JP2013106339A - Broadband a/d conversion apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide such means that a band of any arbitrary frequency can be selected as an observation band and the selected one observation band can be sampled by one A/D conversion element regardless of a boundary of Nyquist frequencies of A/D conversion elements when accomplishing a receiving device of a direct conversion system in which a high frequency signal is band-divided and covered while being partially charged by a plurality of A/D conversion elements.SOLUTION: A boundary of Nyquist frequencies which is generated when dividing and sampling a band through a plurality of A/D conversion elements is avoided by combining and using auxiliary A/D conversion elements which operate in different sampling frequencies, and any arbitrary one observation band is sampled by one A/D conversion element.

Description

  The present invention relates to an AD conversion apparatus, an AD conversion method, and a radio reception apparatus for receiving a broadband high-frequency analog signal.

  In wireless receivers, radio wave measuring devices, and the like, it is necessary to select and receive a desired band from a wideband high-frequency analog signal. For example, in the case of a radio astronomy observation apparatus which is a type of radio measurement apparatus, a plurality of bandwidths of about 1 GHz are selected from a wide frequency range of several hundred MHz to several tens GHz, and these are received as observation signal bands and are measured.

  In recent wireless receivers and radio wave measuring apparatuses, it is common to perform necessary processing by digital signal processing after sampling an analog signal with an AD conversion element and converting it to digital data.

  Since the frequency and bandwidth of a signal that can be input to a normal AD conversion element are small compared to the frequency and bandwidth of an input high-frequency analog signal, the frequency and bandwidth are input in advance as an observation signal before inputting the high-frequency signal to the AD conversion element. After distributing to the required number, the frequency of each distributed high-frequency signal is lowered by a frequency converter called a down converter, band-limited by a low-pass filter, and then input to a plurality of AD conversion elements. The method of performing the latter digital signal processing is taken. An example of such a configuration is shown in FIG.

  In the above configuration, a down converter using analog technology is indispensable. However, since a down converter requires a highly stable local oscillator and a high performance mixer, the number of down converters is required when the number of observation signal bands required is large. In response to this increase, the scale and cost of the system increase. In addition, the phase fluctuation of the local transmitter incorporated in the down converter is directly reflected in the phase fluctuation of the observation signal, so it is fatal in applications where the phase information of the observation signal is important, such as radio astronomy observation equipment. This may be a common error factor.

  In recent years, in order to solve the above-described problems, a method called direct conversion that does not require an analog down converter has been realized. Direct conversion uses an AD conversion element that can input a high-frequency and wide-band signal. A wide-band high-frequency analog signal is input to the AD conversion element in a lump and converted to digital data. This is a method of extracting a plurality of signals having desired frequencies and bandwidths as observation signal bands by performing conversion and band limitation.

  On the other hand, in the case of a device that measures a very wide band, such as several GHz to several tens GHz, such as a radio astronomy observation device, even if the direct conversion method is used, it is possible to cover the entire band with one AD conversion element. Can not. For example, in an apparatus that needs to observe a signal with a bandwidth of 1 GHz from a frequency range of 2 GHz to 14 GHz, in order to capture the entire band with one AD conversion element, a signal up to 14 GHz can be input and a sampling frequency of 28 GHz However, in the currently available radio wave astronomy AD converters, the upper limit of the input frequency is 20 GHz or more, and the input signal frequency can be handled, but the sampling frequency is Since it is limited to about 16 GHz, the entire band cannot be captured.

In this case, a configuration may be considered in which a broadband high-frequency signal is divided into a plurality of bands by a band-pass filter having a bandwidth that can be input to the AD conversion element, and each is captured using a plurality of AD conversion elements. In this case, the frequency of the high-frequency signal is higher than the Nyquist frequency defined by the sampling frequency of the AD conversion element, but since the signal can be captured by sampling in the high-order Nyquist region, the analog down converter is It is unnecessary. An example of such a configuration is shown in FIG. Further, as shown in Non-Patent Document 1, an experimental approach has already been made on the configuration of a radio astronomy observation device that simplifies the system by this method.
VLBI with high-order mode sampling 32MHz 4ch system

  As shown in FIG. 4, in the case of a direct conversion method in which a band is divided and a plurality of AD conversion elements are used for sampling in a high-order Nyquist region, a desired observation signal band is analogized from a received wide-band high-frequency signal. Although it is possible to sample and extract without using a down converter, in the high-frequency signal as shown in FIG. 5, the observation signal band B3 (513) extending over the Nyquist frequency of the AD conversion element is one AD conversion. Since sampling cannot be performed by the element, it is necessary to limit the setting of a desired observation signal band so as not to cross the Nyquist frequency. On the other hand, in the case of a radio receiver or radio astronomy observation device, it may be necessary to arbitrarily select a desired observation signal band. In such a case, the method shown in FIG. A down converter must be introduced.

A technique has been devised in which an observation signal band extending over the Nyquist frequency is sampled by a plurality of AD conversion elements and then combined into one sampling data by digital signal processing (Patent Document 1). In this method, the observation signal band that crosses the Nyquist frequency is sampled by a plurality of AD conversion elements including both sides of the Nyquist frequency in the sampling band, and the signal of the observation signal band partially included in the output data of each AD conversion element is obtained. The frequency is converted by FFT and added in the frequency domain, or extracted by a digital filter and added in the time domain to be combined into a single digital data. According to this method, it is possible to sample and extract an arbitrary observation signal band from a wide-band high-frequency signal, but the output data of a plurality of AD conversion elements includes the phase difference of the analog circuit between the AD conversion elements and The phase does not exactly match due to the phase difference of the sampling clock. When phase continuity within the observation signal band is particularly important, such as in radio astronomy observation equipment, the phase difference between the output data of multiple AD conversion elements is a major problem, and special calibration means must be used to correct this. In order to avoid this, it is desirable to sample one observation signal band with a single AD conversion element.
Patent Publication 2006-319537

  The problem to be solved by the present invention is that a receiving device that selects and samples a single or a plurality of desired observation signal bands from a broadband high-frequency signal is divided by a plurality of AD conversion elements by dividing the high-frequency signal into bands. In the case of realization by the direct conversion method that covers, the frequency band of any frequency can be selected as an observation signal band regardless of the boundary of the Nyquist frequency of the AD conversion element, and one selected observation signal band can be selected as a single AD band. It is to provide a means for sampling with a conversion element.

  The present invention uses the boundary of the Nyquist frequency generated when a wideband high-frequency signal is sampled by dividing a band by a plurality of AD converter elements in combination with an auxiliary AD converter element operating at another sampling frequency. This is characterized in that one arbitrary observation signal band is sampled by a single AD conversion element.

  For example, in the case where four 1 GHz-width observation signal bands are AD-converted from a wide-band high-frequency signal of 0 to 15 GHz, the direct conversion method receiving apparatus having the configuration shown in FIG. Thus, if a high frequency signal of 0 to 15 GHz is divided into three 5 GHz width bands (501, 502, 503) and sampled by three AD conversion elements operating at a sampling frequency of 10 GHz, the Nyquist frequency is 5 GHz. The observation signal bands B1 (511), B2 (512), and B4 (514) that do not span multiples of can be sampled without any problem by any one of the three AD conversion elements. However, the observation signal band B3 (513) straddling the Nyquist frequency of 10 GHz cannot be sampled by a single AD conversion element. Similarly, an observation signal band that crosses the 5 GHz Nyquist frequency cannot be sampled.

  Here, in addition to a basic AD conversion element that operates at a sampling frequency of 10 GHz, an AD conversion element that operates at a sampling frequency of 8 GHz is added as an auxiliary AD conversion element. As shown in FIG. In addition to the 5 GHz-wide band (101, 102, 103) sampled by the basic AD converter element of (4), the auxiliary AD converter element newly adds a band of 4 to 8 GHz (104) and a band of 8 to 12 GHz ( 105) is sampled, the high frequency signal is sampled by five AD converter elements as a whole, and the optimum output of the AD converter element is selected from among them. The entire observation signal band of 1 GHz width can always be sampled by any one single AD conversion element. In the above example, the observation signal band B3 (114) that could not be sampled by the three basic AD conversion elements is the newly added auxiliary AD conversion element that operates at the sampling frequency of 8 GHz. The whole can be sampled by an AD conversion element sharing 8 to 12 GHz.

  As is apparent from the above description, according to the present invention, a receiving apparatus that selects and samples a single or a plurality of desired observation signal bands from a wideband high-frequency signal is divided into a plurality of high-frequency signals by band division. In the case of realization by a direct conversion method that is shared and covered by an AD conversion element, a band of any frequency can be selected as an observation signal band regardless of the boundary of the Nyquist frequency of the AD conversion element, and one selected observation signal The band can be sampled by a single AD conversion element.

  For example, it is possible to configure a receiver without using an analog downconverter in applications where it is necessary to select an arbitrary frequency, such as a radio astronomy observation device, and phase information of the acquired signal is important. In addition to reducing the phase error, it is possible to reduce the scale and cost of the entire system.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 2 shows, as a typical embodiment of the present invention, a receiving apparatus for selectively sampling four observation signal bands from a wideband high-frequency signal and outputting them as digital data. In order to interpolate the boundary of the band due to the Nyquist frequency in these AD conversion elements, two auxiliary AD conversion elements are used, and a total of five AD conversion elements are used. The structure of the case is shown.

  The receiving apparatus shown in FIG. 2 shows an example of a receiving apparatus used for a radio astronomy observation apparatus. The high-frequency signal input to the receiving apparatus has a very wide band, and among these, the signal selected as the observation signal band is a signal having an arbitrary bandwidth of 1 GHz in the frequency range of 0 to 15 GHz. In addition, four different bands are selected as observation signal bands. The signals in the four observation signal bands are finally output to the subsequent apparatus as four digital data having a sampling frequency of 2 GHz. The sampling frequency of the basic AD conversion element is 10 GHz, and the sampling frequency of the auxiliary AD conversion element is 8 GHz.

  As shown in FIG. 1, B1 (111) of 4 to 5 GHz, B2 (112) of 6 to 7 GHz, B3 (113) of 9.2 to 10.2 GHz, B4 (12 to 13 GHz) as the observation signal band. 114) are desired.

  The high frequency signal received by the antenna (201) is amplified by the low noise amplifier (211), distributed to five systems, and band-limited by the five band pass filters BPF1 (221) to BPF5 (225). These band-pass filters are anti-aliasing filters for preventing aliasing in the AD conversion element at the subsequent stage. As shown in FIG. 1, the passband of each bandpass filter covers the entire high-frequency signal by RF3 (103) that is the passband of RF1 (101) to BPF3 (223) that is the passband of BPF1 (221). , RF4 (104), which is the passband of BPF4 (224), and RF5 (105), which is the passband of BPF5 (225), are selected to interpolate the passband boundaries of the three bandpass filters. Yes.

  The high-frequency signal band-limited by the bandpass filter is input to the AD conversion elements ADC1 (231) to ADC5 (235) and sampled. Here, ADC1 (231) to ADC3 (233) operate at the sampling frequency fs1 (241) as basic AD conversion elements, and ADC4 (234) and ADC5 (235) as the auxiliary AD conversion elements, sampling frequency fs2. (242). Here, 10 GHz is selected for fs1 (241), and 8 GHz is selected for fs2 (242). Each AD conversion element can input a signal up to 15 GHz and supports sampling in a high-order Nyquist region. FIG. 6 shows the relationship between the observation signal band input to each AD conversion element and the sampling frequency.

  Data sampled by ADC1 (231) to ADC5 (235) is selected by four selectors (251 to 254) and input to digital downconverter 1 (261) to digital downconverter 4 (264). In each digital down converter, the frequency is converted by the local signals LO1 (271) to LO4 (274) so that the desired observation signal band becomes a baseband frequency with 0 GHz as the lower end. The frequency conversion inside these digital down converters is all performed by logical arithmetic processing on the digital signal, so that no error due to phase fluctuation of the local signal that occurs in an analog down converter occurs.

  The correspondence between ADC1 (231) to ADC5 (235) and digital down converter 1 (261) to digital down converter 4 (264), and the frequency of local signals LO1 (271) to LO4 (274) in each digital down converter are digital. It is determined by which observation signal band is output from each of the down converter 1 (261) to the digital down converter 4 (264). As in this example, B1 (111) of 4 to 5 GHz in FIG. 1 is digital down converter 1 (261), B2 (112) of 6 to 7 GHz is digital down converter 2 (262), and 9.2 to 10 When B2 (113) of 2 GHz is output from the digital down converter 3 (263) and B4 (114) of 12 to 13 GHz is output from the digital down converter 4 (264), in the digital down converter 1 (261), the observation signal band The output of ADC1 (231) including B1 (111) is selected, and the frequency of LO1 (271) is set to 4 GHz which is the frequency at the lower end of the observation signal band B1 (111). In the digital down converter 2 (262), the ADC 2 (232) including the observation signal band B2 (112) is selected. However, since the ADC 2 (232) is sampled in the second Nyquist region by fs1 (241) of 10 GHz. The sampled data is converted into a baseband whose frequency is reduced by 5 GHz, and the frequency direction is reversed. Therefore, the frequency of LO2 (272) is set to 4 GHz corresponding to the lower end of the observation signal band B2 (112) folded back to the baseband, and the lower sideband (LSB) is used in order to set the frequency direction in the normal order. Output a signal. In the digital down converter 3 (263), an AD conversion element including the observation signal band B3 (113) is selected. The observation signal band B3 (113) is a basic AD conversion element, ADC2 (232). Since these A / D converter elements cannot be correctly sampled because they extend over the Nyquist frequency of ADC 3 (233) and ADC3 (233), by selecting ADC5 (235), which is an auxiliary AD converter element, the basic AD converter element Sampling can be correctly performed with a single AD conversion element while avoiding the Nyquist frequency. Since the ADC 5 (235) samples in the third Nyquist region using 8 GHz fs2 (242), the sampled data is converted to a baseband whose frequency is reduced by 8 GHz, and the frequency direction is the same. Therefore, the frequency of LO3 (273) is set to 1.2 GHz corresponding to the lower end of the observation signal band B3 (113) converted into the baseband. In the digital down converter 4 (264), the ADC 3 (233) including the observation signal band B4 (114) is selected. However, since the ADC 3 (233) is sampled in the third Nyquist region by fs1 (241) of 10 GHz. The sampled data is converted to a baseband whose frequency is reduced by 10 GHz, and the frequency direction is the same as before. Therefore, the frequency of LO4 (274) is set to 2 GHz corresponding to the frequency at the lower end of the observation signal band B4 (114) converted into the baseband. The observation signal bands B1 (111) to B4 (114) included in the high-frequency signal by the procedure so far are converted into basebands having a lower end of 0 GHz. FIG. 7 shows the frequency relationship between the sampled data, local signal, and frequency-converted data at this time.

  In each digital down converter, the baseband frequency-converted data in which the lower end of the observation signal band is 0 GHz is band-limited by the low-pass filters LPF1 (281) to LPF4 (284) to a bandwidth having an upper limit frequency of 1 GHz.

  The data of each observation signal band limited to the bandwidth of 1 GHz is down-sampled by the decimator 1 (291) to the decimator 4 (294) to the sampling frequency fs3 (2i1), and finally the sampling frequency is fs3 (2i1). Output as digital data. In this case, the sampling frequency fs3 (2i1) is 2 GHz. Further, the downsampling ratio by the decimator is the ratio of fs1 (241) or fs2 (242), which is the sampling frequency of the AD conversion element selected as the input, and fs3 (2i1), which is the sampling frequency of the output digital data. It depends on. In the example shown here, decimator 1 (291), decimator 2 (292), and decimator 4 (294) perform downsampling at a ratio of 1/5 and decimator 3 (293) 1/4.

  The data down-sampled by the decimator 1 (291) to the decimator 4 (294) is output data 1 (2ii1) to output data 4 (digital data corresponding to the observation signal band B1 (111) to the observation signal band B4 (114). 2ii4).

  According to the above procedure, in a direct conversion type receiver that divides a band by a plurality of AD conversion elements and samples a wide band high-frequency signal without using an analog down-converter, one unit is used regardless of the Nyquist frequency. Any one of the observed signal bands can be sampled by a single AD conversion element.

  In the receiving apparatus configured by the method of the present invention, when an auxiliary AD conversion element is added so as not to straddle the Nyquist frequency for all observation signal bands, the input band of each AD conversion element and the observation Signal band frequency relationship.   The block diagram of the receiver of the direct conversion system which added the auxiliary AD conversion element by the method of this invention.   The block diagram of the receiver comprised using the analog down converter by the conventional method.   The block diagram of the receiver of the direct conversion system comprised only with the basic AD conversion element by the conventional method.   The relationship between the input band of each AD conversion element and the frequency of the observation signal band when a specific observation signal band crosses the Nyquist frequency in a receiving apparatus configured by a conventional method.   The relationship between the observation signal zone | band and sampling frequency which are input into each AD conversion element in the receiver comprised by the method of this invention.   The frequency relationship of sampling data, local frequency, and frequency-converted data in a receiving apparatus configured by the method of the present invention.

101-105 Input bands 111-114 of AD conversion elements 1-5 Observation signal bands B1-B4
201 Antenna 211 Low-noise amplifiers 221 to 225 Anti-alias bandpass filters 231 to 233 for AD conversion elements 1 to 5 Basic AD conversion elements 1 to 3
234 to 235 Auxiliary AD conversion elements 4 to 5
241 Sampling clock 242 for basic AD conversion elements 1 to 3 Sampling clocks 251 to 254 for auxiliary AD conversion elements 4 and 5 Input selectors 261 to 264 for digital down converters 1 to 4 Digital down converters 1 to 4
271 to 274 Local signals 1 to 4
281 to 284 Low-pass filters 1 to 4
291-294 Decimators 1-4
2i1 Output data sampling clocks 2ii1 to 2ii4 Output data 501 to 503 Input bands 511 to 514 to three AD conversion elements according to the conventional method Observation signal bands B1 to B4

Claims (3)

  A combination of a basic AD converter for sampling a high-frequency signal and an auxiliary AD converter operating at a sampling frequency different from that of the basic AD converter is An AD conversion device characterized in that sampling can be performed so as not to cross the Nyquist frequency by an AD conversion element.   A combination of a basic AD converter for sampling a high-frequency signal and an auxiliary AD converter operating at a sampling frequency different from that of the basic AD converter is An AD conversion method characterized in that sampling can be performed by an AD conversion element so as not to cross the Nyquist frequency.   A combination of a basic AD converter for sampling a high-frequency signal and an auxiliary AD converter operating at a sampling frequency different from that of the basic AD converter is A radio receiving apparatus having an AD conversion unit, characterized in that sampling can be performed by an AD conversion element so as not to cross a Nyquist frequency.

Images