A quadrature data-dependent DEM algorithm to improve image rejection of a complex capital sigma Delta modulator

A dynamic element matching (DEM) algorithm is presented that is controlled by the quadrature output data of a complex sigma-delta modulator. This DEM technique is used to correct the gain and phase errors between the circuits in the in-phase and quadrature-phase feedback paths of the modulator. The key feature of this DEM technique is that it does not cause leakage of high-frequency quantization noise in the signal band, as encounters with the periodic or pseudorandom DEM techniques. No test signal is required to measure the gain and phase errors, and as the DEM circuit is operating continuously, it compensates for changes in, e.g., temperature and supply voltage. A 0.35- mu m CMOS prototype chip has been designed to test the DEM circuit. A batch of 38 measured samples shows a typical mismatch-independent image rejection ratio of 63 dB with DEM