The data sheet provides noise and effective resolution for a 5V reference. How do these parameters vary when a lower voltage reference is used?
The RMS noise value changes with respect to the output data rate and gain of the ADC, but is constant through varying voltage reference values.
On the other hand, the effective resolution(RMS resolution) is dependent on the value of the reference voltage.
This is because, the value of the RMS resolution of AD7190 is taken from the full scale input range, in which the full scale input range is limited to the value of the reference voltage. This is shown in the equation below:
RMS Resolution = log2(FS input range/RMS noise)
Where: RMS resolution = effective resolution of the AD7190
FS input range= full scale input range; given by the equation:
where: VREF= reference voltage
RMS noise= effective noise value
For example: Bipolar, sinc4, chop disabled gain=128; RMS noise=8.5nV; ODR=4.7Hz
FS input range= 2*VREF/gain
RMS Resolution= log2(FS input range/RMS noise)
= 23.13 bits
= log2(39.0625mV /8.5nV)
= 22.13 bits
The RMS resolution using a reference voltage of 2.5V is 1 bit lower compared to the RMS resolution using a reference voltage of 5V.
Thanks and Best Regards,
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