An Analytical Method of Seeking Cutoff Frequency in Bode Diagram

Bode diagram is composed of two curves,logarithm amplitude frequency characteristic and logarithm phase frequency characteristic. During the practical teaching process,we find that it is not easy to get exact cutoff frequency by drawing bode curve. In this paper,the analytical expression of open loop logarithm amplitude frequency asymptotic characteristic is discussed,which is usually used to calculate cutoff frequency of open loop systems. The solving method and application are introduced through examples. Though the presented expression is helpful for students to analyze and synthesize control systems by frequency characteristic method,the importance of drawing bode diagram should still be emphasized during the teaching process.