Tool/software:
FDC2114 converts the resonant frequency of the circuit into a digital output.
If the capacitance changes during the conversion period, what would be the final output? Is it going to be the average value?
In other words, what is the converting mechanism of the FDC?
Thanks,
Xinyu
Xinyu,
The device measures capacitance via the RCOUNT parameter that sets the measurement interval time relative to reference clock cycles, as shown in equation (5) in the data sheet:
Over this interval, the device estimates the sensor frequency by measuring the number of sensor waveform cycles, and then providing a DATA value as shown in equation (1) in the data sheet:
which can be rewritten as DATAx = (TREFx/TSensorx) ⋅ 212.
So if the capacitance varies over the measurement interval, this will in turn cause the sensor frequency to change over the interval, making Tsensorx look like an average value.
Since Tsensorx is in the denominator, the value of DATAx won't look exactly like an average of DATAx over the interval., but it will be some kind of intermediate value.
Regards,
John
