ELEC211 notes
ELEC202 L7-12
L7-8 PM 和 FM
PM 和 FM 的输出信号是无法区分的，都是变频。但是同样的输入信号会得到不一样的输出信号。
PM：频率变化的导数 = 相位 = 信号
FM：相位变化的积分 = 频率 = 信号。
调制区别：
FM比较常用所以多半考FM。
Frequency/modulation sensitivity：频率/调制灵敏度
Frequency deviation：频率偏差(实际频率与中央频率之差) = frequency sensitivity * max(message) = \(k_{f}\ \cdot A_m\)
Frequency swing：= 2*Frequency deviation
Modulation index ：调制指数 = maximum frequency deviation / baseband bandwidth = \(\beta = \Delta f/f_m\)
FM bandwidth:
若\(\beta>1\), \(B=2(1+\beta)f_m\)
若\(\beta<<1\), \(B=2f_m\)
L9 Digitisation
采样，老东西
预防混叠：
•Pre-filtering prevents aliasing happening by limiting the signal bandwidth. •Post-filtering mitigates the effects of aliasing by removing the corrupted portion of the spectrum. •Pre-filtering is more effective.
数字化 Digitisation: sampling + quantisation
Dynamic Range = 最大范围/最小量化 = \({V_{p-p}}/{\Delta}\)
Non-uniform quantisation 非均匀量化