Цитата
For example, if the rejection of power-line frequencies is desired, then the data-output rate can simply be set to the
power-line frequency. For 50Hz rejection, the system CLK frequency must be 19.200kHz, and this will set the dataoutput
rate to 50Hz (see Table I and Figure 4). For 60Hz rejection, the system CLK frequency must be 20.040kHz,
and this will set the data-output rate to 60Hz (see Table I and Figure 5). If both 50Hz and 60Hz rejection is required, then
the system CLK must be 3.840kHz; this will set the dataoutput rate to 10Hz and reject both 50Hz and 60Hz (see Table I and Figure 6).
power-line frequency. For 50Hz rejection, the system CLK frequency must be 19.200kHz, and this will set the dataoutput
rate to 50Hz (see Table I and Figure 4). For 60Hz rejection, the system CLK frequency must be 20.040kHz,
and this will set the data-output rate to 60Hz (see Table I and Figure 5). If both 50Hz and 60Hz rejection is required, then
the system CLK must be 3.840kHz; this will set the dataoutput rate to 10Hz and reject both 50Hz and 60Hz (see Table I and Figure 6).
И это мне абсолютно понятно. А вот для AD7796:
Цитата
The output rate of the AD7796/AD7797 (fADC) is user-programmable. The allowable update rates, along with the corresponding settling times, are listed in Table 14. Normal mode rejection is the major function of the digital filter. Simultaneous 50 Hz and 60 Hz rejection is optimized when the update rate equals 16.7 Hz or less because notches are placed at both 50 Hz and 60 Hz with these update rates (see Figure 12).
The AD7796/AD7797 use slightly different filter types, depending on the output update rate used to optimize the rejection of quantization noise and device noise. When the update rate is 4.17 Hz to 12.5 Hz, a Sinc3 filter and an averaging filter are used. When the update rate is 16.7 Hz to 33.2 Hz, a modified Sinc3 filter is used. This filter gives simultaneous 50 Hz/60 Hz rejection when the update rate equals 16.7 Hz. A Sinc4 filter is used when the update rate is from 50 Hz to 123 Hz. Figure 11 to Figure 13 show the frequency response of the different filter types for some of the update rates.
The AD7796/AD7797 use slightly different filter types, depending on the output update rate used to optimize the rejection of quantization noise and device noise. When the update rate is 4.17 Hz to 12.5 Hz, a Sinc3 filter and an averaging filter are used. When the update rate is 16.7 Hz to 33.2 Hz, a modified Sinc3 filter is used. This filter gives simultaneous 50 Hz/60 Hz rejection when the update rate equals 16.7 Hz. A Sinc4 filter is used when the update rate is from 50 Hz to 123 Hz. Figure 11 to Figure 13 show the frequency response of the different filter types for some of the update rates.
Такая иллюстрация:
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Как видно из последнего графика, подавление 50Гц в случае аналогичного (50Гц) OUTPUT DATA RATE значительно слабее.
Похожая ситуация с AD7783:
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только здесь даже для Output rate = 19.8Hz подавление 50Гц сравнительно неглубокое. Я понимаю, что фильтры (алгоритмы) в каждом случае используются иные, но мне казалось естественным наилучшее подавление 50Гц (и кратных ей) именно на той же Output Data Rate. Конечно из упрощённых представлений о фильтрации. Как объясняется иное?
