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 data sheet provides noise and effective resolution for a 5V reference. How do these parameters vary when a lower voltage reference is used?

Hi smacleod,

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:**2*VREF/gain(for bipolar)**VREF/gain(for unipolar)**where: VREF= reference voltage**RMS noise= effective noise value*For example: Bipolar, sinc4, chop disabled gain=128; RMS noise=8.5nV; ODR=4.7Hz

*@VREF=5V**FS input range= 2*VREF/gain**= 2*5V/128**= 78.125mV**RMS Resolution= log2(FS input range/RMS noise)**= log2(78.125mV/8.5nV)**= 23.13 bits**@VREF=2.5V**FS input range= 2*VREF/gain**= 2*2.5V/128**= 39.0625mV**RMS Resolution= log2(FS input range/RMS noise)**= 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,

Chris

Hi smacleod,

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 AD7190FS input range= full scale input range; given by the equation:2*VREF/gain(for bipolar)VREF/gain(for unipolar)where: VREF= reference voltageRMS noise= effective noise valueFor example: Bipolar, sinc4, chop disabled gain=128; RMS noise=8.5nV; ODR=4.7Hz

@VREF=5VFS input range= 2*VREF/gain= 2*5V/128= 78.125mVRMS Resolution= log2(FS input range/RMS noise)= log2(78.125mV/8.5nV)= 23.13 bits@VREF=2.5VFS input range= 2*VREF/gain= 2*2.5V/128= 39.0625mVRMS Resolution= log2(FS input range/RMS noise)= log2(39.0625mV /8.5nV)= 22.13 bitsThe 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,

Chris