Decimation of encoding errors in an optimum SNS folding ADC

The symmetrical number system (SNS) can be used as an efficient preprocessing technique to reduce the number of comparators in a folding ADC. This paper examines the issue of encoding errors that result when the separate channels m_i are brought back together to derive the input analog voltage. As an example, a unipolar 7-bit SNS ADC using pairwise relatively prime (PRP) moduli m₁=4, m₂=5 and m₃=7 is evaluated numerically. Steady state transfer functions are shown which detail encoding errors that occur when the folded input samples lie at one of the code transition points. To discard the encoding errors that occur, a decimation band is constructed at each transition point. The effectiveness of the decimation band in eliminating the encoding errors is also quantified