1)设计一个IIR低通滤波器，用它去处理一个30kHz的方波信号，得到1kHz干净的正弦波信号，设采样频率为30kHz

2）用直接二型实现结构、二阶级联实现结构和并联实现结构去进行滤波

3）在滤波的时候，假设输入、滤波器系数和滤波结果均被量化，保留小数点后两位-A) Design of a low-pass IIR filter, it is to deal with a 30kHz square wave signal to obtain a clean 1kHz sine wave signal, the sampling frequency is set to 30kHz 2) direct implementation structure II, class II and parallel implementation structure associated implementation structure to be filtered 3) in the filter, I assume that the input filter coefficients and filter the results are quantified, retain two decimal places