I. Project design background and overview
1.1 Technical background
The signal generator is one of the most important measuring instruments. With the diversification of test objects and the advancement of digital technology, signal generators have been widely used and rapidly developed. As the most basic electronic instrument in the field of electronic technology, sinusoidal signal generator is widely used in aerospace measurement and control, communication systems, electronic countermeasures, electronic measurement, scientific research and other fields. It can meet the various requirements of the test system and become an indispensable part of the system comprehensive test.
The main implementation methods of signal generation can be divided into analog and digital according to the implementation ideas. According to the implementation method, it can be divided into direct method, phase-lock method, direct digital method and hybrid method.
The direct method has the advantages of high speed and phase noise, but the structure is complicated and the spurs are many. The phase-locked frequency synthesis technology used in the phase-locked method has developed rapidly in recent years, and its application is also extensive. However, its frequency conversion speed is not fast and circuit control is complicated, which makes the application of this technology subject to certain restrictions. The direct digital method uses direct digital synthesis (DDS) to achieve signal generation. This technology has the outstanding features of fast frequency conversion, high frequency resolution and easy control. Among the several technologies in which signals occur, direct digital synthesis technology appears the latest, but it has developed the fastest in recent years. With the development of large-scale integration technology and digital-analog mixed-signal integration technology, monolithic integrated DDS chips have emerged, and there is a great potential in the application field. The mixing rule refers to the signal generation by using two or more of the above methods.
With the development of modern information industry, the test objects are continuously enriched, and modern communication systems and electronic systems put forward higher and higher requirements for test systems, and thus higher requirements are placed on signal generators. We summarize the current requirements for signal generation components in the industry into the following four points:
(1) High spectral purity and wide frequency band.
With the development of technology, the improvement of the performance index of the tested object necessarily requires the performance of the test system to be correspondingly improved.
(2) Fast and multi-point frequency agility.
In order to meet the needs of electronic warfare, the new generation of radars is required to achieve multi-point frequency agility, the agile time should be of the order of us, and the electronic countermeasures require a magnitude of 0. lus. Communication requires a lot of frequency points. The signal generation components in the corresponding test system should also be able to achieve these metrics.
(3) Serialization and modularization.
There are many types of electronic systems, and the system is different. The test system and the signal generating components of the test system should also be diversified. This will be achieved by means of serialization of the signal generating components. At the same time, in order to facilitate the formation of the test system, modularity is also a must-have feature of signal generation components.
(4) Miniaturization and engineering.
With the continuous development of science and technology, the discipline of test science and technology has undergone great changes. Since the 1990s, the introduction of more complex artificial intelligence in instruments to achieve intelligent measurement has become an important development trend. The development trend of the instrumentation discipline is to make more and better use of digital signal processing technology in all aspects of the test system, so that the instrument can replace (or partially replace) the tester in the measurement process to perform complex and precise operations. Measurement results that are difficult to obtain with traditional methods.
Because digital signals have unique advantages in signal processing, storage and transmission, modern electronic measurement systems mostly use digital signal processing methods to optimize the various aspects of the test, calculate and process the signals, and achieve test system performance. Improvement. The introduction of digital signal measurement systems has fundamentally improved the level of measurement technology and has begun new developments in measurement technology. Similarly, the use of digital technology in the generation of test excitation signals has greatly improved the performance of the excitation signal and improved the test level.
The digital idea is used in signal generation. The basic idea is to reconstruct continuous analog signals based on discrete digital sequences. The basic theory is the Nyquist sampling theorem. The digital processing technology mainly focuses on the generation of discrete digital sequences. The generation of discrete digital sequences can usually be summarized into two methods. One is a waveform-based method, which is to interpolate and extract the original data generated by sampling and simulation to generate the required discrete digital sequence; the other method is based on The method of feature is to generate a sequence of discrete numbers based on signal characteristics (eg, frequency components, amplitudes of components, relative phase, etc.). Digital processing technology is the core technology of these two methods. Due to the introduction of digital processing technology, digital signal generation hardware has been substantially reduced to computers, D/A converters, and low-pass filters and analog channels. The computer performs digital processing to obtain a discrete digital sequence, which is converted into an analog signal by the D/A converter and finally filtered by a low-pass filter to generate the required continuous analog signal through the analog channel.
1.2 Development status of sinusoidal signal generator
With the development of electronic information technology, the performance requirements are also higher and higher, such as high frequency stability and fast conversion speed, with amplitude modulation, frequency modulation, and equalization functions.
As a basic electronic device, the signal source is widely used in teaching, scientific research, and technical support for troops. As a general-purpose electronic test instrument, the signal source is an indispensable test instrument for our military to carry out high-tech warfare. Therefore, in-depth study of the occurrence of signals from theory to engineering has a positive significance from the perspective of teaching and research, as well as from the perspective of military technical support services. With the development of science and technology and the advancement of measurement technology, the requirements for signal sources are getting higher and higher, and ordinary signal generators can no longer meet the needs of scientific research and teaching in the field of digital technology. DDS technology is an emerging frequency synthesis technology. It has the advantages of high frequency resolution, fast frequency switching, continuous switching phase, low phase noise of output signal, programmable, all-digital easy integration, small size and light weight.
Applying it to the signal source according to the characteristics of the DDS can greatly improve the resolution of the signal source, and can effectively reduce the cost and reduce the volume.
Waveform generator is the heart of electronic system. With the development of science and technology, modern radar systems and electronic countermeasure systems have higher and higher requirements on signal sources. Improving signal source performance has become the main direction of domestic and foreign engineers. DDS is a new frequency synthesis technology. The emergence of DDS has opened up a new era for the research of signal sources. Now this frequency synthesis has been used more and more in the field of electronics. Based on the research of the basic principles of DDS, this paper completes the circuit design and programming of the waveform. The waveform generator designed by this method has a simple structure, low cost, and improved resolution of the signal source output signal.
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