, and make the determined value of foreign frequency response will obtain along with the stepping of frequency upgrading like this.In certain embodiments, centre frequency is regulated by the local oscillator that is controlled in the frequency mixer.In a further embodiment, filter coefficient is stored in the storer so that the calculating of filter coefficient is only done once.Only calculate a filter coefficient and improved the speed of when external calibration is provided, carrying out spectrum measurement.
As shown in Figure 5, embodiments of the invention do not need low-converter or frequency mixer.In certain embodiments, external calibration is based on that the output of the ADC that ignores any adjusting of input signal or need not input signal is regulated is provided.
As shown in Figure 6, outside corrector was provided before digital intermediate frequency (DIF) module 22 in additional embodiment.In certain embodiments, external calibration is based on from the real-valued output of ADC.In other various embodiment, the output of ADC can be digital intermediate frequency (DIF) component or base band.Rely on the realization of each embodiment, the output of ADC can be compound I and Q signal, is perhaps only produced by real component.
As shown in Figure 7, DIF module 22 can be deleted in certain embodiments fully.
Although embodiment more described herein relate to spectrum analyzer, some other embodiment may be applicable to the time domain processing, perhaps measures.These embodiment will not need the frequency domain conversion, and perhaps any frequency spectrum is created.
Claims (12)
1, a kind of system that is used to carry out external calibration comprises:
Be used to receive the external unit of simulating signal, wherein this external unit has the frequency dependence response;
Analog to digital converter is used for analog signal conversion to the time domain digital signal;
Spectral processor is used for the time-domain digital conversion of signals is become frequency spectrum; And
Be connected the external calibration device between analog to digital converter and the spectral processor, be used to the frequency dependence response of external unit that correction is provided.
2, the system as claimed in claim 1, wherein this external calibration device comprises digital filter.
3, system as claimed in claim 2 further comprises the digital intermediate frequency module, is used for the time-domain digital conversion of signals is become base band homophase and orthogonal data.
4, system as claimed in claim 3, wherein this digital intermediate frequency module is connected between analog to digital converter and the external calibration device.
5, system as claimed in claim 3, wherein this digital intermediate frequency module is connected between external calibration device and the spectral processor.
6, the system as claimed in claim 1 further comprises being connected external calibration device trigger circuit afterwards.
7, the system as claimed in claim 1 further comprises being connected external calibration device digital phosphor video-stream processor afterwards.
8, a kind of method of carrying out external calibration comprises:
Determine the frequency response of external unit;
Determine the gain at centre frequency place;
Settling the standard frequency response;
Make up inverse filter;
Inverse filter is applied to the digitizing time domain data; And
The conversion result.
9, method as claimed in claim 8 determines that wherein frequency response comprises the combination frequency response of the external unit of determining a plurality of connections.
10, method as claimed in claim 9, wherein this combination frequency response is to determine from the frequency response of this external unit of the external calibration form gained of each single external unit self by combination.
11, method as claimed in claim 9, wherein the response of this combination frequency is to obtain from the single external calibration form based on the feature of the external unit of whole combination.
12, method as claimed in claim 8 further is included in the conversion end value and steps to new centre frequency and turn back to the step of determining in the gain at this centre frequency place afterwards.
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| Application Number | Priority Date | Filing Date | Title |
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| CN200810088186A CN101520500A (en) | 2008-02-27 | 2008-02-27 | System and method for executing external calibration |
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| CN200810088186A CN101520500A (en) | 2008-02-27 | 2008-02-27 | System and method for executing external calibration |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102419389A (en) * | 2010-08-13 | 2012-04-18 | 特克特朗尼克公司 | Time-domain measurements in a test and measurement instrument |
| CN112986679A (en) * | 2021-04-27 | 2021-06-18 | 深圳市鼎阳科技股份有限公司 | Calibration compensation device and method for spectrum analyzer and spectrum analyzer |
-
2008
- 2008-02-27 CN CN200810088186A patent/CN101520500A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102419389A (en) * | 2010-08-13 | 2012-04-18 | 特克特朗尼克公司 | Time-domain measurements in a test and measurement instrument |
| CN102419389B (en) * | 2010-08-13 | 2016-08-03 | 特克特朗尼克公司 | Time domain measurement in test and sensing device |
| CN112986679A (en) * | 2021-04-27 | 2021-06-18 | 深圳市鼎阳科技股份有限公司 | Calibration compensation device and method for spectrum analyzer and spectrum analyzer |
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Open date: 20090902 |