从数字电路角度，分析PI(比例和积分）环路滤波电路所组成的闭环控制环路的传输函数以及误差传输函数的形状，从中可以看书环路的peaking，3db带宽以及稳定性等性能-From the perspective of digital circuits, analyze the PI（propotional & integral) loop filter s closed-loop transfer function as well as the error transfer function, fr