采样理论(Sampling Theory) 和周期性信号采样 (Coherent sampling)
2012-07-05 16:48
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If a function x(t) contains no frequencies higher than Bhertz, it is completely determined by giving its ordinates at a series of points spaced 1/(2B) seconds
apart.
换句话说就是,采样的频率F1和所传输信号的频率F2的关系如果满足,F1>=2F2,那么该传输信号可与等同于采样后生成的信号。
如果F1<F2,这种情况被称为Undersampling,这样会导致测试最后生成的波形的频率比F2小,
如果F1>> 2F2,这种情况被称为Oversampling,这样可以提高测试精度。
所以为了找到一个合适的采样频率和合适的采样次数,引人Coherent sampling(周期信号取样)
UTP is a time interval over which unique information is spread(用来确保采样的唯一性)
假设:
被测device是:8-bit 21MHz ADC Test
采样频率Fs是: 20MHz
被测试信号的频率Fin:5MHz
采样次数Msamples是:N ≧ 2的9次方 =512
带入公式的Ncycles=512/4=128
因为“This integer number should be chosen carefully. We have three possible types of integers, even, odd, and prime. Even is not a good idea since we would hit the same code every M samples, where M can be much less than N. Odd is a better idea since it takes
longer to hit the same code.”,
所以我们将Ncycles改成129,然后计算出新的Fin=5.03MHz
http://en.wikipedia.org/wiki/Coherent_sampling
apart.
换句话说就是,采样的频率F1和所传输信号的频率F2的关系如果满足,F1>=2F2,那么该传输信号可与等同于采样后生成的信号。
如果F1<F2,这种情况被称为Undersampling,这样会导致测试最后生成的波形的频率比F2小,
如果F1>> 2F2,这种情况被称为Oversampling,这样可以提高测试精度。
所以为了找到一个合适的采样频率和合适的采样次数,引人Coherent sampling(周期信号取样)
UTP is a time interval over which unique information is spread(用来确保采样的唯一性)
假设:
被测device是:8-bit 21MHz ADC Test
采样频率Fs是: 20MHz
被测试信号的频率Fin:5MHz
采样次数Msamples是:N ≧ 2的9次方 =512
带入公式的Ncycles=512/4=128
因为“This integer number should be chosen carefully. We have three possible types of integers, even, odd, and prime. Even is not a good idea since we would hit the same code every M samples, where M can be much less than N. Odd is a better idea since it takes
longer to hit the same code.”,
所以我们将Ncycles改成129,然后计算出新的Fin=5.03MHz
http://en.wikipedia.org/wiki/Coherent_sampling
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