The detection system performs real-time recognition processing on the input spatial transient optical radiation signal, and inverts the estimated spatial transient signal energy and reports the occurrence time. Using digital processing scheme of DSP+CPLD, real-time identification and processing of transient signals can be realized by using the high-speed digital signal processing characteristics of dsp and the complex logic programmable features of cold. Among them, cpld is used to realize a/d variable rate sampling, which solves the contradiction between the limited area of ​​the embedded system circuit board and the large-capacity storage space required for real-time processing.
Real-time processing of China's active space transient optical radiation signal detection system, the old models are more, most of them are not equipped with automatic detection and admission equipment. The admission, data processing and reporting of spatial transient signals are mostly carried out manually, which is difficult to meet the requirements of fast and accurate admission of signals and meteorological information in complex environments. In order to meet the requirements of modern meteorological analysis, the use of dsp+cpld will greatly improve the automatic admission and analysis capabilities of existing space transient signal detection.
In the real-time signal processing technology, the dsp+cpld method is currently a relatively common method in the world, such as the United States, Russia, and the like. The dsp is a programmable digital microprocessor. Compared with single-chip microcomputers, dsp chips have software and hardware resources that are more suitable for digital signal processing and can be used for complex digital signal processing algorithms. This article uses TI's tms320c3x series floating-point dsp chip tms320c32 as the host of the whole system, using it to complete the system control and digital signal processing functions.
Cpld is a versatile, high-density complex programmable logic device that integrates some or all of the system's functions on a single chip. It is designed to be flexible, easy to modify, and greatly reduces development time and reduces System hardware complexity. This paper uses the max7000s series cpld chip epm7128slc84 of Altera Corporation of the United States to realize a/d variable rate sampling and other logic control by using cpld.
1 system composition and basic principles
The detection system mainly solves the contradiction between the limited area of ​​the embedded system circuit board and the large amount of storage space required for real-time data processing, and real-time processing of signals.
The real-time detection system of space transient optical radiation signal is mainly composed of three modules: pre-processing circuit module, a/d variable rate sampling module, dsp signal identification and storage module.
The main functions of each module are:
(1) The pre-stage pre-processing circuit module is responsible for tasks such as photoelectric conversion, background subtraction, and dynamic range compression of the spatial transient optical radiation signal;
(2) a/d variable rate sampling module, responsible for trigger signal generation, rising rate initial judgment, signal acquisition timing control, a/d variable rate sampling and fifo buffer storage;
(3) dsp signal identification and storage module, responsible for fast identification of spatial transient signals, inversion of energy calculation, reporting of event occurrence time and storage and transmission of data; control of the entire system, and with PC or other systems Transmission data is sent.
2 pre-processing circuit module
2.1 photoelectric conversion
Since the spatial transient optical radiation signal has a fast speed and a large dynamic range, the optical radiation detector is required to be high. This paper uses Japan's Hamamatsu company's s2387-1010r silicon photodiode, which has high sensitivity, large dynamic range, fast time response and large coverage.
2.2 Background deduction
Solar radiation energy is several orders of magnitude higher than the energy of a spatial transient optical radiation signal. For the system, due to the influence of sunlight, the target signal is very weak, and most of it is buried in strong noise. Therefore, the strong background signal must be deducted to extract useful target event transient signals.
In the automatic signal processing and analysis technology, the extraction of weak signals in a strong background is a difficult point. In this paper, based on the slow change of the background signal and the rapid change of the target signal, the background subtraction is performed on the signal by the high-pass filter.
The high-pass filter can be implemented in digital or analog circuits. In order to simplify the circuit and reduce the pressure of the subsequent processing circuit, this paper uses capacitors, resistors, etc. to construct an analog high-pass filter for background subtraction.
The transfer function of the filter is:
h(s)=r/[(1/sc)+r]=src/(1+src)
Background subtraction of the target signal can be achieved by selecting the appropriate resistor and capacitor values.
2.3 Dynamic Range Compression
The dynamic range of the spatial transient optical radiation signal is too large. If it is directly a/d converted, the quantization resolution of a/d is at least 15 bits, and the amount of data processed by the latter digital signal is increased due to the large number of bits. Reduce the real-time nature of the system. Therefore, logarithmic amplifiers are used for logarithmic compression of the dynamic range of the signal. The 12-bit a/d converter can meet the requirements, and the amount of data processed is reduced, and the real-time performance of the system is improved. This article uses TI's tl441m logarithmic amplifier. It is a monolithic high performance log amp chip cascaded by a four-stage 30db log amp that provides an input voltage dynamic range of 120db.
3 a/d variable rate sampling module
3.1 Threshold trigger
After pre-processing, the target signal enters the voltage comparator in the threshold trigger circuit. Dsp sets the threshold signal, which is latched and output to the voltage comparator via d/a conversion, and compared with the input target signal: if the target signal exceeds the threshold signal, a trigger signal is generated and the timing control circuit and the a/d conversion circuit are driven to work. ; otherwise it doesn't work.
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