Tree-Structured DEM DACs with Arbitrary Numbers of Levels

Unity-weighted tree-structured dynamic element matching (DEM) DACs are widely used in delta-sigma (¿¿) data converters to ensure that mismatches among nominally identical analog components give rise to shaped noise instead of nonlinear distortion. Tree-structured DEM DACs offer an advantage over other published DEM DACs in that the shaped noise from component mismatches can be made free of spurious tones. However, previously published unity-weighted tree-structured DEM DACs have the disadvantage that they require a power-of-two number of nominally identical 1-bit DACs. When applied to a ¿¿ data converter with a non-power-of-two number of quantization steps, this requires the DEM DAC to have a larger input range than needed by the ¿¿ data converter which wastes power and circuit area. This paper presents a generalized tree-structured DEM encoder applicable to DEM DACs with any number of 1-bit DACs, thereby avoiding this limitation.

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