I. Energy signal and power signal There are two important concepts: the energy signal and the power signal. The energy-limited signal is the energy signal, and its average power is zero. The power-limited signal is the energy signal, and its energy is infinite. About the energy signal and the power signal. Computation, involving a very important theorem, that is, the Parseval theorem, which is often taken in the postgraduate examination, is an important knowledge point. Simply put, the calculation of the energy and power of the signal can be in the time domain ( In the time domain), it can also be performed in the frequency domain (frequency domain), and the calculation result is the same. The application of the Pasewa theorem provides some opportunities for questions, such as letting you calculate an integral, the physical meaning is Calculating the energy of the signal in the time domain, but the calculation is very difficult, then you can use the Pasewa theorem to translate into the frequency domain, which is often simpler. However, some of the postgraduate questions are not good, without the Paseva theorem. It can be solved directly by using the knowledge of higher mathematics. Two forms of Paseva theorem Second, the operation of the signal The operation of the signal basically involves only mathematical knowledge, that is, the operation of the function, but also involves some important concepts, such as linearity and modulation. Linearity is homogeneity and additivity, involving the addition of signals; Multiplying a high-frequency sinusoidal signal is a modulation process that implements the shifting of the spectrum. There is also a contraction of the signal, which is then linked to the corresponding relationship in the frequency domain: the signal stretches in the time domain, then in the frequency domain Compression, and vice versa, the frequency domain and time domain are just the opposite. When a signal has a time domain width of zero, then the frequency domain width is infinite, such as an impulse signal. The drawing in the signal operation is Basic skills, middle school students with good mathematics should be able to draw pictures. 3. The derivative and integral of the (continuous) signal The functions of higher mathematics are generally good, and can be continuously derived and integrated. However, some of the signals introduced in this course, such as impulse signals and step signals, are very bad in nature, but we can still introduce The operation of the derivative and the quadrature often brings convenience to some calculations. Sometimes, the worst-performing signal has the best properties, such as the impulse signal δ(t) and any signal is convoluted to obtain the signal. In itself, ie The worst-performing signal δ(t), the position in the operation of convolution, is the same as the position of 1 in ordinary multiplication! So, don't be afraid of these so-called bad signals, they may be in other ways. It is very good! The derivation and integration of signals have corresponding properties in various transformations, such as using Laplace transform to solve differential equations, involving the Laplace transform of the derivative of the signal. Differences and overlaps of (discrete) signals The difference between these two operations and the continuous signal is integrated. The difference is divided into forward difference and backward difference. Most of the textbooks use the form of backward difference. The two difference forms are essentially the same. A little difference, when we talk about the time domain analysis of discrete signals and systems, we can see the difference between the two differences from the example. The overlap is a kind of summation. Five important signals In continuous and discrete systems, two important basic signals are introduced respectively. We must distinguish their names: in the continuous system, the step signal ε(t) and the impulse signal δ(t) are respectively in the discrete system. It is a step sequence ε(k) and a pulse sequence δ(k), where the pulse sequence δ(k) is called a unit sampling sequence in some digital signal processing textbooks. It is said that the name is not correct, we have to Various signals are clearly expressed to avoid confusion. Takeaway Box Led Display,Led Light Box Menu,Led Sign Board For Restaurant,Neon Menu Board ShenZhen Megagem Tech Co.,Ltd , https://www.megleddisplay.com
