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Printing version 2.6
•JUL2017
flat frequency response in the bandwidth of interest and a small phase error. The
analog filter precedes the analog sampler. The analog sampler operates at 256
times the selected sample rate for rates below 51.2 kS/s, 128 times for rates
between 51.2 kS/s and 102.4 kS/s. For rates over 102.4 kS/s the oversampling is
64 times. That means, the ADC operates at 13.1072 MS/s if you select a sample
rate of 102.4 kS/s (128 * 102.4 kS/s).
The 1-bit oversampled data is passed to a digital anti-aliasing filter. This filter has
no phase error and an extremely flat frequency response. It also has an
extremely sharp roll-off near the cutoff frequency (0.38 to 0.494 times the sample
rate) and the rejection above 0.5465 times the sample rate is greater than 92 dB.
The output stage of the digital filter resamples higher frequencies to 24-bit
samples.
The digital filter passes only signal components within the Nyquist bandwidth or
within multiples of the Nyquist bandwidth of 64, 128 or 256 times (depending on
sampling rate). The analog filter rejects most noise near these multiples. The
following diagrams show the frequency response of the input circuitry.
Sample rate 0.1kS/s to 51.2kS/s:
