The hottest short wave array signal generator base

2022-10-24
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Short wave array signal generator based on DSP Duc 1. Introduction as an important branch of digital signal processing, array signal processing is widely used in radar, sonar, communication, seismic exploration, medical imaging and many other fields; Short wave band is commonly used in short wave direction finding and beam synthesis technology

in the short wave band, the array signal processing equipment usually includes three main components: the short wave antenna array, the short wave multichannel receiver, and the back-end array signal processor. Among them, the short wave antenna array receives the spatial short wave signal, the short wave receiver performs analog down conversion on the HF signal, and the array signal processor digitally samples the output signal of the short wave multi-channel receiver and carries out the corresponding array signal processing algorithm, and gives the final calculation result

due to the limitation of the short wave frequency band, the size of the antenna unit is usually relatively large, and the aperture of the antenna array is also relatively large, often covering an area of nearly ten mu; Moreover, in order to achieve better reception effect, the requirements of short wave antenna array on the surrounding electromagnetic environment are also quite high. This brings great inconvenience to the debugging and testing of the short wave array signal processor in the development process, and it is also not conducive to the research and verification of various DSP algorithms of the array signal processor for different array flow patterns of short wave signals

according to the actual situation of the development and debugging of short wave array signal processing equipment, the author selects digital signal processor chip (DSP) and digital upconverter chip (Duc) to design an array signal generator that simulates the output signal of short wave antenna array, which can replace short wave antenna array in laboratory environment and generate short wave array signals corresponding to different array flow patterns, Provide debugging and verification conditions for array signal processor DSP algorithm

II. Design idea

according to the design idea, the array signal generator should be able to flexibly generate short wave array signals corresponding to different array forms (carrying the amplitude difference and phase difference corresponding to different array forms) and basically covering the frequency range of 1 ~ 30MHz

if the traditional analog up conversion circuit is used to realize RF output, it is difficult to meet the design idea. Therefore, the author adopts the idea of software radio, selects digital up converter (Duc), performs up conversion in the digital domain, and then generates short wave high-frequency analog signals through d/a conversion. In order to realize the amplitude difference and phase difference caused by different array forms, the author selects DSP chip to add different amplitude and phase differences to multiple signals in the digital domain

as shown in Figure 1, the overall design idea of the array signal generator is: Taking DSP and Duc as the core, using the a/d sampling data input by the external audio signal as the modulation signal data, the DSP digitally modulates the prefabricated carrier signal (lower frequency), and adds 9 different amplitude differences and phase differences to the modulated digital signal according to the optional different array flow patterns, and then sends them to 9 DUCS through FPGA, After digital up conversion and d/a conversion, 9 short wave array signals are output

in the design, because the actual audio modulation signal needs to be digitally modulated by DSP chip and then allocated to 9 DUCS, a large-scale FPGA logic chip is used as the data exchange interface between DSP chip and 9 DUCS

III. device selection

p

as the core device of this design, the DSP chip has high requirements for computing power, and at the same time, it has the characteristics of a large amount of data exchange in the process of computing. After comprehensive comparison, the author selects ADSP-21060 in the arc-dsp series of analog device company

adsp-21060 is a 32-bit floating-point DSP, which uses a 40 MHz master clock and has an operation capacity of 120 MFLOPS; There is a 4 Mbit dual port SRAM in the chip (for this design, there is no need to expand the external memory, and all the storage space required for operation is internally supported, which greatly reduces the DSP time overhead of exchanging data with the external memory); It supports 10 DMA channels for on-chip SRAM to exchange data with external memory, serial port, etc. (this design uses its DMA channel to transmit audio sampling data)

2. Serial a/d

the reason why this design uses serial a/d to digitally sample the external input audio is that the external input signal should enter the memory of DSP uninterruptedly, and the serial port DMA mode of ADSP-21060 can be used to transmit data. Therefore, the author selects the dual channel serial audio sampler ad1847 of analog device company

3. The main function of the digital up converter

duc is to perform frequency conversion and spectrum shift on the input data, that is, to realize mixing in the digital domain. The author selects AD9857 of analog device company as the Duc of this design

ad9857 is a 1/3 AC digital up converter (qduc) whose processing tolerance of 14 bit positive die is plastic tolerance. The maximum working clock is 200 MHz. It is internally integrated with high-speed direct digital synthesizer (DDS), digital interpolation filter, clock frequency multiplier circuit and user programmable function; And there is a 14 digit analog-to-digital converter (DAC) integrated inside, which can directly output analog high-frequency signals

because AD9857 transfers the data transmission path from the analog field to the digital field, the analog circuit function is physically separated from the digital components. Therefore, when modifying the circuit parameters or upgrading the system, you only need to make some simple modifications to the internal registers through the SPI serial programming port of AD9857, and you do not need to change the hardware circuit

ga

due to the large amount of high-speed data exchange in this design, the FPGA as the data interface between DSP and Duc requires relatively large scale. The author selects epf10k50e in the flex series of Altera company

the typical number of logic gates of epf10k50e is 50000, and the chip contains 40 kbit ram, which can meet the requirements of a large amount of data cache and data exchange

fourth, design and implementation

in the design and implementation, the main work of this design focuses on DSP programming and FPGA software debugging

p program

dsp, as the master controller of the whole design, mainly completes the following three functions with the help of the function layer:

first, DSP simply configures the serial a/d sampler ad1847, such as sampling rate, data format, etc., and configures its own receiving serial port, which is set to the chain DMA mode, so as to repeatedly store and refresh audio sampling data in a specified memory interval

secondly, DSP will perform digital modulation operation on the data in DMA storage space, and the carrier signal uses one of the preset cosine signals of several groups of lower frequencies (such as 5 kHz, 10 kHz, etc.); Then add different amplitude and phase differences to the adjusted digital signals according to different array flow patterns. The utilization range of the film blowing machine is mainly based on different materials, forming an array signal with amplitude and phase differences; Finally, the array signal data is written into the corresponding temporary FIFO in FPGA in parallel according to different port addresses, and FPGA is responsible for allocating it to each Duc data port

thirdly, DSP configures 9 internal registers of Duc, including up conversion multiple, output carrier frequency, spectrum shift mode, output analog signal amplitude, etc. DSP configures the Duc by writing parallel data words to the external ports of different addresses, and then converts it into serial spi data format through the data conversion function of FPGA, and configures registers for each Duc respectively

The function of

GA program

FPGA is to realize the data format conversion and distribution between DSP and 9 DUCS. As shown in Figure 2, FPGA transfers DSP data bus to different Duc (1 ~ 9) interface units according to different addresses

for the Duc configuration data, each Duc interface unit latches it first, then performs parallel/serial conversion on the latched data, converts it into SPI form serial data, and sets its internal register for each Duc respectively

for the data to be up converted, each Duc interface unit will first send it to a 64 × In the 16 bit dual clock FIFO, then 9 DUCS read out their respective data to be up converted from the FIFO at the same time, perform Duc operation, and output them as analog signals

The short wave array signal generator introduced in this paper has been used in the laboratory verification of the actual short wave direction finding system, and its multi-channel short wave array analog signal output can be directly sent to the short wave multi-channel receiver

since this signal generator has 9 outputs in total, it can be applied to the simulation of antenna array signals with 9 elements and below. Through the selection of DSP program in the signal generator, the array to be simulated can be selected, and the desired incoming wave direction can be set, so as to generate multi-channel array signals with array amplitude and phase information, which can be provided to the actual verification environment of DSP algorithm

at present, the commonly used linear array and square array have been tested (3 × 3,2 × 2) , circular array (uniform, non-uniform) and other formations, the test results have achieved the expected results

in addition, this design samples external dual channel audio. By adding different audio signals to the left and right channels, two different modulation signals can be obtained. By superimposing the two signals in the DSP program, the situation of multiple signals of the same frequency often encountered in short wave direction finding can be simulated to verify the discrimination ability of the direction finding algorithm for multiple signals of the same frequency

in the debugging process of the array signal processor, the short shows that the processor has the professional ability to process this kind of advanced high molecular materials into the most demanding components in many industries. The application of the wave array signal generator greatly facilitates the laboratory development and debugging of the short wave band array signal processing equipment, and greatly shortens the field debugging time of the equipment

references

[1] Yang Xiaoniu, Lou Caiyi, Xu Jianliang Principle and application of software radio [M] Beijing: Electronic Industry Press, 2001

[2]Analog Devices 9857 Data Sheets[DB/OL].

[3]Analog Devices SP21060 Data Sheets[DB/OL].- Sheets/ADSP-21060-L-f,2000. (end)

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