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A/D Conversion转换
D/A Conversion转换
Undersampling欠采样
Oversampling过采样
A/D Converter
抗混叠
采样保持
量化编码
Anti-Aliasing抗混叠 p.35 Fig2.7
Nyquist
Theorem定理:p.37 Fig2.9
A signal with a maximum frequency
of W Hz ( called a band -
limited
signal) must be sampled at least 2W
samples(样本) per second to ensure
accurate recording.
Sample
& Hold
Sampling Intervals间隔
Sampling Period周期
Ts
Sampling Frequency频率 fs
Quantization (N-Bit Converter)
Bit Rate比特率: Nfs
Precision精度: Q = R/2N
(R :
Magnitude Range)
Error量化误差: [-Q/2,
+Q/2]
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Dynamic Range 动态范围：(Decibel: dB)
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Signal-to-Noise Ratio (SNR): 信噪比
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D/A Converter
零阶保持 消像滤波器
Zero Order Holding: Generates Analog Signal
Low Pass Filter: Remove Images
Spectrum of
Stair-Like
Signal
Spectrum of Analog Signal
连续的 离散的
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Analog signal driving A/D
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Sample and hold signal from A/D
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Zero order hold signal from D/A
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Reconstructed signal from D/A
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Undersampling欠采样
Narrow Band
Signal窄带信号， B << W
B : Bandwidth 带宽
W: Central or Carrying Frequency
中频或载频
Set fs = B, then Base Band
Filtering基带滤波
Oversampling过采样
Analog Signal
has Infinite Bandwidth!
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Anti-Aliasing Filter,
Analog, High Cost
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Quantizer, Digital,
Low Cost
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W
Cutoff, High Order, Cost More
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fs = 2W
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3W
Cutoff, Low Order, Cost Less
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fs > 2W
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