3 Alternative Method to Summation

Using two ADCs or channels within the same IC yields better results, since many parameters of the converters like gain, gain error, offset, and bandwidth are typically well-matched and do not introduce unwanted errors when the two signals are summed and averaged together. In theoretical conditions, when Vin = Vin1= Vin2, the resulting output is (Vin1+Vin2)/2 = Vin. However if there is a common error added to the input, it is passed along to the output. To avoid this situation, it is possible to invert one of the inputs to one ADC and instead of summation, a digital subtraction can be performed at the output. This method, in essence, is the same as the summation method with the additional advantage of canceling out any common error to both devices. Equation 10 mathematically expresses the two converters inputs of Vin1+e and Vin2+e.

But since Vin2 = -Vin1, Equation 11 can be expressed as the following equation to eliminate the common error (e).

Either of the above methods can improve the SNR by 3 dB for every doubling of the number of converters used.