Novel Wideband Cascaded Sigma-Delta Modulator with Digital on-Line Calibration

This work presents a novel noise-shaping cascaded sigma-delta modulator that incorporates two stages. The first stage is realized by low-order single bit architecture, while the second stage is realized by a high-order feed-forward multi-bit architecture. Moreover, the error cancellation schemes can be added in the digital circuit part to cancel the coarse quantization errors and thus effectively reduce the non-ideal effects such as DAC mismatch. The mismatches between the two stages such as in the gain error and pole error may seriously degrade performance. The blind on-line calibration technique is used to eliminate these imperfect analog circuit errors in the digital circuit. Accordingly, this architecture can reduce the over sampling ratio (OSR) and the in-band noise can be significantly suppressed to achieve a high resolution in Matlab and Switcap2 simulations. Simulation results indicate this sigma-delta modulator is very efficient in wide bandwidth applications. Key-Words: Sigma-Delta Modulator, wideband, digital calibration, xDSL