AD7740 AD7740: maximum input frequency

Document created by analog-archivist Employee on Feb 23, 2016
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I can't find the parameter about the maximum frequency of the input signal at
the VIN Pin. Would you please give me some advices?


The 7740 uses a sigma-delta type architecture. The input goes into a switched
capacitor integrator and then to a comparator. The 7740 output is essentially
the comparator output. The 7740 has minimal effect on the filter response - the
switched cap circuit has a low-pass filtering effect - about 6dB down at Fclk/2
- but has negligible effect at lower frequencies.
The system response will be dominated by what comes after the 7740.
Most applications would involve counting 1's on the output of the 7740 to
determine the frequency, possibly to turn the VFC into an ADC type function.
This counting process is an averaging step, and will low-pass-filter the 7740
output. The low pass filter cutoff will depend on the average size, which will
in turn determine the resolution, but would typically be 1000 times less than
the Fclk. This frequency response will have a far greater effect than the 7740