Sigma-Delta Modulator Refinery

The Intrinsix Sigma-Delta Modulator Refinery (or SDM Refinery) is a design automation suite developed by Intrinsix which allows fast, optimized design of Sigma-Delta Modulators (SDMs) used in over-sampled Digital-to-Analog and Analog-to-Digital converters (DACs and ADCs, respectively) and Fractional-N synthesizers.  An oversampled converter trades off amplitude accuracy with time accuracy by pushing the frequency of the quantization noise outside the band of interest.  The challenge in SDM design is the "noise shaping", which is characterized by the Noise Transfer Function (NTF).  The optimized SDM design can also be used for low spur Fractional-N synthesizer design.

The Intrinsix SDM Refinery automates this process.  In the case of a DAC design, the engineer specifies an Over-Sampling Ratio (OSR), quantization levels, order of complexity and center frequency.  The refinery first estimates the zero and pole locations, then optimizes the locations, estimates the Signal-to-Noise Ratio (SNR) as well as the Effective Number of Bits (ENOB) and then computes binary weighted modulator coefficients to achieve a stable, implemental modulator.  In many cases, an SDM DAC can be implemented efficiently in a digital ASIC using only logic gates or with minimal off chip passive filters.

A complete data converter often needs to attenuate the aliased out-of-band frequency components from the sampling process.  A DAC will often need the input interpolated (increased samples per second), while an ADC will need the output decimated (lower samples per second).  The SDM Refinery is also used to generate highly computationally, efficient Poly-Phase Half-Band filters to attenuate out-of-band noise.  The SDM Refinery designs the filter to a desired specification and optimizes this basic design such that it can be implemented using Conic Signed Digit (CSD) math.  With CSD, each multiply of the filter is implemented using only shifts and adds.  SDM Refinery tries multiple filters until it finds the optimal design that meets the design specifications with the fewest number of adders.