Abstract: To alleviate the folded noise caused by coefficient mismatches between the two channels of two-channel time-interleaved (TI) ΣΔ modulators and simplify the circuit of the modulators, a novel two-channel time-interleaved high-order ΣΔ modulator is proposed. Adding a zero at the frequency of F_s/2 to a conventional noise transfers function (NTF), the amplitude of the NTF at the high frequency can be reduced, and then the amount of the folded noise is reduced. Based on the theory of block digital filters and the method of timing equivalence, the implemented circuit for the proposed modulator is derived from the prototype of a conventional single-channel single-loop forth-order 4-bit distributed feedforward ΣΔ modulator, in which the opamps can be shared by tow channels of the first three stages, resulting in simplification in hardware complexity. A system model containing coefficient mismatches is built and simulated. Simulation results show that the proposed two-channel TI high-order ΣΔ modulator can alleviate the folded noise and improve the performance.

Key words: ΣΔ modulators, folded noise, time-interleaved, block digital filters